175/70R13 vs 185/55R15
Switching from 175/70R13 to 185/55R15 increases the overall diameter by 9.3 mm (1.6%). That is within the usual ±3% guideline.
| 175/70R13 | 185/55R15 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 175 mm | 185 mm | +10.0 |
| Sidewall height | 122.5 mm | 101.8 mm | -20.7 |
| Rim diameter | 330.2 mm | 381.0 mm | +50.8 |
| Overall diameter | 575.2 mm | 584.5 mm | +9.3 |
| Circumference | 1,807.0 mm | 1,836.3 mm | +29.3 |
| Revolutions | 553 per km | 545 per km | -8.0 |
Speedometer effect
With 185/55R15 fitted on a car calibrated for 175/70R13, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.8 km/h |
| 80 km/h | 81.3 km/h |
| 100 km/h | 101.6 km/h |
| 120 km/h | 121.9 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 185 mm tire has a manufacturer-specified rim width range.
175/70R13 dimensions · 185/55R15 dimensions · Open in calculator