285/35R18 vs 225/45R18

225/45R18 is 0.12 in (3.0 mm) taller than 285/35R18, a +0.46% diameter difference. With the speedometer set for 285/35R18, an indicated 60 mph is 60.3 mph on 225/45R18.

Is this a safe swap?

Diameter difference +0.46%: under 1%

By overall diameter alone, 225/45R18 is a near match for 285/35R18; 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.

285/35R18 vs 225/45R18 differences
Measurement	285/35R18	225/45R18	Difference	% diff
Overall diameter	25.85 in (656.7 mm)	25.97 in (659.7 mm)	+0.12 in (+3.0 mm)	+0.46%
Sidewall height	3.93 in (99.8 mm)	3.99 in (101.3 mm)	+0.06 in (+1.5 mm)	+1.50%
Section width	11.22 in (285.0 mm)	8.86 in (225.0 mm)	−2.36 in (−60.0 mm)	−21.05%
Circumference	81.22 in (2,063.1 mm)	81.59 in (2,072.5 mm)	+0.37 in (+9.4 mm)	+0.46%
Revolutions per mile	780	777	−4	−0.45%

True speed with the speedometer calibrated for 285/35R18
Indicated	Actual on 285/35R18	Actual on 225/45R18	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	75.3 mph	+0.3 mph

Ride-height change: 225/45R18 raises the vehicle by 0.06 in (1.5 mm) at the axle (half the +3.0 mm diameter difference).

225/45R18 is 0.12 in taller than 285/35R18 and 60 mm narrower, a 0.46% difference in overall diameter.

With the speedometer calibrated for 285/35R18, an indicated 60 mph is actually 60.3 mph on 225/45R18, and revolutions per mile change from 780 to 777.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 285/35R18

Other comparisons with 225/45R18

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