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Discussion Starter #1
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

HI, Cor -

Are you saying narrower is lower RR, or wider is lower RR, and can you tell
me why you think that?


I understand that the RE92 is relatively low RR . Although I haven't seen
any published data on the RE92, it does seem likely that Toyota would
choose a low RR tire for their Prius.

But I don't see how that demonstrates a relationship between tire width and
rolling resistance.


There seems to be widely held belief that narrower tires means lower RR, but
I haven't seem any data (or even any explanation as to why it might be true)
to support that.


My first, unproven, guess would be that wider tires have lower RR.

This is because a wider tire will deflect ( vertically) less for a given
load and pressure than a narrow tire,

Less tire deflection means less strain energy that is put into the tire
itself during each rotation, and for the same damping factor, less strain
energy means less energy loss in damping.
But, it may be that the tire width also affects the damping factor (
different ratio of sidewall to tread than narrower tires) so this may be an
overly simplified argument.



Phil


>From: Cor van de Water <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>Subject: RE: Bridgestone Ecopia EP-03 Tires
>Date: Sat, 28 Jul 2007 16:19:55 -0700
>
>Oh yes, width will definitely impact the rolling resistance.
>
>The Bridgestone Potenza RE92 are the OEM tire specified for the
>Prius from years 2001 to 2003, they used the XL variant, which
>allows a higher load rating than the standard RE92.
>
>They certainly have a low rolling resistance.
>
>In fact, I switched from the RE92 to HTR-200 on my Prius
>and noticed an MPG hit (which is normal when putting new tires
>on a car, as the increased amount of rubber means more energy
>wasted in friction during compression)
>
>Hth,
>
>Cor van de Water
>Systems Architect
>Proxim Wireless Corporation http://www.proxim.com
>Email: [email protected] Private: http://www.cvandewater.com
>Skype: cor_van_de_water IM: [email protected]
>Tel: +1 408 542 5225 VoIP: +31 20 3987567 FWD# 25925
>Fax: +1 408 731 3675 eFAX: +31-87-784-1130
>Second Life: www.secondlife.com/?u=3b42cb3f4ae249319edb487991c30acb
>

_________________________________________________________________
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Discussion Starter #2
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

>From: Brian Jackson <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>CC: Phil Marino <[email protected]>
>Subject: Re: Bridgestone Ecopia EP-03 Tires
>Date: Sat, 28 Jul 2007 22:50:39 -0700
>
>Phil,
>
>The reason I want a narrow tire is that a narrower tire will usually have a
>lower rolling resistance. This assumes that the tire it's being compared to
>is made of the same rubber compound and has the same tread.


Brian - why do you think that a narrower tire will have lower rolling
resistance?

Phil

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Discussion Starter #3
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

A narrower tire will have a smaller contact patch. The smaller the contact patch, the lower the rolling resistance. It's no coincidence that cars like the Honda Insight and the Toyota Prius have pizza cutters under them while cars like the Ford mustang and the Chevy Corvette have rolling pins.

As someone else already pointed out though, there is a sweet spot. Narrower tires are only better to a point. Go beyond that point, and the tires become TOO narrow. If the tire is too narrow, the tires contact patch could conceivably increase from front to back. Having a tire that is too harrow could also lead to more side wall flex. If the car is always working to squish the sidewall, then energy is being lost. In general though, skinnier tires should offer less rolling resistance.

Balancing tire width with the weight of the car is important in racing too. I recall one article written by a guy who was racing in NASA's (North American Sportscar Association) Factory Five Racing's Ford Cobra spec-racer series. Nearly all of the competitors were running the same width tires, which was the maximum width allowed. However, one of the drivers was using a tire that was a few mm narrower than the rest of the field, and his corner exit speeds were great enough that he won the event.

When it comes to race cars with big hp, wider tires are better... to a point.
When it comes to efficient cars with low energy density batteries, narrower is better... to a point.

Brian



- Phil Marino <[email protected]> wrote:

=============



>From: Brian Jackson <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>CC: Phil Marino <[email protected]>
>Subject: Re: Bridgestone Ecopia EP-03 Tires
>Date: Sat, 28 Jul 2007 22:50:39 -0700
>
>Phil,
>
>The reason I want a narrow tire is that a narrower tire will usually have a
>lower rolling resistance. This assumes that the tire it's being compared to
>is made of the same rubber compound and has the same tread.


Brian - why do you think that a narrower tire will have lower rolling
resistance?

Phil

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Discussion Starter #4
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

>From: Brian Jackson <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>CC: Phil Marino <[email protected]>
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>Date: Sun, 29 Jul 2007 11:29:05 -0700
>
>A narrower tire will have a smaller contact patch.

No. The area of the contact patch depends only on the load on the wheel,
and the air pressure in the tire.

As a result, the contact patch for a narrow tire is narrower ( side to side)
and longer (front to back) than the contact patch of a wider tire with the
same load and air pressure.
But, the patch area will be the same.


>The smaller the contact patch, the lower the rolling resistance.

I don't follow that reasoning. Even if the contact patch were smaller for
a narrow tire ( and it isn't) , I don't see why the rolling resistance would
be less with a smaller patch. Could you explain why you say that? It's not
the friction between the tire and the road which causes rolling resistance.
It's primarily the energy lost in deforming the tire.



> It's no coincidence that cars like the Honda Insight and the Toyota Prius
have pizza cutters under >them while cars like the Ford mustang and the
Chevy Corvette have rolling pins.


It's certainly true that wider tires are necessary for better cornering
performance, and for better straight-line performance with powerful engines.
But, that doesn't mean the their width alone makes the rolling resistance
higher.

Also, narrower tires are usually lighter weight, cost less, and fit more
easily in a narrow car - other good reasons why high-mileage cars use them.
And, Prius and Insight drivers are not generally looking for the sporty,
aggressive look of wider tires.


>
>As someone else already pointed out though, there is a sweet spot.
>Narrower tires are only better to a point. Go beyond that point, and the
>tires become TOO narrow. If >the tire is too narrow, the tires contact
>patch could conceivably increase from front to back.
>

ANY time you compare two tires with the same load and tire pressure, the
narrower tire will have a longer patch from front to back. ( see above).
There is no "sweet spot" in tire width where the patch suddenly gets longer
as the tire gets narrower. It happens for any reduction in tire width.

>Having a tire that is too harrow could also lead to more side wall flex. If
>the car is always working to >squish the sidewall, then energy is being
>lost.

This statement I understand, because a narrower tire will deflect more for
the same load and pressure. It seems to me that this disadvantage should
apply to all narrower tires.

>In general though, skinnier tires should offer less rolling resistance.

You already said that, but why???



>
>Balancing tire width with the weight of the car is important in racing too.
>I recall one article written by a guy who was racing in NASA's (North
>American Sportscar Association) Factory Five Racing's Ford Cobra spec-racer
>series. Nearly all of the competitors were running the same width tires,
>which was the maximum width allowed. However, one of the drivers was using
>a tire that was a few mm narrower than the rest of the field, and his
>corner exit speeds were great enough that he won the event.

Even if that driver's success were due to the narrower tires, that would
only show that, in this case, the narrower tire performed better, not that
they had lower RR.

>
>When it comes to race cars with big hp, wider tires are better... to a
>point.
>When it comes to efficient cars with low energy density batteries, narrower
>is better... to a point.

Could you explain that? Why is narrower better, and what happens if they
are too narrow that starts the rolling resistance rising again?

Phil Marino
>
>Brian
>
>
>
>- Phil Marino <[email protected]> wrote:
>
>=============
>
>
>
> >From: Brian Jackson <[email protected]>
> >Reply-To: [email protected]
> >To: [email protected]
> >CC: Phil Marino <[email protected]>
> >Subject: Re: Bridgestone Ecopia EP-03 Tires
> >Date: Sat, 28 Jul 2007 22:50:39 -0700
> >
> >Phil,
> >
> >The reason I want a narrow tire is that a narrower tire will usually have
>a
> >lower rolling resistance. This assumes that the tire it's being compared
>to
> >is made of the same rubber compound and has the same tread.
>
>
>Brian - why do you think that a narrower tire will have lower rolling
>resistance?
>
>Phil
>
>_________________________________________________________________
>http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migration_HM_mini_2G_0507
>

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Discussion Starter #5
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Well, if decreasing the width of the tire causes it to deflect more, then yes, the contact patch may remain constant. Then again, it could decrease. It could increase as well. Whether the contact patch are decreases, increases, or stays the same depends on tire pressure, vehicle weight (or mass for all of you metric wing nuts out there :-D ), side wall stiffness. Oh heck, while we're at it, lets throw in tire air temperature. I don't think that a tire's contact patch is as directly proportional to tire pressure and vehicle weight as you claim. I could be wrong though.

However, if I am wrong, why do road riders (bicyclists) use such narrow tires? Why do so many small EVs and cars like GM's Sun Racer use such narrow tires? Is it only for the sake of keeping rotating weight down? I don't think that's the only reason.

Oh here's another example, though one that people are probably not as familiar with. Why did my street luge go so much faster with 4 roller blade wheels on it than it did with 4 skate board wheels on it? It also had less traction with the roller blade wheels. Man, that was a scary ride! :) Roller blade and skate board wheels don't really flex at all, but man, what a difference in top speed!

Again, maybe I'm wrong, but I have been successfully operating with the understanding that a narrower tire will give a smaller contact patch and therefore decrease rolling resistance for so long that I have a hard time believing that contact patch is dependent only on tire pressure and vehicle mass.

Brian



---- Phil Marino <[email protected]> wrote:

=============



>From: Brian Jackson <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>CC: Phil Marino <[email protected]>
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>Date: Sun, 29 Jul 2007 11:29:05 -0700
>
>A narrower tire will have a smaller contact patch.

