225/55R17 vs 245/45R18

245/45R18 is 0.06 in (1.6 mm) shorter than 225/55R17, a −0.24% diameter difference. With the speedometer set for 225/55R17, an indicated 60 mph is 59.9 mph on 245/45R18.

Is this a safe swap?

Diameter difference −0.24%: under 1%

By overall diameter alone, 245/45R18 is a near match for 225/55R17; 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.

225/55R17 vs 245/45R18 differences
Measurement	225/55R17	245/45R18	Difference	% diff
Overall diameter	26.74 in (679.3 mm)	26.68 in (677.7 mm)	−0.06 in (−1.6 mm)	−0.24%
Sidewall height	4.87 in (123.8 mm)	4.34 in (110.3 mm)	−0.53 in (−13.5 mm)	−10.91%
Section width	8.86 in (225.0 mm)	9.65 in (245.0 mm)	+0.79 in (+20.0 mm)	+8.89%
Circumference	84.02 in (2,134.1 mm)	83.82 in (2,129.1 mm)	−0.20 in (−5.0 mm)	−0.24%
Revolutions per mile	754	756	+2	+0.24%

True speed with the speedometer calibrated for 225/55R17
Indicated	Actual on 225/55R17	Actual on 245/45R18	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.9 mph	−0.1 mph
75 mph	75.0 mph	74.8 mph	−0.2 mph

Ride-height change: 245/45R18 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.6 mm diameter difference).

245/45R18 is 0.06 in shorter than 225/55R17 and 20 mm wider, a 0.24% difference in overall diameter.

With the speedometer calibrated for 225/55R17, an indicated 60 mph is actually 59.9 mph on 245/45R18, and revolutions per mile change from 754 to 756.

245/45R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 225/55R17.

Size pages

Other comparisons with 225/55R17

Other comparisons with 245/45R18

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