255/80R17 vs 285/70R18

285/70R18 is 0.65 in (16.4 mm) taller than 255/80R17, a +1.95% diameter difference. With the speedometer set for 255/80R17, an indicated 60 mph is 61.2 mph on 285/70R18.

Is this a safe swap?

Diameter difference +1.95%: within the ±3% guideline

By overall diameter alone, 285/70R18 falls inside the ±3% range commonly used as a guideline when replacing 255/80R17. 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.

255/80R17 vs 285/70R18 differences
Measurement	255/80R17	285/70R18	Difference	% diff
Overall diameter	33.06 in (839.8 mm)	33.71 in (856.2 mm)	+0.65 in (+16.4 mm)	+1.95%
Sidewall height	8.03 in (204.0 mm)	7.85 in (199.5 mm)	−0.18 in (−4.5 mm)	−2.21%
Section width	10.04 in (255.0 mm)	11.22 in (285.0 mm)	+1.18 in (+30.0 mm)	+11.76%
Circumference	103.87 in (2,638.3 mm)	105.90 in (2,689.8 mm)	+2.03 in (+51.5 mm)	+1.95%
Revolutions per mile	610	598	−12	−1.92%

True speed with the speedometer calibrated for 255/80R17
Indicated	Actual on 255/80R17	Actual on 285/70R18	Difference
30 mph	30.0 mph	30.6 mph	+0.6 mph
60 mph	60.0 mph	61.2 mph	+1.2 mph
75 mph	75.0 mph	76.5 mph	+1.5 mph

Ride-height change: 285/70R18 raises the vehicle by 0.32 in (8.2 mm) at the axle (half the +16.4 mm diameter difference).

285/70R18 is 0.65 in taller than 255/80R17 and 30 mm wider, a 1.95% difference in overall diameter.

With the speedometer calibrated for 255/80R17, an indicated 60 mph is actually 61.2 mph on 285/70R18, and revolutions per mile change from 610 to 598.

285/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/80R17.

Size pages

Other comparisons with 255/80R17

Other comparisons with 285/70R18

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