285/65R18 vs 255/60R20

255/60R20 is 0.54 in (13.7 mm) shorter than 285/65R18, a −1.66% diameter difference. With the speedometer set for 285/65R18, an indicated 60 mph is 59.0 mph on 255/60R20.

Is this a safe swap?

Diameter difference −1.66%: within the ±3% guideline

By overall diameter alone, 255/60R20 falls inside the ±3% range commonly used as a guideline when replacing 285/65R18. 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.

285/65R18 vs 255/60R20 differences
Measurement	285/65R18	255/60R20	Difference	% diff
Overall diameter	32.59 in (827.7 mm)	32.05 in (814.0 mm)	−0.54 in (−13.7 mm)	−1.66%
Sidewall height	7.29 in (185.3 mm)	6.02 in (153.0 mm)	−1.27 in (−32.2 mm)	−17.41%
Section width	11.22 in (285.0 mm)	10.04 in (255.0 mm)	−1.18 in (−30.0 mm)	−10.53%
Circumference	102.37 in (2,600.3 mm)	100.68 in (2,557.3 mm)	−1.69 in (−43.0 mm)	−1.66%
Revolutions per mile	619	629	+10	+1.68%

True speed with the speedometer calibrated for 285/65R18
Indicated	Actual on 285/65R18	Actual on 255/60R20	Difference
30 mph	30.0 mph	29.5 mph	−0.5 mph
60 mph	60.0 mph	59.0 mph	−1.0 mph
75 mph	75.0 mph	73.8 mph	−1.2 mph

Ride-height change: 255/60R20 lowers the vehicle by 0.27 in (6.9 mm) at the axle (half the −13.7 mm diameter difference).

255/60R20 is 0.54 in shorter than 285/65R18 and 30 mm narrower, a 1.66% difference in overall diameter.

With the speedometer calibrated for 285/65R18, an indicated 60 mph is actually 59.0 mph on 255/60R20, and revolutions per mile change from 619 to 629.

255/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 285/65R18.

Size pages

Other comparisons with 285/65R18

Other comparisons with 255/60R20

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