255/40R20 vs 245/30R22

245/30R22 is 0.24 in (6.2 mm) shorter than 255/40R20, a −0.87% diameter difference. With the speedometer set for 255/40R20, an indicated 60 mph is 59.5 mph on 245/30R22.

Is this a safe swap?

Diameter difference −0.87%: under 1%

By overall diameter alone, 245/30R22 is a near match for 255/40R20; 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.

255/40R20 vs 245/30R22 differences
Measurement	255/40R20	245/30R22	Difference	% diff
Overall diameter	28.03 in (712.0 mm)	27.79 in (705.8 mm)	−0.24 in (−6.2 mm)	−0.87%
Sidewall height	4.02 in (102.0 mm)	2.89 in (73.5 mm)	−1.12 in (−28.5 mm)	−27.94%
Section width	10.04 in (255.0 mm)	9.65 in (245.0 mm)	−0.39 in (−10.0 mm)	−3.92%
Circumference	88.06 in (2,236.8 mm)	87.30 in (2,217.3 mm)	−0.77 in (−19.5 mm)	−0.87%
Revolutions per mile	719	726	+6	+0.88%

True speed with the speedometer calibrated for 255/40R20
Indicated	Actual on 255/40R20	Actual on 245/30R22	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.5 mph	−0.5 mph
75 mph	75.0 mph	74.3 mph	−0.7 mph

Ride-height change: 245/30R22 lowers the vehicle by 0.12 in (3.1 mm) at the axle (half the −6.2 mm diameter difference).

245/30R22 is 0.24 in shorter than 255/40R20 and 10 mm narrower, a 0.87% difference in overall diameter.

With the speedometer calibrated for 255/40R20, an indicated 60 mph is actually 59.5 mph on 245/30R22, and revolutions per mile change from 719 to 726.

245/30R22 mounts on a 22-inch wheel, a plus-2 fitment from the 20-inch wheel of 255/40R20.

Size pages

Other comparisons with 255/40R20

Other comparisons with 245/30R22

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