No. The area of the contact patch depends only on the load on the wheel,
and the air pressure in the tire.

As a result, the contact patch for a narrow tire is narrower ( side to side)
and longer (front to back) than the contact patch of a wider tire with the
same load and air pressure.
But, the patch area will be the same.


>The smaller the contact patch, the lower the rolling resistance.

I don't follow that reasoning. Even if the contact patch were smaller for
a narrow tire ( and it isn't) , I don't see why the rolling resistance would
be less with a smaller patch. Could you explain why you say that? It's not
the friction between the tire and the road which causes rolling resistance.
It's primarily the energy lost in deforming the tire.



> It's no coincidence that cars like the Honda Insight and the Toyota Prius
have pizza cutters under >them while cars like the Ford mustang and the
Chevy Corvette have rolling pins.


It's certainly true that wider tires are necessary for better cornering
performance, and for better straight-line performance with powerful engines.
But, that doesn't mean the their width alone makes the rolling resistance
higher.

Also, narrower tires are usually lighter weight, cost less, and fit more
easily in a narrow car - other good reasons why high-mileage cars use them.
And, Prius and Insight drivers are not generally looking for the sporty,
aggressive look of wider tires.


>
>As someone else already pointed out though, there is a sweet spot.
>Narrower tires are only better to a point. Go beyond that point, and the
>tires become TOO narrow. If >the tire is too narrow, the tires contact
>patch could conceivably increase from front to back.
>

ANY time you compare two tires with the same load and tire pressure, the
narrower tire will have a longer patch from front to back. ( see above).
There is no "sweet spot" in tire width where the patch suddenly gets longer
as the tire gets narrower. It happens for any reduction in tire width.

>Having a tire that is too harrow could also lead to more side wall flex. If
>the car is always working to >squish the sidewall, then energy is being
>lost.

This statement I understand, because a narrower tire will deflect more for
the same load and pressure. It seems to me that this disadvantage should
apply to all narrower tires.

>In general though, skinnier tires should offer less rolling resistance.

You already said that, but why???



>
>Balancing tire width with the weight of the car is important in racing too.
>I recall one article written by a guy who was racing in NASA's (North
>American Sportscar Association) Factory Five Racing's Ford Cobra spec-racer
>series. Nearly all of the competitors were running the same width tires,
>which was the maximum width allowed. However, one of the drivers was using
>a tire that was a few mm narrower than the rest of the field, and his
>corner exit speeds were great enough that he won the event.

Even if that driver's success were due to the narrower tires, that would
only show that, in this case, the narrower tire performed better, not that
they had lower RR.

>
>When it comes to race cars with big hp, wider tires are better... to a
>point.
>When it comes to efficient cars with low energy density batteries, narrower
>is better... to a point.

Could you explain that? Why is narrower better, and what happens if they
are too narrow that starts the rolling resistance rising again?

Phil Marino
>
>Brian
>
>
>
>- Phil Marino <[email protected]> wrote:
>
>=============
>
>
>
> >From: Brian Jackson <[email protected]>
> >Reply-To: [email protected]
> >To: [email protected]
> >CC: Phil Marino <[email protected]>
> >Subject: Re: Bridgestone Ecopia EP-03 Tires
> >Date: Sat, 28 Jul 2007 22:50:39 -0700
> >
> >Phil,
> >
> >The reason I want a narrow tire is that a narrower tire will usually have
>a
> >lower rolling resistance. This assumes that the tire it's being compared
>to
> >is made of the same rubber compound and has the same tread.
>
>
>Brian - why do you think that a narrower tire will have lower rolling
>resistance?
>
>Phil
>
>_________________________________________________________________
>http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migration_HM_mini_2G_0507
>

_________________________________________________________________
Local listings, incredible imagery, and driving directions - all in one
place! http://maps.live.com/?wip=69&FORM=MGAC01
 

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Discussion Starter #6
Re: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Brian Jackson wrote:

> Again, maybe I'm wrong, but I have been successfully operating with
> the understanding that a narrower tire will give a smaller contact
> patch and therefore decrease rolling resistance for so long that I
> have a hard time believing that contact patch is dependent only on
> tire pressure and vehicle mass.

Well, consider this...

What tire size do the super high millage cars run now days? It seems
that many of them are 65 series tires (Prius and Insight come to
mind.) Now with open tires I'd guess the narrower the better - but
that could be a wind resistance thing.

Paul Gooch
 

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Discussion Starter #7
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Hi, Brian
>

Phil Marino here. I'll put my comments within your post:


>From: Brian Jackson <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>CC: Phil Marino <[email protected]>
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>Date: Mon, 30 Jul 2007 0:42:29 -0700
>
>Well, if decreasing the width of the tire causes it to deflect more, then
>yes, the contact patch may >remain constant. Then again, it could decrease.
>It could increase as well. Whether the contact patch >are decreases,
>increases, or stays the same depends on tire pressure, vehicle weight (or
>mass for all of >you metric wing nuts out there :-D ), side wall stiffness.
>Oh heck, while we're at it, lets throw in tire >air temperature. I don't
>think that a tire's contact patch is as directly proportional to tire
>pressure and >vehicle weight as you claim. I could be wrong though.

The contact patch size does not directly affect rolling resistance. I've
read that it does several times on this list, but I haven't yet heard a
logical explanation for that link.

But, to answer the contact patch vs tire width question anyway, here is a
quote from a technical paper by Boeing Aircraft ( search for Boeing, and
"calculating tire area")

" The tire contact area for any aircraft tire is calculated by dividing the
single wheel load by the tire inflation pressure. If the load is expressed
in pounds, and the tire pressure in pounds per square inch, then the area is
in inches squared. "

They are referring to aircraft tires. But, the same principle applies to
car tires. To demonstrate this for yourself, see how much load a mounted
tire with no air pressure will support. That will show how little the
sidewall stiffness contributes to supporting the load on the tire. Almost
all of the load is supported by the tire pressure.

>
>However, if I am wrong, why do road riders (bicyclists) use such narrow
>tires? Why do so many small >EVs and cars like GM's Sun Racer use such
>narrow tires? Is it only for the sake of keeping rotating >weight down? I
>don't think that's the only reason.


Good questions. I answered them a couple of posts ago, but here is a better
explanation. This is from the Schwalbe tire company -
http://www.schwalbetires.com/tech_info/rolling_resistance

First, here is their explanation of why wider tires have lower rolling
resistance ( at the same pressure):



"Which factors affect rolling resistance?

Tire pressure, tire diameter, tire construction, tire tread and other
factors all have an effect on rolling resistance.

The higher the tire pressure, the less is tire deformation and thus the
rolling resistance.

Small diameter tires have a higher rolling resistance at the same tire
pressure, because tire deformation is proportionally more important, in
other words the tire is “less round”.

Wider tires roll better than narrow ones. This assertion generally generates
skepticism, nevertheless at the same tire pressure a narrow tire deflects
more and so deforms more."


And, in more detail: ( still from Schwalbe):

"Why do wide tires roll better than narrow ones?

The answer to this question lies in tire deflection. Each tire is flattened
a little under load. This creates a flat contact area.

At the same tire pressure, a wide and a narrow tire have the same contact
area. A wide tire is flattened over its width whereas a narrow tire has a
slimmer but longer contact area.

The flattened area can be considered as a counterweight to tire rotation.
Because of the longer flattened area of the narrow tire, the wheel loses
more of its “roundness” and produces more deformation during rotation.
However, in the wide tire, the radial length of the flattened area is
shorter, making the tire “rounder” and so it rolls better."

And here is why bicycle racers use narrow tires ( again, from Schwalbe)

"Why do Pros ride narrow tires if wide tires roll better?

Wide tires only roll better at the same inflation pressure, but narrow tires
can be inflated to higher pressures than wide tires. However, they then
obviously give a less comfortable ride.

In addition to this, narrow tires have an advantage over wide ones at higher
speeds, as they provide less air resistance.

Above all, a bicycle with narrow tires is much easier to accelerate because
the rotating mass of the wheels is lower and the bicycle is much more
agile."


>
>Oh here's another example, though one that people are probably not as
>familiar with. Why did my street luge go so much faster with 4 roller blade
>wheels on it than it did with 4 skate board wheels on it? It also had less
>traction with the roller blade wheels. Man, that was a scary ride! :)
>Roller blade and skate board wheels don't really flex at all, but man, what
>a difference in top speed!
>
>Again, maybe I'm wrong, but I have been successfully operating with the
>understanding that a narrower tire will give a smaller contact patch and
>therefore decrease rolling resistance for so long that I have a hard time
>believing that contact patch is dependent only on tire pressure and vehicle
>mass.

Well, Schwabe said that the fact that wide tires have lower RR generates
skepticism, so you're certainly not alone.

Phil



>
>Brian
>
>
>

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Discussion Starter #8
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Paul wrote:

> What tire size do the super high millage cars run now days? It seems
> that many of them are 65 series tires (Prius and Insight come to
> mind.) Now with open tires I'd guess the narrower the better - but
> that could be a wind resistance thing.

I'm not sure what the point is that you're trying to make.

'65' is the aspect ratio of the tire and has nothing to do with how wide
or narrow the tire is; although it isn't possible to find really wide
tires in a 65-series aspect ratio, 215/65 is common and all the way up
to 275/65 can be had. However, I'm running 165/65R13s on my EV, which
many would consider to be verging on pizza-cutters. Though the narrowest
tires tend to be 75 or 80-series (e.g. 155/80R13), some of the narrowest
ones I've found are 65's: 145/65R15 (the sort of tire that might show up
on an EV Beetle, or perhaps the front end of your buggy).

Are you perhaps suggesting that rather than placing the emphasis on the
tire width, we should be more concerned with the aspect ratio instead?

