50% of your EV energy consumption comes from wheels and tires

[aerohead]

Originally Posted by j-c-c

If we accept the premise that any loss of traction by a selected tire has no real word downside (which I strongly do not accept), it seems to me an extreme solution might be best, a very narrow tread-less hard compound high pressure slick would be the ultimate fuel saver, least rolling resistance, least frontal area, and likely the quietest (sound being wasted energy).

That's exactly correct, and the exact realization of GM's Sunraycer engineer's experience in 1987, at the World Solar Challenge.
Bridgestone would go on to produce their ECOPIA, solar race car tire to exactly these specifications, with the exception of the rubber compound.
Safety was paramount for the teams competing, and the tires had to perform to stringent wet and dry traction criteria. They were only good for a rated 200-miles of treadwear. Better than F-1, INDYCAR, and NASCAR.

[j-c-c]

So no real world application for normal street driving like most of us here endure on this forum, got it.

[aerohead]

Out of respect for j-c-c's instincts, I located the original article from CAR and DRIVER, August, 1992, pages 95-96:
'How Tough Are the Compact Spares', by Don Schroeder.
Thirty-one years later, my brain managed to pretty-much destroy the original contents.
* A Corvette, and a Ford Taurus LX were the test cars.
* Only 'ONE' tire was replaced by the donut.
* Cars were tested OEM, with a donut on the front, and then on the rear.
* They were tested for:
1) acceleration to 60-mph
2) braking from 70-mph
3) emergency double lane change
4) roadholding on the 300-ft skidpad.
--------------------------------------------------------------------------------------
For the Corvette:
* The compact spare had 56% the width of the OEM tire it replaced.
* 0-60 took 1/10th second longer, 5.2-secs vs 5.1-secs with donut on rear ( front was not tested ), it's a RWD car.
* 70-to-0 was 174-ft, compared to 165-ft with donut on front
* 70-to-0 was 174-ft vs 165, on the rear.
* lane change was 62.2-mph vs 62.9-mph at front.
* 59.6-mph vs 62.9-mph at rear
* On the skidpad, 0.84G vs 0.92g at front
* 0.90g vs 0.92g at rear
-------------------------------------------------------------------------------------
For the Taurus:
* No width comparison data was provided
* 0-60 was 9.7-secs vs 9.8-secs at front ( a FWD car )
* 70-to-0 = 214-ft vs 200-ft @ front
* 215-ft vs 200-ft @ rear
* lane change was 53.6-mph vs 57.5-mph at front
* 57.2-mph vs 57.5-mph at rear
* 0.73G vs 0.76g at front
* 0.76g vs 0.76g at rear

[aerohead]

* load capacity increases in direct proportion to the enclosed air volume.
* lower profile tires must be accompanied by wider sections or offset by stronger and more expensive construction techniques.
* At a given load capacity, if a tire is widened, it's contact patch widens, however the contact patch becomes proportionately 'shorter.'
* The wider tire may exhibit higher cornering grip, however, may give up some braking grip.
* The wider tire is more prone to hydro-planing unless aqua-channels are engineered into the tread design to compensate.

[Phase]

Can someone explain the difference in fuel economy of a 15 inch rim but a thicker tire versus a 17 inch rim but skinnier tire? Both would be the same diameter top to bottom

[freebeard]

Agreed on all five points.

Phase -- That's [the inverse of] his first two points.

[CapriRacer]

Originally Posted by Phase

Can someone explain the difference in fuel economy of a 15 inch rim but a thicker tire versus a 17 inch rim but skinnier tire? Both would be the same diameter top to bottom

The problem here is that tire size doesn't have as much effect as the tread rubber does.

Put another way, the variation between tires of the same size is way, way bigger than the difference between tire sizes. upwards of 50% difference versus single digit percent.

I go into more detail here: Barry's Tire Tech:
Rolling Resistance and Fuel Economy (Continued)

[bwilson4web]

I appreciate the reports you've accumulated. About two years ago, the video author did a YouTube video about EV wheel size vs efficiency:
https://youtu.be/NYvKxsYFqO8?si=Rwh6LX41z47XUgfG&t=382

Here is another analysis with an EV emphasis on efficiency impact:
https://youtu.be/8pM9o2Ifcro?si=oc7e1923zbc2_X1Q

A former bicyclist (1970s), I had direct mechanical input to the size of the tires. Fatter, wider tires required significantly more force to move but they could deal with soft and rough terrain. In contrast, narrow, high-pressure tires, 100 psi, were almost effortless on pavement compared to fatter, wider, lower pressure, 50 psi tires. Even today, my BMW i3 has taller, narrower tires than my Tesla Model 3.

There is a lot of 'tire marketing' versus 'tire testing'. Worse, tire models within a brand can (and do) easily disappear or get changed. That part is maddening.

I monitor both tire pressure and temperature. The temperature seems to correlate with rolling resistance, higher temperature, higher rolling drag.

Speculation, we could put different tires on the non-driven wheels and after alignment, observe temperature on the road at the same tire pressure. The cooler tire would be the more efficient. Get a second, efficient one and the less efficient tire goes into storage, returned, or sold.

Bob Wilson

[j-c-c]

Originally Posted by aerohead

Out of respect for j-c-c's instincts, I located the original article from CAR and DRIVER, August, 1992, pages 95-96:
'How Tough Are the Compact Spares', by Don Schroeder.
Thirty-one years later, my brain managed to pretty-much destroy the original contents.

For the Corvette:
* The compact spare had 56% the width of the OEM tire it replaced.
* 0-60 took 1/10th second longer, 5.2-secs vs 5.1-secs with donut on rear ( front was not tested ), it's a RWD car.

I'm sticking with my instincts.
I'll address the above easy to debunk claim, even though acceleration claims are not important IMO in assessing the merits of real-life use of narrow tires vs tires wider/larger tire contact patch for mileage increase.

If the Corvette noted here has a limited slip differential or similar, which is likely, and the tested wider single other tire had sufficient grip needed for the engine/driveline, the contact patch configuration of the narrower/donut tire tested would matter little, and if it had less rotational mass, it could account for improved tested acceleration numbers. That appears to be what the test indicates.

That oversight, intentional, or inept, on C&D part, if correctly quoted here, IMO puts all the reported numbers and conclusions, in question.

[freebeard]

This is mostly about trains, but it draws comparisons with cars:

Which Is Easier To Pull? (Railcars vs. Road Cars)

At 10:14 there is a very interesting clip of a thin-fender era car in a wind tunnel.

Trains have drag that cars don't, like flanges squealing on the sides of the rail on corners. But car tire's tread blocks deform on corners and lift one edge. So tires performance should be different on a [industry standard 100ft] circle versus a straight track.

Oh, and he could not pull a flat car by hand. I've done so a few times, but I used a car bar.


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