285/75R18 vs 325/60R20

325/60R20 is 0.52 in (13.3 mm) taller than 285/75R18, a +1.50% diameter difference. With the speedometer set for 285/75R18, an indicated 60 mph is 60.9 mph on 325/60R20.

Is this a safe swap?

Diameter difference +1.50%: within the ±3% guideline

By overall diameter alone, 325/60R20 falls inside the ±3% range commonly used as a guideline when replacing 285/75R18. 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 325/60R20 differences
Measurement	285/75R18	325/60R20	Difference	% diff
Overall diameter	34.83 in (884.7 mm)	35.35 in (898.0 mm)	+0.52 in (+13.3 mm)	+1.50%
Sidewall height	8.42 in (213.8 mm)	7.68 in (195.0 mm)	−0.74 in (−18.7 mm)	−8.77%
Section width	11.22 in (285.0 mm)	12.80 in (325.0 mm)	+1.57 in (+40.0 mm)	+14.04%
Circumference	109.42 in (2,779.4 mm)	111.07 in (2,821.2 mm)	+1.65 in (+41.8 mm)	+1.50%
Revolutions per mile	579	570	−9	−1.48%

True speed with the speedometer calibrated for 285/75R18
Indicated	Actual on 285/75R18	Actual on 325/60R20	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	60.9 mph	+0.9 mph
75 mph	75.0 mph	76.1 mph	+1.1 mph

Ride-height change: 325/60R20 raises the vehicle by 0.26 in (6.6 mm) at the axle (half the +13.3 mm diameter difference).

325/60R20 is 0.52 in taller than 285/75R18 and 40 mm wider, a 1.50% difference in overall diameter.

With the speedometer calibrated for 285/75R18, an indicated 60 mph is actually 60.9 mph on 325/60R20, and revolutions per mile change from 579 to 570.

325/60R20 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 325/60R20

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