# [EVDL] Don't have a clue regarding RPM, MPH, Gear ratio's

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The transaxle you propose below, is 13.25/1 in
forward. So is this math correct: My wheels have to
go 800 revolutions to travel 1 mile, Therefore 13.25
x 800 = 10,600rpm for the motor if directly connected.
Does this mean for the vehicle to reach 60mph, the
motor would have to run this 10,600rpm continuously
stay at that cruising speed?

I ask, because I've found a donor VW, without a
tranny, thinking of using a modified differential
between the drive hubs and direct connect the electric
motor to that differential. I'd like to see the car
reach 80mph, with a typical cruising speed of 65 on
the highway. So I'm trying to figure out a gear ratio
to look for, that would accomplish this speed range
for a typical dc traction motor rpm sweet spot.

Any enlightnment on the proper math formula would be
greatly appreciated.

> Here ya go, transaxle :
>
>
http://www.surpluscenter.com/Item.asp?UID=2007102516472855&catname=powerTrans&item=13-1431

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I'd suggest you find a Geo Metro 5-speed transaxle,
they are small and light and can be had relatively
cheap and easy.
Jack
--- "M. Barkley" <[email protected]> wrote:

> The transaxle you propose below, is 13.25/1 in
> forward. So is this math correct: My wheels have
> to
> go 800 revolutions to travel 1 mile, Therefore
> 13.25
> x 800 = 10,600rpm for the motor if directly
> connected.
> Does this mean for the vehicle to reach 60mph, the
> motor would have to run this 10,600rpm continuously
> stay at that cruising speed?
>
> I ask, because I've found a donor VW, without a
> tranny, thinking of using a modified differential
> between the drive hubs and direct connect the
> electric
> motor to that differential. I'd like to see the car
> reach 80mph, with a typical cruising speed of 65 on
> the highway. So I'm trying to figure out a gear
> ratio
> to look for, that would accomplish this speed range
> for a typical dc traction motor rpm sweet spot.
>
> Any enlightnment on the proper math formula would be
> greatly appreciated.
>
>
> > Here ya go, transaxle :
> >
> >
>
http://www.surpluscenter.com/Item.asp?UID=2007102516472855&catname=powerTrans&item=13-1431
>
>
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
Your math is correct. To determine the correct gear ratio for your
vehicle for a single-speed setup, take the desired rpm you want to drive
your motor at 60 mph and divide it by 800. For example, if I have a
motor that I want to be at 4000rpm at 60mph, I want my gear ratio to be
4000/800 or 5.

If you have questions regarding whether this is an appropriate gear for
overall performance, you might try searching the archives, because the
transmission vs. no transmission thing has been discussed extensively.

If you have questions as to whether that transaxle would be appropriate
for a 60 mph vehicle, my personal opinion is a resounding NO. That
looks like a golf cart part, and the specs indicate that as well.

Brian

P.S. But it might work really well with a certain 5hp Baylor on a go
cart!

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of M. Barkley
Sent: Thursday, October 25, 2007 4:13 PM
To: [email protected]; Electric Vehicle Discussion List
Subject: [EVDL] Don't have a clue regarding RPM, MPH, Gear ratio's

The transaxle you propose below, is 13.25/1 in forward. So is this math
correct: My wheels have to go 800 revolutions to travel 1 mile,
Therefore 13.25 x 800 = 10,600rpm for the motor if directly connected.
Does this mean for the vehicle to reach 60mph, the motor would have to
run this 10,600rpm continuously stay at that cruising speed?

I ask, because I've found a donor VW, without a tranny, thinking of
using a modified differential between the drive hubs and direct connect
the electric motor to that differential. I'd like to see the car reach
80mph, with a typical cruising speed of 65 on the highway. So I'm
trying to figure out a gear ratio to look for, that would accomplish
this speed range for a typical dc traction motor rpm sweet spot.

Any enlightnment on the proper math formula would be greatly
appreciated.

> Here ya go, transaxle :
>
>
http://www.surpluscenter.com/Item.asp?UID=2007102516472855&catname=power
Trans&item=13-1431

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev

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Here is the formula for calculation mph per overall ratio.

RPM x Tire Circumference In Inches
Mph = ---------------------------
Overall Ratio x 1056

To measure the rolling tire circumference, put a mark on the tire and one on
the floor and rotated one turn and measure between two marks.

Let say you tires are about 83 inches in circumference which is about the
norm and your motor is at 6000 rpm, than:

6000 x 83 498000
MPH = ------------ = ------- = 39.9 mph
13.25 x 1056 13492

Formula converted for RPM:

MPH x Ratio x 1056 60 x 13.25 x 1056
RPM = ------------------ = ----------------- = 10114 rpm
Tire Circumference 83

The 13.25:1 is normally a ratio for a 1st gear transmission in some EV's.
This is about the same ratio for my transmission in 2nd gear which I can
take the EV up 35 mph at 6000 rpm and then I shift to a 5.57 gear for a
speed of 60 mph at 4000 rpm or about 90 mph at 6000 rpm.

