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Speed Change From Tire Size Change
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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