255/80R17 vs 265/70R18

265/70R18 is 0.46 in (11.6 mm) shorter than 255/80R17, a −1.38% diameter difference. With the speedometer set for 255/80R17, an indicated 60 mph is 59.2 mph on 265/70R18.

Is this a safe swap?

Diameter difference −1.38%: within the ±3% guideline

By overall diameter alone, 265/70R18 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 265/70R18 differences
Measurement	255/80R17	265/70R18	Difference	% diff
Overall diameter	33.06 in (839.8 mm)	32.61 in (828.2 mm)	−0.46 in (−11.6 mm)	−1.38%
Sidewall height	8.03 in (204.0 mm)	7.30 in (185.5 mm)	−0.73 in (−18.5 mm)	−9.07%
Section width	10.04 in (255.0 mm)	10.43 in (265.0 mm)	+0.39 in (+10.0 mm)	+3.92%
Circumference	103.87 in (2,638.3 mm)	102.44 in (2,601.9 mm)	−1.43 in (−36.4 mm)	−1.38%
Revolutions per mile	610	619	+9	+1.40%

True speed with the speedometer calibrated for 255/80R17
Indicated	Actual on 255/80R17	Actual on 265/70R18	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.2 mph	−0.8 mph
75 mph	75.0 mph	74.0 mph	−1.0 mph

Ride-height change: 265/70R18 lowers the vehicle by 0.23 in (5.8 mm) at the axle (half the −11.6 mm diameter difference).

265/70R18 is 0.46 in shorter than 255/80R17 and 10 mm wider, a 1.38% difference in overall diameter.

With the speedometer calibrated for 255/80R17, an indicated 60 mph is actually 59.2 mph on 265/70R18, and revolutions per mile change from 610 to 619.

265/70R18 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 265/70R18

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