265/45R19 vs 305/30R21

305/30R21 is 0.19 in (4.7 mm) shorter than 265/45R19, a −0.65% diameter difference. With the speedometer set for 265/45R19, an indicated 60 mph is 59.6 mph on 305/30R21.

Is this a safe swap?

Diameter difference −0.65%: under 1%

By overall diameter alone, 305/30R21 is a near match for 265/45R19; 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.

265/45R19 vs 305/30R21 differences
Measurement	265/45R19	305/30R21	Difference	% diff
Overall diameter	28.39 in (721.1 mm)	28.20 in (716.4 mm)	−0.19 in (−4.7 mm)	−0.65%
Sidewall height	4.69 in (119.3 mm)	3.60 in (91.5 mm)	−1.09 in (−27.7 mm)	−23.27%
Section width	10.43 in (265.0 mm)	12.01 in (305.0 mm)	+1.57 in (+40.0 mm)	+15.09%
Circumference	89.19 in (2,265.4 mm)	88.61 in (2,250.6 mm)	−0.58 in (−14.8 mm)	−0.65%
Revolutions per mile	710	715	+5	+0.66%

True speed with the speedometer calibrated for 265/45R19
Indicated	Actual on 265/45R19	Actual on 305/30R21	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: 305/30R21 lowers the vehicle by 0.09 in (2.3 mm) at the axle (half the −4.7 mm diameter difference).

305/30R21 is 0.19 in shorter than 265/45R19 and 40 mm wider, a 0.65% difference in overall diameter.

With the speedometer calibrated for 265/45R19, an indicated 60 mph is actually 59.6 mph on 305/30R21, and revolutions per mile change from 710 to 715.

305/30R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 265/45R19.

Size pages

Other comparisons with 265/45R19

Other comparisons with 305/30R21

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