4 Link Class Is In Session......
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From: Upstate NY
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4 Link Class Is In Session......
Here's a simple examination of the 4 link, or why we hate ladder bars on street cars. wink.gif Hopefully it's not too confusing for some of you guys. 
The 4-link is a common suspension design that has been utilized, successfully, in many different applications. Typically, the design includes 4 equal or unequal length control arms, a lateral locating bar, springs, and shock absorbers.
One benefit of a 4-link is that, when the bars are of equal or near-equal length, and the front and rear mounting points are oriented such that the bars are parallel, there is a reasonably unrestricted range of vertical motion for the axle, while maintaining an efficent coupling. In addition, because each pair of links is independent of the other, the axle can "rotate" freely, allowing for roll. In practical terms, this means that when one wheel has to travel in a different vertical path than the other wheel (over a bump, up a driveway), the unaffected wheel stays in contact with the ground. Or, imagine a turn: The body rolls to the outside of the turn, decreasing the distance bewteen the frame/body and the outside axle end, and increasing the distance between the frame/body and the inside axle end. The 4-link design, with it's parallel links that pivot at each end, is designed to resolve this relatively complex set of dynamic variables.
This basic design is found in many factory applications. GM cars, like Chevelles, come to mind, as do late-model Corvettes. Of course, the design is very popular in drag racing, on sprint cars, and on street rods.
Side-to-side movement is controlled by a Panhard rod or a track locator. A Panhard rod is mounted laterally between the axle, at one end, and the frame at the other. A track locator is mounted diagonally between the opposing front and rear pivot points of the lower 4-link bars.
What about Ladder Bars? From the perspective of a street-driven car, the basic problem is that the ladder bar design does not resolve for axle rotation, except in the vertical axis. Nothing against ladder bars, it's just that it's not an efficient method of suspension attachment for street cars. In their intended environment, a doorslammer drag car, ladder bars allow for a solid coupling and an easy determination of instant center. But as a street suspension, ladder bars are woefully inadequate.
Visualize holding a door, like the front door of your house. In this visualization, you will be acting as the forward ladder bar mount. Orient the door so that you're holding the hinges; the door should be horizontal, held out away from you, and swinging, up and down, on the hinges. Now, visualize a wheel, one at each of the two outside corners opposite the hinges; the long edge of the door, opposite you, will be the rear axle.
What we've done is to model a typical ladder bar suspension. To see how it works, visualize the door swinging up and down. As long as the door is pivoting on it's hinges, with no rotational forces involved, everything works great. Now, try moving the corners opposite you (The corners that we're calling "wheels") in different directions...one corner up, one corner down. See what happens? The door wants to rotate right out of your hands! This is precisely what happens when you turn a corner, or go up a driveway, in a ladder bar-equipped street car. Ouch!
The design considerations necessary to resolve this problem include lengthening the bar, moving the front ladder bar mounting points closer together (triangulating), and using a large, soft bushing. Take a look underneath a mid-60's GM pickup ( or a Grand National stock car, for that matter...). All use long, triangulated bars with big bushings. The only ladder bar that even comes close is the Chassiswork's Pro Street bar, which doesn't use a triangulated design, but does use a urethane bushing.
What's the bottom line? Obviously, ladder bars are very popular, likely because of the design's simplicity. The 4-link design is more complex, often requiring some engineering and fabrication. On the plus side, the 4-link is a superior method of axle control, especially in street cars, offers infinite adjustablility, and is the only way to get your hot rod really low. So...think about it first. Design your ride for safety and longevity; don't use race-car parts or designs in street cars unless you're sure that they'll live.
[ December 28, 2001: Message edited by: 2000Lo&ShowTibby ]
The 4-link is a common suspension design that has been utilized, successfully, in many different applications. Typically, the design includes 4 equal or unequal length control arms, a lateral locating bar, springs, and shock absorbers.
One benefit of a 4-link is that, when the bars are of equal or near-equal length, and the front and rear mounting points are oriented such that the bars are parallel, there is a reasonably unrestricted range of vertical motion for the axle, while maintaining an efficent coupling. In addition, because each pair of links is independent of the other, the axle can "rotate" freely, allowing for roll. In practical terms, this means that when one wheel has to travel in a different vertical path than the other wheel (over a bump, up a driveway), the unaffected wheel stays in contact with the ground. Or, imagine a turn: The body rolls to the outside of the turn, decreasing the distance bewteen the frame/body and the outside axle end, and increasing the distance between the frame/body and the inside axle end. The 4-link design, with it's parallel links that pivot at each end, is designed to resolve this relatively complex set of dynamic variables.
