255/50R20 vs 255/55R20 at a glance
| Measure | 255/50R20 (current) | 255/55R20 (new) | Difference |
|---|---|---|---|
| Overall height | 30.04 in | 31.04 in | +1.00 in (+3.34%) |
| Width | 10.04 in (255 mm) | 10.04 in (255 mm) | +0 mm |
| Sidewall | 5.02 in | 5.52 in | +0.50 in |
| Wheel | 20 in | 20 in | +0 in |
| Circumference | 94.4 in | 97.5 in | +3.2 in |
| Revs per mile | 671.4 | 649.7 | −21.7 |
Verdict: check clearance and speedometer
Over 3% and up to 5%: worth checking clearance, the speedometer and gearing before you buy. Going from 255/50R20 to 255/55R20 is a 3.3% increase in overall height (+1.00 in), and the vehicle sits about 0.50 in higher. The tire is the same width. The 3% rule of thumb comes from Discount Tire and 1010tires; it is not a guarantee of fit.
True speed and odometer
| Speedometer shows | You are really doing | Difference |
|---|---|---|
| 35 mph | 36.2 mph | +1.2 mph |
| 45 mph | 46.5 mph | +1.5 mph |
| 55 mph | 56.8 mph | +1.8 mph |
| 60 mph | 62.0 mph | +2.0 mph |
| 65 mph | 67.2 mph | +2.2 mph |
| 70 mph | 72.3 mph | +2.3 mph |
| 75 mph | 77.5 mph | +2.5 mph |
Odometer: 1,000 indicated miles is 1,033 real miles, and 10,000 is 10,334.
The math
255/50R20: 20 + 2 × (255 × 50% ÷ 25.4) = 30.04 in. 255/55R20: 20 + 2 × (255 × 55% ÷ 25.4) = 31.04 in. Change = 31.04 ÷ 30.04 − 1 = +3.34%. True speed at 60 = 60 × 31.04 ÷ 30.04 = 62.01 mph.
Check next
- Regear and RPM at cruise for this swap
- Speedometer and odometer correction
- Other sizes within ±3% of 255/50R20
Calculated from the size alone. Real tires vary a little by brand and model, and the loaded radius is a bit smaller. Confirm the wheel width range, clearance, load index and speed rating for your vehicle. See how to read a tire size, the load index chart and the speed rating chart.
Size pages: 255/50R20 · 255/55R20. More swaps: all tire size comparisons.