235/55R18 vs 235/65R16
Switching from 235/55R18 to 235/65R16 decreases the overall diameter by 3.8 mm (0.5%). That is within the usual ±3% guideline.
| 235/55R18 | 235/65R16 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 235 mm | 235 mm | +0.0 |
| Sidewall height | 129.2 mm | 152.8 mm | +23.6 |
| Rim diameter | 457.2 mm | 406.4 mm | -50.8 |
| Overall diameter | 715.7 mm | 711.9 mm | -3.8 |
| Circumference | 2,248.4 mm | 2,236.5 mm | -11.9 |
| Revolutions | 445 per km | 447 per km | +2.0 |
Speedometer effect
With 235/65R16 fitted on a car calibrated for 235/55R18, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 49.7 km/h |
| 80 km/h | 79.6 km/h |
| 100 km/h | 99.5 km/h |
| 120 km/h | 119.4 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 235 mm tire has a manufacturer-specified rim width range.
235/55R18 dimensions · 235/65R16 dimensions · Open in calculator