Sorry to say this, but now that I looked at the tire size list, the biggest tires(front and back, equal size)are on the Z concept, which are 20"s....look really odd on my MR Beetle.
Ohh, and if you want faster cars, use the power multiplyer...you can adjust the power(both hp and torque)easily, and not get turbo lag or just lag from using switched parts(try putting NA on a turbo engine...you get from idle to 3k rpm in 20 sec lol).
I try using either turbo or NA(based on the engine) from the car the engine is from, or from the car that the engine is now in. That seems to work fairly well.