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Old 09-03-2012, 07:31 AM   #13 (permalink)
Tire Geek
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Originally Posted by 2000mc View Post
capriracer- on the rolling resistance coefficient chart you have on Barry's Tire Tech it seems generally, taller and wider is better.
however the exact order that the 14" tires in sizes i might switch to seems inconsistent 185/75, 185/70, 195/70, 185/65, 175/65, 175/70. i have 175/70-14 tires.

195/70 out performed by a 185/70, 175/70 outperformed by 175/65, and 215/75 outperformed by a 3 sizes smaller tire 185/75.

do you think that overall rule of thumb, wider, taller is better works, and the specific tires used caused this? or do you think that there are certain sizes that cause an inherent disadvantage somehow?
What I did was run a regression analysis on all the data to derive a generaized formula that covers the 3 dimensions used in the tire sizing. The formula has an r squared value of 66% - which is NOT very good - meaning the formula doesn't explain the numbers very well. I would need to add more factors to get a better fit.

However, the data is what it is. It is the ONLY data I have seen that compares tires only by size. I have my doubts that this is EXACTLY true - and that may be why the data doesn't fit very well. I am pretty sure there are OE tires in that mix, but they do not jump out as outliers.

So I stand by the analysis. It is the best information available.

A side note: While you looked at 14", the same principle ought to work in 15". That why I did the regression. It looks at ALL the data.

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