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Four link theory question.
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Bucky hit the nail on the head.

The complete, technical name for what we call IC is actually "Instant Center of Rotation." To even have an IC, there must be rotating motion of one object, relative to another. The moment you replace the shocks with solid links, the rear end can no longer move, relative to the chassis. It has become a solid mount and has no IC.

https://en.wikipedia.org/wiki/...t_centre_of_rotation

If you continue to move the 4-link bars with a solid link, you will change the forces within each bar, but the net effect on the chassis will be the same. Unless moving the bars has a detectable effect on how the chassis flexes, it is no longer a tuning tool.

Here's another way to think about it. Take a car with a solid mounted rear-end. Cut off the mounting brackets from the rear end and the chassis. Weld on new brackets that have the bolt holes in different locations, but positions the rear end in exactly the same place. Will the car behave any differently? If not, then how could moving the 4-link bars have an effect, with a solid link in place of the shock?


Ben Rawe 383H
1965 Chevy II Nova
 
Posts: 226 | Location: Alexandria, KY | Registered: April 04, 2003Reply With QuoteReport This Post
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quote:
Originally posted by Rawe Power:


The complete, technical name for what we call IC is actually "Instant Center of Rotation." To even have an IC, there must be rotating motion of one object, relative to another. The moment you replace the shocks with solid links, the rear end can no longer move, relative to the chassis. It has become a solid mount and has no IC.

https://en.wikipedia.org/wiki/...t_centre_of_rotation

If you continue to move the 4-link bars with a solid link, you will change the forces within each bar, but the net effect on the chassis will be the same. Unless moving the bars has a detectable effect on how the chassis flexes, it is no longer a tuning tool.

Here's another way to think about it. Take a car with a solid mounted rear-end. Cut off the mounting brackets from the rear end and the chassis. Weld on new brackets that have the bolt holes in different locations, but positions the rear end in exactly the same place. Will the car behave any differently? If not, then how could moving the 4-link bars have an effect, with a solid link in place of the shock?


IC are meaningless without bar angles in any operating 4 link system! In fact "IC" is a 4 link buzz word most want to use because that's what they hear and also what they can understand but bar angles are more important! You can have a number of bar angles that give you the same IC but will react totally differently.

If you change the 4 link bars in a fixed or shock equipped 4 link system in the front only, you do not change the force in that bar, just the direction/angle & location in which it acts on the chassis. If you change the back location of the bars (At the rear) then you change both the force in the bar along with the direction it acts on the chassis.

A fixed 4 link will act the same as a normal hardtail that has a number of different mounting holes on the rear & chassis. Does the IC matter with the later?
 
Posts: 2145 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
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Picture of Curly1
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Okay so lets say it does not make any difference at all.

If that is true then engine angle in a hard tail would not matter or change how it hooks yet it does. Why is that? Cant have it both ways, it does or it doesn't. We know that engine angle makes a big difference on a hard tail but this would not? The rear end is trying to rotate and push the weight of the car forward. Where it is pushing in relation to the weight makes a difference. The high engine angle on the old altereds was why they were so evil handling. It was trying to wheelie and drive under the weight or center of gravity. When they started putting engine angle closer to 0* they started hooking up and handling better. Too far down and it tries to spin tires and not hook up. We know these things and I suspect it is similar if you move four link bars with solid struts to a certain extent?

I absolutely agree that when you make it solid it removes all of the movement and limits adjustment. That is a fact. But I still think that how it is set up will have some effect on it but to a lesser extent than with shocks. Changes how the power is applied to the chassis and how it reacts. Similar to changing engine angle on a hard tail. You are still changing how and where the forward thrust is applied to chassis in relation to the weight and center of gravity of the car and motor.

Solid or not the rear end tries to rotate opposite tire rotation and push car. Where it is pushed forward in relation to the weight of the car should make a difference in how the car reacts.

Most important do not get pissed off if you do not agree. I do not think anyone really knows the answer to this as I do not know of anyone who has tried and tested it. I do know people who had a good working four link car and once they started going faster than 4.60 they put a strut in there and it helped. But the key there is it was working good before and they have not moved it around to see if it makes any difference. I am not saying anyone is wrong.


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.

4X NE2 CHAMPION. 2020 TDRA NE2 Champion
 
Posts: 3994 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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Probably the reason no one you know has bothered to to test it is because they realized it wasnt going to make a difference. Sometimes when most people dont do something that means its probably not a good idea.
 
Posts: 35 | Location: new jersey | Registered: January 08, 2017Reply With QuoteReport This Post
DRR Sportsman
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Curly:

A) With the solid strut rod in place (And to a bigger degree than most will admit with a sprung 4 link) the tire is pushing against the actual center of gravity of the vehicle, it does not matter where the axle mount attaches. (Solid only)

B)The reason the hit changes on a hard tail dragster when you change the engine angle is not the new engine angle but the new center of gravity.

C) Back in the day they did not lower the engine and start hooking better, the slicks got better and they had to lower the engine to keep full power applied with the added grip.

Savvy Kemosabe...?
 
