255/60R20 vs 305/40R22

305/40R22 is 0.44 in (11.2 mm) shorter than 255/60R20, a −1.38% diameter difference. With the speedometer set for 255/60R20, an indicated 60 mph is 59.2 mph on 305/40R22.

Is this a safe swap?

Diameter difference −1.38%: within the ±3% guideline

By overall diameter alone, 305/40R22 falls inside the ±3% range commonly used as a guideline when replacing 255/60R20. 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.

255/60R20 vs 305/40R22 differences
Measurement	255/60R20	305/40R22	Difference	% diff
Overall diameter	32.05 in (814.0 mm)	31.61 in (802.8 mm)	−0.44 in (−11.2 mm)	−1.38%
Sidewall height	6.02 in (153.0 mm)	4.80 in (122.0 mm)	−1.22 in (−31.0 mm)	−20.26%
Section width	10.04 in (255.0 mm)	12.01 in (305.0 mm)	+1.97 in (+50.0 mm)	+19.61%
Circumference	100.68 in (2,557.3 mm)	99.29 in (2,522.1 mm)	−1.39 in (−35.2 mm)	−1.38%
Revolutions per mile	629	638	+9	+1.40%

True speed with the speedometer calibrated for 255/60R20
Indicated	Actual on 255/60R20	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	74.0 mph	−1.0 mph

Ride-height change: 305/40R22 lowers the vehicle by 0.22 in (5.6 mm) at the axle (half the −11.2 mm diameter difference).

305/40R22 is 0.44 in shorter than 255/60R20 and 50 mm wider, a 1.38% difference in overall diameter.

With the speedometer calibrated for 255/60R20, an indicated 60 mph is actually 59.2 mph on 305/40R22, and revolutions per mile change from 629 to 638.

305/40R22 mounts on a 22-inch wheel, a plus-2 fitment from the 20-inch wheel of 255/60R20.

Size pages

Other comparisons with 255/60R20

Other comparisons with 305/40R22

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