Originally Posted by polonus
Sure. That's why cars like Bugatti (21" in rear!), Audi R8, all Ferraris and Lamborghinis, Corvette ZR1 and many others high performance cars use 19 and 20 inch rims. Just for looks, compromising performance.
Of course you can buy "regular" Corvette with 18 inch rims, but no ZR1. ZR1 is "good looking" model, for performance go with C6 Coupe on 18 inch wheels.
I did too. And that is why I say you have no idea what you are talking about. You right - big difference. 18 inch tires are "comfy" - or, to be precise, little more comfortable on potholes then 19 inch tires. Better ride? Sure. Better performance? In your dreams.
Either you didn't drive back to back M3 with 18 and 19 inch wheels, or you didn't pay any attention. There is a good reason why you cannot buy any Ferrari or Lamborghini on 18 inch wheels and it is not looks.
And I'm not saying, that 18 inch wheels cannot perform extremely well, but when you compare tires 265/40-18 to 265/35-19 there is no way car will handle better on tires with smaller rim, taller sides. Difference may be small, but always that difference will be for 19 inch tire advantage.
...Unless, of course, ride quality is your goal. In that case I suggest you to buy a Buick.
Certain cars require larger wheels to clear large brake discs and calipers. In fact, this is how the whole large wheel trend started. Then the fad took on a life of its own. And yes, beyond a certain point, larger wheels are just for looks. And yes, even the exotic car makers will use them because this is what sells. They are in the business, after all, of selling cars.
You also can't really compare between different cars. A given car with its OEM spec tire on a 20" wheel may, in fact, have the same sidewall height as different car on an 18" wheel. A 295/30 for example has the same sidewall height whether it is on an 18", 19" or 20" wheel. This is not what we are referring to here. We are referring here to increasing the wheel size, and simultaneously decreasing the tire aspect ratio on a given car to maintain OEM rolling diameter.
On other larger cars, you just need a larger wheel to aesthetically balance the look, however, this, again, is not related to performance. They also don't necessarily decrease the tire's aspect ratio. They just use a larger tire with the same aspect ratio on the larger wheel. When a tire sidewall is too large, responsiveness will be diminished, but going to a shorter sidewall only goes so far. So while 16" or 17" is clearly leaves you with too much sidewall on an M3 (if they would even clear the brakes), 18" does not.
Look at most track set-ups on the M3. They all run 18's. If 19's are so superior in terms of performance, why do most serious track set ups use 18? By your argument, 20" is even better than 19". How many 20" track set ups do you see? Why don't you see professional race cars using the largest wheels possible?