I am making this tool available to you, so you can quickly make your own comparisons. The numbers generated by this calculator are theoretical. Actual tire diameters are effected by inflation and load. Actual MPH numbers will probably vary slightly. USE THIS CALCULATOR AT YOUR OWN RISK!
To comply with local and federal speed laws, you should have your speedometer calibrated by a licensed speedometer shop.
These calculations were designed for a manual transmission. I do not have any experience with automatic transmissions. As such, these numbers may not be accurate for automatic transmissions.
If you have any questions or comments, direct them to Daris.
Note:JavaScript must be enabled in your browser for the calculator to work.
| Common Tires Sizes | ||
| Size | Dia. | RPM |
| 11.00 R 20 | 42.6 | 488 |
| 11x22.5 | 41.4 | 502 |
| 11x24.5 | 43.3 | 478 |
| 12x22.5 | 42.7 | 485 |
| These numbers were derived by sampling three or four tires from different manufacturers, and then averaging the numbers. For the most accurate numbers, use the ACTUAL diameter of your drive tires. | ||
| Gear Ratios | ||||
| Gear Ratio | = | rearend ratio | * | 4th Gear ratio |
| (example: my 4106 has a 4 1/8 (4.125:1) rearend and 4th gear is .808:1) | ||||
| 3.333 | = | 4.125 | * | .808 |