255/60R20 vs 305/55R20
305/55R20 is outside the ±3% rule as a replacement for 255/60R20: the diameter differs by +3.62%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 305/55R20 on a car calibrated for 255/60R20, the speedometer reads 57.9 mph when you're really doing 60, and the odometer under-counts by 3.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.1 mph |
| 45 mph | 46.6 mph |
| 60 mph | 62.2 mph |
| 70 mph | 72.5 mph |
| 80 mph | 82.9 mph |
Other sizes close to 255/60R20
- 255/60R20 vs 275/55R20-0.43%
- 255/60R20 vs 275/60R20+2.95%
- 255/60R20 vs 255/55R20-3.13%
- 255/60R20 vs 265/60R20+1.47%
- 255/60R20 vs 285/55R20+0.92%
- 255/60R20 vs 285/60R20+4.42%
- 255/60R20 vs 275/50R20-3.81%
- 255/60R20 vs 33x12.50R20+2.97%
- 255/60R20 vs 295/55R20+2.27%
- 255/60R20 vs 285/50R20-2.58%
- 255/60R20 vs 245/60R20-1.47%
- 255/60R20 vs 305/50R20-0.12%
Questions
Can I replace 255/60R20 with 305/55R20?
305/55R20 is outside the ±3% rule as a replacement for 255/60R20: the diameter differs by +3.62%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/60R20 and 305/55R20?
305/55R20 is 1.16" taller and 50 mm wider; the sidewall is +0.58". At an indicated 60 mph you'd actually be doing 62.2 mph.
Will 305/55R20 fit on 255/60R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 305 mm tire and the fender clearance.