Cheers,

Roger.
 

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Discussion Starter #9
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Actually, the 65 is a percentage OF the width. 65 percent of the
section width (215 in the example below) is the distance between the rim
and the edge of the tire. So a 215/65R 15 is shorter than a 215/70R 15.
That means for a given tire size, a 65 aspect ratio will have a smaller
contact patch that an equal width 80 aspect ratio. BUT a 65 aspect
ratio will have less revolutions per mile.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Roger Stockton
Sent: Tuesday, July 31, 2007 12:24
To: [email protected]
Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Paul wrote:

> What tire size do the super high millage cars run now days? It seems
> that many of them are 65 series tires (Prius and Insight come to
> mind.) Now with open tires I'd guess the narrower the better - but
> that could be a wind resistance thing.

I'm not sure what the point is that you're trying to make.

'65' is the aspect ratio of the tire and has nothing to do with how wide
or narrow the tire is; although it isn't possible to find really wide
tires in a 65-series aspect ratio, 215/65 is common and all the way up
to 275/65 can be had. However, I'm running 165/65R13s on my EV, which
many would consider to be verging on pizza-cutters. Though the narrowest
tires tend to be 75 or 80-series (e.g. 155/80R13), some of the narrowest
ones I've found are 65's: 145/65R15 (the sort of tire that might show up
on an EV Beetle, or perhaps the front end of your buggy).

Are you perhaps suggesting that rather than placing the emphasis on the
tire width, we should be more concerned with the aspect ratio instead?

Cheers,

Roger.
 

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Discussion Starter #10
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

>From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G" <[email protected]>
>Reply-To: [email protected]
>To: <[email protected]>
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>Date: Tue, 31 Jul 2007 12:49:48 -0400
>
>Actually, the 65 is a percentage OF the width. 65 percent of the
>section width (215 in the example below) is the distance between the rim
>and the edge of the tire. So a 215/65R 15 is shorter than a 215/70R 15.
>That means for a given tire size, a 65 aspect ratio will have a smaller
>contact patch that an equal width 80 aspect ratio.

No, it doesn't. The tire patch area equals the load on the car ( in lbs)
divided by the tire pressure ( in psi).

And, since a 215/65-15 has the same tread width as a 215/70-15, and the
patch area is the same (assuming both tires have the same load and tire
pressure) then the patch width AND length will be the same for both tires.

Patch size has no particular relevance to tire rolling resistance, though.

Phil

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Discussion Starter #11
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Phil Marino wrote:

> >From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G"
> >
> >That means for a given tire size, a 65 aspect ratio will
> >have a smaller contact patch that an equal width 80 aspect ratio.
>
> No, it doesn't. The tire patch area equals the load on the
> car ( in lbs) divided by the tire pressure ( in psi).
>
> And, since a 215/65-15 has the same tread width as a
> 215/70-15, and the patch area is the same (assuming
> both tires have the same load and tire pressure) then
> the patch width AND length will be the same for both tires.

Thanks Phil, you saved me the effort of pointing out the same thing.

> Patch size has no particular relevance to tire rolling
> resistance, though.

Size may not, but it has been suggested that shape does (i.e. wide and
short is better than narrow and long), so in Jody's comparison of two
different 215 tires even the patch shape is the same.

One remaining difference is that the 80-series tire is a bit taller and
this might actually result in it having slightly *lower* rolling
resistance than the shorter 65-series tire.

It is also worth noting that while it is important to minimise rolling
resistance, it is only one loss affected by the tire size. Fitting a
315/40 tire ~might~ result in lower rolling resistance when measured at
extremely low speed (e.g. pull/push test), but could represent a greater
total loss in normal driving due to greater aero losses or greater
rolling losses on less than perfectly smooth streets due to having a
stiffer sidewall (necessary since the shorter tire results in less
distance between the wheel and the road) such that the entire wheel is
deflected upwards over small pebbles, etc. instead of the tread/sidewall
deflecting to absorb small obstacles.

Cheers,

Roger.
 

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70 Posts
Discussion Starter #12
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

BUT, if the tire is shorter, the circumference is less, which means the
tire patch IS smaller (length). Two 215 tires will have the same width
patch, but with different aspect ratios their contact patch is
different. Granted, it will not be much, but it IS longer on a higher
aspect ratio tire.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Roger Stockton
Sent: Tuesday, July 31, 2007 15:09
To: [email protected]
Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Phil Marino wrote:

> >From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G"
> >
> >That means for a given tire size, a 65 aspect ratio will have a
> >smaller contact patch that an equal width 80 aspect ratio.
>
> No, it doesn't. The tire patch area equals the load on the
> car ( in lbs) divided by the tire pressure ( in psi).
>
> And, since a 215/65-15 has the same tread width as a 215/70-15, and
> the patch area is the same (assuming both tires have the same load and

> tire pressure) then the patch width AND length will be the same for
> both tires.

Thanks Phil, you saved me the effort of pointing out the same thing.

> Patch size has no particular relevance to tire rolling resistance,
> though.

Size may not, but it has been suggested that shape does (i.e. wide and
short is better than narrow and long), so in Jody's comparison of two
different 215 tires even the patch shape is the same.

One remaining difference is that the 80-series tire is a bit taller and
this might actually result in it having slightly *lower* rolling
resistance than the shorter 65-series tire.

It is also worth noting that while it is important to minimise rolling
resistance, it is only one loss affected by the tire size. Fitting a
315/40 tire ~might~ result in lower rolling resistance when measured at
extremely low speed (e.g. pull/push test), but could represent a greater
total loss in normal driving due to greater aero losses or greater
rolling losses on less than perfectly smooth streets due to having a
stiffer sidewall (necessary since the shorter tire results in less
distance between the wheel and the road) such that the entire wheel is
deflected upwards over small pebbles, etc. instead of the tread/sidewall
deflecting to absorb small obstacles.

Cheers,

Roger.
 

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70 Posts
Discussion Starter #13
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Phil,

Good explanation! It makes me think that I might want to go from
155/80R13 tires on my Geo to 185/70R13 tires. If wider tires at the
same PSI offer lower rolling resistance I might actually gain a mpg out
of em. I will have to research the exact size required to get the same
revs per mile though. Luckily tirerack.com has a great specs page for
tires that tells all the particulars of different brands of tires.

Jody

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Phil Marino
Sent: Monday, July 30, 2007 23:09
To: [email protected]
Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Hi, Brian
>

Phil Marino here. I'll put my comments within your post:


>From: Brian Jackson <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>CC: Phil Marino <[email protected]>
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>Date: Mon, 30 Jul 2007 0:42:29 -0700
>
>Well, if decreasing the width of the tire causes it to deflect more,
>then yes, the contact patch may >remain constant. Then again, it could
decrease.
>It could increase as well. Whether the contact patch >are decreases,
>increases, or stays the same depends on tire pressure, vehicle weight
>(or mass for all of >you metric wing nuts out there :-D ), side wall
stiffness.
>Oh heck, while we're at it, lets throw in tire >air temperature. I
>don't think that a tire's contact patch is as directly proportional to
>tire pressure and >vehicle weight as you claim. I could be wrong
though.

The contact patch size does not directly affect rolling resistance.
I've read that it does several times on this list, but I haven't yet
heard a logical explanation for that link.

But, to answer the contact patch vs tire width question anyway, here is
a quote from a technical paper by Boeing Aircraft ( search for Boeing,
and "calculating tire area")

" The tire contact area for any aircraft tire is calculated by dividing
the single wheel load by the tire inflation pressure. If the load is
expressed in pounds, and the tire pressure in pounds per square inch,
then the area is in inches squared. "

They are referring to aircraft tires. But, the same principle applies
to car tires. To demonstrate this for yourself, see how much load a
mounted tire with no air pressure will support. That will show how
little the sidewall stiffness contributes to supporting the load on the
tire. Almost all of the load is supported by the tire pressure.

>
>However, if I am wrong, why do road riders (bicyclists) use such narrow

>tires? Why do so many small >EVs and cars like GM's Sun Racer use such
>narrow tires? Is it only for the sake of keeping rotating >weight down?

>I don't think that's the only reason.


Good questions. I answered them a couple of posts ago, but here is a
better explanation. This is from the Schwalbe tire company -
http://www.schwalbetires.com/tech_info/rolling_resistance

First, here is their explanation of why wider tires have lower rolling
resistance ( at the same pressure):



"Which factors affect rolling resistance?

Tire pressure, tire diameter, tire construction, tire tread and other
factors all have an effect on rolling resistance.

The higher the tire pressure, the less is tire deformation and thus the
rolling resistance.

Small diameter tires have a higher rolling resistance at the same tire
pressure, because tire deformation is proportionally more important, in
other words the tire is "less round".

Wider tires roll better than narrow ones. This assertion generally
generates
skepticism, nevertheless at the same tire pressure a narrow tire
deflects
more and so deforms more."


And, in more detail: ( still from Schwalbe):

"Why do wide tires roll better than narrow ones?

The answer to this question lies in tire deflection. Each tire is
flattened
a little under load. This creates a flat contact area.

At the same tire pressure, a wide and a narrow tire have the same
contact
area. A wide tire is flattened over its width whereas a narrow tire has
a
slimmer but longer contact area.

The flattened area can be considered as a counterweight to tire
rotation.
Because of the longer flattened area of the narrow tire, the wheel loses

more of its "roundness" and produces more deformation during rotation.
However, in the wide tire, the radial length of the flattened area is
shorter, making the tire "rounder" and so it rolls better."

And here is why bicycle racers use narrow tires ( again, from Schwalbe)

"Why do Pros ride narrow tires if wide tires roll better?

Wide tires only roll better at the same inflation pressure, but narrow
tires
can be inflated to higher pressures than wide tires. However, they then
obviously give a less comfortable ride.

