315/75R16 vs 285/75R18

285/75R18 is 0.23 in (5.8 mm) taller than 315/75R16, a +0.66% diameter difference. With the speedometer set for 315/75R16, an indicated 60 mph is 60.4 mph on 285/75R18.

Is this a safe swap?

Diameter difference +0.66%: under 1%

By overall diameter alone, 285/75R18 is a near match for 315/75R16; 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.

315/75R16 vs 285/75R18 differences
Measurement	315/75R16	285/75R18	Difference	% diff
Overall diameter	34.60 in (878.9 mm)	34.83 in (884.7 mm)	+0.23 in (+5.8 mm)	+0.66%
Sidewall height	9.30 in (236.3 mm)	8.42 in (213.8 mm)	−0.89 in (−22.5 mm)	−9.52%
Section width	12.40 in (315.0 mm)	11.22 in (285.0 mm)	−1.18 in (−30.0 mm)	−9.52%
Circumference	108.71 in (2,761.1 mm)	109.42 in (2,779.4 mm)	+0.72 in (+18.2 mm)	+0.66%
Revolutions per mile	583	579	−4	−0.66%

True speed with the speedometer calibrated for 315/75R16
Indicated	Actual on 315/75R16	Actual on 285/75R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.5 mph	+0.5 mph

Ride-height change: 285/75R18 raises the vehicle by 0.11 in (2.9 mm) at the axle (half the +5.8 mm diameter difference).

285/75R18 is 0.23 in taller than 315/75R16 and 30 mm narrower, a 0.66% difference in overall diameter.

With the speedometer calibrated for 315/75R16, an indicated 60 mph is actually 60.4 mph on 285/75R18, and revolutions per mile change from 583 to 579.

285/75R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 315/75R16.

Size pages

Other comparisons with 315/75R16

Other comparisons with 285/75R18

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