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Four link theory question.
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Picture of Curly1
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I understand fairly well about how a four link suspension works but have a question.
On some really high power Altereds they make the for link into solid suspension by putting a bar in there. I have seen where putting the solid strut will make a car go down track when it was struggling with four link.

I have been told that once you make it solid then it does not matter what the IC settings are as it is solid. That is what I do not understand. With regular four link if it is off it will pull hard wheelies or not plant tires and hook. Adjustment is critical.

Seems to me that it would still make a difference on how it plants tires etc. The solid strut would eliminate shock separation but seems the the IC would still help determine how it it plants tires and lifts front?

Any thoughts and real world experience?


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Posts: 3916 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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Once it's solid, the only things that matter are engine location/pinion angle/center of gravity/weight bias F-R.
The bars aren't moving anymore.


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Posts: 81 | Location: Amherst, Ny | Registered: May 14, 2001Reply With QuoteReport This Post
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My understanding of 4-link is basic at best. In fact this is the first I've heard of a "solid 4-link". Trying to reconcile this basic understanding, doesn't street 4-link adjustment, where both bars are equal length & parallel to the ground accomplish about the same effect? Just wondering.


Illegitimi non carborundum
 
Posts: 2318 | Location: OKC, OK | Registered: February 15, 2008Reply With QuoteReport This Post
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I think he's talking about removing the shocks and installing a solid bar in their place. Doing so makes the rear suspension solid.

The 4-link would then just be an extension of the frame. Where the IC is positioned should still be in effect because torque on the axle tubes would still be transmitted down the link bars and push/pull on the bars.

The advantage of that over a completely solid suspension is that the IC can be located below ground.

The disadvantage is that without suspension travel, how the vehicle reacts is entirely with the tires. Watch a fuel altered launch and they usually jump and dart all over the track.

Solid suspension was the norm decades ago on altereds and dragsters and many people still do it for cost and simplicity. Installing a 4-link made them a lot more driveable.


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Posts: 1347 | Location: Calgary | Registered: June 06, 2001Reply With QuoteReport This Post
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quote:
I think he's talking about removing the shocks and installing a solid bar in their place. Doing so makes the rear suspension solid.

Oh. Thanks for that education.


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Posts: 2318 | Location: OKC, OK | Registered: February 15, 2008Reply With QuoteReport This Post
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quote:
Originally posted by AlkyIROC:


Where the IC is positioned should still be in effect because torque on the axle tubes would still be transmitted down the link bars and push/pull on the bars.





That is my thinking on it but I just do not know for sure. If that is true then it may be an advantage to build car as a four link even if you use solid bars for shocks so you can adjust IC where car performs best? One other little advantage with using a solid strut is you can still put some preload in chassis to make it go straight.

Which may bring up a related question. On a hard tail how much does engine angle effect how hard it plants tires and hooks up? Which my way of thinking is engine angle acts like IC to a certain extent? On the hard tail the engine must be straight in line with the rear end but the engine angle is different on some.


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"Dunning-Kruger Effect"
-a type of Cognitive bias where people with little expertise or ability assume they have superior expertise or ability. This overestimation occurs as a result of the fact that they do not have enough knowledge to know they don't have enough knowledge.

Before you argue with someone ask yourself, "Is this person mentally mature enough to grasp the concept of a different perspective?" If not there is no point to argue.

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Posts: 3916 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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without the dynamics of the movement of the suspension, it is a static model. It will act exactly like a hard tail car at that point. You can think of it this way...If you cut off the supports for the axle on a hard tail car on the front, and move the mount forward significantly and weld it all back together, would it act differently? No. If you add gussets or additional support to that brace, is it any different? Nope. It is a non moving and connected single model at that point.

I think your theory on pre loading may be correct...you can still jack weight into one corner with preload of the four link bars. But remember what you are doing is putting a bind/twist into the chassis. I suspect that the chassis will absorb that twist more quickly without the freedom of movement of the rear, and you will have to add this preload back in periodically until something permanently gives.

As far as driveline angle and hook: The angle itself has no affect...just like pinion angle by itself has no affect. In the case of a hard tail, you affect driveline angle by raising or lowering the engine, which does affect how hard it hits the tires on launch.

Those are my thoughts anyhow.


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Posts: 6318 | Location: Illinois | Registered: July 08, 2004Reply With QuoteReport This Post



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A very high powered altered would be much like a funny car with no body, which are hard tails of course. At some point in a light short high hp chassis the advantage of suspension down track is out weighed by the problems caused on the starting line. As already mentioned the only adjustment that would have any effect would be preload if the shocks were solid. Without suspension the flex in the chassis is the spring. Four links are not magic, some times they just fit better than a ladder bar in some cars that need longer instant centers . Most cars will only have two or three practical bar combinations. With adjustable shocks the car can usually be made to leave exactly the same in any of those two or three bar settings. The combination that allows the lightest shock on the starting line will let the suspension work better down track. This is why the electric adjustable shocks were developed for prostocks. Just a little food for thought.
 
