305/50R20 vs 305/40R22

305/40R22 is 0.40 in (10.2 mm) shorter than 305/50R20, a −1.25% diameter difference. With the speedometer set for 305/50R20, an indicated 60 mph is 59.2 mph on 305/40R22.

Is this a safe swap?

Diameter difference −1.25%: within the ±3% guideline

By overall diameter alone, 305/40R22 falls inside the ±3% range commonly used as a guideline when replacing 305/50R20. 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.

305/50R20 vs 305/40R22 differences
Measurement	305/50R20	305/40R22	Difference	% diff
Overall diameter	32.01 in (813.0 mm)	31.61 in (802.8 mm)	−0.40 in (−10.2 mm)	−1.25%
Sidewall height	6.00 in (152.5 mm)	4.80 in (122.0 mm)	−1.20 in (−30.5 mm)	−20.00%
Section width	12.01 in (305.0 mm)	12.01 in (305.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	100.56 in (2,554.1 mm)	99.29 in (2,522.1 mm)	−1.26 in (−32.0 mm)	−1.25%
Revolutions per mile	630	638	+8	+1.27%

True speed with the speedometer calibrated for 305/50R20
Indicated	Actual on 305/50R20	Actual on 305/40R22	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	74.1 mph	−0.9 mph

Ride-height change: 305/40R22 lowers the vehicle by 0.20 in (5.1 mm) at the axle (half the −10.2 mm diameter difference).

305/40R22 is 0.40 in shorter than 305/50R20 and the same width, a 1.25% difference in overall diameter.

With the speedometer calibrated for 305/50R20, an indicated 60 mph is actually 59.2 mph on 305/40R22, and revolutions per mile change from 630 to 638.

305/40R22 mounts on a 22-inch wheel, a plus-2 fitment from the 20-inch wheel of 305/50R20.

Size pages

Other comparisons with 305/50R20

Other comparisons with 305/40R22

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