In addition to this, narrow tires have an advantage over wide ones at
higher
speeds, as they provide less air resistance.

Above all, a bicycle with narrow tires is much easier to accelerate
because
the rotating mass of the wheels is lower and the bicycle is much more
agile."


>
>Oh here's another example, though one that people are probably not as
>familiar with. Why did my street luge go so much faster with 4 roller
blade
>wheels on it than it did with 4 skate board wheels on it? It also had
less
>traction with the roller blade wheels. Man, that was a scary ride! :)
>Roller blade and skate board wheels don't really flex at all, but man,
what
>a difference in top speed!
>
>Again, maybe I'm wrong, but I have been successfully operating with the

>understanding that a narrower tire will give a smaller contact patch
and
>therefore decrease rolling resistance for so long that I have a hard
time
>believing that contact patch is dependent only on tire pressure and
vehicle
>mass.

Well, Schwabe said that the fact that wide tires have lower RR
generates
skepticism, so you're certainly not alone.

Phil



>
>Brian
>
>
>

_________________________________________________________________
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migr
ation_HM_mini_pcmag_0507
 

·
Registered
Joined
·
70 Posts
Discussion Starter #14
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Jody -

I still think that the single most important thing is to make sure you have
tires that have documented low values of rolling resistance.

You can find RR values for a lot of different tires here:

www.trb.org/publications/sr/sr286.pdf

Also, take a look at the greenseal tire rolling resistance report here:

http://www.greenseal.org/resources/reports/CGR_tire_rollingresistance.pdf


Probably the next most important thing is the inflation pressure. If you
have taken care of these first two, it might be worth it to get a wider
tire.

Phil


>From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G" <[email protected]>
>Reply-To: [email protected]
>To: <[email protected]>
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>Date: Wed, 1 Aug 2007 08:58:08 -0400
>
>Phil,
>
>Good explanation! It makes me think that I might want to go from
>155/80R13 tires on my Geo to 185/70R13 tires. If wider tires at the
>same PSI offer lower rolling resistance I might actually gain a mpg out
>of em. I will have to research the exact size required to get the same
>revs per mile though. Luckily tirerack.com has a great specs page for
>tires that tells all the particulars of different brands of tires.
>
>Jody
>
>-----Original Message-----
>From: [email protected] [mailto:[email protected]] On
>Behalf Of Phil Marino
>Sent: Monday, July 30, 2007 23:09
>To: [email protected]
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>
>Hi, Brian
> >
>
>Phil Marino here. I'll put my comments within your post:
>
>
> >From: Brian Jackson <[email protected]>
> >Reply-To: [email protected]
> >To: [email protected]
> >CC: Phil Marino <[email protected]>
> >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> >Date: Mon, 30 Jul 2007 0:42:29 -0700
> >
> >Well, if decreasing the width of the tire causes it to deflect more,
> >then yes, the contact patch may >remain constant. Then again, it could
>decrease.
> >It could increase as well. Whether the contact patch >are decreases,
> >increases, or stays the same depends on tire pressure, vehicle weight
> >(or mass for all of >you metric wing nuts out there :-D ), side wall
>stiffness.
> >Oh heck, while we're at it, lets throw in tire >air temperature. I
> >don't think that a tire's contact patch is as directly proportional to
> >tire pressure and >vehicle weight as you claim. I could be wrong
>though.
>
>The contact patch size does not directly affect rolling resistance.
>I've read that it does several times on this list, but I haven't yet
>heard a logical explanation for that link.
>
>But, to answer the contact patch vs tire width question anyway, here is
>a quote from a technical paper by Boeing Aircraft ( search for Boeing,
>and "calculating tire area")
>
>" The tire contact area for any aircraft tire is calculated by dividing
>the single wheel load by the tire inflation pressure. If the load is
>expressed in pounds, and the tire pressure in pounds per square inch,
>then the area is in inches squared. "
>
>They are referring to aircraft tires. But, the same principle applies
>to car tires. To demonstrate this for yourself, see how much load a
>mounted tire with no air pressure will support. That will show how
>little the sidewall stiffness contributes to supporting the load on the
>tire. Almost all of the load is supported by the tire pressure.
>
> >
> >However, if I am wrong, why do road riders (bicyclists) use such narrow
>
> >tires? Why do so many small >EVs and cars like GM's Sun Racer use such
> >narrow tires? Is it only for the sake of keeping rotating >weight down?
>
> >I don't think that's the only reason.
>
>
>Good questions. I answered them a couple of posts ago, but here is a
>better explanation. This is from the Schwalbe tire company -
>http://www.schwalbetires.com/tech_info/rolling_resistance
>
>First, here is their explanation of why wider tires have lower rolling
>resistance ( at the same pressure):
>
>
>
>"Which factors affect rolling resistance?
>
>Tire pressure, tire diameter, tire construction, tire tread and other
>factors all have an effect on rolling resistance.
>
>The higher the tire pressure, the less is tire deformation and thus the
>rolling resistance.
>
>Small diameter tires have a higher rolling resistance at the same tire
>pressure, because tire deformation is proportionally more important, in
>other words the tire is "less round".
>
>Wider tires roll better than narrow ones. This assertion generally
>generates
>skepticism, nevertheless at the same tire pressure a narrow tire
>deflects
>more and so deforms more."
>
>
>And, in more detail: ( still from Schwalbe):
>
>"Why do wide tires roll better than narrow ones?
>
>The answer to this question lies in tire deflection. Each tire is
>flattened
>a little under load. This creates a flat contact area.
>
>At the same tire pressure, a wide and a narrow tire have the same
>contact
>area. A wide tire is flattened over its width whereas a narrow tire has
>a
>slimmer but longer contact area.
>
>The flattened area can be considered as a counterweight to tire
>rotation.
>Because of the longer flattened area of the narrow tire, the wheel loses
>
>more of its "roundness" and produces more deformation during rotation.
>However, in the wide tire, the radial length of the flattened area is
>shorter, making the tire "rounder" and so it rolls better."
>
>And here is why bicycle racers use narrow tires ( again, from Schwalbe)
>
>"Why do Pros ride narrow tires if wide tires roll better?
>
>Wide tires only roll better at the same inflation pressure, but narrow
>tires
>can be inflated to higher pressures than wide tires. However, they then
>obviously give a less comfortable ride.
>
>In addition to this, narrow tires have an advantage over wide ones at
>higher
>speeds, as they provide less air resistance.
>
>Above all, a bicycle with narrow tires is much easier to accelerate
>because
>the rotating mass of the wheels is lower and the bicycle is much more
>agile."
>
>
> >
> >Oh here's another example, though one that people are probably not as
> >familiar with. Why did my street luge go so much faster with 4 roller
>blade
> >wheels on it than it did with 4 skate board wheels on it? It also had
>less
> >traction with the roller blade wheels. Man, that was a scary ride! :)
> >Roller blade and skate board wheels don't really flex at all, but man,
>what
> >a difference in top speed!
> >
> >Again, maybe I'm wrong, but I have been successfully operating with the
>
> >understanding that a narrower tire will give a smaller contact patch
>and
> >therefore decrease rolling resistance for so long that I have a hard
>time
> >believing that contact patch is dependent only on tire pressure and
>vehicle
> >mass.
>
>Well, Schwabe said that the fact that wide tires have lower RR
>generates
>skepticism, so you're certainly not alone.
>
>Phil
>
>
>
> >
> >Brian
> >
> >
> >
>
>_________________________________________________________________
>http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migr
>ation_HM_mini_pcmag_0507
>

_________________________________________________________________
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migration_HM_mini_pcmag_0507
 

·
Registered
Joined
·
70 Posts
Discussion Starter #15
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Awesome! Good information on tires and rolling resistance! I was unable
to find information on specific tires in the first link. The second
link gave exact brands of tires but didn't have any tested in the 13"
range. I can use a 185/70R14 tire but I would have to change rims. I
also wish they would have tested the Khumo tires. I am looking at the
Khumo SR21 tires since they have them in the size I need (155/80R13) and
they have a 640AA treadwear rating. Plus the fact that they are $34 a
piece is really hard to beat.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Phil Marino
Sent: Wednesday, August 01, 2007 12:20
To: [email protected]
Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Jody -

I still think that the single most important thing is to make sure you
have tires that have documented low values of rolling resistance.

You can find RR values for a lot of different tires here:

www.trb.org/publications/sr/sr286.pdf

Also, take a look at the greenseal tire rolling resistance report here:

http://www.greenseal.org/resources/reports/CGR_tire_rollingresistance.pd
f


Probably the next most important thing is the inflation pressure. If
you have taken care of these first two, it might be worth it to get a
wider tire.

