TireSizesFinder

255/50R20 vs 255/55R20

255/55R20 is 1.00 in (25.5 mm) taller than 255/50R20, a +3.34% diameter difference. With the speedometer set for 255/50R20, an indicated 60 mph is 62.0 mph on 255/55R20.

Is this a safe swap?

Diameter difference +3.34%: outside the ±3% guideline

By overall diameter alone, 255/55R20 falls outside the ±3% range commonly used as a guideline when replacing 255/50R20; speedometer and ride-height changes are larger. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 255/50R20 (30.04 in) vs 255/55R20 (31.04 in)255/50R2030.04 in × 10.04 in255/55R2031.04 in × 10.04 in
Side profile and tread width, drawn to the same scale.
255/50R20 vs 255/55R20 differences
Measurement255/50R20255/55R20Difference% diff
Overall diameter30.04 in (763.0 mm)31.04 in (788.5 mm)+1.00 in (+25.5 mm)+3.34%
Sidewall height5.02 in (127.5 mm)5.52 in (140.3 mm)+0.50 in (+12.8 mm)+10.00%
Section width10.04 in (255.0 mm)10.04 in (255.0 mm)0.00 in (0.0 mm)0.00%
Circumference94.37 in (2,397.0 mm)97.53 in (2,477.1 mm)+3.15 in (+80.1 mm)+3.34%
Revolutions per mile671650−22−3.23%
True speed with the speedometer calibrated for 255/50R20
IndicatedActual on 255/50R20Actual on 255/55R20Difference
30 mph30.0 mph31.0 mph+1.0 mph
60 mph60.0 mph62.0 mph+2.0 mph
75 mph75.0 mph77.5 mph+2.5 mph

Ride-height change: 255/55R20 raises the vehicle by 0.50 in (12.8 mm) at the axle (half the +25.5 mm diameter difference).

255/55R20 is 1.00 in taller than 255/50R20 and the same width, a 3.34% difference in overall diameter.

With the speedometer calibrated for 255/50R20, an indicated 60 mph is actually 62.0 mph on 255/55R20, and revolutions per mile change from 671 to 650.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 255/50R20

Other comparisons with 255/55R20

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.