Posted by Roger on August 19, 1999 at 17:32:07:
In Reply to: Tire Size posted by Bob on August 18, 1999 at 11:24:49:
David's explination is essentially correct. However most major tire companies here in the US follow Tire & Rim Assoc Design guide which gived the "Design" section width, "Design" OD and something called "Minimum size factor.
The Min Size factor can be calculated by measuring the OD and Section on the measurement rim, adding together and comparing to the Min Size factor. The tire should exceed the Min Size factor.
Tire & Rim does give a tol on section saying it shouldn't be more than 104% of design.
They also give a tol on section height of 103% of design.
Example P205/60R15 on 6.0 rim Design section 8.23, Design OD 24.69 Min Size factor 32.36.
So the min section theoretically could be calculated as follows:
103% x Sect Ht x 2 = OD
103 x 4.845 x 2 = 24.98
32.36-24.98 = 7.38 section or almost 1" small but that is highly unlikely as most tires are designed to be near nominal. Also the tread with the belts etc is one of the more expensive parts of the tire so it makes little sense to go big in OD (lots of tread).
Hope this wasn't too technical.
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