Gear Speed 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 Gear Speed

This 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. 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.

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

To use this app you need five (5) pieces of information. The tire size of the driven wheel (tread width, sidewall 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 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

The transmission gear ratio needs to be expresses in a decimal formate, like 1.444.

The differential ratio 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 Data Entry and Results


Gear Speed PDF Results

alt : test.pdf


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