Tire Size Box

315/30R22 vs 315/40R22

315/40R22 compared with 315/30R22

+8.4% diameter, 0.0" width

315/40R22 is 31.92" tall vs 29.44". More than the 3% rule of thumb, so check carefully before switching.

29.4"22" rim3.7"12.4" wide
315/30R22 (solid) compared with 315/40R22 (dashed outline), drawn to scale

With 315/40R22 tires, when your speedometer says 60 mph you are really going

65.1 mph

315/40R22 is +2.48 inches (+8.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/30R22315/40R22Difference%
Overall diameter29.44"31.92"+2.48"+8.4%
Section width12.40"12.40"0.00"0.0%
Sidewall height3.72"4.96"+1.24"+33.3%
Circumference92.49"100.28"+7.79"+8.4%
Revolutions per mile685.0631.8−53.2−7.8%

Speedometer difference

If your vehicle came with 315/30R22 and you fit 315/40R22, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.7 mph+1.7 mph
30 mph32.5 mph+2.5 mph
40 mph43.4 mph+3.4 mph
50 mph54.2 mph+4.2 mph
60 mph65.1 mph+5.1 mph
65 mph70.5 mph+5.5 mph
70 mph75.9 mph+5.9 mph
75 mph81.3 mph+6.3 mph
80 mph86.7 mph+6.7 mph

Each size on its own

Questions

Which is bigger, 315/30R22 or 315/40R22?
315/40R22 is taller by 2.48 inches (31.92" vs 29.44"). 315/30R22 is the same width.
Can I replace 315/30R22 with 315/40R22?
It is not recommended without checking carefully. The diameter difference is +8.4%, more than the 3% most shops and makers allow. It will throw off the speedometer and may affect ABS, stability control and clearance.
How much will 315/40R22 change my speedometer?
When your speedometer reads 60 mph with 315/40R22 fitted (calibrated for 315/30R22), your real speed is 65.1 mph. Your odometer will under-count miles by about 8.4%.
Will 315/40R22 lift my vehicle?
Ride height changes by half the diameter difference: +1.24 inches of ground clearance at the axle.

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