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      01-15-2015, 08:56 PM   #10
fe1rx
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Drives: 135i, 328i, Cayman S
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Quote:
Originally Posted by 128Convertibleguy View Post
Wouldn't it be more correct to say the ball joint has an extremely large spring rate? There is no metal fabrication with a zero spring rate, but some are extremely large.
Apparently Sir Henry Royce (of Rolls-Royce fame) said "In the final analysis, every engineering material is rubber." That is the significance of Young's Modulus.

So you have a point, but you are confusing the torsional spring rate of the bushing/ball joint with the axial spring. A rubber bushing acts like a torsional spring, resisting vertical deflection of the suspension and trying to restore the suspension to its normal ride height. A ball joint offers a small amount of friction but no restoring force, so it has zero torsional spring rate. I didn't show you how I measured the torsional spring rates of all the suspension bushings relative to wheel travel, but it is relatively simple once you remove your springs and shocks.

As far as axial spring rate goes, both ball joints and straight arms have very large axial stiffness. Curved arms and rubber bushings have less axial stiffness.

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Last edited by fe1rx; 01-15-2015 at 09:02 PM..
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