TireSizesFinder

235/40R17 vs 225/35R18

225/35R18 is 0.20 in (5.1 mm) shorter than 235/40R17, a −0.82% diameter difference. With the speedometer set for 235/40R17, an indicated 60 mph is 59.5 mph on 225/35R18.

Is this a safe swap?

Diameter difference −0.82%: under 1%

By overall diameter alone, 225/35R18 is a near match for 235/40R17; 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: 235/40R17 (24.40 in) vs 225/35R18 (24.20 in)235/40R1724.40 in × 9.25 in225/35R1824.20 in × 8.86 in
Side profile and tread width, drawn to the same scale.
235/40R17 vs 225/35R18 differences
Measurement235/40R17225/35R18Difference% diff
Overall diameter24.40 in (619.8 mm)24.20 in (614.7 mm)−0.20 in (−5.1 mm)−0.82%
Sidewall height3.70 in (94.0 mm)3.10 in (78.8 mm)−0.60 in (−15.2 mm)−16.22%
Section width9.25 in (235.0 mm)8.86 in (225.0 mm)−0.39 in (−10.0 mm)−4.26%
Circumference76.66 in (1,947.2 mm)76.03 in (1,931.1 mm)−0.63 in (−16.0 mm)−0.82%
Revolutions per mile827833+7+0.83%
True speed with the speedometer calibrated for 235/40R17
IndicatedActual on 235/40R17Actual on 225/35R18Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.5 mph−0.5 mph
75 mph75.0 mph74.4 mph−0.6 mph

Ride-height change: 225/35R18 lowers the vehicle by 0.10 in (2.5 mm) at the axle (half the −5.1 mm diameter difference).

225/35R18 is 0.20 in shorter than 235/40R17 and 10 mm narrower, a 0.82% difference in overall diameter.

With the speedometer calibrated for 235/40R17, an indicated 60 mph is actually 59.5 mph on 225/35R18, and revolutions per mile change from 827 to 833.

225/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 235/40R17.

Size pages

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