MPH Offset / Corrected MPH
Enter your original and new tire sizes into the table below and select a base speed to calculate your speedometer's offset and your vehicles actual speed.
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Corrected Speed Calculation Basics
Your vehicle's speedometer reading is based on the diameter of the original tires so when you install larger (or smaller) tires, your speedometer reading will no longer be accurate. Additionally, the greater the difference in tires size and the faster you drive, the more inaccurate your speedometer will be. Ideally, you should install new ring and pinion gears (see out gear ratio calculator) or an engine programmer to adjust for the new tires, however, until then, you can calculate your estimated speed by dividing your new tire diameter by the OEM tire diameter and multiplying that by your vehicle speed.
[ (New Tire Diameter / OEM Tire Diameter) x Vehicle Speed ] = [ (37 / 31) x 60 ] = [ 71.61 MPH ]
Actual Speeds For Popular Tire Changes
31" OEM Tires
| Speedometer | 35" Tires | 37" Tires | 40" Tires |
| 30 MPH | 33.9 MPH | 35.8 MPH | 38.7 MPH |
| 45 MPH | 50.8 MPH | 53.7 MPH | 58.1 MPH |
| 60 MPH | 67.7 MPH | 71.6 MPH | 77.4 MPH |
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33" OEM Tires
| Speedometer | 35" Tires | 37" Tires | 40" Tires |
| 30 MPH | 33.9 MPH | 35.8 MPH | 38.7 MPH |
| 45 MPH | 50.8 MPH | 53.7 MPH | 58.1 MPH |
| 60 MPH | 67.7 MPH | 71.6 MPH | 77.4 MPH |
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