TireSizesFinder

255/50R17 vs 225/50R18

225/50R18 is 0.18 in (4.6 mm) shorter than 255/50R17, a −0.67% diameter difference. With the speedometer set for 255/50R17, an indicated 60 mph is 59.6 mph on 225/50R18.

Is this a safe swap?

Diameter difference −0.67%: under 1%

By overall diameter alone, 225/50R18 is a near match for 255/50R17; 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: 255/50R17 (27.04 in) vs 225/50R18 (26.86 in)255/50R1727.04 in × 10.04 in225/50R1826.86 in × 8.86 in
Side profile and tread width, drawn to the same scale.
255/50R17 vs 225/50R18 differences
Measurement255/50R17225/50R18Difference% diff
Overall diameter27.04 in (686.8 mm)26.86 in (682.2 mm)−0.18 in (−4.6 mm)−0.67%
Sidewall height5.02 in (127.5 mm)4.43 in (112.5 mm)−0.59 in (−15.0 mm)−11.76%
Section width10.04 in (255.0 mm)8.86 in (225.0 mm)−1.18 in (−30.0 mm)−11.76%
Circumference84.95 in (2,157.6 mm)84.38 in (2,143.2 mm)−0.57 in (−14.5 mm)−0.67%
Revolutions per mile746751+5+0.67%
True speed with the speedometer calibrated for 255/50R17
IndicatedActual on 255/50R17Actual on 225/50R18Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.6 mph−0.4 mph
75 mph75.0 mph74.5 mph−0.5 mph

Ride-height change: 225/50R18 lowers the vehicle by 0.09 in (2.3 mm) at the axle (half the −4.6 mm diameter difference).

225/50R18 is 0.18 in shorter than 255/50R17 and 30 mm narrower, a 0.67% difference in overall diameter.

With the speedometer calibrated for 255/50R17, an indicated 60 mph is actually 59.6 mph on 225/50R18, and revolutions per mile change from 746 to 751.

225/50R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/50R17.

Size pages

Other comparisons with 255/50R17

Other comparisons with 225/50R18

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