245/40R20 vs 255/30R22

255/30R22 is 0.31 in (7.8 mm) taller than 245/40R20, a +1.11% diameter difference. With the speedometer set for 245/40R20, an indicated 60 mph is 60.7 mph on 255/30R22.

Is this a safe swap?

Diameter difference +1.11%: within the ±3% guideline

By overall diameter alone, 255/30R22 falls inside the ±3% range commonly used as a guideline when replacing 245/40R20. 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.

245/40R20 vs 255/30R22 differences
Measurement	245/40R20	255/30R22	Difference	% diff
Overall diameter	27.72 in (704.0 mm)	28.02 in (711.8 mm)	+0.31 in (+7.8 mm)	+1.11%
Sidewall height	3.86 in (98.0 mm)	3.01 in (76.5 mm)	−0.85 in (−21.5 mm)	−21.94%
Section width	9.65 in (245.0 mm)	10.04 in (255.0 mm)	+0.39 in (+10.0 mm)	+4.08%
Circumference	87.07 in (2,211.7 mm)	88.04 in (2,236.2 mm)	+0.96 in (+24.5 mm)	+1.11%
Revolutions per mile	728	720	−8	−1.10%

True speed with the speedometer calibrated for 245/40R20
Indicated	Actual on 245/40R20	Actual on 255/30R22	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 255/30R22 raises the vehicle by 0.15 in (3.9 mm) at the axle (half the +7.8 mm diameter difference).

255/30R22 is 0.31 in taller than 245/40R20 and 10 mm wider, a 1.11% difference in overall diameter.

With the speedometer calibrated for 245/40R20, an indicated 60 mph is actually 60.7 mph on 255/30R22, and revolutions per mile change from 728 to 720.

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

Size pages

Other comparisons with 245/40R20

Other comparisons with 255/30R22

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