255/75R17 vs 265/70R18

265/70R18 is 0.55 in (13.9 mm) taller than 255/75R17, a +1.71% diameter difference. With the speedometer set for 255/75R17, an indicated 60 mph is 61.0 mph on 265/70R18.

Is this a safe swap?

Diameter difference +1.71%: within the ±3% guideline

By overall diameter alone, 265/70R18 falls inside the ±3% range commonly used as a guideline when replacing 255/75R17. 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.

255/75R17 vs 265/70R18 differences
Measurement	255/75R17	265/70R18	Difference	% diff
Overall diameter	32.06 in (814.3 mm)	32.61 in (828.2 mm)	+0.55 in (+13.9 mm)	+1.71%
Sidewall height	7.53 in (191.3 mm)	7.30 in (185.5 mm)	−0.23 in (−5.7 mm)	−3.01%
Section width	10.04 in (255.0 mm)	10.43 in (265.0 mm)	+0.39 in (+10.0 mm)	+3.92%
Circumference	100.72 in (2,558.2 mm)	102.44 in (2,601.9 mm)	+1.72 in (+43.7 mm)	+1.71%
Revolutions per mile	629	619	−11	−1.68%

True speed with the speedometer calibrated for 255/75R17
Indicated	Actual on 255/75R17	Actual on 265/70R18	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	61.0 mph	+1.0 mph
75 mph	75.0 mph	76.3 mph	+1.3 mph

Ride-height change: 265/70R18 raises the vehicle by 0.27 in (7.0 mm) at the axle (half the +13.9 mm diameter difference).

265/70R18 is 0.55 in taller than 255/75R17 and 10 mm wider, a 1.71% difference in overall diameter.

With the speedometer calibrated for 255/75R17, an indicated 60 mph is actually 61.0 mph on 265/70R18, and revolutions per mile change from 629 to 619.

265/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/75R17.

Size pages

Other comparisons with 255/75R17

Other comparisons with 265/70R18

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