TireSizesFinder

225/55R16 vs 245/40R18

245/40R18 is 0.03 in (0.7 mm) shorter than 225/55R16, a −0.11% diameter difference. With the speedometer set for 225/55R16, an indicated 60 mph is 59.9 mph on 245/40R18.

Is this a safe swap?

Diameter difference −0.11%: under 1%

By overall diameter alone, 245/40R18 is a near match for 225/55R16; 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: 225/55R16 (25.74 in) vs 245/40R18 (25.72 in)225/55R1625.74 in × 8.86 in245/40R1825.72 in × 9.65 in
Side profile and tread width, drawn to the same scale.
225/55R16 vs 245/40R18 differences
Measurement225/55R16245/40R18Difference% diff
Overall diameter25.74 in (653.9 mm)25.72 in (653.2 mm)−0.03 in (−0.7 mm)−0.11%
Sidewall height4.87 in (123.8 mm)3.86 in (98.0 mm)−1.01 in (−25.7 mm)−20.81%
Section width8.86 in (225.0 mm)9.65 in (245.0 mm)+0.79 in (+20.0 mm)+8.89%
Circumference80.88 in (2,054.3 mm)80.79 in (2,052.1 mm)−0.09 in (−2.2 mm)−0.11%
Revolutions per mile783784+1+0.11%
True speed with the speedometer calibrated for 225/55R16
IndicatedActual on 225/55R16Actual on 245/40R18Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 245/40R18 lowers the vehicle by 0.01 in (0.3 mm) at the axle (half the −0.7 mm diameter difference).

245/40R18 is 0.03 in shorter than 225/55R16 and 20 mm wider, a 0.11% difference in overall diameter.

With the speedometer calibrated for 225/55R16, an indicated 60 mph is actually 59.9 mph on 245/40R18, and revolutions per mile change from 783 to 784.

245/40R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 225/55R16.

Size pages

Other comparisons with 225/55R16

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