255/80R17 vs 285/65R18

285/65R18 is 0.48 in (12.1 mm) shorter than 255/80R17, a −1.44% diameter difference. With the speedometer set for 255/80R17, an indicated 60 mph is 59.1 mph on 285/65R18.

Is this a safe swap?

Diameter difference −1.44%: within the ±3% guideline

By overall diameter alone, 285/65R18 falls inside the ±3% range commonly used as a guideline when replacing 255/80R17. 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.

255/80R17 vs 285/65R18 differences
Measurement	255/80R17	285/65R18	Difference	% diff
Overall diameter	33.06 in (839.8 mm)	32.59 in (827.7 mm)	−0.48 in (−12.1 mm)	−1.44%
Sidewall height	8.03 in (204.0 mm)	7.29 in (185.3 mm)	−0.74 in (−18.7 mm)	−9.19%
Section width	10.04 in (255.0 mm)	11.22 in (285.0 mm)	+1.18 in (+30.0 mm)	+11.76%
Circumference	103.87 in (2,638.3 mm)	102.37 in (2,600.3 mm)	−1.50 in (−38.0 mm)	−1.44%
Revolutions per mile	610	619	+9	+1.46%

True speed with the speedometer calibrated for 255/80R17
Indicated	Actual on 255/80R17	Actual on 285/65R18	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.1 mph	−0.9 mph
75 mph	75.0 mph	73.9 mph	−1.1 mph

Ride-height change: 285/65R18 lowers the vehicle by 0.24 in (6.0 mm) at the axle (half the −12.1 mm diameter difference).

285/65R18 is 0.48 in shorter than 255/80R17 and 30 mm wider, a 1.44% difference in overall diameter.

With the speedometer calibrated for 255/80R17, an indicated 60 mph is actually 59.1 mph on 285/65R18, and revolutions per mile change from 610 to 619.

285/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/80R17.

Size pages

Other comparisons with 255/80R17

Other comparisons with 285/65R18

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