265/40R20 vs 275/35R21

275/35R21 is 0.23 in (5.9 mm) taller than 265/40R20, a +0.82% diameter difference. With the speedometer set for 265/40R20, an indicated 60 mph is 60.5 mph on 275/35R21.

Is this a safe swap?

Diameter difference +0.82%: under 1%

By overall diameter alone, 275/35R21 is a near match for 265/40R20; 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.

265/40R20 vs 275/35R21 differences
Measurement	265/40R20	275/35R21	Difference	% diff
Overall diameter	28.35 in (720.0 mm)	28.58 in (725.9 mm)	+0.23 in (+5.9 mm)	+0.82%
Sidewall height	4.17 in (106.0 mm)	3.79 in (96.3 mm)	−0.38 in (−9.7 mm)	−9.20%
Section width	10.43 in (265.0 mm)	10.83 in (275.0 mm)	+0.39 in (+10.0 mm)	+3.77%
Circumference	89.05 in (2,261.9 mm)	89.78 in (2,280.5 mm)	+0.73 in (+18.5 mm)	+0.82%
Revolutions per mile	711	706	−6	−0.81%

True speed with the speedometer calibrated for 265/40R20
Indicated	Actual on 265/40R20	Actual on 275/35R21	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 275/35R21 raises the vehicle by 0.12 in (2.9 mm) at the axle (half the +5.9 mm diameter difference).

275/35R21 is 0.23 in taller than 265/40R20 and 10 mm wider, a 0.82% difference in overall diameter.

With the speedometer calibrated for 265/40R20, an indicated 60 mph is actually 60.5 mph on 275/35R21, and revolutions per mile change from 711 to 706.

275/35R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 265/40R20.

Size pages

Other comparisons with 265/40R20

Other comparisons with 275/35R21

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