TireSizesFinder

305/70R16 vs 285/65R18

285/65R18 is 0.22 in (5.7 mm) shorter than 305/70R16, a −0.68% diameter difference. With the speedometer set for 305/70R16, an indicated 60 mph is 59.6 mph on 285/65R18.

Is this a safe swap?

Diameter difference −0.68%: under 1%

By overall diameter alone, 285/65R18 is a near match for 305/70R16; 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: 305/70R16 (32.81 in) vs 285/65R18 (32.59 in)305/70R1632.81 in × 12.01 in285/65R1832.59 in × 11.22 in
Side profile and tread width, drawn to the same scale.
305/70R16 vs 285/65R18 differences
Measurement305/70R16285/65R18Difference% diff
Overall diameter32.81 in (833.4 mm)32.59 in (827.7 mm)−0.22 in (−5.7 mm)−0.68%
Sidewall height8.41 in (213.5 mm)7.29 in (185.3 mm)−1.11 in (−28.2 mm)−13.23%
Section width12.01 in (305.0 mm)11.22 in (285.0 mm)−0.79 in (−20.0 mm)−6.56%
Circumference103.08 in (2,618.2 mm)102.37 in (2,600.3 mm)−0.71 in (−17.9 mm)−0.68%
Revolutions per mile615619+4+0.69%
True speed with the speedometer calibrated for 305/70R16
IndicatedActual on 305/70R16Actual on 285/65R18Difference
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: 285/65R18 lowers the vehicle by 0.11 in (2.8 mm) at the axle (half the −5.7 mm diameter difference).

285/65R18 is 0.22 in shorter than 305/70R16 and 20 mm narrower, a 0.68% difference in overall diameter.

With the speedometer calibrated for 305/70R16, an indicated 60 mph is actually 59.6 mph on 285/65R18, and revolutions per mile change from 615 to 619.

285/65R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 305/70R16.

Size pages

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