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.

New Tire Diameter:
OEM Tire Diameter:
Speedometer (MPH):

Actual Speed: MPH
Speed Offset: %

(Calculated actual speed is only an estimate. For reference use only.)



NEW! - Need help with this calculator? Check out the new comments section below!


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
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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Street Legal Laws

To find the street legal laws for your state including maximum suspension lift heights and tire size rules visit LiftLaws.com