255/40R17 vs 265/35R18

265/35R18 is 0.27 in (6.9 mm) taller than 255/40R17, a +1.09% diameter difference. With the speedometer set for 255/40R17, an indicated 60 mph is 60.7 mph on 265/35R18.

Is this a safe swap?

Diameter difference +1.09%: within the ±3% guideline

By overall diameter alone, 265/35R18 falls inside the ±3% range commonly used as a guideline when replacing 255/40R17. 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.

255/40R17 vs 265/35R18 differences
Measurement	255/40R17	265/35R18	Difference	% diff
Overall diameter	25.03 in (635.8 mm)	25.30 in (642.7 mm)	+0.27 in (+6.9 mm)	+1.09%
Sidewall height	4.02 in (102.0 mm)	3.65 in (92.8 mm)	−0.36 in (−9.2 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	78.64 in (1,997.4 mm)	79.49 in (2,019.1 mm)	+0.85 in (+21.7 mm)	+1.09%
Revolutions per mile	806	797	−9	−1.07%

True speed with the speedometer calibrated for 255/40R17
Indicated	Actual on 255/40R17	Actual on 265/35R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 265/35R18 raises the vehicle by 0.14 in (3.5 mm) at the axle (half the +6.9 mm diameter difference).

265/35R18 is 0.27 in taller than 255/40R17 and 10 mm wider, a 1.09% difference in overall diameter.

With the speedometer calibrated for 255/40R17, an indicated 60 mph is actually 60.7 mph on 265/35R18, and revolutions per mile change from 806 to 797.

265/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/40R17.

Size pages

Other comparisons with 255/40R17

Other comparisons with 265/35R18

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