255/45R18 vs 265/45R18

265/45R18 is 0.35 in (9.0 mm) taller than 255/45R18, a +1.31% diameter difference. With the speedometer set for 255/45R18, an indicated 60 mph is 60.8 mph on 265/45R18.

Is this a safe swap?

Diameter difference +1.31%: within the ±3% guideline

By overall diameter alone, 265/45R18 falls inside the ±3% range commonly used as a guideline when replacing 255/45R18. 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.

255/45R18 vs 265/45R18 differences
Measurement	255/45R18	265/45R18	Difference	% diff
Overall diameter	27.04 in (686.7 mm)	27.39 in (695.7 mm)	+0.35 in (+9.0 mm)	+1.31%
Sidewall height	4.52 in (114.8 mm)	4.69 in (119.3 mm)	+0.18 in (+4.5 mm)	+3.92%
Section width	10.04 in (255.0 mm)	10.43 in (265.0 mm)	+0.39 in (+10.0 mm)	+3.92%
Circumference	84.93 in (2,157.3 mm)	86.05 in (2,185.6 mm)	+1.11 in (+28.3 mm)	+1.31%
Revolutions per mile	746	736	−10	−1.29%

True speed with the speedometer calibrated for 255/45R18
Indicated	Actual on 255/45R18	Actual on 265/45R18	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 265/45R18 raises the vehicle by 0.18 in (4.5 mm) at the axle (half the +9.0 mm diameter difference).

265/45R18 is 0.35 in taller than 255/45R18 and 10 mm wider, a 1.31% difference in overall diameter.

With the speedometer calibrated for 255/45R18, an indicated 60 mph is actually 60.8 mph on 265/45R18, and revolutions per mile change from 746 to 736.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 255/45R18

Other comparisons with 265/45R18

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