265/40R18 vs 305/30R19

305/30R19 is 0.14 in (3.6 mm) shorter than 265/40R18, a −0.54% diameter difference. With the speedometer set for 265/40R18, an indicated 60 mph is 59.7 mph on 305/30R19.

Is this a safe swap?

Diameter difference −0.54%: under 1%

By overall diameter alone, 305/30R19 is a near match for 265/40R18; 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.

265/40R18 vs 305/30R19 differences
Measurement	265/40R18	305/30R19	Difference	% diff
Overall diameter	26.35 in (669.2 mm)	26.20 in (665.6 mm)	−0.14 in (−3.6 mm)	−0.54%
Sidewall height	4.17 in (106.0 mm)	3.60 in (91.5 mm)	−0.57 in (−14.5 mm)	−13.68%
Section width	10.43 in (265.0 mm)	12.01 in (305.0 mm)	+1.57 in (+40.0 mm)	+15.09%
Circumference	82.77 in (2,102.4 mm)	82.32 in (2,091.0 mm)	−0.45 in (−11.3 mm)	−0.54%
Revolutions per mile	765	770	+4	+0.54%

True speed with the speedometer calibrated for 265/40R18
Indicated	Actual on 265/40R18	Actual on 305/30R19	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.7 mph	−0.3 mph
75 mph	75.0 mph	74.6 mph	−0.4 mph

Ride-height change: 305/30R19 lowers the vehicle by 0.07 in (1.8 mm) at the axle (half the −3.6 mm diameter difference).

305/30R19 is 0.14 in shorter than 265/40R18 and 40 mm wider, a 0.54% difference in overall diameter.

With the speedometer calibrated for 265/40R18, an indicated 60 mph is actually 59.7 mph on 305/30R19, and revolutions per mile change from 765 to 770.

305/30R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 265/40R18.

Size pages

Other comparisons with 265/40R18

Other comparisons with 305/30R19

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