205/55R17 vs 225/45R18

225/45R18 is 0.09 in (2.4 mm) taller than 205/55R17, a +0.37% diameter difference. With the speedometer set for 205/55R17, an indicated 60 mph is 60.2 mph on 225/45R18.

Is this a safe swap?

Diameter difference +0.37%: under 1%

By overall diameter alone, 225/45R18 is a near match for 205/55R17; 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.

205/55R17 vs 225/45R18 differences
Measurement	205/55R17	225/45R18	Difference	% diff
Overall diameter	25.88 in (657.3 mm)	25.97 in (659.7 mm)	+0.09 in (+2.4 mm)	+0.37%
Sidewall height	4.44 in (112.8 mm)	3.99 in (101.3 mm)	−0.45 in (−11.5 mm)	−10.20%
Section width	8.07 in (205.0 mm)	8.86 in (225.0 mm)	+0.79 in (+20.0 mm)	+9.76%
Circumference	81.30 in (2,065.0 mm)	81.59 in (2,072.5 mm)	+0.30 in (+7.5 mm)	+0.37%
Revolutions per mile	779	777	−3	−0.36%

True speed with the speedometer calibrated for 205/55R17
Indicated	Actual on 205/55R17	Actual on 225/45R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 225/45R18 raises the vehicle by 0.05 in (1.2 mm) at the axle (half the +2.4 mm diameter difference).

225/45R18 is 0.09 in taller than 205/55R17 and 20 mm wider, a 0.37% difference in overall diameter.

With the speedometer calibrated for 205/55R17, an indicated 60 mph is actually 60.2 mph on 225/45R18, and revolutions per mile change from 779 to 777.

225/45R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 205/55R17.

Size pages

Other comparisons with 205/55R17

Other comparisons with 225/45R18

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