When it comes time to put a new set of wheels and tires on a car, most hot rodders want to stuff as big of a tire as possible in the rear. The front end is less about maximum size and more about turning radius - making sure you stay off the fenders at full lock. To measure for maximum rim width and the correct backspacing, you can always use a straight edge and a measuring tape to figure out what you need, but a Percy's Wheelrite fitment tool makes the process much easier. The tool bolts to your hub, and is adjustable for a wide range of sizes, and also features an adjustable wire that simulates the size and shape of your desired tire.
Percy's Wheelrite Fitment Tool