275/35R21 vs 285/35R21

285/35R21 is 0.28 in (7.0 mm) taller than 275/35R21, a +0.96% diameter difference. With the speedometer set for 275/35R21, an indicated 60 mph is 60.6 mph on 285/35R21.

Is this a safe swap?

Diameter difference +0.96%: under 1%

By overall diameter alone, 285/35R21 is a near match for 275/35R21; 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.

275/35R21 vs 285/35R21 differences
Measurement	275/35R21	285/35R21	Difference	% diff
Overall diameter	28.58 in (725.9 mm)	28.85 in (732.9 mm)	+0.28 in (+7.0 mm)	+0.96%
Sidewall height	3.79 in (96.3 mm)	3.93 in (99.8 mm)	+0.14 in (+3.5 mm)	+3.64%
Section width	10.83 in (275.0 mm)	11.22 in (285.0 mm)	+0.39 in (+10.0 mm)	+3.64%
Circumference	89.78 in (2,280.5 mm)	90.65 in (2,302.5 mm)	+0.87 in (+22.0 mm)	+0.96%
Revolutions per mile	706	699	−7	−0.96%

True speed with the speedometer calibrated for 275/35R21
Indicated	Actual on 275/35R21	Actual on 285/35R21	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	75.7 mph	+0.7 mph

Ride-height change: 285/35R21 raises the vehicle by 0.14 in (3.5 mm) at the axle (half the +7.0 mm diameter difference).

285/35R21 is 0.28 in taller than 275/35R21 and 10 mm wider, a 0.96% difference in overall diameter.

With the speedometer calibrated for 275/35R21, an indicated 60 mph is actually 60.6 mph on 285/35R21, and revolutions per mile change from 706 to 699.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 275/35R21

Other comparisons with 285/35R21

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