Posts: 35 | Location: new jersey | Registered: January 08, 2017Reply With QuoteReport This Post
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The idea of being able to adjust pre-load in a non-sprung chassis is giving me pause to think. As is the idea of a four-link instant center adjustment making a difference with or without shocks. All interesting food for thought.

Adding to the puzzle, do the shock substitute bars have rod ends? Or, bolted solid?

Will the chassis material make a difference? Does tubing size make a difference?

At this point, I want to hear about a number of positive result from several different race teams.


Larry Woodfin



 
Posts: 1816 | Location: Kilgore TX | Registered: March 12, 2004Reply With QuoteReport This Post
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The way I saw them do it was they used a bar with adjustable rod ends similar to a four link bar and with those bars they could adjust ride height and preload some. Set it at say 11.75 inches or what ever static shock height was and then put a few flats preload in right rear bar as needed.

What he is doing is working quite well but I still do not know about the IC settings and how much they effect it if you put the solid bar in place of shocks.

We have got several different answers here and they are not all the same on the IC. (When I say IC I am not just referring to that I really mean complete settings)

We all agree that when you put solid bar in there the rear end is solid and it makes the car a hardtail in effect. Question still remains is does the settings make a difference if you do that? If it is way off is car going to try to go straight up and pull huge wheelies or not plant rear tires hard? With these cars we are always trying to get them to work right and get as much power to the ground as possible.

I still think when you put the solid bars in there will reduce the effect of IC settings because you have stopped all suspension travel but four link settings in my mind should still help determine how the car works and plants the tires. On a four link the bottom bar still pushes car forward and top bar still tries to pull back trying to raise front of car. Those forces are still in effect. Those physics do not go away and if done right could be used to your advantage even if you have it set up as a "HardTail"

I am reminded when I first got my altered it was way off and the car wanted to go straight up at the hit with huge wheelies until it hit wheelie bars. Hard to drive and dangerous. After learning some and making changes then it gently pulls front wheels and carries them way out and the wheelie bars were not as important. Made the difference from trying to flip over or go forward. Made the car easy and fun to drive.

By my way of thinking those settings would still be somewhat important in how car plants tires and car works.

I am not saying anyone is wrong here I am asking if anyone has real world experience to see if it makes a difference on settings if solid strut is in there?


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"Dunning-Kruger Effect"
-a type of Cognitive bias where people with little expertise or ability assume they have superior expertise or ability. This overestimation occurs as a result of the fact that they do not have enough knowledge to know they don't have enough knowledge.

Before you argue with someone ask yourself, "Is this person mentally mature enough to grasp the concept of a different perspective?" If not there is no point to argue.

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Posts: 3916 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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With a locked four link you create a hard tail that is adjustable! With the four link bars you can change the position and angles the forces carried by the bars are applied to the chassis where it's fixed with your typical hardtail car. Not sure if prolong would do anything with the bars locked.

BTW most big HP cars basically lock the shocks up during the launch using timers to soften the shocks down track!

Also you don't adjust a four link to fix wheelies. Weight and wheelie bars do that!
 
Posts: 2123 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
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quote:
Originally posted by TOP38:
With a locked four link you create a hard tail that is adjustable! With the four link bars you can change the position and angles the forces carried by the bars are applied to the chassis where it's fixed with your typical hardtail car. Not sure if prolong would do anything with the bars locked.

BTW most big HP cars basically lock the shocks up during the launch using timers to soften the shocks down track!

Also you don't adjust a four link to fix wheelies. Weight and wheelie bars do that!


This is my thinking for the most part. As for the four link lowering the top bar on my altered was a huge help. It was trying to go straight up lowering it front and back made a huge difference and now it goes forward with minimal wheelies and easy to drive. Then fine tune it with weight and the wheelie bars.


https://postimg.cc/gallery/np3zpruo/
"Dunning-Kruger Effect"
-a type of Cognitive bias where people with little expertise or ability assume they have superior expertise or ability. This overestimation occurs as a result of the fact that they do not have enough knowledge to know they don't have enough knowledge.

Before you argue with someone ask yourself, "Is this person mentally mature enough to grasp the concept of a different perspective?" If not there is no point to argue.

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Posts: 3916 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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quote:
Originally posted by Curly1:
quote:
Originally posted by TOP38:
With a locked four link you create a hard tail that is adjustable! With the four link bars you can change the position and angles the forces carried by the bars are applied to the chassis where it's fixed with your typical hardtail car. Not sure if prolong would do anything with the bars locked.

BTW most big HP cars basically lock the shocks up during the launch using timers to soften the shocks down track!

Also you don't adjust a four link to fix wheelies. Weight and wheelie bars do that!


This is my thinking for the most part. As for the four link lowering the top bar on my altered was a huge help. It was trying to go straight up lowering it front and back made a huge difference and now it goes forward with minimal wheelies and easy to drive. Then fine tune it with weight and the wheelie bars.


You adjust the four link & shocks to get the rear to do what you want, if it wheelies big time then the car is unbalanced. If what you did works, then that's ok too,,, but I bet your not going fast so you can get away with it.
 
