This article was originall written for V8TV. It details a slick way to exactly determine the right size wheel & tire combination for your car or truck using the Wheelrite invention by Percy's Performance.

Wheel and Tire 101 - Measuring and Fitting Properly
******* a few excerpts below, but the entire article is worth checking out:
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Selecting wheels and tires is a crucial element when it comes to styling your ride… as every pro builder will tell you, there’s nothing more important than the car’s stance and attitude, both of which are directly to the wheel and tire choices.

If you’re going to run wheels and tires that are the same size as stock, than the choice is simple. But if you’re going to upsize the combination, there are a couple things to keep in mind when measuring the for the right sizes.....

....All these measurements are easy to take from a wheel, but what do you do when you are trying to measure a car to see what wheel will fit and look right?.....We found this tool called the Wheelrite from Percy’s High Performance. The Wheelrite is a wheel and tire simulator which bolts to the hub and lets you fit a wheel and tire to the car and actually check the clearance before you order your wheels.