TireSizesFinder

215/65R16 vs 285/40R18

285/40R18 is 0.03 in (0.7 mm) shorter than 215/65R16, a −0.10% diameter difference. With the speedometer set for 215/65R16, an indicated 60 mph is 59.9 mph on 285/40R18.

Is this a safe swap?

Diameter difference −0.10%: under 1%

By overall diameter alone, 285/40R18 is a near match for 215/65R16; 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: 215/65R16 (27.00 in) vs 285/40R18 (26.98 in)215/65R1627.00 in × 8.46 in285/40R1826.98 in × 11.22 in
Side profile and tread width, drawn to the same scale.
215/65R16 vs 285/40R18 differences
Measurement215/65R16285/40R18Difference% diff
Overall diameter27.00 in (685.9 mm)26.98 in (685.2 mm)−0.03 in (−0.7 mm)−0.10%
Sidewall height5.50 in (139.8 mm)4.49 in (114.0 mm)−1.01 in (−25.7 mm)−18.43%
Section width8.46 in (215.0 mm)11.22 in (285.0 mm)+2.76 in (+70.0 mm)+32.56%
Circumference84.84 in (2,154.8 mm)84.75 in (2,152.6 mm)−0.09 in (−2.2 mm)−0.10%
Revolutions per mile747748+1+0.10%
True speed with the speedometer calibrated for 215/65R16
IndicatedActual on 215/65R16Actual on 285/40R18Difference
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: 285/40R18 lowers the vehicle by 0.01 in (0.3 mm) at the axle (half the −0.7 mm diameter difference).

285/40R18 is 0.03 in shorter than 215/65R16 and 70 mm wider, a 0.10% difference in overall diameter.

With the speedometer calibrated for 215/65R16, an indicated 60 mph is actually 59.9 mph on 285/40R18, and revolutions per mile change from 747 to 748.

285/40R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 215/65R16.

Size pages

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