depending on who built your car, you will probaly max out with a 9" rim on there, so i would say use an 8,5" tyre on a 9" rim for the road, I dont go by the numbers on the tyres on road tyres as they are not accurate as the sidewall tread is included in the measurement, You'll have to take a rule with you when you buy. As tyre widths vary with manufacturer.

For your 15's and again depending on whose built the car, you'll have to run a low profile on something like a 185 to 205 width if you want to lower the car.

The car should fit the wheels, not the wheels fit the car, as the wheels hub height dictates the suspension pick up points.