215/45R18 vs 245/40R18
Switching from 215/45R18 to 245/40R18 increases the overall diameter by 2.5 mm (0.4%). That is within the usual ±3% guideline.
| 215/45R18 | 245/40R18 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 215 mm | 245 mm | +30.0 |
| Sidewall height | 96.8 mm | 98.0 mm | +1.2 |
| Rim diameter | 457.2 mm | 457.2 mm | +0.0 |
| Overall diameter | 650.7 mm | 653.2 mm | +2.5 |
| Circumference | 2,044.2 mm | 2,052.1 mm | +7.9 |
| Revolutions | 489 per km | 487 per km | -2.0 |
Speedometer effect
With 245/40R18 fitted on a car calibrated for 215/45R18, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.2 km/h |
| 80 km/h | 80.3 km/h |
| 100 km/h | 100.4 km/h |
| 120 km/h | 120.5 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 245 mm tire has a manufacturer-specified rim width range.
215/45R18 dimensions · 245/40R18 dimensions · Open in calculator