255/60R20 vs 275/50R21

275/50R21 is 0.22 in (5.6 mm) shorter than 255/60R20, a −0.69% diameter difference. With the speedometer set for 255/60R20, an indicated 60 mph is 59.6 mph on 275/50R21.

Is this a safe swap?

Diameter difference −0.69%: under 1%

By overall diameter alone, 275/50R21 is a near match for 255/60R20; 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.

255/60R20 vs 275/50R21 differences
Measurement	255/60R20	275/50R21	Difference	% diff
Overall diameter	32.05 in (814.0 mm)	31.83 in (808.4 mm)	−0.22 in (−5.6 mm)	−0.69%
Sidewall height	6.02 in (153.0 mm)	5.41 in (137.5 mm)	−0.61 in (−15.5 mm)	−10.13%
Section width	10.04 in (255.0 mm)	10.83 in (275.0 mm)	+0.79 in (+20.0 mm)	+7.84%
Circumference	100.68 in (2,557.3 mm)	99.99 in (2,539.7 mm)	−0.69 in (−17.6 mm)	−0.69%
Revolutions per mile	629	634	+4	+0.69%

True speed with the speedometer calibrated for 255/60R20
Indicated	Actual on 255/60R20	Actual on 275/50R21	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.6 mph	−0.4 mph
75 mph	75.0 mph	74.5 mph	−0.5 mph

Ride-height change: 275/50R21 lowers the vehicle by 0.11 in (2.8 mm) at the axle (half the −5.6 mm diameter difference).

275/50R21 is 0.22 in shorter than 255/60R20 and 20 mm wider, a 0.69% difference in overall diameter.

With the speedometer calibrated for 255/60R20, an indicated 60 mph is actually 59.6 mph on 275/50R21, and revolutions per mile change from 629 to 634.

275/50R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 255/60R20.

Size pages

Other comparisons with 255/60R20

Other comparisons with 275/50R21

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