Phil


>From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G" <[email protected]>
>Reply-To: [email protected]
>To: <[email protected]>
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>Date: Wed, 1 Aug 2007 08:58:08 -0400
>
>Phil,
>
>Good explanation! It makes me think that I might want to go from
>155/80R13 tires on my Geo to 185/70R13 tires. If wider tires at the
>same PSI offer lower rolling resistance I might actually gain a mpg out

>of em. I will have to research the exact size required to get the same

>revs per mile though. Luckily tirerack.com has a great specs page for
>tires that tells all the particulars of different brands of tires.
>
>Jody
>
>-----Original Message-----
>From: [email protected] [mailto:[email protected]] On

>Behalf Of Phil Marino
>Sent: Monday, July 30, 2007 23:09
>To: [email protected]
>Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>
>Hi, Brian
> >
>
>Phil Marino here. I'll put my comments within your post:
>
>
> >From: Brian Jackson <[email protected]>
> >Reply-To: [email protected]
> >To: [email protected]
> >CC: Phil Marino <[email protected]>
> >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> >Date: Mon, 30 Jul 2007 0:42:29 -0700
> >
> >Well, if decreasing the width of the tire causes it to deflect more,
> >then yes, the contact patch may >remain constant. Then again, it
> >could
>decrease.
> >It could increase as well. Whether the contact patch >are decreases,
> >increases, or stays the same depends on tire pressure, vehicle weight

> >(or mass for all of >you metric wing nuts out there :-D ), side wall
>stiffness.
> >Oh heck, while we're at it, lets throw in tire >air temperature. I
> >don't think that a tire's contact patch is as directly proportional
> >to tire pressure and >vehicle weight as you claim. I could be wrong
>though.
>
>The contact patch size does not directly affect rolling resistance.
>I've read that it does several times on this list, but I haven't yet
>heard a logical explanation for that link.
>
>But, to answer the contact patch vs tire width question anyway, here is

>a quote from a technical paper by Boeing Aircraft ( search for Boeing,
>and "calculating tire area")
>
>" The tire contact area for any aircraft tire is calculated by dividing

>the single wheel load by the tire inflation pressure. If the load is
>expressed in pounds, and the tire pressure in pounds per square inch,
>then the area is in inches squared. "
>
>They are referring to aircraft tires. But, the same principle applies
>to car tires. To demonstrate this for yourself, see how much load a
>mounted tire with no air pressure will support. That will show how
>little the sidewall stiffness contributes to supporting the load on the

>tire. Almost all of the load is supported by the tire pressure.
>
> >
> >However, if I am wrong, why do road riders (bicyclists) use such
> >narrow
>
> >tires? Why do so many small >EVs and cars like GM's Sun Racer use
> >such narrow tires? Is it only for the sake of keeping rotating
>weight down?
>
> >I don't think that's the only reason.
>
>
>Good questions. I answered them a couple of posts ago, but here is a
>better explanation. This is from the Schwalbe tire company -
>http://www.schwalbetires.com/tech_info/rolling_resistance
>
>First, here is their explanation of why wider tires have lower rolling
>resistance ( at the same pressure):
>
>
>
>"Which factors affect rolling resistance?
>
>Tire pressure, tire diameter, tire construction, tire tread and other
>factors all have an effect on rolling resistance.
>
>The higher the tire pressure, the less is tire deformation and thus the

>rolling resistance.
>
>Small diameter tires have a higher rolling resistance at the same tire
>pressure, because tire deformation is proportionally more important, in

>other words the tire is "less round".
>
>Wider tires roll better than narrow ones. This assertion generally
>generates skepticism, nevertheless at the same tire pressure a narrow
>tire deflects more and so deforms more."
>
>
>And, in more detail: ( still from Schwalbe):
>
>"Why do wide tires roll better than narrow ones?
>
>The answer to this question lies in tire deflection. Each tire is
>flattened a little under load. This creates a flat contact area.
>
>At the same tire pressure, a wide and a narrow tire have the same
>contact area. A wide tire is flattened over its width whereas a narrow
>tire has a slimmer but longer contact area.
>
>The flattened area can be considered as a counterweight to tire
>rotation.
>Because of the longer flattened area of the narrow tire, the wheel
>loses
>
>more of its "roundness" and produces more deformation during rotation.
>However, in the wide tire, the radial length of the flattened area is
>shorter, making the tire "rounder" and so it rolls better."
>
>And here is why bicycle racers use narrow tires ( again, from Schwalbe)
>
>"Why do Pros ride narrow tires if wide tires roll better?
>
>Wide tires only roll better at the same inflation pressure, but narrow
>tires can be inflated to higher pressures than wide tires. However,
>they then obviously give a less comfortable ride.
>
>In addition to this, narrow tires have an advantage over wide ones at
>higher speeds, as they provide less air resistance.
>
>Above all, a bicycle with narrow tires is much easier to accelerate
>because the rotating mass of the wheels is lower and the bicycle is
>much more agile."
>
>
> >
> >Oh here's another example, though one that people are probably not as

> >familiar with. Why did my street luge go so much faster with 4 roller
>blade
> >wheels on it than it did with 4 skate board wheels on it? It also had
>less
> >traction with the roller blade wheels. Man, that was a scary ride! :)

> >Roller blade and skate board wheels don't really flex at all, but
> >man,
>what
> >a difference in top speed!
> >
> >Again, maybe I'm wrong, but I have been successfully operating with
> >the
>
> >understanding that a narrower tire will give a smaller contact patch
>and
> >therefore decrease rolling resistance for so long that I have a hard
>time
> >believing that contact patch is dependent only on tire pressure and
>vehicle
> >mass.
>
>Well, Schwabe said that the fact that wide tires have lower RR
>generates skepticism, so you're certainly not alone.
>
>Phil
>
>
>
> >
> >Brian
> >
> >
> >
>
>_________________________________________________________________
>http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_mig
>r
>ation_HM_mini_pcmag_0507
>

_________________________________________________________________
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migr
ation_HM_mini_pcmag_0507
 

·
Registered
Joined
·
70 Posts
Discussion Starter #16
Re: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Ok, now that you have your new tires, what PSI air pressure do you use? Do
you have it air up by the tire installer which was normally set at 35 lbs,
because he says, I air all the tires to this pressure.

Could it be 40, 45, 50, 60 or even 65 PSI?

The first thing you do before you buy any tire, is to weigh the load at each
wheel. For example, my rear load at each wheel is 2340 lbs and my front
load at each wheel is 1090 lbs. So I need to find a tire at the maximum
load rating at least 2340 lbs and then must adjust the psi when using the
this tire on the front with only a load of 1090 lbs.

The new tires with a very low RR will have a very stiff thread face and a
very soft side wall that deflects, but does not deflect the tire face as a
stiff high ply side wall on the tire.

To adjust the PSI per the load rating of the tire, which will give the
minimum tire deflection of the thread face of the tire. Jack up the vehicle
so the tire is off grade. Then air up the tire to the maximum load rating @
PSI that is listed on the side of the tire.

Now measure the height of the sidewall from the face of the tire to the edge
of the wheel for a reference point. Lets say this is 4-inches. Ink the
bottom of the tire and now lower it on to a white poster paper which will
print the foot print contact patch.

Measure the height again from the floor to the edge of the wheel, and lets
say its 3.5 inches on a stiff 4 or 6 ply side wall. This is a 0.50 inch
deflection rate which is too much deflection. It is over 10 percent of the
height of the side wall. You either have the wrong tires at the load rating
or not enough PSI. It is best to keep the deflection between 5 to 7 percent
of the height of the side wall.

Truckers with there 20 inch tires, try to keep the deflection to not more
than 5 percent of the side wall height.

The RR tires that have a very soft 2 ply side walls but has a very stiff
face, the side walls in these tires absorb the deflection and does not
transmit this deflection to the tread as much. The side wall deflection
measurements do not work on these tires because of this design.

This is will the ink foot print comes in. As stated on this list of who I
cannot keep track of what who said what, is to divide the wheel load by the
PSI. Then I think you have to take percentage of the circumference of the
tire to the length of the contact patch to get a deflection percentage. I
have not done this test on my new tires which have a very stiff 6 ply face
and a soft 2 ply side wall which does the deflection.

Roland




----- Original Message -----
From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G" <[email protected]>
To: <[email protected]>
Sent: Wednesday, August 01, 2007 10:52 AM
Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR


