205/40R18 vs 245/30R19

245/30R19 is 0.33 in (8.4 mm) taller than 205/40R18, a +1.35% diameter difference. With the speedometer set for 205/40R18, an indicated 60 mph is 60.8 mph on 245/30R19.

Is this a safe swap?

Diameter difference +1.35%: within the ±3% guideline

By overall diameter alone, 245/30R19 falls inside the ±3% range commonly used as a guideline when replacing 205/40R18. 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.

205/40R18 vs 245/30R19 differences
Measurement	205/40R18	245/30R19	Difference	% diff
Overall diameter	24.46 in (621.2 mm)	24.79 in (629.6 mm)	+0.33 in (+8.4 mm)	+1.35%
Sidewall height	3.23 in (82.0 mm)	2.89 in (73.5 mm)	−0.33 in (−8.5 mm)	−10.37%
Section width	8.07 in (205.0 mm)	9.65 in (245.0 mm)	+1.57 in (+40.0 mm)	+19.51%
Circumference	76.83 in (1,951.6 mm)	77.87 in (1,977.9 mm)	+1.04 in (+26.4 mm)	+1.35%
Revolutions per mile	825	814	−11	−1.33%

True speed with the speedometer calibrated for 205/40R18
Indicated	Actual on 205/40R18	Actual on 245/30R19	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 245/30R19 raises the vehicle by 0.17 in (4.2 mm) at the axle (half the +8.4 mm diameter difference).

245/30R19 is 0.33 in taller than 205/40R18 and 40 mm wider, a 1.35% difference in overall diameter.

With the speedometer calibrated for 205/40R18, an indicated 60 mph is actually 60.8 mph on 245/30R19, and revolutions per mile change from 825 to 814.

245/30R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 205/40R18.

Size pages

Other comparisons with 205/40R18

Other comparisons with 245/30R19

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