285/65R17 vs 255/70R18

255/70R18 is 0.47 in (11.9 mm) taller than 285/65R17, a +1.48% diameter difference. With the speedometer set for 285/65R17, an indicated 60 mph is 60.9 mph on 255/70R18.

Is this a safe swap?

Diameter difference +1.48%: within the ±3% guideline

By overall diameter alone, 255/70R18 falls inside the ±3% range commonly used as a guideline when replacing 285/65R17. 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.

285/65R17 vs 255/70R18 differences
Measurement	285/65R17	255/70R18	Difference	% diff
Overall diameter	31.59 in (802.3 mm)	32.06 in (814.2 mm)	+0.47 in (+11.9 mm)	+1.48%
Sidewall height	7.29 in (185.3 mm)	7.03 in (178.5 mm)	−0.27 in (−6.7 mm)	−3.64%
Section width	11.22 in (285.0 mm)	10.04 in (255.0 mm)	−1.18 in (−30.0 mm)	−10.53%
Circumference	99.23 in (2,520.5 mm)	100.70 in (2,557.9 mm)	+1.47 in (+37.4 mm)	+1.48%
Revolutions per mile	639	629	−9	−1.46%

True speed with the speedometer calibrated for 285/65R17
Indicated	Actual on 285/65R17	Actual on 255/70R18	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.9 mph	+0.9 mph
75 mph	75.0 mph	76.1 mph	+1.1 mph

Ride-height change: 255/70R18 raises the vehicle by 0.23 in (6.0 mm) at the axle (half the +11.9 mm diameter difference).

255/70R18 is 0.47 in taller than 285/65R17 and 30 mm narrower, a 1.48% difference in overall diameter.

With the speedometer calibrated for 285/65R17, an indicated 60 mph is actually 60.9 mph on 255/70R18, and revolutions per mile change from 639 to 629.

255/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 285/65R17.

Size pages

Other comparisons with 285/65R17

Other comparisons with 255/70R18

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