225/45R18 vs 225/40R19

225/40R19 is 0.11 in (2.9 mm) taller than 225/45R18, a +0.44% diameter difference. With the speedometer set for 225/45R18, an indicated 60 mph is 60.3 mph on 225/40R19.

Is this a safe swap?

Diameter difference +0.44%: under 1%

By overall diameter alone, 225/40R19 is a near match for 225/45R18; 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.

225/45R18 vs 225/40R19 differences
Measurement	225/45R18	225/40R19	Difference	% diff
Overall diameter	25.97 in (659.7 mm)	26.09 in (662.6 mm)	+0.11 in (+2.9 mm)	+0.44%
Sidewall height	3.99 in (101.3 mm)	3.54 in (90.0 mm)	−0.44 in (−11.2 mm)	−11.11%
Section width	8.86 in (225.0 mm)	8.86 in (225.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	81.59 in (2,072.5 mm)	81.95 in (2,081.6 mm)	+0.36 in (+9.1 mm)	+0.44%
Revolutions per mile	777	773	−3	−0.44%

True speed with the speedometer calibrated for 225/45R18
Indicated	Actual on 225/45R18	Actual on 225/40R19	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 225/40R19 raises the vehicle by 0.06 in (1.4 mm) at the axle (half the +2.9 mm diameter difference).

225/40R19 is 0.11 in taller than 225/45R18 and the same width, a 0.44% difference in overall diameter.

With the speedometer calibrated for 225/45R18, an indicated 60 mph is actually 60.3 mph on 225/40R19, and revolutions per mile change from 777 to 773.

225/40R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 225/45R18.

Size pages

Other comparisons with 225/45R18

Other comparisons with 225/40R19

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