255/45R20 vs 235/55R20
235/55R20 is outside the ±3% rule as a replacement for 255/45R20: the diameter differs by +3.93%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 235/55R20 on a car calibrated for 255/45R20, the speedometer reads 57.7 mph when you're really doing 60, and the odometer under-counts by 3.9%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.2 mph |
| 45 mph | 46.8 mph |
| 60 mph | 62.4 mph |
| 70 mph | 72.8 mph |
| 80 mph | 83.1 mph |
Other sizes close to 255/45R20
- 255/45R20 vs 235/55R19+0.49%
- 255/45R20 vs 245/45R20-1.22%
- 255/45R20 vs 255/50R19+0.01%
- 255/45R20 vs 275/40R20-1.29%
- 255/45R20 vs 255/50R20+3.46%
- 255/45R20 vs 245/40R20-4.54%
- 255/45R20 vs 265/50R20+4.81%
- 255/45R20 vs 245/50R20+2.10%
- 255/45R20 vs 275/45R20+2.44%
- 255/45R20 vs 255/40R20-3.46%
- 255/45R20 vs 265/45R20+1.22%
- 255/45R20 vs 285/35R20-4.07%
Questions
Can I replace 255/45R20 with 235/55R20?
235/55R20 is outside the ±3% rule as a replacement for 255/45R20: the diameter differs by +3.93%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/45R20 and 235/55R20?
235/55R20 is 1.14" taller and 20 mm narrower; the sidewall is +0.57". At an indicated 60 mph you'd actually be doing 62.4 mph.
Will 235/55R20 fit on 255/45R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 235 mm tire and the fender clearance.