I think a 20" is OK if the right tire is on it. These "rubber band", low profile tires on a 20" just make it "ghetto" for me. Im a sidewall guy.
The 1st Shelby's to have 20"s had the low profile tires & my 1st impression of the car when I saw it, "ugh, those tires, wtf
". But thats just me.
18"'s & tuck em up in the wheel wells I say.