TireSizesFinder

275/40R21 vs 315/30R22

315/30R22 is 0.22 in (5.6 mm) shorter than 275/40R21, a −0.74% diameter difference. With the speedometer set for 275/40R21, an indicated 60 mph is 59.6 mph on 315/30R22.

Is this a safe swap?

Diameter difference −0.74%: under 1%

By overall diameter alone, 315/30R22 is a near match for 275/40R21; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 275/40R21 (29.66 in) vs 315/30R22 (29.44 in)275/40R2129.66 in × 10.83 in315/30R2229.44 in × 12.40 in
Side profile and tread width, drawn to the same scale.
275/40R21 vs 315/30R22 differences
Measurement275/40R21315/30R22Difference% diff
Overall diameter29.66 in (753.4 mm)29.44 in (747.8 mm)−0.22 in (−5.6 mm)−0.74%
Sidewall height4.33 in (110.0 mm)3.72 in (94.5 mm)−0.61 in (−15.5 mm)−14.09%
Section width10.83 in (275.0 mm)12.40 in (315.0 mm)+1.57 in (+40.0 mm)+14.55%
Circumference93.18 in (2,366.9 mm)92.49 in (2,349.3 mm)−0.69 in (−17.6 mm)−0.74%
Revolutions per mile680685+5+0.75%
True speed with the speedometer calibrated for 275/40R21
IndicatedActual on 275/40R21Actual on 315/30R22Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.6 mph−0.4 mph
75 mph75.0 mph74.4 mph−0.6 mph

Ride-height change: 315/30R22 lowers the vehicle by 0.11 in (2.8 mm) at the axle (half the −5.6 mm diameter difference).

315/30R22 is 0.22 in shorter than 275/40R21 and 40 mm wider, a 0.74% difference in overall diameter.

With the speedometer calibrated for 275/40R21, an indicated 60 mph is actually 59.6 mph on 315/30R22, and revolutions per mile change from 680 to 685.

315/30R22 mounts on a 22-inch wheel, a plus-1 fitment from the 21-inch wheel of 275/40R21.

Size pages

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Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.