This basic design is found in many factory applications. GM cars, like Chevelles, come to mind, as do late-model Corvettes. Of course, the design is very popular in drag racing, on sprint cars, and on street rods.
Side-to-side movement is controlled by a Panhard rod or a track locator. A Panhard rod is mounted laterally between the axle, at one end, and the frame at the other. A track locator is mounted diagonally between the opposing front and rear pivot points of the lower 4-link bars.
What about Ladder Bars? From the perspective of a street-driven car, the basic problem is that the ladder bar design does not resolve for axle rotation, except in the vertical axis. Nothing against ladder bars, it's just that it's not an efficient method of suspension attachment for street cars. In their intended environment, a doorslammer drag car, ladder bars allow for a solid coupling and an easy determination of instant center. But as a street suspension, ladder bars are woefully inadequate.
Visualize holding a door, like the front door of your house. In this visualization, you will be acting as the forward ladder bar mount. Orient the door so that you're holding the hinges; the door should be horizontal, held out away from you, and swinging, up and down, on the hinges. Now, visualize a wheel, one at each of the two outside corners opposite the hinges; the long edge of the door, opposite you, will be the rear axle.
What we've done is to model a typical ladder bar suspension. To see how it works, visualize the door swinging up and down. As long as the door is pivoting on it's hinges, with no rotational forces involved, everything works great. Now, try moving the corners opposite you (The corners that we're calling "wheels") in different directions...one corner up, one corner down. See what happens? The door wants to rotate right out of your hands! This is precisely what happens when you turn a corner, or go up a driveway, in a ladder bar-equipped street car. Ouch!
The design considerations necessary to resolve this problem include lengthening the bar, moving the front ladder bar mounting points closer together (triangulating), and using a large, soft bushing. Take a look underneath a mid-60's GM pickup ( or a Grand National stock car, for that matter...). All use long, triangulated bars with big bushings. The only ladder bar that even comes close is the Chassiswork's Pro Street bar, which doesn't use a triangulated design, but does use a urethane bushing.
What's the bottom line? Obviously, ladder bars are very popular, likely because of the design's simplicity. The 4-link design is more complex, often requiring some engineering and fabrication. On the plus side, the 4-link is a superior method of axle control, especially in street cars, offers infinite adjustablility, and is the only way to get your hot rod really low. So...think about it first. Design your ride for safety and longevity; don't use race-car parts or designs in street cars unless you're sure that they'll live.
[ December 28, 2001: Message edited by: 2000Lo&ShowTibby ]
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Although I have seen them on plenty of the old school domestic iron I am trying to visualize how you could build a 4 link for a FWD car. I mean on a street driven FWD car. Rwd cars wether independent rear susspension or soid tube don't have the axcess problems that we do. Some of the main concerns with a FWD car is that the drive wheels need to turn. There are many other problems that I can think of.
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QUOTE
Originally posted by DESIGN:
Although I have seen them on plenty of the old school domestic iron I am trying to visualize how you could build a 4 link for a FWD car. I mean on a street driven FWD car. Rwd cars wether independent rear susspension or soid tube don't have the axcess problems that we do. Some of the main concerns with a FWD car is that the drive wheels need to turn. There are many other problems that I can think of.
Although I have seen them on plenty of the old school domestic iron I am trying to visualize how you could build a 4 link for a FWD car. I mean on a street driven FWD car. Rwd cars wether independent rear susspension or soid tube don't have the axcess problems that we do. Some of the main concerns with a FWD car is that the drive wheels need to turn. There are many other problems that I can think of.
Guilty..good call. I was wondering if anyone was going to catch that. wink.gif Props to ya. 4 Links are the greatest things of all time if you have a RWD drag car, and if you have a truck that you plan lowering to the ground. But as far as a FWD car...I'm not too sure on how, if you even could...install these.
Speaking of which..did you have a 4 or 3 link on your truck with the bags? I had them on both my Mazda's. Fun stuff...great times! 
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2K: This is DESIGN, not Guilty by Design. Thanks for the info though!! Many of the top names in FWD drag are working on developing better ways to put traction on the ground. That seems one of their biggest issues right now. They need massive improvements with that and they need sequential gear boxes for faster shifts.
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From: Texas
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LOL to answer your question 2K I had a two link first didnt work worth a **** kept throwing the pinion angle out of wack. So I ordered a four link from Cali and everything was clean as green.
