255/45R17 vs 285/35R18

285/35R18 is 0.18 in (4.6 mm) shorter than 255/45R17, a −0.70% diameter difference. With the speedometer set for 255/45R17, an indicated 60 mph is 59.6 mph on 285/35R18.

Is this a safe swap?

Diameter difference −0.70%: under 1%

By overall diameter alone, 285/35R18 is a near match for 255/45R17; 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.

255/45R17 vs 285/35R18 differences
Measurement	255/45R17	285/35R18	Difference	% diff
Overall diameter	26.04 in (661.3 mm)	25.85 in (656.7 mm)	−0.18 in (−4.6 mm)	−0.70%
Sidewall height	4.52 in (114.8 mm)	3.93 in (99.8 mm)	−0.59 in (−15.0 mm)	−13.07%
Section width	10.04 in (255.0 mm)	11.22 in (285.0 mm)	+1.18 in (+30.0 mm)	+11.76%
Circumference	81.79 in (2,077.5 mm)	81.22 in (2,063.1 mm)	−0.57 in (−14.5 mm)	−0.70%
Revolutions per mile	775	780	+5	+0.70%

True speed with the speedometer calibrated for 255/45R17
Indicated	Actual on 255/45R17	Actual on 285/35R18	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.6 mph	−0.4 mph
75 mph	75.0 mph	74.5 mph	−0.5 mph

Ride-height change: 285/35R18 lowers the vehicle by 0.09 in (2.3 mm) at the axle (half the −4.6 mm diameter difference).

285/35R18 is 0.18 in shorter than 255/45R17 and 30 mm wider, a 0.70% difference in overall diameter.

With the speedometer calibrated for 255/45R17, an indicated 60 mph is actually 59.6 mph on 285/35R18, and revolutions per mile change from 775 to 780.

285/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/45R17.

Size pages

Other comparisons with 255/45R17

Other comparisons with 285/35R18

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