315/75R16 vs 285/70R18

285/70R18 is 0.89 in (22.7 mm) shorter than 315/75R16, a −2.58% diameter difference. With the speedometer set for 315/75R16, an indicated 60 mph is 58.5 mph on 285/70R18.

Is this a safe swap?

Diameter difference −2.58%: within the ±3% guideline

By overall diameter alone, 285/70R18 falls inside the ±3% range commonly used as a guideline when replacing 315/75R16. 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 285/70R18 differences
Measurement	315/75R16	285/70R18	Difference	% diff
Overall diameter	34.60 in (878.9 mm)	33.71 in (856.2 mm)	−0.89 in (−22.7 mm)	−2.58%
Sidewall height	9.30 in (236.3 mm)	7.85 in (199.5 mm)	−1.45 in (−36.7 mm)	−15.56%
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)	105.90 in (2,689.8 mm)	−2.81 in (−71.3 mm)	−2.58%
Revolutions per mile	583	598	+15	+2.65%

True speed with the speedometer calibrated for 315/75R16
Indicated	Actual on 315/75R16	Actual on 285/70R18	Difference
30 mph	30.0 mph	29.2 mph	−0.8 mph
60 mph	60.0 mph	58.5 mph	−1.5 mph
75 mph	75.0 mph	73.1 mph	−1.9 mph

Ride-height change: 285/70R18 lowers the vehicle by 0.45 in (11.3 mm) at the axle (half the −22.7 mm diameter difference).

285/70R18 is 0.89 in shorter than 315/75R16 and 30 mm narrower, a 2.58% difference in overall diameter.

With the speedometer calibrated for 315/75R16, an indicated 60 mph is actually 58.5 mph on 285/70R18, and revolutions per mile change from 583 to 598.

285/70R18 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 285/70R18

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