235/45R21 vs 315/30R22

315/30R22 is 0.11 in (2.9 mm) taller than 235/45R21, a +0.39% diameter difference. With the speedometer set for 235/45R21, an indicated 60 mph is 60.2 mph on 315/30R22.

Is this a safe swap?

Diameter difference +0.39%: under 1%

By overall diameter alone, 315/30R22 is a near match for 235/45R21; 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.

235/45R21 vs 315/30R22 differences
Measurement	235/45R21	315/30R22	Difference	% diff
Overall diameter	29.33 in (744.9 mm)	29.44 in (747.8 mm)	+0.11 in (+2.9 mm)	+0.39%
Sidewall height	4.16 in (105.8 mm)	3.72 in (94.5 mm)	−0.44 in (−11.2 mm)	−10.64%
Section width	9.25 in (235.0 mm)	12.40 in (315.0 mm)	+3.15 in (+80.0 mm)	+34.04%
Circumference	92.13 in (2,340.2 mm)	92.49 in (2,349.3 mm)	+0.36 in (+9.1 mm)	+0.39%
Revolutions per mile	688	685	−3	−0.39%

True speed with the speedometer calibrated for 235/45R21
Indicated	Actual on 235/45R21	Actual on 315/30R22	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 315/30R22 raises the vehicle by 0.06 in (1.4 mm) at the axle (half the +2.9 mm diameter difference).

315/30R22 is 0.11 in taller than 235/45R21 and 80 mm wider, a 0.39% difference in overall diameter.

With the speedometer calibrated for 235/45R21, an indicated 60 mph is actually 60.2 mph on 315/30R22, and revolutions per mile change from 688 to 685.

315/30R22 mounts on a 22-inch wheel, a plus-1 fitment from the 21-inch wheel of 235/45R21.

Size pages

Other comparisons with 235/45R21

Other comparisons with 315/30R22

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