255/70R17 vs 265/65R18
Switching from 255/70R17 to 265/65R18 increases the overall diameter by 12.9 mm (1.6%). That is within the usual ±3% guideline.
| 255/70R17 | 265/65R18 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 255 mm | 265 mm | +10.0 |
| Sidewall height | 178.5 mm | 172.2 mm | -6.3 |
| Rim diameter | 431.8 mm | 457.2 mm | +25.4 |
| Overall diameter | 788.8 mm | 801.7 mm | +12.9 |
| Circumference | 2,478.1 mm | 2,518.6 mm | +40.5 |
| Revolutions | 404 per km | 397 per km | -7.0 |
Speedometer effect
With 265/65R18 fitted on a car calibrated for 255/70R17, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.8 km/h |
| 80 km/h | 81.3 km/h |
| 100 km/h | 101.6 km/h |
| 120 km/h | 122.0 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 265 mm tire has a manufacturer-specified rim width range.
255/70R17 dimensions · 265/65R18 dimensions · Open in calculator