255/75R17 vs 285/65R18

285/65R18 is 0.53 in (13.4 mm) taller than 255/75R17, a +1.65% diameter difference. With the speedometer set for 255/75R17, an indicated 60 mph is 61.0 mph on 285/65R18.

Is this a safe swap?

Diameter difference +1.65%: within the ±3% guideline

By overall diameter alone, 285/65R18 falls inside the ±3% range commonly used as a guideline when replacing 255/75R17. 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.

255/75R17 vs 285/65R18 differences
Measurement	255/75R17	285/65R18	Difference	% diff
Overall diameter	32.06 in (814.3 mm)	32.59 in (827.7 mm)	+0.53 in (+13.4 mm)	+1.65%
Sidewall height	7.53 in (191.3 mm)	7.29 in (185.3 mm)	−0.24 in (−6.0 mm)	−3.14%
Section width	10.04 in (255.0 mm)	11.22 in (285.0 mm)	+1.18 in (+30.0 mm)	+11.76%
Circumference	100.72 in (2,558.2 mm)	102.37 in (2,600.3 mm)	+1.66 in (+42.1 mm)	+1.65%
Revolutions per mile	629	619	−10	−1.62%

True speed with the speedometer calibrated for 255/75R17
Indicated	Actual on 255/75R17	Actual on 285/65R18	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	61.0 mph	+1.0 mph
75 mph	75.0 mph	76.2 mph	+1.2 mph

Ride-height change: 285/65R18 raises the vehicle by 0.26 in (6.7 mm) at the axle (half the +13.4 mm diameter difference).

285/65R18 is 0.53 in taller than 255/75R17 and 30 mm wider, a 1.65% difference in overall diameter.

With the speedometer calibrated for 255/75R17, an indicated 60 mph is actually 61.0 mph on 285/65R18, and revolutions per mile change from 629 to 619.

285/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/75R17.

Size pages

Other comparisons with 255/75R17

Other comparisons with 285/65R18

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