Tire Size Calculator

Version 3.5

Copyright © 1998-2017 Scott Galaba

The Gear Speed and Tire Size Calculator application is available for download on the App Store for iOS iPad, iPhone, iPod and Mac OS X, and on Google Play for Android devices.

About Tire Size

This app is for comparing the original equipment tire size to alternate after market tire sizes, with results include percentage(%) difference and new speedometer reading. All calculations are round up. Calculations are to be treated as approximate only, due to variations in how tires are manufactured. Navigation bar "S" provides return and drop-down menu functions are found in the upper right.

Calculations can be printed or saved into a PDF by selecting Share PDF Results.

Multitasking / Slide Over / Split View support is included for the latest iOS iPad devices.

To use this app you need seven (7) pieces of information. The tire tread width, sidewall ratio, wheel rim diameter from each of the two tires to be compared, and a speedometer reading to be used to compute the effect the after market tire size has on your speedometer.

The following is an example to help to decode a tire size like 185/65R14
185 = tire width in millimeters, measured from sidewall to sidewall
65 = sidewall ratio, the ratio of sidewall height to tire width
14 = wheel rim diameter in inches

This app is setup to compare either U.S. / English (rim size in inches) or TRX (rim size in millimeters) tires.

App Reviews

RPM to MPH/KPH
Rating - 5 Stars
by faa440 - May 7, 2016
Review Source - Apple iTunes

Very nice app that converts engine rpm to vehicle speed by taking into consideration transmission gear ratio, final drive ratio, and tire size. Results are presented in a table, comprehensive graph and printed document. My Dodge Charger has an 8 speed AT that can be switched into a paddle shifted MT and this app handles all 8 rations. In addition when I change between the Dodge approved 20 inch summer and the 18 inch winter tires, this app calculates any resulting vehicle speed differences. you can also input the new gear ratio if you're one who changes out the rear axle gearing for street vs. track. Author is responsive to suggestions and continually seeks ways to improve the app. Well Done.

U.S. (English) Tires Information and Comparison


Tire Size PDF Results

alt : test.pdf

Metric (TRX) Tires Information and Comparison


TRX Tire Size PDF Results

alt : test.pdf


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