Tire Size Calculator
Gear Speed and Tire Size Application
The Gear Speed and Tire Size Calculator application is available for download on the App Store for iOS iPad, iPhone, and macOS Mac devices. Release 3.9.37 adds support for iOS 17, iPhone 15, iPhone 15 plus, iPhone 15 Pro, iPhone 15 Pro Max, iPhone SE, iPad, iPad Air, iPad Pro (11-inch), iPad Pro (12.9-inch), iPad mini and as a (Designed for iPad) app for Apple Silicon (arm64) Mac’s including the latest MacBook Air, MacBook Pro, iMac, Mac mini, Mac Studio, Mac Pro and Apple Vision Pro.
Tire Size Application
The Tire Size 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.
See U.S. (English) Tire Size - PDF Results and
Metric (TRX) Tire Size - PDF Results for example outputs.
Multitasking / Slide Over / Split View support is included for the latest iOS iPad devices.
To use the application, (7) pieces of information are required: Tire Size of the driven wheel (Tire Tread Width, Sidewall Aspect Ratio, and 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 example is to help to decode a tire size like 185/65R14
185 = Tire Tread Width in millimeters, measured from sidewall to sidewall
65 = Sidewall Aspect Ratio, the ratio of sidewall height to tire width
14 = Wheel Rim Diameter in inches or millimeters
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) Tire Size - PDF Results
The example U.S. (English) Tire Size - PDF Results shown below was generated directly from the Gear Speed and Tire Size Calculator application.
Metric (TRX) Tire Size - PDF Results
The example Metric (TRX) Tire Size - PDF Results shown below was generated directly from the Gear Speed and Tire Size Calculator application.
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