245/50R18 vs 285/35R20

285/35R20 is 0.21 in (5.3 mm) taller than 245/50R18, a +0.75% diameter difference. With the speedometer set for 245/50R18, an indicated 60 mph is 60.5 mph on 285/35R20.

Is this a safe swap?

Diameter difference +0.75%: under 1%

By overall diameter alone, 285/35R20 is a near match for 245/50R18; 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.

245/50R18 vs 285/35R20 differences
Measurement	245/50R18	285/35R20	Difference	% diff
Overall diameter	27.65 in (702.2 mm)	27.85 in (707.5 mm)	+0.21 in (+5.3 mm)	+0.75%
Sidewall height	4.82 in (122.5 mm)	3.93 in (99.8 mm)	−0.90 in (−22.7 mm)	−18.57%
Section width	9.65 in (245.0 mm)	11.22 in (285.0 mm)	+1.57 in (+40.0 mm)	+16.33%
Circumference	86.85 in (2,206.0 mm)	87.51 in (2,222.7 mm)	+0.66 in (+16.7 mm)	+0.75%
Revolutions per mile	730	724	−5	−0.75%

True speed with the speedometer calibrated for 245/50R18
Indicated	Actual on 245/50R18	Actual on 285/35R20	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 285/35R20 raises the vehicle by 0.10 in (2.6 mm) at the axle (half the +5.3 mm diameter difference).

285/35R20 is 0.21 in taller than 245/50R18 and 40 mm wider, a 0.75% difference in overall diameter.

With the speedometer calibrated for 245/50R18, an indicated 60 mph is actually 60.5 mph on 285/35R20, and revolutions per mile change from 730 to 724.

285/35R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 245/50R18.

Size pages

Other comparisons with 245/50R18

Other comparisons with 285/35R20

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