> Awesome! Good information on tires and rolling resistance! I was unable
> to find information on specific tires in the first link. The second
> link gave exact brands of tires but didn't have any tested in the 13"
> range. I can use a 185/70R14 tire but I would have to change rims. I
> also wish they would have tested the Khumo tires. I am looking at the
> Khumo SR21 tires since they have them in the size I need (155/80R13) and
> they have a 640AA treadwear rating. Plus the fact that they are $34 a
> piece is really hard to beat.
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Phil Marino
> Sent: Wednesday, August 01, 2007 12:20
> To: [email protected]
> Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>
> Jody -
>
> I still think that the single most important thing is to make sure you
> have tires that have documented low values of rolling resistance.
>
> You can find RR values for a lot of different tires here:
>
> www.trb.org/publications/sr/sr286.pdf
>
> Also, take a look at the greenseal tire rolling resistance report here:
>
> http://www.greenseal.org/resources/reports/CGR_tire_rollingresistance.pd
> f
>
>
> Probably the next most important thing is the inflation pressure. If
> you have taken care of these first two, it might be worth it to get a
> wider tire.
>
> Phil
>
>
> >From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G" <[email protected]>
> >Reply-To: [email protected]
> >To: <[email protected]>
> >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> >Date: Wed, 1 Aug 2007 08:58:08 -0400
> >
> >Phil,
> >
> >Good explanation! It makes me think that I might want to go from
> >155/80R13 tires on my Geo to 185/70R13 tires. If wider tires at the
> >same PSI offer lower rolling resistance I might actually gain a mpg out
>
> >of em. I will have to research the exact size required to get the same
>
> >revs per mile though. Luckily tirerack.com has a great specs page for
> >tires that tells all the particulars of different brands of tires.
> >
> >Jody
> >
> >-----Original Message-----
> >From: [email protected] [mailto:[email protected]] On
>
> >Behalf Of Phil Marino
> >Sent: Monday, July 30, 2007 23:09
> >To: [email protected]
> >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> >
> >Hi, Brian
> > >
> >
> >Phil Marino here. I'll put my comments within your post:
> >
> >
> > >From: Brian Jackson <[email protected]>
> > >Reply-To: [email protected]
> > >To: [email protected]
> > >CC: Phil Marino <[email protected]>
> > >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> > >Date: Mon, 30 Jul 2007 0:42:29 -0700
> > >
> > >Well, if decreasing the width of the tire causes it to deflect more,
> > >then yes, the contact patch may >remain constant. Then again, it
> > >could
> >decrease.
> > >It could increase as well. Whether the contact patch >are decreases,
> > >increases, or stays the same depends on tire pressure, vehicle weight
>
> > >(or mass for all of >you metric wing nuts out there :-D ), side wall
> >stiffness.
> > >Oh heck, while we're at it, lets throw in tire >air temperature. I
> > >don't think that a tire's contact patch is as directly proportional
> > >to tire pressure and >vehicle weight as you claim. I could be wrong
> >though.
> >
> >The contact patch size does not directly affect rolling resistance.
> >I've read that it does several times on this list, but I haven't yet
> >heard a logical explanation for that link.
> >
> >But, to answer the contact patch vs tire width question anyway, here is
>
> >a quote from a technical paper by Boeing Aircraft ( search for Boeing,
> >and "calculating tire area")
> >
> >" The tire contact area for any aircraft tire is calculated by dividing
>
> >the single wheel load by the tire inflation pressure. If the load is
> >expressed in pounds, and the tire pressure in pounds per square inch,
> >then the area is in inches squared. "
> >
> >They are referring to aircraft tires. But, the same principle applies
> >to car tires. To demonstrate this for yourself, see how much load a
> >mounted tire with no air pressure will support. That will show how
> >little the sidewall stiffness contributes to supporting the load on the
>
> >tire. Almost all of the load is supported by the tire pressure.
> >
> > >
> > >However, if I am wrong, why do road riders (bicyclists) use such
> > >narrow
> >
> > >tires? Why do so many small >EVs and cars like GM's Sun Racer use
> > >such narrow tires? Is it only for the sake of keeping rotating
> >weight down?
> >
> > >I don't think that's the only reason.
> >
> >
> >Good questions. I answered them a couple of posts ago, but here is a
> >better explanation. This is from the Schwalbe tire company -
> >http://www.schwalbetires.com/tech_info/rolling_resistance
> >
> >First, here is their explanation of why wider tires have lower rolling
> >resistance ( at the same pressure):
> >
> >
> >
> >"Which factors affect rolling resistance?
> >
> >Tire pressure, tire diameter, tire construction, tire tread and other
> >factors all have an effect on rolling resistance.
> >
> >The higher the tire pressure, the less is tire deformation and thus the
>
> >rolling resistance.
> >
> >Small diameter tires have a higher rolling resistance at the same tire
> >pressure, because tire deformation is proportionally more important, in
>
> >other words the tire is "less round".
> >
> >Wider tires roll better than narrow ones. This assertion generally
> >generates skepticism, nevertheless at the same tire pressure a narrow
> >tire deflects more and so deforms more."
> >
> >
> >And, in more detail: ( still from Schwalbe):
> >
> >"Why do wide tires roll better than narrow ones?
> >
> >The answer to this question lies in tire deflection. Each tire is
> >flattened a little under load. This creates a flat contact area.
> >
> >At the same tire pressure, a wide and a narrow tire have the same
> >contact area. A wide tire is flattened over its width whereas a narrow
> >tire has a slimmer but longer contact area.
> >
> >The flattened area can be considered as a counterweight to tire
> >rotation.
> >Because of the longer flattened area of the narrow tire, the wheel
> >loses
> >
> >more of its "roundness" and produces more deformation during rotation.
> >However, in the wide tire, the radial length of the flattened area is
> >shorter, making the tire "rounder" and so it rolls better."
> >
> >And here is why bicycle racers use narrow tires ( again, from Schwalbe)
> >
> >"Why do Pros ride narrow tires if wide tires roll better?
> >
> >Wide tires only roll better at the same inflation pressure, but narrow
> >tires can be inflated to higher pressures than wide tires. However,
> >they then obviously give a less comfortable ride.
> >
> >In addition to this, narrow tires have an advantage over wide ones at
> >higher speeds, as they provide less air resistance.
> >
> >Above all, a bicycle with narrow tires is much easier to accelerate
> >because the rotating mass of the wheels is lower and the bicycle is
> >much more agile."
> >
> >
> > >
> > >Oh here's another example, though one that people are probably not as
>
> > >familiar with. Why did my street luge go so much faster with 4 roller
> >blade
> > >wheels on it than it did with 4 skate board wheels on it? It also had
> >less
> > >traction with the roller blade wheels. Man, that was a scary ride! :)
>
> > >Roller blade and skate board wheels don't really flex at all, but
> > >man,
> >what
> > >a difference in top speed!
> > >
> > >Again, maybe I'm wrong, but I have been successfully operating with
> > >the
> >
> > >understanding that a narrower tire will give a smaller contact patch
> >and
> > >therefore decrease rolling resistance for so long that I have a hard
> >time
> > >believing that contact patch is dependent only on tire pressure and
> >vehicle
> > >mass.
> >
> >Well, Schwabe said that the fact that wide tires have lower RR
> >generates skepticism, so you're certainly not alone.
> >
> >Phil
> >
> >
> >
> > >
> > >Brian
> > >
> > >
> > >
> >
> >_________________________________________________________________
> >http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_mig
> >r
> >ation_HM_mini_pcmag_0507
> >
>
> _________________________________________________________________
> http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migr
> ation_HM_mini_pcmag_0507
>
>
 

·
Registered
Joined
·
70 Posts
Discussion Starter #17
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Roland,

How did you measure your corner weight? Did you rent/buy the
scales capable or did you do the Archemedes bathroom scale method?


Jody

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Roland Wiench
Sent: Wednesday, August 01, 2007 13:58
To: [email protected]
Subject: Re: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Ok, now that you have your new tires, what PSI air pressure do you use?
Do you have it air up by the tire installer which was normally set at 35
lbs, because he says, I air all the tires to this pressure.

Could it be 40, 45, 50, 60 or even 65 PSI?

The first thing you do before you buy any tire, is to weigh the load at
each wheel. For example, my rear load at each wheel is 2340 lbs and my
front load at each wheel is 1090 lbs. So I need to find a tire at the
maximum load rating at least 2340 lbs and then must adjust the psi when
using the this tire on the front with only a load of 1090 lbs.

The new tires with a very low RR will have a very stiff thread face and
a very soft side wall that deflects, but does not deflect the tire face
as a stiff high ply side wall on the tire.

To adjust the PSI per the load rating of the tire, which will give the
minimum tire deflection of the thread face of the tire. Jack up the
vehicle so the tire is off grade. Then air up the tire to the maximum
load rating @ PSI that is listed on the side of the tire.

Now measure the height of the sidewall from the face of the tire to the
edge of the wheel for a reference point. Lets say this is 4-inches. Ink
the bottom of the tire and now lower it on to a white poster paper which
will print the foot print contact patch.

Measure the height again from the floor to the edge of the wheel, and
lets say its 3.5 inches on a stiff 4 or 6 ply side wall. This is a 0.50
inch deflection rate which is too much deflection. It is over 10
percent of the height of the side wall. You either have the wrong tires
at the load rating or not enough PSI. It is best to keep the deflection
between 5 to 7 percent of the height of the side wall.

Truckers with there 20 inch tires, try to keep the deflection to not
more than 5 percent of the side wall height.

The RR tires that have a very soft 2 ply side walls but has a very stiff
face, the side walls in these tires absorb the deflection and does not
transmit this deflection to the tread as much. The side wall deflection
measurements do not work on these tires because of this design.

This is will the ink foot print comes in. As stated on this list of who
I cannot keep track of what who said what, is to divide the wheel load
by the PSI. Then I think you have to take percentage of the
circumference of the
tire to the length of the contact patch to get a deflection percentage.
I
have not done this test on my new tires which have a very stiff 6 ply
face and a soft 2 ply side wall which does the deflection.

Roland




----- Original Message -----
From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G" <[email protected]>
To: <[email protected]>
Sent: Wednesday, August 01, 2007 10:52 AM
Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR


