225/50R18 vs 255/35R20
Switching from 225/50R18 to 255/35R20 increases the overall diameter by 4.3 mm (0.6%). That is within the usual ±3% guideline.
| 225/50R18 | 255/35R20 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 225 mm | 255 mm | +30.0 |
| Sidewall height | 112.5 mm | 89.2 mm | -23.3 |
| Rim diameter | 457.2 mm | 508.0 mm | +50.8 |
| Overall diameter | 682.2 mm | 686.5 mm | +4.3 |
| Circumference | 2,143.2 mm | 2,156.7 mm | +13.5 |
| Revolutions | 467 per km | 464 per km | -3.0 |
Speedometer effect
With 255/35R20 fitted on a car calibrated for 225/50R18, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.3 km/h |
| 80 km/h | 80.5 km/h |
| 100 km/h | 100.6 km/h |
| 120 km/h | 120.8 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.
225/50R18 dimensions · 255/35R20 dimensions · Open in calculator