Bridgestone article on rolling resistance

[California98Civic]

That double claim of larger diameter (for lower RR) and narrower width (for drag reduction) has come up before in our debates, but maybe without resolution. So it is great to see confirmation from a manufacturer. The i3 tires drew all of our attention. But the claim here, by Bridgestone of increased wet weather traction is new. Anyone believe that?

[Ecky]

Originally Posted by California98Civic

That double claim of larger diameter (for lower RR) and narrower width (for drag reduction) has come up before in our debates, but maybe without resolution. So it is great to see confirmation from a manufacturer. The i3 tires drew all of our attention. But the claim here, by Bridgestone of increased wet weather traction is new. Anyone believe that?

I've been reading a lot about tires lately, and here's what I've picked up:

Many people put wider tires on performance cars to get a larger contact patch and more traction. This is WRONG. More contact patch does improve traction (despite what the standard friction equation from physics would have you think). However, contact patch is mostly a function of weight and air pressure, so a wider tire (all else being equal) has a contact patch with the same area that's wider but less long. This will give increased traction from lateral movement (e.g. cornering) but actually reduce traction when accelerating and braking, especially in wet conditions.

[Frank Lee]

Originally Posted by Ecky

I've been reading a lot about tires lately, and here's what I've picked up:

Many people put wider tires on performance cars to get a larger contact patch and more traction. This is WRONG. More contact patch does improve traction (despite what the standard friction equation from physics would have you think). However, contact patch is mostly a function of weight and air pressure, so a wider tire (all else being equal) has a contact patch with the same area that's wider but less long. This will give increased traction from lateral movement (e.g. cornering) but actually reduce traction when accelerating and braking, especially in wet conditions.

I measured contact patch at various pressures and it didn't correlate well at all.

[Ecky]

Originally Posted by Frank Lee

I measured contact patch at various pressures and it didn't correlate well at all.

One article I read shows that with soft rubber compounds, you can actually roughly estimate the corner weight in a vehicle based on contact patch and pressure.

Sidewall stiffness and rubber compounds also affect the slope of the curve, of course, but the relationship is there. Or, should be at least.

[Hersbird]

The contact patch size doesn't matter in that the weight per square inch goes up or down and therefore the traction available never changes. What a bigger contact patch helps with is the ability not to melt the rubber when the limits of traction are exceeded. Once the rubber starts to melt it is like driving on butter. So in the rain (or snow and ice) the narrow tire isn't melting and the smaller contact patch has an ability to poke through the standing water to the pavement.

[CapriRacer]

Originally Posted by Frank Lee

I measured contact patch at various pressures and it didn't correlate well at all.

Frank, Did you publish your results?

Also, Frank is right. The idea that you can calculate the size of a tire's contact patch knowing the load and the tire pressure is incorrect. Also, a wider tire has a slightly larger footprint than a narrower tires - all other things being equal.

There used to be a webpage called "Fact or Fiction" that had data from Avon tires that proved this point, but that web page has disappeared. You can find other studies that have the data, but you have to wade through a lot of other data, because that is usually NOT the point of the study.

Update: I found an archived version here: https://web.archive.org/web/20090225...on-tires-1.htm

[freebeard]

Neil Blanchard provided the historical context.

Originally Posted by California98Civic

But the claim here, by Bridgestone of increased wet weather traction is new. Anyone believe that?

https://duckduckgo.com/?q=hydroplaning

I would if I could: BMW i3 tires on MG-TC 19x3 wire wheels with knockoffs, else red Model A 19x4s from Dayton Wire Wheel. Adapted to 4x100mm.

edit:
Like this, only 19s:

[Interstatement]

On my 2WD Ranger, I switched from 225/70R15 Goodyears on 15x7 steel rims to 215/70R16 Continental CrossContact LX25s (with “EcoPlus+ Technology” whatever that means exactly) on 16x7 alloy rims. I went this route for several reasons:

-The steelies were a lousy design that had stainless steel face glued to the fronts, which Ford did on many wheels. Unfortunately, this design traps moisture and salt, so the rims were rusting out. The rims weighed about 27 lbs. on a bathroom scale.

-225/70R15 is slipping toward obscurity as a tire size. Choices are limited and underwhelming.

-215/70R16 is the tire size for many popular compact SUVs and crossovers, so more choices, including LRR varieties, are available. Rolling diameter is pretty close, about 4/10 of an inch taller— within the tolerance of treadwear.

-16x7 rims that fit my Ranger were made in vast quantities for Rangers, Explorers, Mustangs, and Crown Victorias, to name a few. The Ranger/Explorer alloys I got cheap on Craigslist weighed 17 lbs. each on the same bathroom scale, a 10 lb. savings per wheel!

Uncorrected MPG figures are basically unchanged, which is actually a slight improvement, given that the new wheels are .4” taller than the old ones. The most dramatic difference is that the truck handles markedly better, especially in wet conditions! The rear wheels used to break loose at the drop of a hat in a drizzle, whereas I can now downshift on a wet curve without wagging its tail.

[kach22i]

Just posting a image.


https://forums.pelicanparts.com/off-...-pics-427.html


And they seem to get wider all the time.

[aerohead]

Some of the highest mpg vehicles have the 1920-esque tires.
Aero 2002, Renault Vesta-II, Daihatsu UFE-III, VW XL1.