> Awesome! Good information on tires and rolling resistance! I was
unable
> to find information on specific tires in the first link. The second
> link gave exact brands of tires but didn't have any tested in the 13"
> range. I can use a 185/70R14 tire but I would have to change rims. I
> also wish they would have tested the Khumo tires. I am looking at the
> Khumo SR21 tires since they have them in the size I need (155/80R13)
and
> they have a 640AA treadwear rating. Plus the fact that they are $34 a
> piece is really hard to beat.
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]
On
> Behalf Of Phil Marino
> Sent: Wednesday, August 01, 2007 12:20
> To: [email protected]
> Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>
> Jody -
>
> I still think that the single most important thing is to make sure you
> have tires that have documented low values of rolling resistance.
>
> You can find RR values for a lot of different tires here:
>
> www.trb.org/publications/sr/sr286.pdf
>
> Also, take a look at the greenseal tire rolling resistance report
here:
>
>
http://www.greenseal.org/resources/reports/CGR_tire_rollingresistance.pd
> f
>
>
> Probably the next most important thing is the inflation pressure. If
> you have taken care of these first two, it might be worth it to get a
> wider tire.
>
> Phil
>
>
> >From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G"
<[email protected]>
> >Reply-To: [email protected]
> >To: <[email protected]>
> >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> >Date: Wed, 1 Aug 2007 08:58:08 -0400
> >
> >Phil,
> >
> >Good explanation! It makes me think that I might want to go from
> >155/80R13 tires on my Geo to 185/70R13 tires. If wider tires at the
> >same PSI offer lower rolling resistance I might actually gain a mpg
out
>
> >of em. I will have to research the exact size required to get the
same
>
> >revs per mile though. Luckily tirerack.com has a great specs page
for
> >tires that tells all the particulars of different brands of tires.
> >
> >Jody
> >
> >-----Original Message-----
> >From: [email protected] [mailto:[email protected]]
On
>
> >Behalf Of Phil Marino
> >Sent: Monday, July 30, 2007 23:09
> >To: [email protected]
> >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> >
> >Hi, Brian
> > >
> >
> >Phil Marino here. I'll put my comments within your post:
> >
> >
> > >From: Brian Jackson <[email protected]>
> > >Reply-To: [email protected]
> > >To: [email protected]
> > >CC: Phil Marino <[email protected]>
> > >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> > >Date: Mon, 30 Jul 2007 0:42:29 -0700
> > >
> > >Well, if decreasing the width of the tire causes it to deflect
more,
> > >then yes, the contact patch may >remain constant. Then again, it
> > >could
> >decrease.
> > >It could increase as well. Whether the contact patch >are
decreases,
> > >increases, or stays the same depends on tire pressure, vehicle
weight
>
> > >(or mass for all of >you metric wing nuts out there :-D ), side
wall
> >stiffness.
> > >Oh heck, while we're at it, lets throw in tire >air temperature. I
> > >don't think that a tire's contact patch is as directly proportional
> > >to tire pressure and >vehicle weight as you claim. I could be wrong
> >though.
> >
> >The contact patch size does not directly affect rolling resistance.
> >I've read that it does several times on this list, but I haven't yet
> >heard a logical explanation for that link.
> >
> >But, to answer the contact patch vs tire width question anyway, here
is
>
> >a quote from a technical paper by Boeing Aircraft ( search for
Boeing,
> >and "calculating tire area")
> >
> >" The tire contact area for any aircraft tire is calculated by
dividing
>
> >the single wheel load by the tire inflation pressure. If the load is
> >expressed in pounds, and the tire pressure in pounds per square inch,
> >then the area is in inches squared. "
> >
> >They are referring to aircraft tires. But, the same principle
applies
> >to car tires. To demonstrate this for yourself, see how much load a
> >mounted tire with no air pressure will support. That will show how
> >little the sidewall stiffness contributes to supporting the load on
the
>
> >tire. Almost all of the load is supported by the tire pressure.
> >
> > >
> > >However, if I am wrong, why do road riders (bicyclists) use such
> > >narrow
> >
> > >tires? Why do so many small >EVs and cars like GM's Sun Racer use
> > >such narrow tires? Is it only for the sake of keeping rotating
> >weight down?
> >
> > >I don't think that's the only reason.
> >
> >
> >Good questions. I answered them a couple of posts ago, but here is a
> >better explanation. This is from the Schwalbe tire company -
> >http://www.schwalbetires.com/tech_info/rolling_resistance
> >
> >First, here is their explanation of why wider tires have lower
rolling
> >resistance ( at the same pressure):
> >
> >
> >
> >"Which factors affect rolling resistance?
> >
> >Tire pressure, tire diameter, tire construction, tire tread and other
> >factors all have an effect on rolling resistance.
> >
> >The higher the tire pressure, the less is tire deformation and thus
the
>
> >rolling resistance.
> >
> >Small diameter tires have a higher rolling resistance at the same
tire
> >pressure, because tire deformation is proportionally more important,
in
>
> >other words the tire is "less round".
> >
> >Wider tires roll better than narrow ones. This assertion generally
> >generates skepticism, nevertheless at the same tire pressure a narrow
> >tire deflects more and so deforms more."
> >
> >
> >And, in more detail: ( still from Schwalbe):
> >
> >"Why do wide tires roll better than narrow ones?
> >
> >The answer to this question lies in tire deflection. Each tire is
> >flattened a little under load. This creates a flat contact area.
> >
> >At the same tire pressure, a wide and a narrow tire have the same
> >contact area. A wide tire is flattened over its width whereas a
narrow
> >tire has a slimmer but longer contact area.
> >
> >The flattened area can be considered as a counterweight to tire
> >rotation.
> >Because of the longer flattened area of the narrow tire, the wheel
> >loses
> >
> >more of its "roundness" and produces more deformation during
rotation.
> >However, in the wide tire, the radial length of the flattened area is
> >shorter, making the tire "rounder" and so it rolls better."
> >
> >And here is why bicycle racers use narrow tires ( again, from
Schwalbe)
> >
> >"Why do Pros ride narrow tires if wide tires roll better?
> >
> >Wide tires only roll better at the same inflation pressure, but
narrow
> >tires can be inflated to higher pressures than wide tires. However,
> >they then obviously give a less comfortable ride.
> >
> >In addition to this, narrow tires have an advantage over wide ones at
> >higher speeds, as they provide less air resistance.
> >
> >Above all, a bicycle with narrow tires is much easier to accelerate
> >because the rotating mass of the wheels is lower and the bicycle is
> >much more agile."
> >
> >
> > >
> > >Oh here's another example, though one that people are probably not
as
>
> > >familiar with. Why did my street luge go so much faster with 4
roller
> >blade
> > >wheels on it than it did with 4 skate board wheels on it? It also
had
> >less
> > >traction with the roller blade wheels. Man, that was a scary ride!
:)
>
> > >Roller blade and skate board wheels don't really flex at all, but
> > >man,
> >what
> > >a difference in top speed!
> > >
> > >Again, maybe I'm wrong, but I have been successfully operating with
> > >the
> >
> > >understanding that a narrower tire will give a smaller contact
patch
> >and
> > >therefore decrease rolling resistance for so long that I have a
hard
> >time
> > >believing that contact patch is dependent only on tire pressure and
> >vehicle
> > >mass.
> >
> >Well, Schwabe said that the fact that wide tires have lower RR
> >generates skepticism, so you're certainly not alone.
> >
> >Phil
> >
> >
> >
> > >
> > >Brian
> > >
> > >
> > >
> >
> >_________________________________________________________________
>
>http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_mig
> >r
> >ation_HM_mini_pcmag_0507
> >
>
> _________________________________________________________________
>
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migr
> ation_HM_mini_pcmag_0507
>
>
 

·
Registered
Joined
·
70 Posts
Discussion Starter #18
Re: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Dewey,

There is a vehicle weight scale that is about 5 blocks from me. I can do
multiple weights on this scale. I first drove on the front wheels, then the
whole weight of the vehicle, the rear axles, the right side and left side.
>From that data I was able to calculated the weight per wheel which was real
close to the half the weight of the axle weight.

To calculated the PSI pressure in the tires, I use 65 psi at the 2360 lbs
for the rear tires. The fronts which are at 1090 lbs, I can proportion that
weight as (65 x 1090)/ 2360 = 30 lbs.

Then I check the deflection factor by measuring the total height of tire
unloaded to loaded. I finally had to increase the front tires to 40 psi,
which works out good for me.

Now there is a thrust factor where every time you brake the vehicle, there
is weight that is transfer from the rear to front which adds about 10 psi to
the front tires.

Roland


----- Original Message -----
From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G" <[email protected]>
To: <[email protected]>
Sent: Wednesday, August 01, 2007 12:32 PM
Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR


