235/80R17 vs 285/60R18

285/60R18 is 0.34 in (8.6 mm) shorter than 235/80R17, a −1.06% diameter difference. With the speedometer set for 235/80R17, an indicated 60 mph is 59.4 mph on 285/60R18.

Is this a safe swap?

Diameter difference −1.06%: within the ±3% guideline

By overall diameter alone, 285/60R18 falls inside the ±3% range commonly used as a guideline when replacing 235/80R17. 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.

235/80R17 vs 285/60R18 differences
Measurement	235/80R17	285/60R18	Difference	% diff
Overall diameter	31.80 in (807.8 mm)	31.46 in (799.2 mm)	−0.34 in (−8.6 mm)	−1.06%
Sidewall height	7.40 in (188.0 mm)	6.73 in (171.0 mm)	−0.67 in (−17.0 mm)	−9.04%
Section width	9.25 in (235.0 mm)	11.22 in (285.0 mm)	+1.97 in (+50.0 mm)	+21.28%
Circumference	99.91 in (2,537.8 mm)	98.85 in (2,510.8 mm)	−1.06 in (−27.0 mm)	−1.06%
Revolutions per mile	634	641	+7	+1.08%

True speed with the speedometer calibrated for 235/80R17
Indicated	Actual on 235/80R17	Actual on 285/60R18	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.4 mph	−0.6 mph
75 mph	75.0 mph	74.2 mph	−0.8 mph

Ride-height change: 285/60R18 lowers the vehicle by 0.17 in (4.3 mm) at the axle (half the −8.6 mm diameter difference).

285/60R18 is 0.34 in shorter than 235/80R17 and 50 mm wider, a 1.06% difference in overall diameter.

With the speedometer calibrated for 235/80R17, an indicated 60 mph is actually 59.4 mph on 285/60R18, and revolutions per mile change from 634 to 641.

285/60R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 235/80R17.

Size pages

Other comparisons with 235/80R17

Other comparisons with 285/60R18

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