305/30R21 vs 245/30R22

245/30R22 is 0.42 in (10.6 mm) shorter than 305/30R21, a −1.48% diameter difference. With the speedometer set for 305/30R21, an indicated 60 mph is 59.1 mph on 245/30R22.

Is this a safe swap?

Diameter difference −1.48%: within the ±3% guideline

By overall diameter alone, 245/30R22 falls inside the ±3% range commonly used as a guideline when replacing 305/30R21. 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.

305/30R21 vs 245/30R22 differences
Measurement	305/30R21	245/30R22	Difference	% diff
Overall diameter	28.20 in (716.4 mm)	27.79 in (705.8 mm)	−0.42 in (−10.6 mm)	−1.48%
Sidewall height	3.60 in (91.5 mm)	2.89 in (73.5 mm)	−0.71 in (−18.0 mm)	−19.67%
Section width	12.01 in (305.0 mm)	9.65 in (245.0 mm)	−2.36 in (−60.0 mm)	−19.67%
Circumference	88.61 in (2,250.6 mm)	87.30 in (2,217.3 mm)	−1.31 in (−33.3 mm)	−1.48%
Revolutions per mile	715	726	+11	+1.50%

True speed with the speedometer calibrated for 305/30R21
Indicated	Actual on 305/30R21	Actual on 245/30R22	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.1 mph	−0.9 mph
75 mph	75.0 mph	73.9 mph	−1.1 mph

Ride-height change: 245/30R22 lowers the vehicle by 0.21 in (5.3 mm) at the axle (half the −10.6 mm diameter difference).

245/30R22 is 0.42 in shorter than 305/30R21 and 60 mm narrower, a 1.48% difference in overall diameter.

With the speedometer calibrated for 305/30R21, an indicated 60 mph is actually 59.1 mph on 245/30R22, and revolutions per mile change from 715 to 726.

245/30R22 mounts on a 22-inch wheel, a plus-1 fitment from the 21-inch wheel of 305/30R21.

Size pages

Other comparisons with 305/30R21

Other comparisons with 245/30R22

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