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      01-03-2013, 02:35 PM   #28
Adriansideways
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Drives: 2008 E90 M3
Join Date: Apr 2012
Location: Pretoria

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Quote:
Originally Posted by mlhj83
Quote:
Originally Posted by doug_999 View Post
check me if I'm wrong Sandy, but the M6 appears to have 20" wheels vs. the 19s on the M5.
Quote:
Originally Posted by SleepyE90 View Post
So you're saying that the m5 is at a disadvantage?
Quote:
Originally Posted by Adriansideways View Post
Bigger rims and wheels are not always a advantage! My E90 M3 is quicker on 18" than on the standard 19" on any track
If the M5 had 20" and the same PSS* tyres, it would be a bit quicker (lap time) than being on 19", but obviously still slightly slower than the M6.

In general, on a smooth surface, lower profile tyres will generate more grip in a corner due to less sidewall flex. Thus, if you compare the same tyre model with the same section width, but with different profiles, the lower profile tyre will be quicker round a track. The overall weight difference between the BMW M 18" and 19" with tyres on, or 19" and 20' with tyres on, isn't significant enough to make as much of a difference in lap times as sidewall flexing does. Straight line acceleration, however, should favour the lighter smaller diameter wheel, but cars spend more time in corners than they do on straights on most circuits.

I've tested my oem 219M 18s and 359M 19s with the same tyres with similar wear on the same track and the 19s generated a much better lap time and significantly less roll with improved steering response. Many people put track biased tyres on their 18s for practical reasons, which are obviously going to be quicker than 19s on the best road tyres.
Then please tell me why has all M vehicles have a normal tyre and not run-flats? Run flats has a stiff sidewall ? And why do formula one tyres have such soft sidewalls?
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