Tire Comparison Calculator

Tire Comparison Calculator

Last Updated August 13, 2019 | Chris Cervenka

Boss 302 Wheel Fitment

In many cases when you’re looking to upgrade to a new set of wheels & tires for your vehicle, you’ll likely be changing the tire size that came as original equipment on your vehicle. It’s important to not only make sure the tire size that you’re looking to get fits your new wheels correctly but also has a similar diameter or tire height, otherwise, your speedometer could read incorrectly.

The reason your speedometer could read incorrectly is that most newer vehicles don’t use a speedometer gear in the transmission to calculate wheel speed, it’s done using a mathematical equation electronically using your tire’s revolutions per mile, or revs/mile for short. Revs/mile is accounting for how many revolutions your tires make in one mile, then equating that to vehicle speed on your dashboard.

To use this tool, all you have to do is insert your current tire size first, then your intended new tire size second and you’ll be able to compare and contrast if it’s a good fit for your vehicle.

Tire Comparison Calculator

Enter Tire Sizes Below

Current Tire
/ R
New Tire
/ R
Compare

Results

Current Tire
New Tire
Difference
Sidewall
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-
-
Section Width
-
-
-
Radius
-
-
-
Diameter
-
-
-
Circumference
-
-
-
Revs / Mile
-
-
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Speedometer Reading
Actual Speed - MPH
Clear All

An example of this tool in action would be if you own a 2019 Mustang GT with the Performance Package. The rear tires on this car are a 275/40-19 on a 9.5-inch wide wheel. Let’s say you’re looking for some more meat in the rear and want to upgrade to a wider wheel & tire package. If you were to hop up to a 20” x 11” rear wheel, you’d not only be looking at 20-inch tires now but also a wider wheel. You’re going to have to make sure that your new tire has a similar tire diameter, otherwise, your speedometer will read incorrectly.

For those that are looking at the above combination, we typically recommend going with a 295/35-20 or 305/30-20 rear tire. That way, the factory 27.7-inch tire (729 revs/mile) comes in close with a 28.1-inch 295/35-20 (717 revs/mile) or 27.2-inch 305/30-20 (742 revs/mile). Now, the speedometer won’t be exactly correct in comparison to the factory tire size, but it’ll be close. The only way to make sure it’s 100% correct is change the revs/mile in your vehicle’s computer using a tuner.

The Equations

The equations for this tire size calculator are actually rather simple! It can get a bit confusing going back and forth between metric and standard measurement systems, but it’s all sorted out in the calculations. Once you have your current and new tire sizes inserted into the calculator, you go from there. Whether you’re looking to calculate revolutions per mile (revs/mile), tire circumference, tire height or actual MPH when comparing two tires, we have you covered!

TireSidewall = (TireWidth) x ((TireAspectRatio x 0.01) / 25.4)

TireSectionWidth = (TireWidth / 25.4)

TireHeight = (((TireWidth / 25.4) x (TireAspectRatio x 0.01) x 2) + WheelSize)

TireRadius = (TireHeight / 2)

TireCircumference = (TireHeight x 3.14159265359)

RevsPerMile = ((63360) / (TireHeight x 3.14159265359)

ActualMPH = ((NewTireHeight / CurrentTireHeight) x SpeedometerReading)

We hope that this tool has been helpful in your tire purchase. If you have any questions, don’t hesitate to call our Customer Service Line at 1-800-888-6473 and we’ll be more than happy to help you find a tire that fits your new wheel all while keeping your speedometer in check. Be sure to follow our social channels for the best automotive content out there!

Tire Comparison Calculator

Purchasing a new set of tires can be exciting but have you considered how different size tires could impact your vehicle? CJ's tire conversion calculator can help you identify the differences between your current tire set up and your new tires to see how the new tires may affect your speedometer.