275/55R20 vs 285/55R20

285/55R20 is 0.43 in (11.0 mm) taller than 275/55R20, a +1.36% diameter difference. With the speedometer set for 275/55R20, an indicated 60 mph is 60.8 mph on 285/55R20.

Is this a safe swap?

Diameter difference +1.36%: within the ±3% guideline

By overall diameter alone, 285/55R20 falls inside the ±3% range commonly used as a guideline when replacing 275/55R20. 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.

275/55R20 vs 285/55R20 differences
Measurement	275/55R20	285/55R20	Difference	% diff
Overall diameter	31.91 in (810.5 mm)	32.34 in (821.5 mm)	+0.43 in (+11.0 mm)	+1.36%
Sidewall height	5.95 in (151.3 mm)	6.17 in (156.8 mm)	+0.22 in (+5.5 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	100.25 in (2,546.3 mm)	101.61 in (2,580.8 mm)	+1.36 in (+34.6 mm)	+1.36%
Revolutions per mile	632	624	−8	−1.34%

True speed with the speedometer calibrated for 275/55R20
Indicated	Actual on 275/55R20	Actual on 285/55R20	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 285/55R20 raises the vehicle by 0.22 in (5.5 mm) at the axle (half the +11.0 mm diameter difference).

285/55R20 is 0.43 in taller than 275/55R20 and 10 mm wider, a 1.36% difference in overall diameter.

With the speedometer calibrated for 275/55R20, an indicated 60 mph is actually 60.8 mph on 285/55R20, and revolutions per mile change from 632 to 624.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 275/55R20

Other comparisons with 285/55R20

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