Tire Size Box

325/30R22 vs 325/40R22

325/40R22 compared with 325/30R22

+8.6% diameter, 0.0" width

325/40R22 is 32.24" tall vs 29.68". More than the 3% rule of thumb, so check carefully before switching.

29.7"22" rim3.8"12.8" wide
325/30R22 (solid) compared with 325/40R22 (dashed outline), drawn to scale

With 325/40R22 tires, when your speedometer says 60 mph you are really going

65.2 mph

325/40R22 is +2.56 inches (+8.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/30R22325/40R22Difference%
Overall diameter29.68"32.24"+2.56"+8.6%
Section width12.80"12.80"0.00"0.0%
Sidewall height3.84"5.12"+1.28"+33.3%
Circumference93.23"101.27"+8.04"+8.6%
Revolutions per mile679.6625.6−53.9−7.9%

Speedometer difference

If your vehicle came with 325/30R22 and you fit 325/40R22, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.7 mph+1.7 mph
30 mph32.6 mph+2.6 mph
40 mph43.4 mph+3.4 mph
50 mph54.3 mph+4.3 mph
60 mph65.2 mph+5.2 mph
65 mph70.6 mph+5.6 mph
70 mph76.0 mph+6.0 mph
75 mph81.5 mph+6.5 mph
80 mph86.9 mph+6.9 mph

Each size on its own

Questions

Which is bigger, 325/30R22 or 325/40R22?
325/40R22 is taller by 2.56 inches (32.24" vs 29.68"). 325/30R22 is the same width.
Can I replace 325/30R22 with 325/40R22?
It is not recommended without checking carefully. The diameter difference is +8.6%, 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 325/40R22 change my speedometer?
When your speedometer reads 60 mph with 325/40R22 fitted (calibrated for 325/30R22), your real speed is 65.2 mph. Your odometer will under-count miles by about 8.6%.
Will 325/40R22 lift my vehicle?
Ride height changes by half the diameter difference: +1.28 inches of ground clearance at the axle.

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