225/60R18 vs 235/75R15
Switching from 225/60R18 to 235/75R15 increases the overall diameter by 6.3 mm (0.9%). That is within the usual ±3% guideline.
| 225/60R18 | 235/75R15 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 225 mm | 235 mm | +10.0 |
| Sidewall height | 135.0 mm | 176.2 mm | +41.2 |
| Rim diameter | 457.2 mm | 381.0 mm | -76.2 |
| Overall diameter | 727.2 mm | 733.5 mm | +6.3 |
| Circumference | 2,284.6 mm | 2,304.4 mm | +19.8 |
| Revolutions | 438 per km | 434 per km | -4.0 |
Speedometer effect
With 235/75R15 fitted on a car calibrated for 225/60R18, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.4 km/h |
| 80 km/h | 80.7 km/h |
| 100 km/h | 100.9 km/h |
| 120 km/h | 121.0 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 235 mm tire has a manufacturer-specified rim width range.
225/60R18 dimensions · 235/75R15 dimensions · Open in calculator