275/55R20 vs 255/60R20

255/60R20 is 0.14 in (3.5 mm) taller than 275/55R20, a +0.43% diameter difference. With the speedometer set for 275/55R20, an indicated 60 mph is 60.3 mph on 255/60R20.

Is this a safe swap?

Diameter difference +0.43%: under 1%

By overall diameter alone, 255/60R20 is a near match for 275/55R20; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

275/55R20 vs 255/60R20 differences
Measurement	275/55R20	255/60R20	Difference	% diff
Overall diameter	31.91 in (810.5 mm)	32.05 in (814.0 mm)	+0.14 in (+3.5 mm)	+0.43%
Sidewall height	5.95 in (151.3 mm)	6.02 in (153.0 mm)	+0.07 in (+1.8 mm)	+1.16%
Section width	10.83 in (275.0 mm)	10.04 in (255.0 mm)	−0.79 in (−20.0 mm)	−7.27%
Circumference	100.25 in (2,546.3 mm)	100.68 in (2,557.3 mm)	+0.43 in (+11.0 mm)	+0.43%
Revolutions per mile	632	629	−3	−0.43%

True speed with the speedometer calibrated for 275/55R20
Indicated	Actual on 275/55R20	Actual on 255/60R20	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 255/60R20 raises the vehicle by 0.07 in (1.8 mm) at the axle (half the +3.5 mm diameter difference).

255/60R20 is 0.14 in taller than 275/55R20 and 20 mm narrower, a 0.43% difference in overall diameter.

With the speedometer calibrated for 275/55R20, an indicated 60 mph is actually 60.3 mph on 255/60R20, and revolutions per mile change from 632 to 629.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 275/55R20

Other comparisons with 255/60R20

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.