TireSizesFinder

235/40R17 vs 245/35R18

245/35R18 is 0.35 in (8.9 mm) taller than 235/40R17, a +1.44% diameter difference. With the speedometer set for 235/40R17, an indicated 60 mph is 60.9 mph on 245/35R18.

Is this a safe swap?

Diameter difference +1.44%: within the ±3% guideline

By overall diameter alone, 245/35R18 falls inside the ±3% range commonly used as a guideline when replacing 235/40R17. 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 245/35R18 (24.75 in)235/40R1724.40 in × 9.25 in245/35R1824.75 in × 9.65 in
Side profile and tread width, drawn to the same scale.
235/40R17 vs 245/35R18 differences
Measurement235/40R17245/35R18Difference% diff
Overall diameter24.40 in (619.8 mm)24.75 in (628.7 mm)+0.35 in (+8.9 mm)+1.44%
Sidewall height3.70 in (94.0 mm)3.38 in (85.8 mm)−0.32 in (−8.2 mm)−8.78%
Section width9.25 in (235.0 mm)9.65 in (245.0 mm)+0.39 in (+10.0 mm)+4.26%
Circumference76.66 in (1,947.2 mm)77.76 in (1,975.1 mm)+1.10 in (+28.0 mm)+1.44%
Revolutions per mile827815−12−1.42%
True speed with the speedometer calibrated for 235/40R17
IndicatedActual on 235/40R17Actual on 245/35R18Difference
30 mph30.0 mph30.4 mph+0.4 mph
60 mph60.0 mph60.9 mph+0.9 mph
75 mph75.0 mph76.1 mph+1.1 mph

Ride-height change: 245/35R18 raises the vehicle by 0.18 in (4.5 mm) at the axle (half the +8.9 mm diameter difference).

245/35R18 is 0.35 in taller than 235/40R17 and 10 mm wider, a 1.44% difference in overall diameter.

With the speedometer calibrated for 235/40R17, an indicated 60 mph is actually 60.9 mph on 245/35R18, and revolutions per mile change from 827 to 815.

245/35R18 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.