235/45R20 vs 255/30R22

255/30R22 is 0.30 in (7.7 mm) shorter than 235/45R20, a −1.07% diameter difference. With the speedometer set for 235/45R20, an indicated 60 mph is 59.4 mph on 255/30R22.

Is this a safe swap?

Diameter difference −1.07%: within the ±3% guideline

By overall diameter alone, 255/30R22 falls inside the ±3% range commonly used as a guideline when replacing 235/45R20. 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.

235/45R20 vs 255/30R22 differences
Measurement	235/45R20	255/30R22	Difference	% diff
Overall diameter	28.33 in (719.5 mm)	28.02 in (711.8 mm)	−0.30 in (−7.7 mm)	−1.07%
Sidewall height	4.16 in (105.8 mm)	3.01 in (76.5 mm)	−1.15 in (−29.2 mm)	−27.66%
Section width	9.25 in (235.0 mm)	10.04 in (255.0 mm)	+0.79 in (+20.0 mm)	+8.51%
Circumference	88.99 in (2,260.4 mm)	88.04 in (2,236.2 mm)	−0.95 in (−24.2 mm)	−1.07%
Revolutions per mile	712	720	+8	+1.08%

True speed with the speedometer calibrated for 235/45R20
Indicated	Actual on 235/45R20	Actual on 255/30R22	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.4 mph	−0.6 mph
75 mph	75.0 mph	74.2 mph	−0.8 mph

Ride-height change: 255/30R22 lowers the vehicle by 0.15 in (3.9 mm) at the axle (half the −7.7 mm diameter difference).

255/30R22 is 0.30 in shorter than 235/45R20 and 20 mm wider, a 1.07% difference in overall diameter.

With the speedometer calibrated for 235/45R20, an indicated 60 mph is actually 59.4 mph on 255/30R22, and revolutions per mile change from 712 to 720.

255/30R22 mounts on a 22-inch wheel, a plus-2 fitment from the 20-inch wheel of 235/45R20.

Size pages

Other comparisons with 235/45R20

Other comparisons with 255/30R22

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