Originally Posted by W///
If the width is the same, why would a larger diameter wheel be better as you claim?
Diameter of the whole wheel on rear axle in M3 is identical regardless of the factory rim size. Tire on 19 inch rim has shorter/lower sides, which means that is less "giving" on twisty roads. And that, in my book, is always better.
Of course I realize we are comparing very similar tires and difference in performance between 265/40 - 18 and 165/35 - 19 will be miniscules. However I refuse to accept that 18-inch wheel will be better in any performance category except, to some point, straight line accelerations. After reading the C&D test I can agree that smaller wheel with taller tire could have here slight advantage, but I cannot agree with those statements I read in this tread:
"19's are an OPTION for looks not performance" and "The only reason to get 19's are for looks."
LarThaL himself states::
The M3 should have come with 18x9.5 front and 18x10.5" rear with 265/35/18 front and 285/35/18 rear tires. You can get this exact set-up in the proper offsets using Apex wheels. I have driven this set-up and it is better in every way possible when it comes to performance and ride.
So... why 35 tires are better on 18 inch wheels and do nothing on 19 inch rims? The whole tread is about factory options and we do not have from factory 285/35-18 tires. We can get 265/40-18 or 265/35-19. So maybe... just maybe 19 inch wheels are not only for looks?
I have 19 inch rims, because I bought used car with that options. I drove several M3's with 18 and 19 inch wheels, on streets, with moderate speed. No track experience with 18 inch wheels, however even on streets I can feel how much sharper car is with 19 inch wheels and 35 series tires. Sure, ride is slightly harsher, but if I want to feel like riding on clouds, I can borrow my wife's Audi A4 or my daughters old Taurus.
If we look at the road tests published in car magazines we won't get any answers either - difference is too small and varies from one test to other. So in real world it is coming down to personal preferences, where looks are not the least important.
I can give you that much: 19 inch will not help a lot, but certainly they will not compromise performance either.