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Old 05-18-2009, 04:28 PM   #7 (permalink)
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Originally Posted by Ernie Rogers View Post
Hello, Racer, you might have to explain your questions--

I don't get the first one. The tire would be mounted on a wheel and set to the desired pressure. Maybe you are suggesting there is a change in pressure between before and after mounting on a car? Such a change could be corrected for.
If you were to measure a tire immediately after inflating it - and then measure it 24 hours later, you'd find the tire would be physically bigger. I think there is even an ASTM test procedure that covers this - and we refer to the dimensions as "24 hour dimensions" to indicate these are "grown" dimensions.

I don't know why I just thought of this, but it is common in most (if not all)tire testing to wait 24 hours after the tire is mounted to conduct the test to account for this growth.

But I guess where I was just brainstorming on this was: It is common for those of us who have done tire testing, to add a few extra psi so that the pressure after growth is correct without adjustment.

Plus I would think that since a half a psi is considered by many to affect the spring rate enough to be felt in racecars, then the pressure for any test where the spring rate becomes important, would also need to be precisely set. For example, tire force and moment testing was always done with a pressure gauge that measured to the nearest 0.1 psi.

So I was wondering - out loud - if you take a tire and repeatedly test it, would small increments in pressure result in large enough differences to make discerning differences in tires difficult.

Originally Posted by Ernie Rogers View Post

Second question, first part--Is it true that tread area dominates rolling resistance?


Originally Posted by Ernie Rogers View Post
That suggests that tread design is also an important factor, if true.
Only in the sense that the volume of rubber is part of the "design". I'm sure that tread patterns with many small elements (like a winter tire) would generate more movement - and therefore more RR - but my sense is this movement is only of minor significance compared to what effect the tread compound has overall.

Originally Posted by Ernie Rogers View Post

Second part--what is a rim flange protector?


It is an projection out from the sidewall that protects the rim flange from hitting the curb (or whatever). It adds quite a bit of weight to the tire, but hardly affects the RR at all! But I wonder if dropping a tire from a height might engage enough of the sidewall to affect the results.
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