245/55R19 vs 265/40R21

265/40R21 is 0.26 in (6.7 mm) shorter than 245/55R19, a −0.89% diameter difference. With the speedometer set for 245/55R19, an indicated 60 mph is 59.5 mph on 265/40R21.

Is this a safe swap?

Diameter difference −0.89%: under 1%

By overall diameter alone, 265/40R21 is a near match for 245/55R19; 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.

245/55R19 vs 265/40R21 differences
Measurement	245/55R19	265/40R21	Difference	% diff
Overall diameter	29.61 in (752.1 mm)	29.35 in (745.4 mm)	−0.26 in (−6.7 mm)	−0.89%
Sidewall height	5.31 in (134.8 mm)	4.17 in (106.0 mm)	−1.13 in (−28.7 mm)	−21.34%
Section width	9.65 in (245.0 mm)	10.43 in (265.0 mm)	+0.79 in (+20.0 mm)	+8.16%
Circumference	93.02 in (2,362.8 mm)	92.19 in (2,341.7 mm)	−0.83 in (−21.0 mm)	−0.89%
Revolutions per mile	681	687	+6	+0.90%

True speed with the speedometer calibrated for 245/55R19
Indicated	Actual on 245/55R19	Actual on 265/40R21	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.5 mph	−0.5 mph
75 mph	75.0 mph	74.3 mph	−0.7 mph

Ride-height change: 265/40R21 lowers the vehicle by 0.13 in (3.3 mm) at the axle (half the −6.7 mm diameter difference).

265/40R21 is 0.26 in shorter than 245/55R19 and 20 mm wider, a 0.89% difference in overall diameter.

With the speedometer calibrated for 245/55R19, an indicated 60 mph is actually 59.5 mph on 265/40R21, and revolutions per mile change from 681 to 687.

265/40R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 245/55R19.

Size pages

Other comparisons with 245/55R19

Other comparisons with 265/40R21

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