Wheel and tire upgrades have been popular in the car hobby almost since day one. Needless to say that with Mustangs it’s often an upgrade that we think of early on. The right wheel and tire combination can make a car look fantastic. However, the wrong combination can cause unwanted issues. Awkward tire gaps, rubbing, speedometer offset, and even diminished performance can all become a factor if your tires aren’t properly sized for the application. Not to mention tire rub and other interference issues.

So how can you determine what fits your Mustang based on the factory fitment, what issues you might have, and how far off your speedometer is going to be? American Muscle, one of the largest aftermarket retailers of Mustang wheels and tires, now has a Mustang Tire Size Calculator to help with some of these issues. This calculator includes stock sizing data for Mustangs from 1994 through 2012 and has been designed specifically for use with Mustangs. This is the only calculator of it’s kind specifically for Mustangs available to the public online. You can also choose to manually enter the tire size of nearly any vehicle, though the AM calculator is setup specifically for late model Mustangs.

Changing tire sizes, or wheel and tire sizes can cause fitment issues if you don’t select the right parts the first time.

The calculator will show you the difference in sidewall height, radius, tire diameter, circumference and revolutions per mile. It also has the ability to show you what your speedometer offset will be at 60 mph. For example, we recently sized some new tires for our 1998 Mustang GT. Entering in the car’s year and model information showed us that we did in fact originally have 16-inch wheels on the car from the factory. Factoring in our new rear tire size of 275/40/18, we can see that our speedometer is off by 3.6 percent at 60 mph. This means that when the speedometer shows 60 we’re actually running 62 mph. This information could be critical to avoiding a speeding ticket, and to getting the car setup properly.

So if you’re in the market for wheel and tire upgrade for your ‘Stang, or just curious as to what will fit it, check out the Mustang Tire Size Calculator, only available from American Muscle.