TireSizesFinder

225/50R16 vs 215/40R18

215/40R18 is 0.09 in (2.2 mm) shorter than 225/50R16, a −0.35% diameter difference. With the speedometer set for 225/50R16, an indicated 60 mph is 59.8 mph on 215/40R18.

Is this a safe swap?

Diameter difference −0.35%: under 1%

By overall diameter alone, 215/40R18 is a near match for 225/50R16; 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: 225/50R16 (24.86 in) vs 215/40R18 (24.77 in)225/50R1624.86 in × 8.86 in215/40R1824.77 in × 8.46 in
Side profile and tread width, drawn to the same scale.
225/50R16 vs 215/40R18 differences
Measurement225/50R16215/40R18Difference% diff
Overall diameter24.86 in (631.4 mm)24.77 in (629.2 mm)−0.09 in (−2.2 mm)−0.35%
Sidewall height4.43 in (112.5 mm)3.39 in (86.0 mm)−1.04 in (−26.5 mm)−23.56%
Section width8.86 in (225.0 mm)8.46 in (215.0 mm)−0.39 in (−10.0 mm)−4.44%
Circumference78.09 in (1,983.6 mm)77.82 in (1,976.7 mm)−0.27 in (−6.9 mm)−0.35%
Revolutions per mile811814+3+0.35%
True speed with the speedometer calibrated for 225/50R16
IndicatedActual on 225/50R16Actual on 215/40R18Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.8 mph−0.2 mph
75 mph75.0 mph74.7 mph−0.3 mph

Ride-height change: 215/40R18 lowers the vehicle by 0.04 in (1.1 mm) at the axle (half the −2.2 mm diameter difference).

215/40R18 is 0.09 in shorter than 225/50R16 and 10 mm narrower, a 0.35% difference in overall diameter.

With the speedometer calibrated for 225/50R16, an indicated 60 mph is actually 59.8 mph on 215/40R18, and revolutions per mile change from 811 to 814.

215/40R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 225/50R16.

Size pages

Other comparisons with 225/50R16

Other comparisons with 215/40R18

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