285/50R20 vs 275/50R21

275/50R21 is 0.61 in (15.4 mm) taller than 285/50R20, a +1.94% diameter difference. With the speedometer set for 285/50R20, an indicated 60 mph is 61.2 mph on 275/50R21.

Is this a safe swap?

Diameter difference +1.94%: within the ±3% guideline

By overall diameter alone, 275/50R21 falls inside the ±3% range commonly used as a guideline when replacing 285/50R20. 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.

285/50R20 vs 275/50R21 differences
Measurement	285/50R20	275/50R21	Difference	% diff
Overall diameter	31.22 in (793.0 mm)	31.83 in (808.4 mm)	+0.61 in (+15.4 mm)	+1.94%
Sidewall height	5.61 in (142.5 mm)	5.41 in (137.5 mm)	−0.20 in (−5.0 mm)	−3.51%
Section width	11.22 in (285.0 mm)	10.83 in (275.0 mm)	−0.39 in (−10.0 mm)	−3.51%
Circumference	98.08 in (2,491.3 mm)	99.99 in (2,539.7 mm)	+1.90 in (+48.4 mm)	+1.94%
Revolutions per mile	646	634	−12	−1.90%

True speed with the speedometer calibrated for 285/50R20
Indicated	Actual on 285/50R20	Actual on 275/50R21	Difference
30 mph	30.0 mph	30.6 mph	+0.6 mph
60 mph	60.0 mph	61.2 mph	+1.2 mph
75 mph	75.0 mph	76.5 mph	+1.5 mph

Ride-height change: 275/50R21 raises the vehicle by 0.30 in (7.7 mm) at the axle (half the +15.4 mm diameter difference).

275/50R21 is 0.61 in taller than 285/50R20 and 10 mm narrower, a 1.94% difference in overall diameter.

With the speedometer calibrated for 285/50R20, an indicated 60 mph is actually 61.2 mph on 275/50R21, and revolutions per mile change from 646 to 634.

275/50R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 285/50R20.

Size pages

Other comparisons with 285/50R20

Other comparisons with 275/50R21

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