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Old 01-18-2013, 10:47 PM
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Originally Posted by 1971BB427 View Post
As mentioned above, a leaf spring can twist in it's length, just from design. If you rely on the rubber bushing to allow flexing instead of the spring's length, then your rubber bushings will also cause sloppy handling, and eventual wear. A poly bushing removes the play but gives you more positive feel for the road.
Car makers use rubber for one reason, it deadens noise transfer to the car. It does so at the cost of handling.
Swaybars and leaf springs do not fight each other, they compliment each other. Almost every performance car ever made that has leaf springs, also has swaybars. If you want positive handling, you can't do much better than multileaf springs with a swaybar front and rear.
First off, I appreciate your opinion and my goal is not to start an argument. I just want to put out some more food for thought...

I would be interested to know where you got the information that a leaf spring can twist longitudinally within its length. If it does, the amount would be so small as to be insignificant. Especially since the center of its length is solidly mounted to the axle housing (except for some factory axle mounts that have a rubber pad). The majority of the rotation of the leaf springs are due to the fact that they are arched. In a one wheel bump the wheel moves up as the arch flattens out and the small amount of rotation is taken up in the bushings. Herb Adams in his book Chassis Engineering points out that since leaf springs are so stiff as to not need a lateral locating device such as a panhard bar (for a race car), he also states that you should never put poly bushings in the front spring eye of a leaf spring "as they will bind up and prevent the body from rolling in relation to the axle". To further illustrate the motion of leaf springs, some Hotchkiss suspension systems even mount the front of the leafs closer together than the rears to cause the rear axle to steer the car toward understeer in order to make it more stable and predictable to drive.

The great thing about rubber bushings, other than noise isolation and low cost, is the fact that they can repeatedly distort and then return to their original shape. Poly will do that also to a very small degree, but they won't be able to do that near as long as rubber.

As to anti-roll bars causing bind, they most certainly do. With an anti-roll bar you are tying one side of the suspension to the other with a very stiff spring. In the relatively small amount of suspension travel in most street cars it really isn't an issue (and as you pointed out it can be used to your advantage) but if you go too big (or stiff if you like) you can bind up your suspension so much it will hardly move. Almost like a solid axle. Look for photos on the web of cars that have too stiff of anti-roll bars, in a corner you can actully lift the inside tire off the ground! That is also why off-road guys who drive their vehicles on the street have quick disconnects on their anti-roll bars, it frees up the suspension when they are off-road so it can rotate to the limits of their axle locating linkage.

Good discussion...
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