265/50R19 vs 305/40R20

305/40R20 is 0.17 in (4.4 mm) taller than 265/50R19, a +0.59% diameter difference. With the speedometer set for 265/50R19, an indicated 60 mph is 60.4 mph on 305/40R20.

Is this a safe swap?

Diameter difference +0.59%: under 1%

By overall diameter alone, 305/40R20 is a near match for 265/50R19; 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.

265/50R19 vs 305/40R20 differences
Measurement	265/50R19	305/40R20	Difference	% diff
Overall diameter	29.43 in (747.6 mm)	29.61 in (752.0 mm)	+0.17 in (+4.4 mm)	+0.59%
Sidewall height	5.22 in (132.5 mm)	4.80 in (122.0 mm)	−0.41 in (−10.5 mm)	−7.92%
Section width	10.43 in (265.0 mm)	12.01 in (305.0 mm)	+1.57 in (+40.0 mm)	+15.09%
Circumference	92.47 in (2,348.7 mm)	93.01 in (2,362.5 mm)	+0.54 in (+13.8 mm)	+0.59%
Revolutions per mile	685	681	−4	−0.59%

True speed with the speedometer calibrated for 265/50R19
Indicated	Actual on 265/50R19	Actual on 305/40R20	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.4 mph	+0.4 mph

Ride-height change: 305/40R20 raises the vehicle by 0.09 in (2.2 mm) at the axle (half the +4.4 mm diameter difference).

305/40R20 is 0.17 in taller than 265/50R19 and 40 mm wider, a 0.59% difference in overall diameter.

With the speedometer calibrated for 265/50R19, an indicated 60 mph is actually 60.4 mph on 305/40R20, and revolutions per mile change from 685 to 681.

305/40R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 265/50R19.

Size pages

Other comparisons with 265/50R19

Other comparisons with 305/40R20

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