235/55R17 vs 265/45R18

265/45R18 is 0.21 in (5.4 mm) taller than 235/55R17, a +0.78% diameter difference. With the speedometer set for 235/55R17, an indicated 60 mph is 60.5 mph on 265/45R18.

Is this a safe swap?

Diameter difference +0.78%: under 1%

By overall diameter alone, 265/45R18 is a near match for 235/55R17; the speedometer changes by less than 1%. 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.

235/55R17 vs 265/45R18 differences
Measurement	235/55R17	265/45R18	Difference	% diff
Overall diameter	27.18 in (690.3 mm)	27.39 in (695.7 mm)	+0.21 in (+5.4 mm)	+0.78%
Sidewall height	5.09 in (129.3 mm)	4.69 in (119.3 mm)	−0.39 in (−10.0 mm)	−7.74%
Section width	9.25 in (235.0 mm)	10.43 in (265.0 mm)	+1.18 in (+30.0 mm)	+12.77%
Circumference	85.38 in (2,168.6 mm)	86.05 in (2,185.6 mm)	+0.67 in (+17.0 mm)	+0.78%
Revolutions per mile	742	736	−6	−0.78%

True speed with the speedometer calibrated for 235/55R17
Indicated	Actual on 235/55R17	Actual on 265/45R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 265/45R18 raises the vehicle by 0.11 in (2.7 mm) at the axle (half the +5.4 mm diameter difference).

265/45R18 is 0.21 in taller than 235/55R17 and 30 mm wider, a 0.78% difference in overall diameter.

With the speedometer calibrated for 235/55R17, an indicated 60 mph is actually 60.5 mph on 265/45R18, and revolutions per mile change from 742 to 736.

265/45R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 235/55R17.

Size pages

Other comparisons with 235/55R17

Other comparisons with 265/45R18

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