33x12.50R18 vs 285/60R20

285/60R20 is 0.46 in (11.8 mm) taller than 33x12.50R18, a +1.41% diameter difference. With the speedometer set for 33x12.50R18, an indicated 60 mph is 60.8 mph on 285/60R20.

Is this a safe swap?

Diameter difference +1.41%: within the ±3% guideline

By overall diameter alone, 285/60R20 falls inside the ±3% range commonly used as a guideline when replacing 33x12.50R18. 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.

33x12.50R18 vs 285/60R20 differences
Measurement	33x12.50R18	285/60R20	Difference	% diff
Overall diameter	33.00 in (838.2 mm)	33.46 in (850.0 mm)	+0.46 in (+11.8 mm)	+1.41%
Sidewall height	7.50 in (190.5 mm)	6.73 in (171.0 mm)	−0.77 in (−19.5 mm)	−10.24%
Section width	12.50 in (317.5 mm)	11.22 in (285.0 mm)	−1.28 in (−32.5 mm)	−10.24%
Circumference	103.67 in (2,633.3 mm)	105.13 in (2,670.4 mm)	+1.46 in (+37.1 mm)	+1.41%
Revolutions per mile	611	603	−8	−1.39%

True speed with the speedometer calibrated for 33x12.50R18
Indicated	Actual on 33x12.50R18	Actual on 285/60R20	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.1 mph	+1.1 mph

Ride-height change: 285/60R20 raises the vehicle by 0.23 in (5.9 mm) at the axle (half the +11.8 mm diameter difference).

285/60R20 is 0.46 in taller than 33x12.50R18 and 33 mm narrower, a 1.41% difference in overall diameter.

With the speedometer calibrated for 33x12.50R18, an indicated 60 mph is actually 60.8 mph on 285/60R20, and revolutions per mile change from 611 to 603.

285/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 33x12.50R18.

Size pages

Other comparisons with 33x12.50R18

Other comparisons with 285/60R20

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