275/55R20 vs 265/50R21

265/50R21 is 0.48 in (12.1 mm) shorter than 275/55R20, a −1.49% diameter difference. With the speedometer set for 275/55R20, an indicated 60 mph is 59.1 mph on 265/50R21.

Is this a safe swap?

Diameter difference −1.49%: within the ±3% guideline

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

275/55R20 vs 265/50R21 differences
Measurement	275/55R20	265/50R21	Difference	% diff
Overall diameter	31.91 in (810.5 mm)	31.43 in (798.4 mm)	−0.48 in (−12.1 mm)	−1.49%
Sidewall height	5.95 in (151.3 mm)	5.22 in (132.5 mm)	−0.74 in (−18.7 mm)	−12.40%
Section width	10.83 in (275.0 mm)	10.43 in (265.0 mm)	−0.39 in (−10.0 mm)	−3.64%
Circumference	100.25 in (2,546.3 mm)	98.75 in (2,508.2 mm)	−1.50 in (−38.0 mm)	−1.49%
Revolutions per mile	632	642	+10	+1.52%

True speed with the speedometer calibrated for 275/55R20
Indicated	Actual on 275/55R20	Actual on 265/50R21	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.1 mph	−0.9 mph
75 mph	75.0 mph	73.9 mph	−1.1 mph

Ride-height change: 265/50R21 lowers the vehicle by 0.24 in (6.1 mm) at the axle (half the −12.1 mm diameter difference).

265/50R21 is 0.48 in shorter than 275/55R20 and 10 mm narrower, a 1.49% difference in overall diameter.

With the speedometer calibrated for 275/55R20, an indicated 60 mph is actually 59.1 mph on 265/50R21, and revolutions per mile change from 632 to 642.

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

Size pages

Other comparisons with 275/55R20

Other comparisons with 265/50R21

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