185/55R16 vs 225/35R18

225/35R18 is 0.19 in (4.8 mm) taller than 185/55R16, a +0.79% diameter difference. With the speedometer set for 185/55R16, an indicated 60 mph is 60.5 mph on 225/35R18.

Is this a safe swap?

Diameter difference +0.79%: under 1%

By overall diameter alone, 225/35R18 is a near match for 185/55R16; 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.

185/55R16 vs 225/35R18 differences
Measurement	185/55R16	225/35R18	Difference	% diff
Overall diameter	24.01 in (609.9 mm)	24.20 in (614.7 mm)	+0.19 in (+4.8 mm)	+0.79%
Sidewall height	4.01 in (101.8 mm)	3.10 in (78.8 mm)	−0.91 in (−23.0 mm)	−22.60%
Section width	7.28 in (185.0 mm)	8.86 in (225.0 mm)	+1.57 in (+40.0 mm)	+21.62%
Circumference	75.44 in (1,916.1 mm)	76.03 in (1,931.1 mm)	+0.59 in (+15.1 mm)	+0.79%
Revolutions per mile	840	833	−7	−0.78%

True speed with the speedometer calibrated for 185/55R16
Indicated	Actual on 185/55R16	Actual on 225/35R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 225/35R18 raises the vehicle by 0.09 in (2.4 mm) at the axle (half the +4.8 mm diameter difference).

225/35R18 is 0.19 in taller than 185/55R16 and 40 mm wider, a 0.79% difference in overall diameter.

With the speedometer calibrated for 185/55R16, an indicated 60 mph is actually 60.5 mph on 225/35R18, and revolutions per mile change from 840 to 833.

225/35R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 185/55R16.

Size pages

Other comparisons with 185/55R16

Other comparisons with 225/35R18

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