265/50R20 vs 275/45R21

275/45R21 is 0.31 in (7.9 mm) taller than 265/50R20, a +1.02% diameter difference. With the speedometer set for 265/50R20, an indicated 60 mph is 60.6 mph on 275/45R21.

Is this a safe swap?

Diameter difference +1.02%: within the ±3% guideline

By overall diameter alone, 275/45R21 falls inside the ±3% range commonly used as a guideline when replacing 265/50R20. 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.

265/50R20 vs 275/45R21 differences
Measurement	265/50R20	275/45R21	Difference	% diff
Overall diameter	30.43 in (773.0 mm)	30.74 in (780.9 mm)	+0.31 in (+7.9 mm)	+1.02%
Sidewall height	5.22 in (132.5 mm)	4.87 in (123.8 mm)	−0.34 in (−8.7 mm)	−6.60%
Section width	10.43 in (265.0 mm)	10.83 in (275.0 mm)	+0.39 in (+10.0 mm)	+3.77%
Circumference	95.61 in (2,428.5 mm)	96.59 in (2,453.3 mm)	+0.98 in (+24.8 mm)	+1.02%
Revolutions per mile	663	656	−7	−1.01%

True speed with the speedometer calibrated for 265/50R20
Indicated	Actual on 265/50R20	Actual on 275/45R21	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.6 mph	+0.6 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 275/45R21 raises the vehicle by 0.16 in (3.9 mm) at the axle (half the +7.9 mm diameter difference).

275/45R21 is 0.31 in taller than 265/50R20 and 10 mm wider, a 1.02% difference in overall diameter.

With the speedometer calibrated for 265/50R20, an indicated 60 mph is actually 60.6 mph on 275/45R21, and revolutions per mile change from 663 to 656.

275/45R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 265/50R20.

Size pages

Other comparisons with 265/50R20

Other comparisons with 275/45R21

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