TireSizesFinder

255/60R18 vs 235/55R20

235/55R20 is 0.13 in (3.3 mm) taller than 255/60R18, a +0.43% diameter difference. With the speedometer set for 255/60R18, an indicated 60 mph is 60.3 mph on 235/55R20.

Is this a safe swap?

Diameter difference +0.43%: under 1%

By overall diameter alone, 235/55R20 is a near match for 255/60R18; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 255/60R18 (30.05 in) vs 235/55R20 (30.18 in)255/60R1830.05 in × 10.04 in235/55R2030.18 in × 9.25 in
Side profile and tread width, drawn to the same scale.
255/60R18 vs 235/55R20 differences
Measurement255/60R18235/55R20Difference% diff
Overall diameter30.05 in (763.2 mm)30.18 in (766.5 mm)+0.13 in (+3.3 mm)+0.43%
Sidewall height6.02 in (153.0 mm)5.09 in (129.3 mm)−0.94 in (−23.7 mm)−15.52%
Section width10.04 in (255.0 mm)9.25 in (235.0 mm)−0.79 in (−20.0 mm)−7.84%
Circumference94.40 in (2,397.7 mm)94.80 in (2,408.0 mm)+0.41 in (+10.4 mm)+0.43%
Revolutions per mile671668−3−0.43%
True speed with the speedometer calibrated for 255/60R18
IndicatedActual on 255/60R18Actual on 235/55R20Difference
30 mph30.0 mph30.1 mph+0.1 mph
60 mph60.0 mph60.3 mph+0.3 mph
75 mph75.0 mph75.3 mph+0.3 mph

Ride-height change: 235/55R20 raises the vehicle by 0.06 in (1.6 mm) at the axle (half the +3.3 mm diameter difference).

235/55R20 is 0.13 in taller than 255/60R18 and 20 mm narrower, a 0.43% difference in overall diameter.

With the speedometer calibrated for 255/60R18, an indicated 60 mph is actually 60.3 mph on 235/55R20, and revolutions per mile change from 671 to 668.

235/55R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 255/60R18.

Size pages

Other comparisons with 255/60R18

Other comparisons with 235/55R20

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