235/40R18 vs 265/35R18
Switching from 235/40R18 to 265/35R18 decreases the overall diameter by 2.5 mm (0.4%). That is within the usual ±3% guideline.
| 235/40R18 | 265/35R18 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 235 mm | 265 mm | +30.0 |
| Sidewall height | 94.0 mm | 92.8 mm | -1.2 |
| Rim diameter | 457.2 mm | 457.2 mm | +0.0 |
| Overall diameter | 645.2 mm | 642.7 mm | -2.5 |
| Circumference | 2,027.0 mm | 2,019.1 mm | -7.9 |
| Revolutions | 493 per km | 495 per km | +2.0 |
Speedometer effect
With 265/35R18 fitted on a car calibrated for 235/40R18, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 49.8 km/h |
| 80 km/h | 79.7 km/h |
| 100 km/h | 99.6 km/h |
| 120 km/h | 119.5 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 265 mm tire has a manufacturer-specified rim width range.
235/40R18 dimensions · 265/35R18 dimensions · Open in calculator