Four Link Suspension, how does it work?

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Les Gibson

Les Gibson

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Since suspension setup in these drag cars we run is what I consider to be voodoo magic can someone give me a Four Link for Dummies class? I was just beginning to gain a basic understanding of the ladder bar set up on the Dart I had previous, and now I have this Arrow with a four link set up. I hear things like 'pre-load' and 'instant center' and other terms like that and I just don't know what it means. I have no understanding of what moving the upper arms up or down, or moving the lower arms up or down does. I haven't touched a thing on the suspension of this car except to loosen or tighten the front shocks a couple of clicks per the recommendation of the previous owner as he told me that's all I'd ever need to do but I would like to have a working knowledge of what the four link does. Can anyone help?
 
Chris Alston has a very in depth easy to understand DVD on 4 link. It was a lot of voodoo to me until I got the disc, then easy as pie to understand.
 
Les Gibson said:
Since suspension setup in these drag cars we run is what I consider to be voodoo magic can someone give me a Four Link for Dummies class? I was just beginning to gain a basic understanding of the ladder bar set up on the Dart I had previous, and now I have this Arrow with a four link set up. I hear things like 'pre-load' and 'instant center' and other terms like that and I just don't know what it means. I have no understanding of what moving the upper arms up or down, or moving the lower arms up or down does. I haven't touched a thing on the suspension of this car except to loosen or tighten the front shocks a couple of clicks per the recommendation of the previous owner as he told me that's all I'd ever need to do but I would like to have a working knowledge of what the four link does. Can anyone help?
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Oh boy Les. This will get interesting and very long lol. I would certainly watch some videos such as posted above from Tim Mcamis and Kevin Wilson both are awesome to watch and break it down nicely. I would also read some articles first.
 
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The simple, but very incomplete answer is a four link allows a change in the leverage, and angle it is applied. A ladder bar has a set leverage length of about 30 inch to 36 inch, from the axle center to the front bolt.
The ladderbar angle change is fairly limited, usually higher or lower no more than a spread of 4 inch.
A four link has many more choices .
Each power level at launch will like a certain amount of down force on the rear axle. The higher the launch power, the less leverage you MAY need.With a ladderbar setup, the rear shocks need to moderate the leverage. The down side of that is if you need a lot of launch control with shocks and a ladderbar, it can affect downtrack performance, since the shocks may need to be set real stiff on extension.
I run a ladderbar on a 980 hp 2900 lb dart. My shocks need to be set tight, and i leave at only 3800 rpm/part throttle to get good consistant 60 fts. At this level of power and starting line ratio of 11/1, a fourlink should work better, but it is qhat i built many years ago.
 
This helps you visualize some terms:

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A good video with model car demonstrations that makes it easy to see how bar changes work.
 
Before you ever decide to make any changes Les, you need video of the car from the SIDE. This is so you can see what the suspension is doing at the release of the trans brake. That will help you make decisions on what to change on the 4 link, if anything. This is also important when tuning the shocks as well.
 
71Demon528 said:
Before you ever decide to make any changes Les, you need video of the car from the SIDE. This is so you can see what the suspension is doing at the release of the trans brake. That will help you make decisions on what to change on the 4 link, if anything. This is also important when tuning the shocks as well.
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Drop the mic right here.
 
A 4 link allows you to change your instant center. Changing the instant center allows you to tailor how hard the car tries to throw the rear axle down and separate. You do need to know what it currently does. To help visualize, the instant center on a pure leaf spring car is the front spring eye. Moving the instant center in relation to the center of gravity is what you are after. You can mathematically determine your center of gravity, but not REALLY necessary, because you can adjust for what the car is doing. Extending an imaginary line from the bars, where they meet is the 4 links instant center. Move that point forward and down softens the separation. Move that point up and back increases the severity of the separation. You want to get the bars to a setting that is in your shock adjustment window. I tune to the side wall shape. Even consistent bulge.
 
71Demon528 said:
Before you ever decide to make any changes Les, you need video of the car from the SIDE. This is so you can see what the suspension is doing at the release of the trans brake. That will help you make decisions on what to change on the 4 link, if anything. This is also important when tuning the shocks as well.
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That's a great suggestion. Now, If I can only get the Crew Chief to go to the track with me to make that video. Got a father's day race on Sunday so hopefully she'll come with me. Otherwise I'll have to recruit one of my friends there to do so. The care just feels like it's not 'hitting' on launch like it should and my 60' times are a bit slow from last season. The only real change that would affect performance is I've gone from the tunnel ram/dual carb induction to a single carb. car launches clean and straight just feels soft and I know I shouldn't go just by feel.
 
Les Gibson said:
That's a great suggestion. Now, If I can only get the Crew Chief to go to the track with me to make that video. Got a father's day race on Sunday so hopefully she'll come with me. Otherwise I'll have to recruit one of my friends there to do so. The care just feels like it's not 'hitting' on launch like it should and my 60' times are a bit slow from last season. The only real change that would affect performance is I've gone from the tunnel ram/dual carb induction to a single carb. car launches clean and straight just feels soft and I know I shouldn't go just by feel.
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Ya video will be able to help you determine. But in addition to video, you do need drivers perspective as well. Cause there’s things you won’t see in the video but you feel in the car.
 
