255/70R17 vs 285/60R18

285/60R18 is 0.41 in (10.4 mm) taller than 255/70R17, a +1.32% diameter difference. With the speedometer set for 255/70R17, an indicated 60 mph is 60.8 mph on 285/60R18.

Is this a safe swap?

Diameter difference +1.32%: within the ±3% guideline

By overall diameter alone, 285/60R18 falls inside the ±3% range commonly used as a guideline when replacing 255/70R17. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

255/70R17 vs 285/60R18 differences
Measurement	255/70R17	285/60R18	Difference	% diff
Overall diameter	31.06 in (788.8 mm)	31.46 in (799.2 mm)	+0.41 in (+10.4 mm)	+1.32%
Sidewall height	7.03 in (178.5 mm)	6.73 in (171.0 mm)	−0.30 in (−7.5 mm)	−4.20%
Section width	10.04 in (255.0 mm)	11.22 in (285.0 mm)	+1.18 in (+30.0 mm)	+11.76%
Circumference	97.56 in (2,478.1 mm)	98.85 in (2,510.8 mm)	+1.29 in (+32.7 mm)	+1.32%
Revolutions per mile	649	641	−8	−1.30%

True speed with the speedometer calibrated for 255/70R17
Indicated	Actual on 255/70R17	Actual on 285/60R18	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 285/60R18 raises the vehicle by 0.20 in (5.2 mm) at the axle (half the +10.4 mm diameter difference).

285/60R18 is 0.41 in taller than 255/70R17 and 30 mm wider, a 1.32% difference in overall diameter.

With the speedometer calibrated for 255/70R17, an indicated 60 mph is actually 60.8 mph on 285/60R18, and revolutions per mile change from 649 to 641.

285/60R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/70R17.

Size pages

Other comparisons with 255/70R17

Other comparisons with 285/60R18

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.