Maybe you'd be best to get one of these. Expensive, but custom wheels and tires ain't cheap. This is inexpensive insurance
Wheelrite - Wheel & Tire Simulator by Percy's High Performance, Percy's High Performance, PCY-01201 - Tuner Tools, the inside line
Also here's the basics on wheel and tire fitment. You prolly know this already. I do but a refresher is sometimes needed due to my CRS.
Wheel & Tire 101 - Measuring Wheels and tires the right way