225/40R17 vs 225/35R18

225/35R18 is 0.11 in (2.9 mm) taller than 225/40R17, a +0.47% diameter difference. With the speedometer set for 225/40R17, an indicated 60 mph is 60.3 mph on 225/35R18.

Is this a safe swap?

Diameter difference +0.47%: under 1%

By overall diameter alone, 225/35R18 is a near match for 225/40R17; 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.

225/40R17 vs 225/35R18 differences
Measurement	225/40R17	225/35R18	Difference	% diff
Overall diameter	24.09 in (611.8 mm)	24.20 in (614.7 mm)	+0.11 in (+2.9 mm)	+0.47%
Sidewall height	3.54 in (90.0 mm)	3.10 in (78.8 mm)	−0.44 in (−11.2 mm)	−12.50%
Section width	8.86 in (225.0 mm)	8.86 in (225.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	75.67 in (1,922.0 mm)	76.03 in (1,931.1 mm)	+0.36 in (+9.1 mm)	+0.47%
Revolutions per mile	837	833	−4	−0.47%

True speed with the speedometer calibrated for 225/40R17
Indicated	Actual on 225/40R17	Actual on 225/35R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.4 mph	+0.4 mph

Ride-height change: 225/35R18 raises the vehicle by 0.06 in (1.5 mm) at the axle (half the +2.9 mm diameter difference).

225/35R18 is 0.11 in taller than 225/40R17 and the same width, a 0.47% difference in overall diameter.

With the speedometer calibrated for 225/40R17, an indicated 60 mph is actually 60.3 mph on 225/35R18, and revolutions per mile change from 837 to 833.

225/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 225/40R17.

Size pages

Other comparisons with 225/40R17

Other comparisons with 225/35R18

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