285/75R18 vs 35x12.50R20

35x12.50R20 is 0.17 in (4.3 mm) taller than 285/75R18, a +0.49% diameter difference. With the speedometer set for 285/75R18, an indicated 60 mph is 60.3 mph on 35x12.50R20.

Is this a safe swap?

Diameter difference +0.49%: under 1%

By overall diameter alone, 35x12.50R20 is a near match for 285/75R18; 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.

285/75R18 vs 35x12.50R20 differences
Measurement	285/75R18	35x12.50R20	Difference	% diff
Overall diameter	34.83 in (884.7 mm)	35.00 in (889.0 mm)	+0.17 in (+4.3 mm)	+0.49%
Sidewall height	8.42 in (213.8 mm)	7.50 in (190.5 mm)	−0.92 in (−23.2 mm)	−10.88%
Section width	11.22 in (285.0 mm)	12.50 in (317.5 mm)	+1.28 in (+32.5 mm)	+11.40%
Circumference	109.42 in (2,779.4 mm)	109.96 in (2,792.9 mm)	+0.53 in (+13.5 mm)	+0.49%
Revolutions per mile	579	576	−3	−0.48%

True speed with the speedometer calibrated for 285/75R18
Indicated	Actual on 285/75R18	Actual on 35x12.50R20	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.4 mph	+0.4 mph

Ride-height change: 35x12.50R20 raises the vehicle by 0.08 in (2.1 mm) at the axle (half the +4.3 mm diameter difference).

35x12.50R20 is 0.17 in taller than 285/75R18 and 33 mm wider, a 0.49% difference in overall diameter.

With the speedometer calibrated for 285/75R18, an indicated 60 mph is actually 60.3 mph on 35x12.50R20, and revolutions per mile change from 579 to 576.

35x12.50R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 285/75R18.

Size pages

Other comparisons with 285/75R18

Other comparisons with 35x12.50R20

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