265/70R17 vs 255/70R18

255/70R18 is 0.45 in (11.4 mm) taller than 265/70R17, a +1.42% diameter difference. With the speedometer set for 265/70R17, an indicated 60 mph is 60.9 mph on 255/70R18.

Is this a safe swap?

Diameter difference +1.42%: within the ±3% guideline

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

265/70R17 vs 255/70R18 differences
Measurement	265/70R17	255/70R18	Difference	% diff
Overall diameter	31.61 in (802.8 mm)	32.06 in (814.2 mm)	+0.45 in (+11.4 mm)	+1.42%
Sidewall height	7.30 in (185.5 mm)	7.03 in (178.5 mm)	−0.28 in (−7.0 mm)	−3.77%
Section width	10.43 in (265.0 mm)	10.04 in (255.0 mm)	−0.39 in (−10.0 mm)	−3.77%
Circumference	99.29 in (2,522.1 mm)	100.70 in (2,557.9 mm)	+1.41 in (+35.8 mm)	+1.42%
Revolutions per mile	638	629	−9	−1.40%

True speed with the speedometer calibrated for 265/70R17
Indicated	Actual on 265/70R17	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 0.22 in (5.7 mm) at the axle (half the +11.4 mm diameter difference).

255/70R18 is 0.45 in taller than 265/70R17 and 10 mm narrower, a 1.42% difference in overall diameter.

With the speedometer calibrated for 265/70R17, an indicated 60 mph is actually 60.9 mph on 255/70R18, and revolutions per mile change from 638 to 629.

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

Size pages

Other comparisons with 265/70R17

Other comparisons with 255/70R18

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