285/65R17 vs 255/65R18

255/65R18 is 0.54 in (13.6 mm) shorter than 285/65R17, a −1.70% diameter difference. With the speedometer set for 285/65R17, an indicated 60 mph is 59.0 mph on 255/65R18.

Is this a safe swap?

Diameter difference −1.70%: within the ±3% guideline

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

285/65R17 vs 255/65R18 differences
Measurement	285/65R17	255/65R18	Difference	% diff
Overall diameter	31.59 in (802.3 mm)	31.05 in (788.7 mm)	−0.54 in (−13.6 mm)	−1.70%
Sidewall height	7.29 in (185.3 mm)	6.53 in (165.8 mm)	−0.77 in (−19.5 mm)	−10.53%
Section width	11.22 in (285.0 mm)	10.04 in (255.0 mm)	−1.18 in (−30.0 mm)	−10.53%
Circumference	99.23 in (2,520.5 mm)	97.55 in (2,477.8 mm)	−1.68 in (−42.7 mm)	−1.70%
Revolutions per mile	639	650	+11	+1.72%

True speed with the speedometer calibrated for 285/65R17
Indicated	Actual on 285/65R17	Actual on 255/65R18	Difference
30 mph	30.0 mph	29.5 mph	−0.5 mph
60 mph	60.0 mph	59.0 mph	−1.0 mph
75 mph	75.0 mph	73.7 mph	−1.3 mph

Ride-height change: 255/65R18 lowers the vehicle by 0.27 in (6.8 mm) at the axle (half the −13.6 mm diameter difference).

255/65R18 is 0.54 in shorter than 285/65R17 and 30 mm narrower, a 1.70% difference in overall diameter.

With the speedometer calibrated for 285/65R17, an indicated 60 mph is actually 59.0 mph on 255/65R18, and revolutions per mile change from 639 to 650.

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

Size pages

Other comparisons with 285/65R17

Other comparisons with 255/65R18

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