265/45R18 vs 265/40R19

265/40R19 is 0.04 in (1.1 mm) shorter than 265/45R18, a −0.16% diameter difference. With the speedometer set for 265/45R18, an indicated 60 mph is 59.9 mph on 265/40R19.

Is this a safe swap?

Diameter difference −0.16%: under 1%

By overall diameter alone, 265/40R19 is a near match for 265/45R18; 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.

265/45R18 vs 265/40R19 differences
Measurement	265/45R18	265/40R19	Difference	% diff
Overall diameter	27.39 in (695.7 mm)	27.35 in (694.6 mm)	−0.04 in (−1.1 mm)	−0.16%
Sidewall height	4.69 in (119.3 mm)	4.17 in (106.0 mm)	−0.52 in (−13.2 mm)	−11.11%
Section width	10.43 in (265.0 mm)	10.43 in (265.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	86.05 in (2,185.6 mm)	85.91 in (2,182.2 mm)	−0.14 in (−3.5 mm)	−0.16%
Revolutions per mile	736	738	+1	+0.16%

True speed with the speedometer calibrated for 265/45R18
Indicated	Actual on 265/45R18	Actual on 265/40R19	Difference
30 mph	30.0 mph	30.0 mph	0.0 mph
60 mph	60.0 mph	59.9 mph	−0.1 mph
75 mph	75.0 mph	74.9 mph	−0.1 mph

Ride-height change: 265/40R19 lowers the vehicle by 0.02 in (0.6 mm) at the axle (half the −1.1 mm diameter difference).

265/40R19 is 0.04 in shorter than 265/45R18 and the same width, a 0.16% difference in overall diameter.

With the speedometer calibrated for 265/45R18, an indicated 60 mph is actually 59.9 mph on 265/40R19, and revolutions per mile change from 736 to 738.

265/40R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 265/45R18.

Size pages

Other comparisons with 265/45R18

Other comparisons with 265/40R19

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