TireSizesFinder

245/55R17 vs 225/55R18

225/55R18 is 0.13 in (3.4 mm) taller than 245/55R17, a +0.48% diameter difference. With the speedometer set for 245/55R17, an indicated 60 mph is 60.3 mph on 225/55R18.

Is this a safe swap?

Diameter difference +0.48%: under 1%

By overall diameter alone, 225/55R18 is a near match for 245/55R17; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 245/55R17 (27.61 in) vs 225/55R18 (27.74 in)245/55R1727.61 in × 9.65 in225/55R1827.74 in × 8.86 in
Side profile and tread width, drawn to the same scale.
245/55R17 vs 225/55R18 differences
Measurement245/55R17225/55R18Difference% diff
Overall diameter27.61 in (701.3 mm)27.74 in (704.7 mm)+0.13 in (+3.4 mm)+0.48%
Sidewall height5.31 in (134.8 mm)4.87 in (123.8 mm)−0.43 in (−11.0 mm)−8.16%
Section width9.65 in (245.0 mm)8.86 in (225.0 mm)−0.79 in (−20.0 mm)−8.16%
Circumference86.74 in (2,203.2 mm)87.16 in (2,213.9 mm)+0.42 in (+10.7 mm)+0.48%
Revolutions per mile730727−4−0.48%
True speed with the speedometer calibrated for 245/55R17
IndicatedActual on 245/55R17Actual on 225/55R18Difference
30 mph30.0 mph30.1 mph+0.1 mph
60 mph60.0 mph60.3 mph+0.3 mph
75 mph75.0 mph75.4 mph+0.4 mph

Ride-height change: 225/55R18 raises the vehicle by 0.07 in (1.7 mm) at the axle (half the +3.4 mm diameter difference).

225/55R18 is 0.13 in taller than 245/55R17 and 20 mm narrower, a 0.48% difference in overall diameter.

With the speedometer calibrated for 245/55R17, an indicated 60 mph is actually 60.3 mph on 225/55R18, and revolutions per mile change from 730 to 727.

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

Size pages

Other comparisons with 245/55R17

Other comparisons with 225/55R18

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