275/35R21 vs 255/45R21
255/45R21 is outside the ±3% rule as a replacement for 275/35R21: the diameter differs by +5.10%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 255/45R21 on a car calibrated for 275/35R21, the speedometer reads 57.1 mph when you're really doing 60, and the odometer under-counts by 5.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.5 mph |
| 45 mph | 47.3 mph |
| 60 mph | 63.1 mph |
| 70 mph | 73.6 mph |
| 80 mph | 84.1 mph |
Other sizes close to 275/35R21
- 275/35R21 vs 245/45R20+0.36%
- 275/35R21 vs 275/40R20+0.29%
- 275/35R21 vs 265/40R21+2.69%
- 275/35R21 vs 315/35R20+0.36%
- 275/35R21 vs 295/35R21+1.93%
- 275/35R21 vs 255/40R21+1.58%
- 275/35R21 vs 265/35R21-0.96%
- 275/35R21 vs 245/35R21-2.89%
- 275/35R21 vs 305/35R20-0.61%
- 275/35R21 vs 285/40R21+4.89%
- 275/35R21 vs 325/30R21+0.34%
- 275/35R21 vs 275/40R21+3.79%
Questions
Can I replace 275/35R21 with 255/45R21?
255/45R21 is outside the ±3% rule as a replacement for 275/35R21: the diameter differs by +5.10%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 275/35R21 and 255/45R21?
255/45R21 is 1.46" taller and 20 mm narrower; the sidewall is +0.73". At an indicated 60 mph you'd actually be doing 63.1 mph.
Will 255/45R21 fit on 275/35R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.