285/60R18 vs 265/55R20

265/55R20 is 0.01 in (0.3 mm) taller than 285/60R18, a +0.04% diameter difference. With the speedometer set for 285/60R18, an indicated 60 mph is 60.0 mph on 265/55R20.

Is this a safe swap?

Diameter difference +0.04%: under 1%

By overall diameter alone, 265/55R20 is a near match for 285/60R18; 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.

285/60R18 vs 265/55R20 differences
Measurement	285/60R18	265/55R20	Difference	% diff
Overall diameter	31.46 in (799.2 mm)	31.48 in (799.5 mm)	+0.01 in (+0.3 mm)	+0.04%
Sidewall height	6.73 in (171.0 mm)	5.74 in (145.8 mm)	−0.99 in (−25.2 mm)	−14.77%
Section width	11.22 in (285.0 mm)	10.43 in (265.0 mm)	−0.79 in (−20.0 mm)	−7.02%
Circumference	98.85 in (2,510.8 mm)	98.89 in (2,511.7 mm)	+0.04 in (+0.9 mm)	+0.04%
Revolutions per mile	641	641	0	−0.04%

True speed with the speedometer calibrated for 285/60R18
Indicated	Actual on 285/60R18	Actual on 265/55R20
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 265/55R20 raises the vehicle by 0.01 in (0.1 mm) at the axle (half the +0.3 mm diameter difference).

265/55R20 is 0.01 in taller than 285/60R18 and 20 mm narrower, a 0.04% difference in overall diameter.

With the speedometer calibrated for 285/60R18, an indicated 60 mph is actually 60.0 mph on 265/55R20, and revolutions per mile change from 641 to 641.

265/55R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 285/60R18.

Size pages

Other comparisons with 285/60R18

Other comparisons with 265/55R20

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