275/45R19 vs 325/30R21

325/30R21 is 0.07 in (1.7 mm) shorter than 275/45R19, a −0.23% diameter difference. With the speedometer set for 275/45R19, an indicated 60 mph is 59.9 mph on 325/30R21.

Is this a safe swap?

Diameter difference −0.23%: under 1%

By overall diameter alone, 325/30R21 is a near match for 275/45R19; 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.

275/45R19 vs 325/30R21 differences
Measurement	275/45R19	325/30R21	Difference	% diff
Overall diameter	28.74 in (730.1 mm)	28.68 in (728.4 mm)	−0.07 in (−1.7 mm)	−0.23%
Sidewall height	4.87 in (123.8 mm)	3.84 in (97.5 mm)	−1.03 in (−26.2 mm)	−21.21%
Section width	10.83 in (275.0 mm)	12.80 in (325.0 mm)	+1.97 in (+50.0 mm)	+18.18%
Circumference	90.30 in (2,293.7 mm)	90.09 in (2,288.3 mm)	−0.21 in (−5.3 mm)	−0.23%
Revolutions per mile	702	703	+2	+0.23%

True speed with the speedometer calibrated for 275/45R19
Indicated	Actual on 275/45R19	Actual on 325/30R21	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.9 mph	−0.1 mph
75 mph	75.0 mph	74.8 mph	−0.2 mph

Ride-height change: 325/30R21 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.7 mm diameter difference).

325/30R21 is 0.07 in shorter than 275/45R19 and 50 mm wider, a 0.23% difference in overall diameter.

With the speedometer calibrated for 275/45R19, an indicated 60 mph is actually 59.9 mph on 325/30R21, and revolutions per mile change from 702 to 703.

325/30R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 275/45R19.

Size pages

Other comparisons with 275/45R19

Other comparisons with 325/30R21

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