225/40R18 vs 245/30R19

245/30R19 is 0.30 in (7.6 mm) shorter than 225/40R18, a −1.19% diameter difference. With the speedometer set for 225/40R18, an indicated 60 mph is 59.3 mph on 245/30R19.

Is this a safe swap?

Diameter difference −1.19%: within the ±3% guideline

By overall diameter alone, 245/30R19 falls inside the ±3% range commonly used as a guideline when replacing 225/40R18. 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.

225/40R18 vs 245/30R19 differences
Measurement	225/40R18	245/30R19	Difference	% diff
Overall diameter	25.09 in (637.2 mm)	24.79 in (629.6 mm)	−0.30 in (−7.6 mm)	−1.19%
Sidewall height	3.54 in (90.0 mm)	2.89 in (73.5 mm)	−0.65 in (−16.5 mm)	−18.33%
Section width	8.86 in (225.0 mm)	9.65 in (245.0 mm)	+0.79 in (+20.0 mm)	+8.89%
Circumference	78.81 in (2,001.8 mm)	77.87 in (1,977.9 mm)	−0.94 in (−23.9 mm)	−1.19%
Revolutions per mile	804	814	+10	+1.21%

True speed with the speedometer calibrated for 225/40R18
Indicated	Actual on 225/40R18	Actual on 245/30R19	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.3 mph	−0.7 mph
75 mph	75.0 mph	74.1 mph	−0.9 mph

Ride-height change: 245/30R19 lowers the vehicle by 0.15 in (3.8 mm) at the axle (half the −7.6 mm diameter difference).

245/30R19 is 0.30 in shorter than 225/40R18 and 20 mm wider, a 1.19% difference in overall diameter.

With the speedometer calibrated for 225/40R18, an indicated 60 mph is actually 59.3 mph on 245/30R19, and revolutions per mile change from 804 to 814.

245/30R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 225/40R18.

Size pages

Other comparisons with 225/40R18

Other comparisons with 245/30R19

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