When setting up your American Pony Car, don't forget that there are minimum wheel (rim with tyre) diameter requirements for front and rear. The purpose of this rule is to keep the cars as accurate-looking as possible. Here's what the rule says:
Tyres: Type of tyre is free. Front tyre minimum diameter: 17mm on wheel. Rear tyre minimum diameter: 19mm on wheel. Rear tyre maximum tread width: 8mm (excluding sidewall).
Of course the wheels must be stock as ship with the car.