245/45R19 vs 275/30R21

275/30R21 is 0.19 in (4.7 mm) shorter than 245/45R19, a −0.67% diameter difference. With the speedometer set for 245/45R19, an indicated 60 mph is 59.6 mph on 275/30R21.

Is this a safe swap?

Diameter difference −0.67%: under 1%

By overall diameter alone, 275/30R21 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 275/30R21 differences
Measurement	245/45R19	275/30R21	Difference	% diff
Overall diameter	27.68 in (703.1 mm)	27.50 in (698.4 mm)	−0.19 in (−4.7 mm)	−0.67%
Sidewall height	4.34 in (110.3 mm)	3.25 in (82.5 mm)	−1.09 in (−27.7 mm)	−25.17%
Section width	9.65 in (245.0 mm)	10.83 in (275.0 mm)	+1.18 in (+30.0 mm)	+12.24%
Circumference	86.96 in (2,208.9 mm)	86.38 in (2,194.1 mm)	−0.58 in (−14.8 mm)	−0.67%
Revolutions per mile	729	733	+5	+0.67%

True speed with the speedometer calibrated for 245/45R19
Indicated	Actual on 245/45R19	Actual on 275/30R21	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.6 mph	−0.4 mph
75 mph	75.0 mph	74.5 mph	−0.5 mph

Ride-height change: 275/30R21 lowers the vehicle by 0.09 in (2.3 mm) at the axle (half the −4.7 mm diameter difference).

275/30R21 is 0.19 in shorter than 245/45R19 and 30 mm wider, a 0.67% difference in overall diameter.

With the speedometer calibrated for 245/45R19, an indicated 60 mph is actually 59.6 mph on 275/30R21, and revolutions per mile change from 729 to 733.

275/30R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 245/45R19.

Size pages

Other comparisons with 245/45R19

Other comparisons with 275/30R21

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