TireSizesFinder

245/35R18 vs 215/40R18

215/40R18 is 0.02 in (0.5 mm) taller than 245/35R18, a +0.08% diameter difference. With the speedometer set for 245/35R18, an indicated 60 mph is 60.0 mph on 215/40R18.

Is this a safe swap?

Diameter difference +0.08%: under 1%

By overall diameter alone, 215/40R18 is a near match for 245/35R18; 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: 245/35R18 (24.75 in) vs 215/40R18 (24.77 in)245/35R1824.75 in × 9.65 in215/40R1824.77 in × 8.46 in
Side profile and tread width, drawn to the same scale.
245/35R18 vs 215/40R18 differences
Measurement245/35R18215/40R18Difference% diff
Overall diameter24.75 in (628.7 mm)24.77 in (629.2 mm)+0.02 in (+0.5 mm)+0.08%
Sidewall height3.38 in (85.8 mm)3.39 in (86.0 mm)+0.01 in (+0.3 mm)+0.29%
Section width9.65 in (245.0 mm)8.46 in (215.0 mm)−1.18 in (−30.0 mm)−12.24%
Circumference77.76 in (1,975.1 mm)77.82 in (1,976.7 mm)+0.06 in (+1.6 mm)+0.08%
Revolutions per mile815814−1−0.08%
True speed with the speedometer calibrated for 245/35R18
IndicatedActual on 245/35R18Actual on 215/40R18Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph60.0 mph0.0 mph
75 mph75.0 mph75.1 mph+0.1 mph

Ride-height change: 215/40R18 raises the vehicle by 0.01 in (0.3 mm) at the axle (half the +0.5 mm diameter difference).

215/40R18 is 0.02 in taller than 245/35R18 and 30 mm narrower, a 0.08% difference in overall diameter.

With the speedometer calibrated for 245/35R18, an indicated 60 mph is actually 60.0 mph on 215/40R18, and revolutions per mile change from 815 to 814.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 245/35R18

Other comparisons with 215/40R18

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