225/45R17 vs 255/35R18

255/35R18 is 0.06 in (1.4 mm) taller than 225/45R17, a +0.22% diameter difference. With the speedometer set for 225/45R17, an indicated 60 mph is 60.1 mph on 255/35R18.

Is this a safe swap?

Diameter difference +0.22%: under 1%

By overall diameter alone, 255/35R18 is a near match for 225/45R17; 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.

225/45R17 vs 255/35R18 differences
Measurement	225/45R17	255/35R18	Difference	% diff
Overall diameter	24.97 in (634.3 mm)	25.03 in (635.7 mm)	+0.06 in (+1.4 mm)	+0.22%
Sidewall height	3.99 in (101.3 mm)	3.51 in (89.3 mm)	−0.47 in (−12.0 mm)	−11.85%
Section width	8.86 in (225.0 mm)	10.04 in (255.0 mm)	+1.18 in (+30.0 mm)	+13.33%
Circumference	78.45 in (1,992.7 mm)	78.63 in (1,997.1 mm)	+0.17 in (+4.4 mm)	+0.22%
Revolutions per mile	808	806	−2	−0.22%

True speed with the speedometer calibrated for 225/45R17
Indicated	Actual on 225/45R17	Actual on 255/35R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 255/35R18 raises the vehicle by 0.03 in (0.7 mm) at the axle (half the +1.4 mm diameter difference).

255/35R18 is 0.06 in taller than 225/45R17 and 30 mm wider, a 0.22% difference in overall diameter.

With the speedometer calibrated for 225/45R17, an indicated 60 mph is actually 60.1 mph on 255/35R18, and revolutions per mile change from 808 to 806.

255/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 225/45R17.

Size pages

Other comparisons with 225/45R17

Other comparisons with 255/35R18

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