285/35R20 vs 295/30R21

295/30R21 is 0.11 in (2.9 mm) taller than 285/35R20, a +0.41% diameter difference. With the speedometer set for 285/35R20, an indicated 60 mph is 60.2 mph on 295/30R21.

Is this a safe swap?

Diameter difference +0.41%: under 1%

By overall diameter alone, 295/30R21 is a near match for 285/35R20; 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.

285/35R20 vs 295/30R21 differences
Measurement	285/35R20	295/30R21	Difference	% diff
Overall diameter	27.85 in (707.5 mm)	27.97 in (710.4 mm)	+0.11 in (+2.9 mm)	+0.41%
Sidewall height	3.93 in (99.8 mm)	3.48 in (88.5 mm)	−0.44 in (−11.2 mm)	−11.28%
Section width	11.22 in (285.0 mm)	11.61 in (295.0 mm)	+0.39 in (+10.0 mm)	+3.51%
Circumference	87.51 in (2,222.7 mm)	87.87 in (2,231.8 mm)	+0.36 in (+9.1 mm)	+0.41%
Revolutions per mile	724	721	−3	−0.41%

True speed with the speedometer calibrated for 285/35R20
Indicated	Actual on 285/35R20	Actual on 295/30R21	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 295/30R21 raises the vehicle by 0.06 in (1.4 mm) at the axle (half the +2.9 mm diameter difference).

295/30R21 is 0.11 in taller than 285/35R20 and 10 mm wider, a 0.41% difference in overall diameter.

With the speedometer calibrated for 285/35R20, an indicated 60 mph is actually 60.2 mph on 295/30R21, and revolutions per mile change from 724 to 721.

295/30R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 285/35R20.

Size pages

Other comparisons with 285/35R20

Other comparisons with 295/30R21

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