245/55R19 vs 275/40R21

275/40R21 is 0.05 in (1.3 mm) taller than 245/55R19, a +0.17% diameter difference. With the speedometer set for 245/55R19, an indicated 60 mph is 60.1 mph on 275/40R21.

Is this a safe swap?

Diameter difference +0.17%: under 1%

By overall diameter alone, 275/40R21 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 275/40R21 differences
Measurement	245/55R19	275/40R21	Difference	% diff
Overall diameter	29.61 in (752.1 mm)	29.66 in (753.4 mm)	+0.05 in (+1.3 mm)	+0.17%
Sidewall height	5.31 in (134.8 mm)	4.33 in (110.0 mm)	−0.97 in (−24.7 mm)	−18.37%
Section width	9.65 in (245.0 mm)	10.83 in (275.0 mm)	+1.18 in (+30.0 mm)	+12.24%
Circumference	93.02 in (2,362.8 mm)	93.18 in (2,366.9 mm)	+0.16 in (+4.1 mm)	+0.17%
Revolutions per mile	681	680	−1	−0.17%

True speed with the speedometer calibrated for 245/55R19
Indicated	Actual on 245/55R19	Actual on 275/40R21	Difference
30 mph	30.0 mph	30.1 mph	+0.1 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: 275/40R21 raises the vehicle by 0.03 in (0.7 mm) at the axle (half the +1.3 mm diameter difference).

275/40R21 is 0.05 in taller than 245/55R19 and 30 mm wider, a 0.17% difference in overall diameter.

With the speedometer calibrated for 245/55R19, an indicated 60 mph is actually 60.1 mph on 275/40R21, and revolutions per mile change from 681 to 680.

275/40R21 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 275/40R21

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