285/70R18 vs 285/60R20

285/60R20 is 0.24 in (6.2 mm) shorter than 285/70R18, a −0.72% diameter difference. With the speedometer set for 285/70R18, an indicated 60 mph is 59.6 mph on 285/60R20.

Is this a safe swap?

Diameter difference −0.72%: under 1%

By overall diameter alone, 285/60R20 is a near match for 285/70R18; 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.

285/70R18 vs 285/60R20 differences
Measurement	285/70R18	285/60R20	Difference	% diff
Overall diameter	33.71 in (856.2 mm)	33.46 in (850.0 mm)	−0.24 in (−6.2 mm)	−0.72%
Sidewall height	7.85 in (199.5 mm)	6.73 in (171.0 mm)	−1.12 in (−28.5 mm)	−14.29%
Section width	11.22 in (285.0 mm)	11.22 in (285.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	105.90 in (2,689.8 mm)	105.13 in (2,670.4 mm)	−0.77 in (−19.5 mm)	−0.72%
Revolutions per mile	598	603	+4	+0.73%

True speed with the speedometer calibrated for 285/70R18
Indicated	Actual on 285/70R18	Actual on 285/60R20	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.6 mph	−0.4 mph
75 mph	75.0 mph	74.5 mph	−0.5 mph

Ride-height change: 285/60R20 lowers the vehicle by 0.12 in (3.1 mm) at the axle (half the −6.2 mm diameter difference).

285/60R20 is 0.24 in shorter than 285/70R18 and the same width, a 0.72% difference in overall diameter.

With the speedometer calibrated for 285/70R18, an indicated 60 mph is actually 59.6 mph on 285/60R20, and revolutions per mile change from 598 to 603.

285/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 285/70R18.

Size pages

Other comparisons with 285/70R18

Other comparisons with 285/60R20

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