Posts: 842 | Location: Illinois | Registered: July 27, 2006Reply With QuoteReport This Post
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quote:
Originally posted by Dbl.O.Five:
B)The reason the hit changes on a hard tail dragster when you change the engine angle is not the new engine angle but the new center of gravity.


Bingo.


Ben Rawe 383H
1965 Chevy II Nova
 
Posts: 226 | Location: Alexandria, KY | Registered: April 04, 2003Reply With QuoteReport This Post
DRR Sportsman
Picture of Boucher Jr
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quote:
Originally posted by Dbl.O.Five:
Curly:

A) With the solid strut rod in place (And to a bigger degree than most will admit with a sprung 4 link) the tire is pushing against the actual center of gravity of the vehicle, it does not matter where the axle mount attaches. (Solid only)

B)The reason the hit changes on a hard tail dragster when you change the engine angle is not the new engine angle but the new center of gravity.

C) Back in the day they did not lower the engine and start hooking better, the slicks got better and they had to lower the engine to keep full power applied with the added grip.

Savvy Kemosabe...?


Would you knock that shyt off?

This is priceless entertainment....

Dimwit #1 "golly gee folks dem bars in the back der under the car hows should i adjusts em?"

Dimwit #2 "ya gots to move that der IC and spend 10k on a set of shocks"

Foxworthy couldnt make this thread up and youre gonna try and teach physics.... gimme a fucn break...
 
Posts: 236 | Location: Il. | Registered: December 31, 2008Reply With QuoteReport This Post



DRR Sportsman
Picture of Boucher Jr
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To be serious for a moment theres one key element to this 4 link abortion thread even dbl oh five left out. When adding a little more power you might find its also beneficial to replace the rack and pinion with a 2 x 4 to go along with the lack of rear shocks. It prevents the car from wanting to move around down track with the front tires locked straight ahead at all times.
 
Posts: 236 | Location: Il. | Registered: December 31, 2008Reply With QuoteReport This Post
DRR Top Comp
Picture of Curly1
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Your opinion is noted and intelligence shows.


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.

4X NE2 CHAMPION. 2020 TDRA NE2 Champion
 
Posts: 3994 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
DRR Sportsman
Picture of Boucher Jr
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quote:
Originally posted by Curly1:
I understand fairly well about how a four link suspension works


Next time, save the punch line for the end of the joke. Still, thanks for the laughs Curly.

Anything else would go over your retarded head.
 
Posts: 236 | Location: Il. | Registered: December 31, 2008Reply With QuoteReport This Post
DRR Trophy
Picture of sammy christian
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let's all go back to the first response I gave--
quote:
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.

period.
if the thing isn't moving, the bar locations don't mean anything.
IT IS NO LONGER A FUNCTIONING 4-LINK.


6.41@221 (so far)
4.11@178
off the shelf/built it myself
 
Posts: 82 | Location: Amherst, Ny | Registered: May 14, 2001Reply With QuoteReport This Post
DRR S/Pro
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quote:
Originally posted by sammy christian:
let's all go back to the first response I gave--
quote:
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.

period.
if the thing isn't moving, the bar locations don't mean anything.
IT IS NO LONGER A FUNCTIONING 4-LINK.


You may want to rethink that statement! Just because it doesn't move doesn't mean moving the bars that attach to either the rear or chassis won't have impacts on the way the car goes down the track!

Example, take a tall box,, call it a frig if you want, push it hard at the bottom, what happens.... it will want to tip over due to it's weight relative to its CG. Now push it in the middle... not the same result... so you think a race car is any different?
 
Posts: 2145 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
DRR Elite
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quote:
Originally posted by TOP38:
quote:
Originally posted by sammy christian:
let's all go back to the first response I gave--
quote:
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.

period.
if the thing isn't moving, the bar locations don't mean anything.
IT IS NO LONGER A FUNCTIONING 4-LINK.


You may want to rethink that statement! Just because it doesn't move doesn't mean moving the bars that attach to either the rear or chassis won't have impacts on the way the car goes down the track!

Example, take a tall box,, call it a frig if you want, push it hard at the bottom, what happens.... it will want to tip over due to it's weight relative to its CG. Now push it in the middle... not the same result... so you think a race car is any different?


The axle is still pushing from the same place regardless of how it is attached. Working four links have much less influence on the chassis than they do on the axle movement.


Foxtrot Juliet Bravo
 
Posts: 6384 | Location: Illinois | Registered: July 08, 2004Reply With QuoteReport This Post
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quote:
Originally posted by Bucky:
quote:
Originally posted by TOP38:
quote:
Originally posted by sammy christian:
let's all go back to the first response I gave--
quote:
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.

period.
if the thing isn't moving, the bar locations don't mean anything.
IT IS NO LONGER A FUNCTIONING 4-LINK.


You may want to rethink that statement! Just because it doesn't move doesn't mean moving the bars that attach to either the rear or chassis won't have impacts on the way the car goes down the track!

Example, take a tall box,, call it a frig if you want, push it hard at the bottom, what happens.... it will want to tip over due to it's weight relative to its CG. Now push it in the middle... not the same result... so you think a race car is any different?


The axle is still pushing from the same place regardless of how it is attached. Working four links have much less influence on the chassis than they do on the axle movement.


