235/85R16 vs 285/60R18

285/60R18 is 0.26 in (6.7 mm) shorter than 235/85R16, a −0.83% diameter difference. With the speedometer set for 235/85R16, an indicated 60 mph is 59.5 mph on 285/60R18.

Is this a safe swap?

Diameter difference −0.83%: under 1%

By overall diameter alone, 285/60R18 is a near match for 235/85R16; 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.

235/85R16 vs 285/60R18 differences
Measurement	235/85R16	285/60R18	Difference	% diff
Overall diameter	31.73 in (805.9 mm)	31.46 in (799.2 mm)	−0.26 in (−6.7 mm)	−0.83%
Sidewall height	7.86 in (199.8 mm)	6.73 in (171.0 mm)	−1.13 in (−28.7 mm)	−14.39%
Section width	9.25 in (235.0 mm)	11.22 in (285.0 mm)	+1.97 in (+50.0 mm)	+21.28%
Circumference	99.68 in (2,531.8 mm)	98.85 in (2,510.8 mm)	−0.83 in (−21.0 mm)	−0.83%
Revolutions per mile	636	641	+5	+0.84%

True speed with the speedometer calibrated for 235/85R16
Indicated	Actual on 235/85R16	Actual on 285/60R18	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.5 mph	−0.5 mph
75 mph	75.0 mph	74.4 mph	−0.6 mph

Ride-height change: 285/60R18 lowers the vehicle by 0.13 in (3.3 mm) at the axle (half the −6.7 mm diameter difference).

285/60R18 is 0.26 in shorter than 235/85R16 and 50 mm wider, a 0.83% difference in overall diameter.

With the speedometer calibrated for 235/85R16, an indicated 60 mph is actually 59.5 mph on 285/60R18, and revolutions per mile change from 636 to 641.

285/60R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 235/85R16.

Size pages

Other comparisons with 235/85R16

Other comparisons with 285/60R18

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