71Demon528 said:
Ya video will be able to help you determine. But in addition to video, you do need drivers perspective as well. Cause there’s things you won’t see in the video but you feel in the car.
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Just watched a video that my bother in law made when he went to Lebanon Valley Raceway with me Memorial Day Weekend of last year. I've watched it before but this time I was paying attention to what the car was doing on launch. Doesn't appear to have too much squat and no body separation that I could see. Did a mild wheel stand of a just a few inches but carried that for maybe 20 feet or so. Of course it's from well over a year ago and the car still had the tunnel ram/dual carb induction. I'll try posting the video here when I get home this afternoon. I'd appreciate any insight you can offer.
 
71Demon528 said:
Before you ever decide to make any changes Les, you need video of the car from the SIDE. This is so you can see what the suspension is doing at the release of the trans brake. That will help you make decisions on what to change on the 4 link, if anything. This is also important when tuning the shocks as well.
Click to expand...
Especially helpful is a camera that enables slo-mo. And video from the driver's side if possible. (a real camcorder with a zoom too, please. No phone videos held wrong/stupid)
And I was gonna recommend Kevin Wilson's you tube video's as well.
 
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Les Gibson said:
Since suspension setup in these drag cars we run is what I consider to be voodoo magic can someone give me a Four Link for Dummies class? I was just beginning to gain a basic understanding of the ladder bar set up on the Dart I had previous, and now I have this Arrow with a four link set up. I hear things like 'pre-load' and 'instant center' and other terms like that and I just don't know what it means. I have no understanding of what moving the upper arms up or down, or moving the lower arms up or down does. I haven't touched a thing on the suspension of this car except to loosen or tighten the front shocks a couple of clicks per the recommendation of the previous owner as he told me that's all I'd ever need to do but I would like to have a working knowledge of what the four link does. Can anyone help?
Click to expand...
Check out this guys Youtube channel.... he has sooo much great info on every suspension type and is easy to follow..
 
33IMP said:
Especially helpful is a camera that enables slo-mo. And video from the driver's side if possible. (a real camcorder with a zoom too, please. No phone videos held wrong/stupid)
And I was gonna recommend Kevin Wilson's you tube video's as well.
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^^This^^

I did some shock testing a few years ago, my buddy came along and videoed the car. In real time it was hard to tell what the car was doing to the tire, in slo-mode it was wadding the tire up.
 
justinp61 said:
^^This^^

I did some shock testing a few years ago, my buddy came along and videoed the car. In real time it was hard to tell what the car was doing to the tire, in slo-mode it was wadding the tire up.
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with an IPhone you can slow it down big time using your thumb. Comes in handy.
 
Just as important as the 4 link setup is the shocks the car has, AND the coil over springs. Too stiff of a spring is no good because it won’t allow the 4 link to do what it’s designed to do. Too soft of a spring will cause grief as well because there will be too much stored energy in the springs. My bet Les, after you get video of the car, along with some working knowledge of the suspension, you will want to make changes to try and make it work more efficiently. Or you may be happy with the way it works and just leave it.
 
71Demon528 said:
Just as important as the 4 link setup is the shocks the car has, AND the coil over springs. Too stiff of a spring is no good because it won’t allow the 4 link to do what it’s designed to do. Too soft of a spring will cause grief as well because there will be too much stored energy in the springs. My bet Les, after you get video of the car, along with some working knowledge of the suspension, you will want to make changes to try and make it work more efficiently. Or you may be happy with the way it works and just leave it.
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I've used some of the resources that have been suggested here and I feel I now have a reasonable working knowledge of how the four link works and what adjustments do. The suspension in the Arrow doesn't have a lot of travel and is pretty stiff. Perhaps it's the nature of the beast given it's a full Alston chassis originally built in 1987. It has the Mustang II front suspension set up and the front shocks are pretty short and they are single adjustable. The rears are a bit longer and are double adjustable. I haven't touched the rears as the previous owner told me there was no need to change them. The best 60' time I've had with this car is a 1.27. Right now it's in the 1.32/33 range. Not a huge difference but it just feels 'soft' on the hit when the transbrake releases. Hopefully I can get some videos this Sunday and be able to see what it's actually doing. The videos I have are not very useful as they were taken from the stands so you can't see a lot of detail.
 
Les Gibson said:
I've used some of the resources that have been suggested here and I feel I now have a reasonable working knowledge of how the four link works and what adjustments do. The suspension in the Arrow doesn't have a lot of travel and is pretty stiff. Perhaps it's the nature of the beast given it's a full Alston chassis originally built in 1987. It has the Mustang II front suspension set up and the front shocks are pretty short and they are single adjustable. The rears are a bit longer and are double adjustable. I haven't touched the rears as the previous owner told me there was no need to change them. The best 60' time I've had with this car is a 1.27. Right now it's in the 1.32/33 range. Not a huge difference but it just feels 'soft' on the hit when the transbrake releases. Hopefully I can get some videos this Sunday and be able to see what it's actually doing. The videos I have are not very useful as they were taken from the stands so you can't see a lot of detail.
Click to expand...

Awesome. I’m sure once you see some good video you will make some good adjustments.
 
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