165/70R14 vs 185/55R15
Switching from 165/70R14 to 185/55R15 decreases the overall diameter by 2.1 mm (0.4%). That is within the usual ±3% guideline.
| 165/70R14 | 185/55R15 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 165 mm | 185 mm | +20.0 |
| Sidewall height | 115.5 mm | 101.8 mm | -13.7 |
| Rim diameter | 355.6 mm | 381.0 mm | +25.4 |
| Overall diameter | 586.6 mm | 584.5 mm | -2.1 |
| Circumference | 1,842.9 mm | 1,836.3 mm | -6.6 |
| Revolutions | 543 per km | 545 per km | +2.0 |
Speedometer effect
With 185/55R15 fitted on a car calibrated for 165/70R14, 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 | 119.6 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 185 mm tire has a manufacturer-specified rim width range.
165/70R14 dimensions · 185/55R15 dimensions · Open in calculator