225/35R19 vs 235/40R18
Switching from 225/35R19 to 235/40R18 increases the overall diameter by 5.1 mm (0.8%). That is within the usual ±3% guideline.
| 225/35R19 | 235/40R18 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 225 mm | 235 mm | +10.0 |
| Sidewall height | 78.8 mm | 94.0 mm | +15.2 |
| Rim diameter | 482.6 mm | 457.2 mm | -25.4 |
| Overall diameter | 640.1 mm | 645.2 mm | +5.1 |
| Circumference | 2,010.9 mm | 2,027.0 mm | +16.1 |
| Revolutions | 497 per km | 493 per km | -4.0 |
Speedometer effect
With 235/40R18 fitted on a car calibrated for 225/35R19, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.4 km/h |
| 80 km/h | 80.6 km/h |
| 100 km/h | 100.8 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.
225/35R19 dimensions · 235/40R18 dimensions · Open in calculator