275/60R18 vs 285/50R20

285/50R20 is 0.23 in (5.8 mm) taller than 275/60R18, a +0.74% diameter difference. With the speedometer set for 275/60R18, an indicated 60 mph is 60.4 mph on 285/50R20.

Is this a safe swap?

Diameter difference +0.74%: under 1%

By overall diameter alone, 285/50R20 is a near match for 275/60R18; 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.

275/60R18 vs 285/50R20 differences
Measurement	275/60R18	285/50R20	Difference	% diff
Overall diameter	30.99 in (787.2 mm)	31.22 in (793.0 mm)	+0.23 in (+5.8 mm)	+0.74%
Sidewall height	6.50 in (165.0 mm)	5.61 in (142.5 mm)	−0.89 in (−22.5 mm)	−13.64%
Section width	10.83 in (275.0 mm)	11.22 in (285.0 mm)	+0.39 in (+10.0 mm)	+3.64%
Circumference	97.36 in (2,473.1 mm)	98.08 in (2,491.3 mm)	+0.72 in (+18.2 mm)	+0.74%
Revolutions per mile	651	646	−5	−0.73%

True speed with the speedometer calibrated for 275/60R18
Indicated	Actual on 275/60R18	Actual on 285/50R20	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 285/50R20 raises the vehicle by 0.11 in (2.9 mm) at the axle (half the +5.8 mm diameter difference).

285/50R20 is 0.23 in taller than 275/60R18 and 10 mm wider, a 0.74% difference in overall diameter.

With the speedometer calibrated for 275/60R18, an indicated 60 mph is actually 60.4 mph on 285/50R20, and revolutions per mile change from 651 to 646.

285/50R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 275/60R18.

Size pages

Other comparisons with 275/60R18

Other comparisons with 285/50R20

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