235/60R16 vs 285/40R18

285/40R18 is 0.13 in (3.2 mm) shorter than 235/60R16, a −0.46% diameter difference. With the speedometer set for 235/60R16, an indicated 60 mph is 59.7 mph on 285/40R18.

Is this a safe swap?

Diameter difference −0.46%: under 1%

By overall diameter alone, 285/40R18 is a near match for 235/60R16; 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.

235/60R16 vs 285/40R18 differences
Measurement	235/60R16	285/40R18	Difference	% diff
Overall diameter	27.10 in (688.4 mm)	26.98 in (685.2 mm)	−0.13 in (−3.2 mm)	−0.46%
Sidewall height	5.55 in (141.0 mm)	4.49 in (114.0 mm)	−1.06 in (−27.0 mm)	−19.15%
Section width	9.25 in (235.0 mm)	11.22 in (285.0 mm)	+1.97 in (+50.0 mm)	+21.28%
Circumference	85.14 in (2,162.7 mm)	84.75 in (2,152.6 mm)	−0.40 in (−10.1 mm)	−0.46%
Revolutions per mile	744	748	+3	+0.47%

True speed with the speedometer calibrated for 235/60R16
Indicated	Actual on 235/60R16	Actual on 285/40R18	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.7 mph	−0.3 mph
75 mph	75.0 mph	74.7 mph	−0.3 mph

Ride-height change: 285/40R18 lowers the vehicle by 0.06 in (1.6 mm) at the axle (half the −3.2 mm diameter difference).

285/40R18 is 0.13 in shorter than 235/60R16 and 50 mm wider, a 0.46% difference in overall diameter.

With the speedometer calibrated for 235/60R16, an indicated 60 mph is actually 59.7 mph on 285/40R18, and revolutions per mile change from 744 to 748.

285/40R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 235/60R16.

Size pages

Other comparisons with 235/60R16

Other comparisons with 285/40R18

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