TireSizesFinder

285/75R17 vs 285/70R18

285/70R18 is 0.12 in (3.1 mm) shorter than 285/75R17, a −0.36% diameter difference. With the speedometer set for 285/75R17, an indicated 60 mph is 59.8 mph on 285/70R18.

Is this a safe swap?

Diameter difference −0.36%: under 1%

By overall diameter alone, 285/70R18 is a near match for 285/75R17; 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: 285/75R17 (33.83 in) vs 285/70R18 (33.71 in)285/75R1733.83 in × 11.22 in285/70R1833.71 in × 11.22 in
Side profile and tread width, drawn to the same scale.
285/75R17 vs 285/70R18 differences
Measurement285/75R17285/70R18Difference% diff
Overall diameter33.83 in (859.3 mm)33.71 in (856.2 mm)−0.12 in (−3.1 mm)−0.36%
Sidewall height8.42 in (213.8 mm)7.85 in (199.5 mm)−0.56 in (−14.2 mm)−6.67%
Section width11.22 in (285.0 mm)11.22 in (285.0 mm)0.00 in (0.0 mm)0.00%
Circumference106.28 in (2,699.6 mm)105.90 in (2,689.8 mm)−0.38 in (−9.7 mm)−0.36%
Revolutions per mile596598+2+0.36%
True speed with the speedometer calibrated for 285/75R17
IndicatedActual on 285/75R17Actual on 285/70R18Difference
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: 285/70R18 lowers the vehicle by 0.06 in (1.5 mm) at the axle (half the −3.1 mm diameter difference).

285/70R18 is 0.12 in shorter than 285/75R17 and the same width, a 0.36% difference in overall diameter.

With the speedometer calibrated for 285/75R17, an indicated 60 mph is actually 59.8 mph on 285/70R18, and revolutions per mile change from 596 to 598.

285/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 285/75R17.

Size pages

Other comparisons with 285/75R17

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