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      11-05-2013, 03:55 PM   #21
Finnegan
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Drives: Z4M/. Z3M, E36/46 M3
Join Date: Oct 2008
Location: Teaching the dog to slalom

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Like the Hack said it depends on the tire. However, as a general rule, running a tire to meet the minimum width requirement of the rim may not yield good results.

My data with the pyrometer show that the center, or middle of the tire tread does most of the work. Basically the tire is "pinched". That extra rubber doesn't achieve the objective of more grip, rather it's counterproductive. That was the case in trying PSS 245/40 and 275/35 on the stock rims, with -2.5 up front. The tires were not happy. Put them on 8.5 and 9.5 inch rims and tire temps (and grip) showed a considerable improvement.

Some tires, particularly those that are square (Star Specs, etc.) and have stiff sidewalls may work "ok" at min. rim size. R comps or competition tires may work fine as well (different rules). But for street tires, if the goal is more grip and effective contact patch, wider may not equal better.

Personally I'd go with the 235/265 combo with stock sized rims. YMMD, I'm offering what I could see at the track with a pyrometer, not trying to describe absolutes.
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