245/45R19 vs 245/40R20

245/40R20 is 0.04 in (0.9 mm) taller than 245/45R19, a +0.13% diameter difference. With the speedometer set for 245/45R19, an indicated 60 mph is 60.1 mph on 245/40R20.

Is this a safe swap?

Diameter difference +0.13%: under 1%

By overall diameter alone, 245/40R20 is a near match for 245/45R19; 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.

245/45R19 vs 245/40R20 differences
Measurement	245/45R19	245/40R20	Difference	% diff
Overall diameter	27.68 in (703.1 mm)	27.72 in (704.0 mm)	+0.04 in (+0.9 mm)	+0.13%
Sidewall height	4.34 in (110.3 mm)	3.86 in (98.0 mm)	−0.48 in (−12.2 mm)	−11.11%
Section width	9.65 in (245.0 mm)	9.65 in (245.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	86.96 in (2,208.9 mm)	87.07 in (2,211.7 mm)	+0.11 in (+2.8 mm)	+0.13%
Revolutions per mile	729	728	−1	−0.13%

True speed with the speedometer calibrated for 245/45R19
Indicated	Actual on 245/45R19	Actual on 245/40R20	Difference
30 mph	30.0 mph	30.0 mph	0.0 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.1 mph	+0.1 mph

Ride-height change: 245/40R20 raises the vehicle by 0.02 in (0.5 mm) at the axle (half the +0.9 mm diameter difference).

245/40R20 is 0.04 in taller than 245/45R19 and the same width, a 0.13% difference in overall diameter.

With the speedometer calibrated for 245/45R19, an indicated 60 mph is actually 60.1 mph on 245/40R20, and revolutions per mile change from 729 to 728.

245/40R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 245/45R19.

Size pages

Other comparisons with 245/45R19

Other comparisons with 245/40R20

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