Posts: 2123 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
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quote:
Originally posted by Curly1:
I understand fairly well about how a four link suspension works


lmao
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Posts: 233 | Location: Il. | Registered: December 31, 2008Reply With QuoteReport This Post



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quote:
Originally posted by Curly1:
I understand fairly well about how a four link suspension works but have a question.
On some really high power Altereds they make the for link into solid suspension by putting a bar in there. I have seen where putting the solid strut will make a car go down track when it was struggling with four link.

I have been told that once you make it solid then it does not matter what the IC settings are as it is solid. That is what I do not understand. With regular four link if it is off it will pull hard wheelies or not plant tires and hook. Adjustment is critical.

Seems to me that it would still make a difference on how it plants tires etc. The solid strut would eliminate shock separation but seems the the IC would still help determine how it it plants tires and lifts front?

Any thoughts and real world experience?


the four link is a massive tuning advantage, do not put solid anything in there. If you don't think the shocks are helping you to tune the suspension then their is probably something wrong with the shocks. Good shocks are essential and can help you tremendously. Forget this idea and work with the instant center.

Remember higher and shorter is a harder hit and longer and lower is a softer hit. You aren't going for the fastest ET, just the most consistent.


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Posts: 2497 | Location: Gilmer, Texas | Registered: June 25, 2002Reply With QuoteReport This Post
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Originally posted by The Bozman:


the four link is a massive tuning advantage, do not put solid anything in there. If you don't think the shocks are helping you to tune the suspension then their is probably something wrong with the shocks. Good shocks are essential and can help you tremendously. Forget this idea and work with the instant center.

Remember higher and shorter is a harder hit and longer and lower is a softer hit. You aren't going for the fastest ET, just the most consistent.


This is not for me or my car, I am not driving the altered any more. I was asking because some of the guys who run outlaw altereds were saying to make the rear end solid once you go faster than say 4.60 in 1/8. They said when you make it solid with a strut it does not matter where IC is. That does not make sense to me. My thinking is it would of course be limited but still have some effect on the car.

There are many forces on a four link that determine how it hooks and making it solid would eliminate some of them but not all. Like a short, high IC will separate chassis planting rear tires harder. You eliminate that with solid rear. But I think the bars still push car forward and top bar still pulls back as it tries to rotate the housing opposite the tires so that effect would still be there?

That is my question is if you make it solid does the fourlink settings still determine how car reacts and hits tires? I just want to learn and get others opinions because nobody really seems to know for sure. By the way I agree with you and thing the four link is a good tuning advantage and shocks are critical.


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"Dunning-Kruger Effect"
-a type of Cognitive bias where people with little expertise or ability assume they have superior expertise or ability. This overestimation occurs as a result of the fact that they do not have enough knowledge to know they don't have enough knowledge.

Before you argue with someone ask yourself, "Is this person mentally mature enough to grasp the concept of a different perspective?" If not there is no point to argue.

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Posts: 3916 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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By definition, the IC is the imaginary point that the radius of the rear end will travel around when the four link moves. If the four link will not move, it is a moot point. The IC location really is for visual reference. The torque is not truly applied at that point. After all, you can have an IC way out in front of the car, and obviously you aren't applying torque in front of the car. The axle is just traveling around a larger radius. You almost have to think of the ic in a normal system as only affecting the movement of the axle, and nothing else. Many will explain the ic as a leverage point or many other definitions. But the torque really rotates at the axle regardless.


Foxtrot Juliet Bravo
 
Posts: 6318 | Location: Illinois | Registered: July 08, 2004Reply With QuoteReport This Post
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That is true but the IC is one of the things we use as a reference to how it is set up.


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"Dunning-Kruger Effect"
-a type of Cognitive bias where people with little expertise or ability assume they have superior expertise or ability. This overestimation occurs as a result of the fact that they do not have enough knowledge to know they don't have enough knowledge.

Before you argue with someone ask yourself, "Is this person mentally mature enough to grasp the concept of a different perspective?" If not there is no point to argue.

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Posts: 3916 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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quote:
Originally posted by Curly1:
That is true but the IC is one of the things we use as a reference to how it is set up.


For sure. But it's location controls how the axle moves. That's the setup. If the axle isn't moving, it's a moot point.


Foxtrot Juliet Bravo
 
Posts: 6318 | Location: Illinois | Registered: July 08, 2004Reply With QuoteReport This Post
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In a 4 link your instant center is changed from your static setup whenever the rear of the car raises or lowers for any reason. It changes at the hit and as you are going down the track for the simple reason rear ride height is changing not constant.This change may be very small if the rear does not raise or lower much during the run or it can be a very big change if the car squats or raises a bunch. What a solid link would do is keep your instant center pretty much where you set it at all times. There really is no need for this as correct shock setup along with springs and bar settings will keep the rear from raising and lowering enough to upset the chassis at the hit and down track. Its a bandaid. You can prove this out by plotting your instant center at different rear heights.
 
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