From a stock 265/70R17 (31.6 in)
| New size | Height | Taller by | 60 on the dash is | 70 on the dash is | 10,000 indicated miles is |
|---|---|---|---|---|---|
| 275/70R17 | 32.2 in | +1.7% | 61.0 mph | 71.2 mph | 10,174 |
| 285/70R17 | 32.7 in | +3.5% | 62.1 mph | 72.4 mph | 10,349 |
| 285/75R17 | 33.8 in | +7.0% | 64.2 mph | 74.9 mph | 10,704 |
| 33x12.50R17 | 33.0 in | +4.4% | 62.6 mph | 73.1 mph | 10,441 |
| 35x12.50R17 | 35.0 in | +10.7% | 66.4 mph | 77.5 mph | 11,074 |
The rule
True speed = indicated speed × new height ÷ old height
Each inch of extra height on a tire about 31.6 in tall is roughly 3.2%. The odometer and trip meter under-count by the same amount, so mileage-based service intervals and warranty miles are also affected. A shorter tire does the opposite.
Fixes
Many vehicles can be recalibrated with a programmer or at a dealer; ask for the new tire height in inches. Check the dash against GPS in the speedometer calculator. Bigger tires also change gearing: see the regear chart.
Calculated from the size alone. Real tires vary a little by brand and model, and the loaded radius is a bit smaller. Confirm the wheel width range, clearance, load index and speed rating for your vehicle. See how to read a tire size, the load index chart and the speed rating chart.