> Roland,
>
> How did you measure your corner weight? Did you rent/buy the
> scales capable or did you do the Archemedes bathroom scale method?
>
>
> Jody
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Roland Wiench
> Sent: Wednesday, August 01, 2007 13:58
> To: [email protected]
> Subject: Re: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>
> Ok, now that you have your new tires, what PSI air pressure do you use?
> Do you have it air up by the tire installer which was normally set at 35
> lbs, because he says, I air all the tires to this pressure.
>
> Could it be 40, 45, 50, 60 or even 65 PSI?
>
> The first thing you do before you buy any tire, is to weigh the load at
> each wheel. For example, my rear load at each wheel is 2340 lbs and my
> front load at each wheel is 1090 lbs. So I need to find a tire at the
> maximum load rating at least 2340 lbs and then must adjust the psi when
> using the this tire on the front with only a load of 1090 lbs.
>
> The new tires with a very low RR will have a very stiff thread face and
> a very soft side wall that deflects, but does not deflect the tire face
> as a stiff high ply side wall on the tire.
>
> To adjust the PSI per the load rating of the tire, which will give the
> minimum tire deflection of the thread face of the tire. Jack up the
> vehicle so the tire is off grade. Then air up the tire to the maximum
> load rating @ PSI that is listed on the side of the tire.
>
> Now measure the height of the sidewall from the face of the tire to the
> edge of the wheel for a reference point. Lets say this is 4-inches. Ink
> the bottom of the tire and now lower it on to a white poster paper which
> will print the foot print contact patch.
>
> Measure the height again from the floor to the edge of the wheel, and
> lets say its 3.5 inches on a stiff 4 or 6 ply side wall. This is a 0.50
> inch deflection rate which is too much deflection. It is over 10
> percent of the height of the side wall. You either have the wrong tires
> at the load rating or not enough PSI. It is best to keep the deflection
> between 5 to 7 percent of the height of the side wall.
>
> Truckers with there 20 inch tires, try to keep the deflection to not
> more than 5 percent of the side wall height.
>
> The RR tires that have a very soft 2 ply side walls but has a very stiff
> face, the side walls in these tires absorb the deflection and does not
> transmit this deflection to the tread as much. The side wall deflection
> measurements do not work on these tires because of this design.
>
> This is will the ink foot print comes in. As stated on this list of who
> I cannot keep track of what who said what, is to divide the wheel load
> by the PSI. Then I think you have to take percentage of the
> circumference of the
> tire to the length of the contact patch to get a deflection percentage.
> I
> have not done this test on my new tires which have a very stiff 6 ply
> face and a soft 2 ply side wall which does the deflection.
>
> Roland
>
>
>
>
> ----- Original Message -----
> From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, August 01, 2007 10:52 AM
> Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
>
>
> > Awesome! Good information on tires and rolling resistance! I was
> unable
> > to find information on specific tires in the first link. The second
> > link gave exact brands of tires but didn't have any tested in the 13"
> > range. I can use a 185/70R14 tire but I would have to change rims. I
> > also wish they would have tested the Khumo tires. I am looking at the
> > Khumo SR21 tires since they have them in the size I need (155/80R13)
> and
> > they have a 640AA treadwear rating. Plus the fact that they are $34 a
> > piece is really hard to beat.
> >
> > -----Original Message-----
> > From: [email protected] [mailto:[email protected]]
> On
> > Behalf Of Phil Marino
> > Sent: Wednesday, August 01, 2007 12:20
> > To: [email protected]
> > Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> >
> > Jody -
> >
> > I still think that the single most important thing is to make sure you
> > have tires that have documented low values of rolling resistance.
> >
> > You can find RR values for a lot of different tires here:
> >
> > www.trb.org/publications/sr/sr286.pdf
> >
> > Also, take a look at the greenseal tire rolling resistance report
> here:
> >
> >
> http://www.greenseal.org/resources/reports/CGR_tire_rollingresistance.pd
> > f
> >
> >
> > Probably the next most important thing is the inflation pressure. If
> > you have taken care of these first two, it might be worth it to get a
> > wider tire.
> >
> > Phil
> >
> >
> > >From: "Dewey, Jody R ATC COMNAVAIRLANT, N422G5G"
> <[email protected]>
> > >Reply-To: [email protected]
> > >To: <[email protected]>
> > >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> > >Date: Wed, 1 Aug 2007 08:58:08 -0400
> > >
> > >Phil,
> > >
> > >Good explanation! It makes me think that I might want to go from
> > >155/80R13 tires on my Geo to 185/70R13 tires. If wider tires at the
> > >same PSI offer lower rolling resistance I might actually gain a mpg
> out
> >
> > >of em. I will have to research the exact size required to get the
> same
> >
> > >revs per mile though. Luckily tirerack.com has a great specs page
> for
> > >tires that tells all the particulars of different brands of tires.
> > >
> > >Jody
> > >
> > >-----Original Message-----
> > >From: [email protected] [mailto:[email protected]]
> On
> >
> > >Behalf Of Phil Marino
> > >Sent: Monday, July 30, 2007 23:09
> > >To: [email protected]
> > >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> > >
> > >Hi, Brian
> > > >
> > >
> > >Phil Marino here. I'll put my comments within your post:
> > >
> > >
> > > >From: Brian Jackson <[email protected]>
> > > >Reply-To: [email protected]
> > > >To: [email protected]
> > > >CC: Phil Marino <[email protected]>
> > > >Subject: RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR
> > > >Date: Mon, 30 Jul 2007 0:42:29 -0700
> > > >
> > > >Well, if decreasing the width of the tire causes it to deflect
> more,
> > > >then yes, the contact patch may >remain constant. Then again, it
> > > >could
> > >decrease.
> > > >It could increase as well. Whether the contact patch >are
> decreases,
> > > >increases, or stays the same depends on tire pressure, vehicle
> weight
> >
> > > >(or mass for all of >you metric wing nuts out there :-D ), side
> wall
> > >stiffness.
> > > >Oh heck, while we're at it, lets throw in tire >air temperature. I
> > > >don't think that a tire's contact patch is as directly proportional
> > > >to tire pressure and >vehicle weight as you claim. I could be wrong
> > >though.
> > >
> > >The contact patch size does not directly affect rolling resistance.
> > >I've read that it does several times on this list, but I haven't yet
> > >heard a logical explanation for that link.
> > >
> > >But, to answer the contact patch vs tire width question anyway, here
> is
> >
> > >a quote from a technical paper by Boeing Aircraft ( search for
> Boeing,
> > >and "calculating tire area")
> > >
> > >" The tire contact area for any aircraft tire is calculated by
> dividing
> >
> > >the single wheel load by the tire inflation pressure. If the load is
> > >expressed in pounds, and the tire pressure in pounds per square inch,
> > >then the area is in inches squared. "
> > >
> > >They are referring to aircraft tires. But, the same principle
> applies
> > >to car tires. To demonstrate this for yourself, see how much load a
> > >mounted tire with no air pressure will support. That will show how
> > >little the sidewall stiffness contributes to supporting the load on
> the
> >
> > >tire. Almost all of the load is supported by the tire pressure.
> > >
> > > >
> > > >However, if I am wrong, why do road riders (bicyclists) use such
> > > >narrow
> > >
> > > >tires? Why do so many small >EVs and cars like GM's Sun Racer use
> > > >such narrow tires? Is it only for the sake of keeping rotating
> > >weight down?
> > >
> > > >I don't think that's the only reason.
> > >
> > >
> > >Good questions. I answered them a couple of posts ago, but here is a
> > >better explanation. This is from the Schwalbe tire company -
> > >http://www.schwalbetires.com/tech_info/rolling_resistance
> > >
> > >First, here is their explanation of why wider tires have lower
> rolling
> > >resistance ( at the same pressure):
> > >
> > >
> > >
> > >"Which factors affect rolling resistance?
> > >
> > >Tire pressure, tire diameter, tire construction, tire tread and other
> > >factors all have an effect on rolling resistance.
> > >
> > >The higher the tire pressure, the less is tire deformation and thus
> the
> >
> > >rolling resistance.
> > >
> > >Small diameter tires have a higher rolling resistance at the same
> tire
> > >pressure, because tire deformation is proportionally more important,
> in
> >
> > >other words the tire is "less round".
> > >
> > >Wider tires roll better than narrow ones. This assertion generally
> > >generates skepticism, nevertheless at the same tire pressure a narrow
> > >tire deflects more and so deforms more."
> > >
> > >
> > >And, in more detail: ( still from Schwalbe):
> > >
> > >"Why do wide tires roll better than narrow ones?
> > >
> > >The answer to this question lies in tire deflection. Each tire is
> > >flattened a little under load. This creates a flat contact area.
> > >
> > >At the same tire pressure, a wide and a narrow tire have the same
> > >contact area. A wide tire is flattened over its width whereas a
> narrow
> > >tire has a slimmer but longer contact area.
> > >
> > >The flattened area can be considered as a counterweight to tire
> > >rotation.
> > >Because of the longer flattened area of the narrow tire, the wheel
> > >loses
> > >
> > >more of its "roundness" and produces more deformation during
> rotation.
> > >However, in the wide tire, the radial length of the flattened area is
> > >shorter, making the tire "rounder" and so it rolls better."
> > >
> > >And here is why bicycle racers use narrow tires ( again, from
> Schwalbe)
> > >
> > >"Why do Pros ride narrow tires if wide tires roll better?
> > >
> > >Wide tires only roll better at the same inflation pressure, but
> narrow
> > >tires can be inflated to higher pressures than wide tires. However,
> > >they then obviously give a less comfortable ride.
> > >
> > >In addition to this, narrow tires have an advantage over wide ones at
> > >higher speeds, as they provide less air resistance.
> > >
> > >Above all, a bicycle with narrow tires is much easier to accelerate
> > >because the rotating mass of the wheels is lower and the bicycle is
> > >much more agile."
> > >
> > >
> > > >
> > > >Oh here's another example, though one that people are probably not
> as
> >
> > > >familiar with. Why did my street luge go so much faster with 4
> roller
> > >blade
> > > >wheels on it than it did with 4 skate board wheels on it? It also
> had
> > >less
> > > >traction with the roller blade wheels. Man, that was a scary ride!
> :)
> >
> > > >Roller blade and skate board wheels don't really flex at all, but
> > > >man,
> > >what
> > > >a difference in top speed!
> > > >
> > > >Again, maybe I'm wrong, but I have been successfully operating with
> > > >the
> > >
> > > >understanding that a narrower tire will give a smaller contact
> patch
> > >and
> > > >therefore decrease rolling resistance for so long that I have a
> hard
> > >time
> > > >believing that contact patch is dependent only on tire pressure and
> > >vehicle
> > > >mass.
> > >
> > >Well, Schwabe said that the fact that wide tires have lower RR
> > >generates skepticism, so you're certainly not alone.
> > >
> > >Phil
> > >
> > >
> > >
> > > >
> > > >Brian
> > > >
> > > >
> > > >
> > >
> > >_________________________________________________________________
> >
> >http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_mig
> > >r
> > >ation_HM_mini_pcmag_0507
> > >
> >
> > _________________________________________________________________
> >
> http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migr
> > ation_HM_mini_pcmag_0507
> >
> >
>
>
 

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Discussion Starter #19
RE: Bridgestone Ecopia EP-03 Tires - tire width vs RR

Dewey, Jody wrote:

> BUT, if the tire is shorter, the circumference is less, which
> means the tire patch IS smaller (length). Two 215 tires will
> have the same width patch, but with different aspect ratios
> their contact patch is different. Granted, it will not be
> much, but it IS longer on a higher aspect ratio tire.

No; if both tires are supporting the same load and are inflated to the
same pressure, then the size (area) of the contact patch will be:

Contact patch area in sq. inches = load (lbs) / pressure (PSI)

What may differ is the shape of the patch; I expect the patches will
both be oval-shaped but they will probably differ somewhat.

Easy enough to check the patch size and shape: just wet the tread with
paint or similar and lower it onto a clean sheet of paper, then jack it
back up and remove the paper to dry. If we note the weight on the tire
and the pressure we might be able to compare results collected by
different people. Might even be able to measure the patch shape/size
for various pressures just to see how it changes as pressure is varied.

Much more difficult to figure out what effect the shape (or size) of the
contact patch has on the rolling resistance... ;^> At speed, I can
imagine that the shape of the patch affects "pumping losses" as the air
between the contact patch and the road must be squeezed out as the tire
rolls, and perhaps a longer 'pointier' oval patch moves the air out of
the way with less drag?

Cheers,

Roger.
 
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