Does anyone know if going to 20" rims I will loose any performance. Also how big can u go in the back and front without rubbing and the rubber sticking past the wheel well??? For a c63coupe

 

well performance really depends on a lot of factors ... for example rotational mass which tends to go up with larger rims as they require more material than a smaller wheel ... now there are really light wheels out there that will make this argument no longer apply. As long as you don't really go bigger or smaller in total diameter, there should be no difference. keep in mind that the bigger the rim the smaller the profile of the tire which can make for a poor ride (comfort) and personally I like a little meat on the sidewalls when i let the rear end cut loose.

 

you can go 9 in the front and i wouldnt go any bigger then 10 in the back, i have 10.5s and if i could do it over again i would just do 10 in the rear

 

20" is for show
18" is for go
19" is a good middle ground IMO

Very light weight 20" wheels would likely have no meaningful impact on performance other than being very uncomfortable. I wouldn't track them though and I would be VERY careful over potholes, etc.

 

^^^ what he said.