TireSizesFinder

255/45R17 vs 225/45R18

225/45R18 is 0.06 in (1.6 mm) shorter than 255/45R17, a −0.24% diameter difference. With the speedometer set for 255/45R17, an indicated 60 mph is 59.9 mph on 225/45R18.

Is this a safe swap?

Diameter difference −0.24%: under 1%

By overall diameter alone, 225/45R18 is a near match for 255/45R17; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 255/45R17 (26.04 in) vs 225/45R18 (25.97 in)255/45R1726.04 in × 10.04 in225/45R1825.97 in × 8.86 in
Side profile and tread width, drawn to the same scale.
255/45R17 vs 225/45R18 differences
Measurement255/45R17225/45R18Difference% diff
Overall diameter26.04 in (661.3 mm)25.97 in (659.7 mm)−0.06 in (−1.6 mm)−0.24%
Sidewall height4.52 in (114.8 mm)3.99 in (101.3 mm)−0.53 in (−13.5 mm)−11.76%
Section width10.04 in (255.0 mm)8.86 in (225.0 mm)−1.18 in (−30.0 mm)−11.76%
Circumference81.79 in (2,077.5 mm)81.59 in (2,072.5 mm)−0.20 in (−5.0 mm)−0.24%
Revolutions per mile775777+2+0.24%
True speed with the speedometer calibrated for 255/45R17
IndicatedActual on 255/45R17Actual on 225/45R18Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.8 mph−0.2 mph

Ride-height change: 225/45R18 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.6 mm diameter difference).

225/45R18 is 0.06 in shorter than 255/45R17 and 30 mm narrower, a 0.24% difference in overall diameter.

With the speedometer calibrated for 255/45R17, an indicated 60 mph is actually 59.9 mph on 225/45R18, and revolutions per mile change from 775 to 777.

225/45R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/45R17.

Size pages

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Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.