255/70R17 vs 265/60R18
Switching from 255/70R17 to 265/60R18 decreases the overall diameter by 13.6 mm (1.7%). That is within the usual ±3% guideline.
| 255/70R17 | 265/60R18 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 255 mm | 265 mm | +10.0 |
| Sidewall height | 178.5 mm | 159.0 mm | -19.5 |
| Rim diameter | 431.8 mm | 457.2 mm | +25.4 |
| Overall diameter | 788.8 mm | 775.2 mm | -13.6 |
| Circumference | 2,478.1 mm | 2,435.4 mm | -42.7 |
| Revolutions | 404 per km | 411 per km | +7.0 |
Speedometer effect
With 265/60R18 fitted on a car calibrated for 255/70R17, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 49.1 km/h |
| 80 km/h | 78.6 km/h |
| 100 km/h | 98.3 km/h |
| 120 km/h | 117.9 km/h |
Smaller tires make the speedometer read higher than the actual speed. 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 265 mm tire has a manufacturer-specified rim width range.
255/70R17 dimensions · 265/60R18 dimensions · Open in calculator