255/40R22 vs 305/30R24

305/30R24 is 1.17 in (29.8 mm) taller than 255/40R22, a +3.91% diameter difference. With the speedometer set for 255/40R22, an indicated 60 mph is 62.3 mph on 305/30R24.

Is this a safe swap?

Diameter difference +3.91%: outside the ±3% guideline

By overall diameter alone, 305/30R24 falls outside the ±3% range commonly used as a guideline when replacing 255/40R22; speedometer and ride-height changes are larger. 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.

255/40R22 vs 305/30R24 differences
Measurement	255/40R22	305/30R24	Difference	% diff
Overall diameter	30.03 in (762.8 mm)	31.20 in (792.6 mm)	+1.17 in (+29.8 mm)	+3.91%
Sidewall height	4.02 in (102.0 mm)	3.60 in (91.5 mm)	−0.41 in (−10.5 mm)	−10.29%
Section width	10.04 in (255.0 mm)	12.01 in (305.0 mm)	+1.97 in (+50.0 mm)	+19.61%
Circumference	94.35 in (2,396.4 mm)	98.03 in (2,490.0 mm)	+3.69 in (+93.6 mm)	+3.91%
Revolutions per mile	672	646	−25	−3.76%

True speed with the speedometer calibrated for 255/40R22
Indicated	Actual on 255/40R22	Actual on 305/30R24	Difference
30 mph	30.0 mph	31.2 mph	+1.2 mph
60 mph	60.0 mph	62.3 mph	+2.3 mph
75 mph	75.0 mph	77.9 mph	+2.9 mph

Ride-height change: 305/30R24 raises the vehicle by 0.59 in (14.9 mm) at the axle (half the +29.8 mm diameter difference).

305/30R24 is 1.17 in taller than 255/40R22 and 50 mm wider, a 3.91% difference in overall diameter.

With the speedometer calibrated for 255/40R22, an indicated 60 mph is actually 62.3 mph on 305/30R24, and revolutions per mile change from 672 to 646.

305/30R24 mounts on a 24-inch wheel, a plus-2 fitment from the 22-inch wheel of 255/40R22.

Size pages

Other comparisons with 255/40R22

Other comparisons with 305/30R24

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