Gear Speed 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 3.9.41 adds support for iOS 18, iPhone 16, iPhone 16 Plus, iPhone 16 Pro, iPhone 16 Pro Max, iPhone SE, iPad, iPad Air 11-inch, iPad Air 13-inch, iPad Pro 11-inch, iPad Pro 13-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.
Gear Speed Application
The Gear Speed app is for calculating the speed in MPH and KPH for a given tire size, transmission gear ratio, and differential ratio combination. The app can be used to compare different tire and wheel combinations to transmission gears and differentials with the results displayed in an interactive Gear Speed Graph. Preload gear ratios are provided and gear speeds 4-8 are selectable to tailor the output results for 4-speed, 5-speed, 6-speed, 7-speed and 8-speed transmission types. RPM Data Points are adjustable, allowing for further tailoring of the Gear Speed Graph and Results, to very specific RPM ranges, or to expanded the ranges beyond 9000 rpm. All calculations are round up. Calculations are to be treated as approximate only. Navigation bar "S" provides return and drop-down menu functions are found in the upper right.
The Gear Speed Graph is interactive and allows one to compare results when hovering over / selecting a line graph point(s) to display the Comparison Graph Results Panel. The Gear Speed Graph also allows one to compare, hide, or show a given gear speed line graph by selecting the corresponding legend indicator to toggle the display of the selected line graph.
Calculations can be printed or saved into a PDF by selecting Share PDF Results. See Gear Speed - PDF Results for example output.
Multitasking / Slide Over / Split View support is included for the latest iOS iPad devices.
To use the application, five (5) pieces of information are required: Tire Size of the driven wheel (Tire Tread Width, Sidewall Aspect Ratio, and Wheel Rim Diameter), Transmission Gear Ratios, and the Differential Ratio (Final Drive).
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
The Transmission Gear Ratio needs to be expresses in a decimal formate, like 1.444.
The Differential Ratio (Final Drive) needs to be expressed in a decimal formate, like 3.444. If you have the number expressed as a ring and pinion like 7:31, you need to calculate the ratio by dividing the second number (31) by the first (7) to come up with the correct format and in this case it would be 4.429.
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.
Gear Speed - PDF Results
The example Gear Speed - PDF Results shown below was generated directly from the Gear Speed and Tire Size Calculator application.
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