TireSizesFinder

235/50R17 vs 215/50R18

215/50R18 is 0.21 in (5.4 mm) taller than 235/50R17, a +0.81% diameter difference. With the speedometer set for 235/50R17, an indicated 60 mph is 60.5 mph on 215/50R18.

Is this a safe swap?

Diameter difference +0.81%: under 1%

By overall diameter alone, 215/50R18 is a near match for 235/50R17; 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: 235/50R17 (26.25 in) vs 215/50R18 (26.46 in)235/50R1726.25 in × 9.25 in215/50R1826.46 in × 8.46 in
Side profile and tread width, drawn to the same scale.
235/50R17 vs 215/50R18 differences
Measurement235/50R17215/50R18Difference% diff
Overall diameter26.25 in (666.8 mm)26.46 in (672.2 mm)+0.21 in (+5.4 mm)+0.81%
Sidewall height4.63 in (117.5 mm)4.23 in (107.5 mm)−0.39 in (−10.0 mm)−8.51%
Section width9.25 in (235.0 mm)8.46 in (215.0 mm)−0.79 in (−20.0 mm)−8.51%
Circumference82.47 in (2,094.8 mm)83.14 in (2,111.8 mm)+0.67 in (+17.0 mm)+0.81%
Revolutions per mile768762−6−0.80%
True speed with the speedometer calibrated for 235/50R17
IndicatedActual on 235/50R17Actual on 215/50R18Difference
30 mph30.0 mph30.2 mph+0.2 mph
60 mph60.0 mph60.5 mph+0.5 mph
75 mph75.0 mph75.6 mph+0.6 mph

Ride-height change: 215/50R18 raises the vehicle by 0.11 in (2.7 mm) at the axle (half the +5.4 mm diameter difference).

215/50R18 is 0.21 in taller than 235/50R17 and 20 mm narrower, a 0.81% difference in overall diameter.

With the speedometer calibrated for 235/50R17, an indicated 60 mph is actually 60.5 mph on 215/50R18, and revolutions per mile change from 768 to 762.

215/50R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 235/50R17.

Size pages

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