TireSizesFinder

215/60R17 vs 285/40R18

285/40R18 is 0.18 in (4.6 mm) shorter than 215/60R17, a −0.67% diameter difference. With the speedometer set for 215/60R17, an indicated 60 mph is 59.6 mph on 285/40R18.

Is this a safe swap?

Diameter difference −0.67%: under 1%

By overall diameter alone, 285/40R18 is a near match for 215/60R17; 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: 215/60R17 (27.16 in) vs 285/40R18 (26.98 in)215/60R1727.16 in × 8.46 in285/40R1826.98 in × 11.22 in
Side profile and tread width, drawn to the same scale.
215/60R17 vs 285/40R18 differences
Measurement215/60R17285/40R18Difference% diff
Overall diameter27.16 in (689.8 mm)26.98 in (685.2 mm)−0.18 in (−4.6 mm)−0.67%
Sidewall height5.08 in (129.0 mm)4.49 in (114.0 mm)−0.59 in (−15.0 mm)−11.63%
Section width8.46 in (215.0 mm)11.22 in (285.0 mm)+2.76 in (+70.0 mm)+32.56%
Circumference85.32 in (2,167.1 mm)84.75 in (2,152.6 mm)−0.57 in (−14.5 mm)−0.67%
Revolutions per mile743748+5+0.67%
True speed with the speedometer calibrated for 215/60R17
IndicatedActual on 215/60R17Actual on 285/40R18Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.6 mph−0.4 mph
75 mph75.0 mph74.5 mph−0.5 mph

Ride-height change: 285/40R18 lowers the vehicle by 0.09 in (2.3 mm) at the axle (half the −4.6 mm diameter difference).

285/40R18 is 0.18 in shorter than 215/60R17 and 70 mm wider, a 0.67% difference in overall diameter.

With the speedometer calibrated for 215/60R17, an indicated 60 mph is actually 59.6 mph on 285/40R18, and revolutions per mile change from 743 to 748.

285/40R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 215/60R17.

Size pages

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