305/40R22 vs 305/30R24

305/30R24 is 0.40 in (10.2 mm) shorter than 305/40R22, a −1.27% diameter difference. With the speedometer set for 305/40R22, an indicated 60 mph is 59.2 mph on 305/30R24.

Is this a safe swap?

Diameter difference −1.27%: within the ±3% guideline

By overall diameter alone, 305/30R24 falls inside the ±3% range commonly used as a guideline when replacing 305/40R22. 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.

305/40R22 vs 305/30R24 differences
Measurement	305/40R22	305/30R24	Difference	% diff
Overall diameter	31.61 in (802.8 mm)	31.20 in (792.6 mm)	−0.40 in (−10.2 mm)	−1.27%
Sidewall height	4.80 in (122.0 mm)	3.60 in (91.5 mm)	−1.20 in (−30.5 mm)	−25.00%
Section width	12.01 in (305.0 mm)	12.01 in (305.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	99.29 in (2,522.1 mm)	98.03 in (2,490.0 mm)	−1.26 in (−32.0 mm)	−1.27%
Revolutions per mile	638	646	+8	+1.29%

True speed with the speedometer calibrated for 305/40R22
Indicated	Actual on 305/40R22	Actual on 305/30R24	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.2 mph	−0.8 mph
75 mph	75.0 mph	74.0 mph	−1.0 mph

Ride-height change: 305/30R24 lowers the vehicle by 0.20 in (5.1 mm) at the axle (half the −10.2 mm diameter difference).

305/30R24 is 0.40 in shorter than 305/40R22 and the same width, a 1.27% difference in overall diameter.

With the speedometer calibrated for 305/40R22, an indicated 60 mph is actually 59.2 mph on 305/30R24, and revolutions per mile change from 638 to 646.

305/30R24 mounts on a 24-inch wheel, a plus-2 fitment from the 22-inch wheel of 305/40R22.

Size pages

Other comparisons with 305/40R22

Other comparisons with 305/30R24

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