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Old 12-20-2005, 01:15 PM
Mean 69 Mean 69 is offline
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There are two issues with regard to drag race style four link and ladder bar systems that make them highly undesireable for street applications. As Marcus pointed out, a suitable lateral locating device such as a long Panhard bar is a must for the street, the drag race kits typically come with a "diagonal" link, useless for controlling side to side motion of the car reliably, and frankly, dangerous as a result. A good friend of mine recently bought a four link 57 Chevy with a diagonal bar, he got "concerned" when he could hear rubbing of the rear tires, and could get a whif of rubber. The rubber turned out to be two things, tires, and far worse, rubbing on the fuel line. Swapping a simple Panhard rod completely transformed the car, and made it remotely livable on the street.

The other issue is that the drag race setups use spherical rod ends for the pivot points. While it is obvious that the ladder bar setup has serious bind issues in roll situations (i.e. any cornering), the same condition exists for the four link setups using rod ends also. The only reason that either of them roll at all is because something in the system is bending, stretching, etc. BOTH are overconstrained in roll, period. I think the reason that folks think the four link systems don't bind is that there is actually more stuff to bend, so the bind is less obvious. Further, using some form of compliant bushing in a four link (rubber, poly, etc) will free things up a bit and allow the setup to roll more, until of course the bushings are fully compressed.

A three link has the advantage of being completely free in roll-bind situations, by design. Each of the links only has one job to do, the redundancy of the two upper links is eliminated by removing one of them. Three link setups also require a Panhard bar or other lateral locating device, such as a Watt's linkage. You will be seeing a good number of three link applications on the market very soon.

Mark

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