255/65R18 vs 255/70R17
Switching from 255/65R18 to 255/70R17 increases the overall diameter by 0.1 mm (0.0%). That is within the usual ±3% guideline.
| 255/65R18 | 255/70R17 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 255 mm | 255 mm | +0.0 |
| Sidewall height | 165.8 mm | 178.5 mm | +12.7 |
| Rim diameter | 457.2 mm | 431.8 mm | -25.4 |
| Overall diameter | 788.7 mm | 788.8 mm | +0.1 |
| Circumference | 2,477.8 mm | 2,478.1 mm | +0.3 |
| Revolutions | 404 per km | 404 per km | +0.0 |
Speedometer effect
With 255/70R17 fitted on a car calibrated for 255/65R18, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.0 km/h |
| 80 km/h | 80.0 km/h |
| 100 km/h | 100.0 km/h |
| 120 km/h | 120.0 km/h |
Larger tires make the car go faster than the speedometer shows. Most speedometers also read slightly high from the factory.
Before you change size
- Check the sizes approved for your vehicle on the door-jamb placard or in the owner's manual.
- Check clearance to suspension, brakes and arches at full lock and full compression.
- Match or exceed the original load index and speed rating.
- Wider tires need an appropriate rim width; a 255 mm tire has a manufacturer-specified rim width range.
255/65R18 dimensions · 255/70R17 dimensions · Open in calculator