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      05-04-2014, 11:34 AM   #21
M6-Coupe
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Quote:
Originally Posted by Boss330 View Post
That's true.

But ideally you don't want to use diameter X 3,14 when calculating the rolling circumference of a tire

A tires rolling circumference is influenced by the contact patch to the road. This creates a "flat spot" on the tire, meaning it's not a true circular shape anymore... AFAIK this means that tires of different dimensions use different "pi" to calculate rolling circumference. At least that's what ETRO (European Tire and Rim Organization) does, and they are "the law" used by the manufacturers and authorities here

The above means that just calculating tolerance based on diameter X 3,14 won't give you the correct % deviation in some cases.
well yes and no
"pi" is always "pi" but what you are referring to is the actual diameter which is changed based on those flat spot you explained and cause different circumferences. My point is the percentage! those "flat spot" are not more than 2-3 mm and this amount for a over 600mm diameter is far less than 5% you mentioned. we are not talking about worn tires or low pressure tires which have a lot diameter and circumference deviation and we are not talking about rainy day and uneven roads which affect the calculation and you know those effects
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