225/40R19 vs 235/45R18
Switching from 225/40R19 to 235/45R18 increases the overall diameter by 6.1 mm (0.9%). That is within the usual ±3% guideline.
| 225/40R19 | 235/45R18 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 225 mm | 235 mm | +10.0 |
| Sidewall height | 90.0 mm | 105.8 mm | +15.8 |
| Rim diameter | 482.6 mm | 457.2 mm | -25.4 |
| Overall diameter | 662.6 mm | 668.7 mm | +6.1 |
| Circumference | 2,081.6 mm | 2,100.8 mm | +19.2 |
| Revolutions | 480 per km | 476 per km | -4.0 |
Speedometer effect
With 235/45R18 fitted on a car calibrated for 225/40R19, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.5 km/h |
| 80 km/h | 80.7 km/h |
| 100 km/h | 100.9 km/h |
| 120 km/h | 121.1 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.
225/40R19 dimensions · 235/45R18 dimensions · Open in calculator