275/30R20 vs 285/30R20

285/30R20 is 0.24 in (6.0 mm) taller than 275/30R20, a +0.89% diameter difference. With the speedometer set for 275/30R20, an indicated 60 mph is 60.5 mph on 285/30R20.

Is this a safe swap?

Diameter difference +0.89%: under 1%

By overall diameter alone, 285/30R20 is a near match for 275/30R20; 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.

275/30R20 vs 285/30R20 differences
Measurement	275/30R20	285/30R20	Difference	% diff
Overall diameter	26.50 in (673.0 mm)	26.73 in (679.0 mm)	+0.24 in (+6.0 mm)	+0.89%
Sidewall height	3.25 in (82.5 mm)	3.37 in (85.5 mm)	+0.12 in (+3.0 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	83.24 in (2,114.3 mm)	83.98 in (2,133.1 mm)	+0.74 in (+18.8 mm)	+0.89%
Revolutions per mile	761	754	−7	−0.88%

True speed with the speedometer calibrated for 275/30R20
Indicated	Actual on 275/30R20	Actual on 285/30R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.7 mph	+0.7 mph

Ride-height change: 285/30R20 raises the vehicle by 0.12 in (3.0 mm) at the axle (half the +6.0 mm diameter difference).

285/30R20 is 0.24 in taller than 275/30R20 and 10 mm wider, a 0.89% difference in overall diameter.

With the speedometer calibrated for 275/30R20, an indicated 60 mph is actually 60.5 mph on 285/30R20, and revolutions per mile change from 761 to 754.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 275/30R20

Other comparisons with 285/30R20

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