265/55R20 vs 275/50R21

275/50R21 is 0.35 in (8.9 mm) taller than 265/55R20, a +1.11% diameter difference. With the speedometer set for 265/55R20, an indicated 60 mph is 60.7 mph on 275/50R21.

Is this a safe swap?

Diameter difference +1.11%: within the ±3% guideline

By overall diameter alone, 275/50R21 falls inside the ±3% range commonly used as a guideline when replacing 265/55R20. 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.

265/55R20 vs 275/50R21 differences
Measurement	265/55R20	275/50R21	Difference	% diff
Overall diameter	31.48 in (799.5 mm)	31.83 in (808.4 mm)	+0.35 in (+8.9 mm)	+1.11%
Sidewall height	5.74 in (145.8 mm)	5.41 in (137.5 mm)	−0.32 in (−8.2 mm)	−5.66%
Section width	10.43 in (265.0 mm)	10.83 in (275.0 mm)	+0.39 in (+10.0 mm)	+3.77%
Circumference	98.89 in (2,511.7 mm)	99.99 in (2,539.7 mm)	+1.10 in (+28.0 mm)	+1.11%
Revolutions per mile	641	634	−7	−1.10%

True speed with the speedometer calibrated for 265/55R20
Indicated	Actual on 265/55R20	Actual on 275/50R21	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 275/50R21 raises the vehicle by 0.18 in (4.4 mm) at the axle (half the +8.9 mm diameter difference).

275/50R21 is 0.35 in taller than 265/55R20 and 10 mm wider, a 1.11% difference in overall diameter.

With the speedometer calibrated for 265/55R20, an indicated 60 mph is actually 60.7 mph on 275/50R21, and revolutions per mile change from 641 to 634.

275/50R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 265/55R20.

Size pages

Other comparisons with 265/55R20

Other comparisons with 275/50R21

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