285/40R20 vs 295/35R21

295/35R21 is 0.15 in (3.9 mm) taller than 285/40R20, a +0.53% diameter difference. With the speedometer set for 285/40R20, an indicated 60 mph is 60.3 mph on 295/35R21.

Is this a safe swap?

Diameter difference +0.53%: under 1%

By overall diameter alone, 295/35R21 is a near match for 285/40R20; 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.

285/40R20 vs 295/35R21 differences
Measurement	285/40R20	295/35R21	Difference	% diff
Overall diameter	28.98 in (736.0 mm)	29.13 in (739.9 mm)	+0.15 in (+3.9 mm)	+0.53%
Sidewall height	4.49 in (114.0 mm)	4.06 in (103.3 mm)	−0.42 in (−10.7 mm)	−9.43%
Section width	11.22 in (285.0 mm)	11.61 in (295.0 mm)	+0.39 in (+10.0 mm)	+3.51%
Circumference	91.03 in (2,312.2 mm)	91.51 in (2,324.5 mm)	+0.48 in (+12.3 mm)	+0.53%
Revolutions per mile	696	692	−4	−0.53%

True speed with the speedometer calibrated for 285/40R20
Indicated	Actual on 285/40R20	Actual on 295/35R21	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.4 mph	+0.4 mph

Ride-height change: 295/35R21 raises the vehicle by 0.08 in (1.9 mm) at the axle (half the +3.9 mm diameter difference).

295/35R21 is 0.15 in taller than 285/40R20 and 10 mm wider, a 0.53% difference in overall diameter.

With the speedometer calibrated for 285/40R20, an indicated 60 mph is actually 60.3 mph on 295/35R21, and revolutions per mile change from 696 to 692.

295/35R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 285/40R20.

Size pages

Other comparisons with 285/40R20

Other comparisons with 295/35R21

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