285/45R18 vs 285/40R19

285/40R19 is 0.12 in (3.1 mm) shorter than 285/45R18, a −0.43% diameter difference. With the speedometer set for 285/45R18, an indicated 60 mph is 59.7 mph on 285/40R19.

Is this a safe swap?

Diameter difference −0.43%: under 1%

By overall diameter alone, 285/40R19 is a near match for 285/45R18; 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.

285/45R18 vs 285/40R19 differences
Measurement	285/45R18	285/40R19	Difference	% diff
Overall diameter	28.10 in (713.7 mm)	27.98 in (710.6 mm)	−0.12 in (−3.1 mm)	−0.43%
Sidewall height	5.05 in (128.3 mm)	4.49 in (114.0 mm)	−0.56 in (−14.2 mm)	−11.11%
Section width	11.22 in (285.0 mm)	11.22 in (285.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	88.27 in (2,242.2 mm)	87.89 in (2,232.4 mm)	−0.38 in (−9.7 mm)	−0.43%
Revolutions per mile	718	721	+3	+0.44%

True speed with the speedometer calibrated for 285/45R18
Indicated	Actual on 285/45R18	Actual on 285/40R19	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.7 mph	−0.3 mph
75 mph	75.0 mph	74.7 mph	−0.3 mph

Ride-height change: 285/40R19 lowers the vehicle by 0.06 in (1.6 mm) at the axle (half the −3.1 mm diameter difference).

285/40R19 is 0.12 in shorter than 285/45R18 and the same width, a 0.43% difference in overall diameter.

With the speedometer calibrated for 285/45R18, an indicated 60 mph is actually 59.7 mph on 285/40R19, and revolutions per mile change from 718 to 721.

285/40R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 285/45R18.

Size pages

Other comparisons with 285/45R18

Other comparisons with 285/40R19

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