To find out what each gear ratio in a transmission is, rise the vehicle on
jack stands. Put a chalk mark on the drive line and a chalk mark on the
shaft of the motor before the transmission. Put in 1st gear and rotate the
motor until the drive shaft makes one turn, while keeping count of the motor
turns. If the motor turns two times while the drive shaft turns one time,
then you have roughly a 2.1:1 1st gear ratio. Then repeat for each gear.

To check for the differential gear, put a chalk mark or a masking tape for a
finer line. Then rotate the the drive shaft until the wheel makes one turn.
If the drive shaft turns four times and a little bit, while the wheel makes
one turn, then you may have a 4.11:1 differential ratio.

The overall ratio, is the 1st gear ratio times the differential gear ratio.
Lite weight vehicles may have a 2.2:1 1st gear and a 4.0:1 differential
which makes a overall ratio of 2.2 x 4.0 = 8.8:1 overall ratio.

A heavy weight vehicle may have a 4.0:1 1st gear and a 5.0:1 axle gear ratio
which would be about 20:1 overall ratio.

Roland

----- Original Message -----
From: "Jack Murray" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Thursday, October 25, 2007 5:54 PM
Subject: Re: [EVDL] Don't have a clue regarding RPM, MPH, Gear ratio's

> I'd suggest you find a Geo Metro 5-speed transaxle,
> they are small and light and can be had relatively
> cheap and easy.
> Jack
> --- "M. Barkley" <[email protected]> wrote:
>
> > The transaxle you propose below, is 13.25/1 in
> > forward. So is this math correct: My wheels have
> > to
> > go 800 revolutions to travel 1 mile, Therefore
> > 13.25
> > x 800 = 10,600rpm for the motor if directly
> > connected.
> > Does this mean for the vehicle to reach 60mph, the
> > motor would have to run this 10,600rpm continuously
> > stay at that cruising speed?
> >
> > I ask, because I've found a donor VW, without a
> > tranny, thinking of using a modified differential
> > between the drive hubs and direct connect the
> > electric
> > motor to that differential. I'd like to see the car
> > reach 80mph, with a typical cruising speed of 65 on
> > the highway. So I'm trying to figure out a gear
> > ratio
> > to look for, that would accomplish this speed range
> > for a typical dc traction motor rpm sweet spot.
> >
> > Any enlightnment on the proper math formula would be
> > greatly appreciated.
> >
> >
> > > Here ya go, transaxle :
> > >
> > >
> >
> http://www.surpluscenter.com/Item.asp?UID=2007102516472855&catname=powerTrans&item=13-1431
> >
> >
> >
> > _______________________________________________
> > For subscription options, see
> > http://lists.sjsu.edu/mailman/listinfo/ev
> >
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

_______________________________________________
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Yes, and that's high even for some electric motors. Plus, you'd probably be=
able to go beyond 60 mph. If that suits your needs, then great.
=

As a electric Beetle owner, I recommend getting a VW transmission and using=
it. Clutch or clutchless, your choice. I'm running 128v and I can get up t=
o 70 mph using my 8v batteries.
=

Here are the gear ratios for a standard VW Beetle transmission:
http://www.thesamba.com/vw/forum/viewtopic.php?t=3D227453&highlight=3Dgear+=
ratio
=

I'm running an ADC L91-4003 6.7" motor. Typically my shift pattern is like =
this:
=

1st- 0-33 mph
2nd- 33-57 mph
3rd- 57-70 mph
=

At 33 mph I draw 60 battery amps
57 mph I draw 80 amps
70 mph I draw 120 amps.
=

Accelerating to those speeds is another story altogether. ;-) I draw anyw=
here from 120 battery amps to 200. I try not to exceed 180 battery amps. I'=
m sure Roland is wincing right now. . I have checked my brush leads and=
they aren't discolored.
=

Hope this helps,
Rich A
---------------------------------------------------------------------------=
--
Message: 28Date: Thu, 25 Oct 2007 16:12:50 -0700 (PDT)From: "M. Barkley" <k=
[email protected]>Subject: [EVDL] Don't have a clue regarding RPM, MPH, Gear=
ratio'sTo: [email protected], Electric Vehicle Discussion List<[email protected]=
su.edu>Message-ID: <[email protected]>Content-Type=
: text/plain; charset=3Diso-8859-1 The transaxle you propose below, is 13.2=
5/1 inforward. So is this math correct: My wheels have togo 800 revolutions=
to travel 1 mile, Therefore 13.25x 800 =3D 10,600rpm for the motor if dire=
ctly connected.Does this mean for the vehicle to reach 60mph, themotor woul=
d have to run this 10,600rpm continuouslystay at that cruising speed? I as=
k, because I've found a donor VW, without atranny, thinking of using a modi=
fied differentialbetween the drive hubs and direct connect the electricmoto=
r to that differential. I'd like to see the carreach 80mph, with a typical =
cruising speed of 65 onthe highway. So I'm trying to figure out a gear rati=
oto look for, that would accomplish this speed rangefor a typical dc tracti=
on motor rpm sweet spot. Any enlightnment on the proper math formula would =
begreatly appreciated.
_________________________________________________________________
Help yourself to FREE treats served up daily at the Messenger Caf=E9. Stop =
by today.
http://www.cafemessenger.com/info/info_sweetstuff2.html?ocid=3DTXT_TAGLM_Oc=
tWLtagline
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