275/70R18 vs 285/60R20

285/60R20 is 0.31 in (7.8 mm) taller than 275/70R18, a +0.93% diameter difference. With the speedometer set for 275/70R18, an indicated 60 mph is 60.6 mph on 285/60R20.

Is this a safe swap?

Diameter difference +0.93%: under 1%

By overall diameter alone, 285/60R20 is a near match for 275/70R18; 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.

275/70R18 vs 285/60R20 differences
Measurement	275/70R18	285/60R20	Difference	% diff
Overall diameter	33.16 in (842.2 mm)	33.46 in (850.0 mm)	+0.31 in (+7.8 mm)	+0.93%
Sidewall height	7.58 in (192.5 mm)	6.73 in (171.0 mm)	−0.85 in (−21.5 mm)	−11.17%
Section width	10.83 in (275.0 mm)	11.22 in (285.0 mm)	+0.39 in (+10.0 mm)	+3.64%
Circumference	104.17 in (2,645.8 mm)	105.13 in (2,670.4 mm)	+0.96 in (+24.5 mm)	+0.93%
Revolutions per mile	608	603	−6	−0.92%

True speed with the speedometer calibrated for 275/70R18
Indicated	Actual on 275/70R18	Actual on 285/60R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.6 mph	+0.6 mph
75 mph	75.0 mph	75.7 mph	+0.7 mph

Ride-height change: 285/60R20 raises the vehicle by 0.15 in (3.9 mm) at the axle (half the +7.8 mm diameter difference).

285/60R20 is 0.31 in taller than 275/70R18 and 10 mm wider, a 0.93% difference in overall diameter.

With the speedometer calibrated for 275/70R18, an indicated 60 mph is actually 60.6 mph on 285/60R20, and revolutions per mile change from 608 to 603.

285/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 275/70R18.

Size pages

Other comparisons with 275/70R18

Other comparisons with 285/60R20

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