TireSizesFinder

245/40R17 vs 235/35R18

235/35R18 is 0.24 in (6.1 mm) shorter than 245/40R17, a −0.97% diameter difference. With the speedometer set for 245/40R17, an indicated 60 mph is 59.4 mph on 235/35R18.

Is this a safe swap?

Diameter difference −0.97%: under 1%

By overall diameter alone, 235/35R18 is a near match for 245/40R17; 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: 245/40R17 (24.72 in) vs 235/35R18 (24.48 in)245/40R1724.72 in × 9.65 in235/35R1824.48 in × 9.25 in
Side profile and tread width, drawn to the same scale.
245/40R17 vs 235/35R18 differences
Measurement245/40R17235/35R18Difference% diff
Overall diameter24.72 in (627.8 mm)24.48 in (621.7 mm)−0.24 in (−6.1 mm)−0.97%
Sidewall height3.86 in (98.0 mm)3.24 in (82.3 mm)−0.62 in (−15.7 mm)−16.07%
Section width9.65 in (245.0 mm)9.25 in (235.0 mm)−0.39 in (−10.0 mm)−4.08%
Circumference77.65 in (1,972.3 mm)76.89 in (1,953.1 mm)−0.75 in (−19.2 mm)−0.97%
Revolutions per mile816824+8+0.98%
True speed with the speedometer calibrated for 245/40R17
IndicatedActual on 245/40R17Actual on 235/35R18Difference
30 mph30.0 mph29.7 mph−0.3 mph
60 mph60.0 mph59.4 mph−0.6 mph
75 mph75.0 mph74.3 mph−0.7 mph

Ride-height change: 235/35R18 lowers the vehicle by 0.12 in (3.0 mm) at the axle (half the −6.1 mm diameter difference).

235/35R18 is 0.24 in shorter than 245/40R17 and 10 mm narrower, a 0.97% difference in overall diameter.

With the speedometer calibrated for 245/40R17, an indicated 60 mph is actually 59.4 mph on 235/35R18, and revolutions per mile change from 816 to 824.

235/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 245/40R17.

Size pages

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