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Speedometer Calibration Calculator And Information This calculator requires the use of Javascript enabled and capable browsers. This calculator is designed to give information related to tire size changes and the general impact they have on the calibration of a speedometer. It determines speedometer error and tire size information based on published and generally accepted tire dimensions as given by the standard US tire system (i.e. 205/45-ZR16). All calculations are based on the assumption of a new tire (as opposed to used) where the numbers on the tire accurately represent the dimensions. The calculator makes no effort to consider the result of any curvature effects of a tire when mounted on a rim it was not designed for. As an example, a 205 width tire mounted on a 15 inch diameter, 5 inch wide wheel will bulge significantly since the tire is designed to be flush with a 7 to 7.5 inch wide wheel. Under that stress, the tire will balloon outward from the sides, which is not taken into consideration within the limitations of this calculator. This tool gives the user a general but reasonable representation of alternative wheel effects. Enter the standard and new tire designation, aspect and wheel size. Click on Calculate for the results. You may click on Clear Values to do another calculation. Consult your tire specialist if you have further questions about such issues. U.S. Tire Information U.S. Tire Required Data Entry Enter Stock Tire Size 165 175 185 195 205 215 225 235 245 255 265 275 285 295 305 315 / 30 35 40 45 50 55 60 65 70 75 80 85 - R 8.5 9 9.5 10 11 12 13 14 15 16 17 18 19 20 Enter New Tire Size 165 175 185 195 205 215 225 235 245 255 265 275 285 295 305 315 / 30 35 40 45 50 55 60 65 70 75 80 85 - R 8.5 9 9.5 10 11 12 13 14 15 16 17 18 19 20 Enter A Reference Speedometer Value MPH or KMH Calculated Results After Tire Changes Stock tire width is inches. New tire width is inches. Stock tire thickness is inches. New tire thickness is inches. Stock tire diameter is inches. New tire diameter is inches. When the vehicle speedometer indicates MPH or KMH The vehicle speed is actually MPH or KMH.
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