TireSizesFinder

235/60R17 vs 255/50R18

255/50R18 is 0.06 in (1.6 mm) shorter than 235/60R17, a −0.22% diameter difference. With the speedometer set for 235/60R17, an indicated 60 mph is 59.9 mph on 255/50R18.

Is this a safe swap?

Diameter difference −0.22%: under 1%

By overall diameter alone, 255/50R18 is a near match for 235/60R17; 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: 235/60R17 (28.10 in) vs 255/50R18 (28.04 in)235/60R1728.10 in × 9.25 in255/50R1828.04 in × 10.04 in
Side profile and tread width, drawn to the same scale.
235/60R17 vs 255/50R18 differences
Measurement235/60R17255/50R18Difference% diff
Overall diameter28.10 in (713.8 mm)28.04 in (712.2 mm)−0.06 in (−1.6 mm)−0.22%
Sidewall height5.55 in (141.0 mm)5.02 in (127.5 mm)−0.53 in (−13.5 mm)−9.57%
Section width9.25 in (235.0 mm)10.04 in (255.0 mm)+0.79 in (+20.0 mm)+8.51%
Circumference88.29 in (2,242.5 mm)88.09 in (2,237.4 mm)−0.20 in (−5.0 mm)−0.22%
Revolutions per mile718719+2+0.22%
True speed with the speedometer calibrated for 235/60R17
IndicatedActual on 235/60R17Actual on 255/50R18Difference
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: 255/50R18 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.6 mm diameter difference).

255/50R18 is 0.06 in shorter than 235/60R17 and 20 mm wider, a 0.22% difference in overall diameter.

With the speedometer calibrated for 235/60R17, an indicated 60 mph is actually 59.9 mph on 255/50R18, and revolutions per mile change from 718 to 719.

255/50R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 235/60R17.

Size pages

Other comparisons with 235/60R17

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