TireSizesFinder

305/65R17 vs 285/65R18

285/65R18 is 0.02 in (0.6 mm) shorter than 305/65R17, a −0.07% diameter difference. With the speedometer set for 305/65R17, an indicated 60 mph is 60.0 mph on 285/65R18.

Is this a safe swap?

Diameter difference −0.07%: under 1%

By overall diameter alone, 285/65R18 is a near match for 305/65R17; 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: 305/65R17 (32.61 in) vs 285/65R18 (32.59 in)305/65R1732.61 in × 12.01 in285/65R1832.59 in × 11.22 in
Side profile and tread width, drawn to the same scale.
305/65R17 vs 285/65R18 differences
Measurement305/65R17285/65R18Difference% diff
Overall diameter32.61 in (828.3 mm)32.59 in (827.7 mm)−0.02 in (−0.6 mm)−0.07%
Sidewall height7.81 in (198.3 mm)7.29 in (185.3 mm)−0.51 in (−13.0 mm)−6.56%
Section width12.01 in (305.0 mm)11.22 in (285.0 mm)−0.79 in (−20.0 mm)−6.56%
Circumference102.45 in (2,602.2 mm)102.37 in (2,600.3 mm)−0.07 in (−1.9 mm)−0.07%
Revolutions per mile6186190+0.07%
True speed with the speedometer calibrated for 305/65R17
IndicatedActual on 305/65R17Actual on 285/65R18Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph60.0 mph0.0 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 285/65R18 lowers the vehicle by 0.01 in (0.3 mm) at the axle (half the −0.6 mm diameter difference).

285/65R18 is 0.02 in shorter than 305/65R17 and 20 mm narrower, a 0.07% difference in overall diameter.

With the speedometer calibrated for 305/65R17, an indicated 60 mph is actually 60.0 mph on 285/65R18, and revolutions per mile change from 618 to 619.

285/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 305/65R17.

Size pages

Other comparisons with 305/65R17

Other comparisons with 285/65R18

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