[alexbeatle]

Hello, folks.
Converting my VW Bay Window from 1972. Thinking of all the forces acting on it to increase efficiency.
Cannot change the shape of the bus, don't want to lower it, don't want to restrict much of the weight (it's a camper after all!).
As of now, in terms of majour mprovements, the plan is to make underbody covers. And (obviously) keep the tyre pressure per spec.

Then I've heard about something called "low rolling resistance tyres". Has anybody tried them on the bus conversions?

Doing some research, the requirements for the tyres for these busses are quite tight - passenger size (14"), but must handle truck load (up to 5000lbs).
Please let me know your thoughts.

 

[remy_martian]

Most EV's are 4000-6000 lb these days, so tire loads on low RR tires are a non-issue. They don't have to be 14", the vehicle has a max tire diameter and width. The bias plies it came with from the factory are garbage.

You're pushing so much air with that box, anything you do is a bit of a joke on aero unless to plan to run it on a track at high speeds. Keeping air out from underneath is more important if you do anything. Without a rear diffuser, it's arguable that you WANT turbulence under it to reduce drag.

 

[brian_]

Fortunately, any available modern tire that roughly matches the original overall size and meets the load requirement will probably be intended for small commercial vehicles in Europe (which is what the Transporter was, after all) and will be a reasonably low rolling resistance design. Just don't put really wide tires on it, but do go for a lower-profile tire on a larger-diameter wheel (is there a suitable 15" size?) if you want to keep the drag down.

 

[remy_martian]

Interesting take on tires, here:

Goodyear’s ElectricDrive GT EV Tire Is a Peek at Where We’re Headed

Many EVs make do with low-rolling resistance tires, but now Goodyear is producing a tire specifically for higher-performance EVs like the Tesla Model Y.

www.motortrend.com

The bug camper would look good on 19's

 

[alexbeatle]

Interesting take on tires, here:

Goodyear’s ElectricDrive GT EV Tire Is a Peek at Where We’re Headed

Many EVs make do with low-rolling resistance tires, but now Goodyear is producing a tire specifically for higher-performance EVs like the Tesla Model Y.

www.motortrend.com

The bug camper would look good on 19's

Interesting thought. Putting on larger wheels, however, would raise the bus -> increase the reference area (bus facing the air flow).....hence will increase the drag force the bus will be facing...

 

[remy_martian]

Um, no, dear child.

You keep the diameter of the tire the same (reread my posting), which lowers the sidewall height and improves both handling and rolling resistance. The width can remain roughly the same.

 

[brian_]

The bug camper would look good on 19's

Appearance is certainly a matter of personal aesthetic preference. I think a ultra low profile tire on a 19" wheel on a VW van looks ridiculous, but many like that look and if they do, they should go for it.

But a 185R14 (the stock size, depending on year, etc) is only 25.5" (648 mm) overall, so with 19" wheels if the overall diameter were not increased the sidewalls would only be 3.25" (83 mm) each. With a 185 mm section width that's an aspect ratio of 45... and lower with the larger width which would actually be used. The load capacity with such a short sidewall would be low.

You can get a 225/35R19 (e.g. Michelin Pilot Sport 4S), but even in an extra load (XL) version (roughly equivalent to Load Range C, requiring 50 PSI for full load capacity) it has a load index of only 88, corresponding to 1,235 lbs per tire (and 10% less if this is considered a passenger car tire used on a van). And that's with 40 mm more section width than stock - in a quick look, I didn't see anything narrower of this overall diameter. Even wider would get a bit more capacity, but even 225 mm is pretty wide for this van and wider makes drag worse.

Perhaps moderation is the key: a 215/50R17 XL (e.g. Michelin Pilot Sport All-Season 4) would match the original in height, would be a reasonable width, and would have more capacity (load index 95, 1,521 lbs... before derating for van use)... still an XL tire so 50 PSI. That's only 10 mm more

One selection approach is to copy modern small commercial vans. For instance, the Ram ProMaster City (a Fiat Doblò rebadged) and Ford Transit Connect both use 215/55R16 tires which are the same overall diameter as the VW van would use, and they're available in XL for load index 97 (and possibly in commercial types) to support these vehicles. The Nissan NV200 - a similar small van - uses (at least in some cases) a 185/60R15C (the "C" means commercial service) with load index 94 (1,475 lbs) (e.g. Michelin Agilis)


The example links that I have used are to TireRack, just because their website is convenient to use for this sort of searching. They have filter criteria on the side of the page, including "Eco Focus":

Tires with an eco-focus are designed to conserve natural resources through methods such as improved fuel economy, long tread life and environmentally-conscious manufacturing techniques.

You might want to select that, to find lower rolling resistance, although it's not exactly that.