twk63

I just fitted Michelin Pilot Sport 4S tires on my RS and like most everyone else am not happy with how the 325s fit, they look stretched. So I am considering either going to 355s on the 21 inch wheels or downsizing to 20 inch wheels for better tire options.

anyone else go the latter route?

usrodeo4

I assume you have a reason, but why not just go with Cup2's?

twk63

I daily my RS and I prefer MP4S for longevity and the wet weather handling characteristics

Track Rat

You will likely have a traction control malfunction if you reduce the diameter of the rear tire, while not also reducing the front diameter. The speed sensors expect a difference in speed based on the difference in tire diameters front to rear. If you found a really tall sidewall that results in a similar tire diameter as the OEM 21” tires, then it would work. But I doubt that tire exists. Another option would be to run 19” front and 20” rear, but that won’t clear the PCCB brakes with sufficient gap with the wheel barrels.

I know this because I run 20” front and rear wheels at the track, and must run with traction and stability control off, or it cuts power and gives me a traction control error.

Track Rat

The Cup 2s likely have good wet weather handling characteristics. The MP4S are better in really cold temperatures and snow, but are not necessarily better in the wet. Most summer tires handle very well in the wet, unless they are extreme R compounds with limited rain grooves, such as the Cup 2Rs