235/45R18 vs 255/35R19
Switching from 235/45R18 to 255/35R19 decreases the overall diameter by 7.6 mm (1.1%). That is within the usual ±3% guideline.
| 235/45R18 | 255/35R19 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 235 mm | 255 mm | +20.0 |
| Sidewall height | 105.8 mm | 89.2 mm | -16.6 |
| Rim diameter | 457.2 mm | 482.6 mm | +25.4 |
| Overall diameter | 668.7 mm | 661.1 mm | -7.6 |
| Circumference | 2,100.8 mm | 2,076.9 mm | -23.9 |
| Revolutions | 476 per km | 481 per km | +5.0 |
Speedometer effect
With 255/35R19 fitted on a car calibrated for 235/45R18, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 49.4 km/h |
| 80 km/h | 79.1 km/h |
| 100 km/h | 98.9 km/h |
| 120 km/h | 118.6 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 255 mm tire has a manufacturer-specified rim width range.
235/45R18 dimensions · 255/35R19 dimensions · Open in calculator