The axle/rear end is connected to the chassis by the four link bars,,, if you can't see that then ask the frig to explain it.
 
Posts: 2145 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post



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There is more than one thing in play here,first a four link functions in exactly the same manner as a tourgue tube setup or lift arm set up or 3 link or truck arm or leaf spring so on and so on. The difference is the ability to adjust the point where the force is applied at the chassis, with a tourque arm,tourque tube, leaf spring setup your adjustability is limited to the attaching points, a ladder bar functions exactly like a 4 link but with no ability to move the i.c forward backward or up and down much the attaching points are the i.c.

The other thing in play is the thrust angle which is where the bars push on the chassis which can also be a big deal, this is what causes changes when changing ladder bar mounting height, leaf front eye height adjustments and lower control arm height and angle adjustments on a tourque arm setup.Thrust angle can be shown by drawing a line from the contact patch thru the i.c, a leaf or ladder bar car has short pretty steep thrust angle, 4,or 3 link or lift arm car can be pretty much where you want it.The thrust angle is the point the bars push on the chassis loading the tires.For example with a short ladder bar raise the front mounting point way up it picks up the rear of the car point it downward some and pushes on a different point loading the tires differently.
To further show thrust angle importance there are a **** ton of 800 h.p 2300 lb cars on 8 inch tire hooking hard enough to carry the front wheels on dry slick dirt tracks with the rearends mounted in birdcages free to rotate except for the upper mounting point whether it be a pull bar, push bar or lift bar all over the country every Saturday night.
 
Posts: 39 | Location: ohio | Registered: August 15, 2009Reply With QuoteReport This Post
DRR Elite
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quote:
Originally posted by TOP38:
quote:
Originally posted by Bucky:
quote:
Originally posted by TOP38:
quote:
Originally posted by sammy christian:
let's all go back to the first response I gave--
quote:
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.

period.
if the thing isn't moving, the bar locations don't mean anything.
IT IS NO LONGER A FUNCTIONING 4-LINK.


You may want to rethink that statement! Just because it doesn't move doesn't mean moving the bars that attach to either the rear or chassis won't have impacts on the way the car goes down the track!

Example, take a tall box,, call it a frig if you want, push it hard at the bottom, what happens.... it will want to tip over due to it's weight relative to its CG. Now push it in the middle... not the same result... so you think a race car is any different?


The axle is still pushing from the same place regardless of how it is attached. Working four links have much less influence on the chassis than they do on the axle movement.


The axle/rear end is connected to the chassis by the four link bars,,, if you can't see that then ask the frig to explain it.


The question at hand here was revolving around instant center locations with regards to the four link bars. You don't need link bars to connect the axle to the chassis in a different location. If you want it to connect to the top of the roll bar, of course that will affect the car differently. But IC has nothing to do with that. IC is the imaginary center of rotation about which the axle moves in a four link suspension. If the axle doesn't move, there is no rotation, and thus no instant center. The axle is connected where it is connected. Yes you can move the four link bars....inches. So you can move your mounting point....inches. Will this have a marginal affect on the car? I doubt it could be measured. IC locations are a completely different thing. They have a great deal of influence on the axle movement.
And sure. Please explain it using static vector diagrams with a given torque applied by the axle and mounting in different locations to show the amount of difference it made. Maybe it will be an eye opener. It's been a while since I have drawn one.


Foxtrot Juliet Bravo
 
Posts: 6384 | Location: Illinois | Registered: July 08, 2004Reply With QuoteReport This Post
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This is for me one of the three C's. Chassis, Converter and Camshaft. You will pretty much never see an opinion from me about any of those. Don't understand them, not going to, ain't gonna happen. Hopefully the chassis builder, engine builder and converter builder do because that's what I'm counting on. LOL Big Grin

Carry on gents!!


Clowns to the left of me, Jokers to the right. Here I am.......
 
Posts: 5299 | Location: stuck in the middle with you! | Registered: March 11, 2002Reply With QuoteReport This Post
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Picture of rusty
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what about the part where the differential houseing is trying to rotate around the axles.


honesty is the best policy,insanity is a better deffense
1.036, 6.16@ 224

 
Posts: 1397 | Location: texas | Registered: February 17, 2006Reply With QuoteReport This Post
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Bucky

First forget IC's, please! Without bar angles you got nothing but a dot in space.

Second, a four link bar can only carry load parallel to itself. (Push or pull on the chassis and or rear housing in order to counter act torque applied from the tires either accelerating or de-accelerating the car) The angle at which they push or pull on the chassis matters whether the bars move during a run or not. The only difference between a fixed/locked four vs one with a shock is during a run the bar angles can change with a shock and are fixed when locked. It still works the same way.

Third, you stated once you lock the four link the bar angles don't mean anything! So your telling me that the angles of the four link bars acting on the chassis during a run mean nothing just because the shock is locked! And therefore I can move the bars around and it will have no effect on the car running down the track. I am telling you that is not true, when you move the bars you change angle and the force in which they are acting on the chassis and therefore will effect how the car goes down the track, hence my extreme example of the frig!

You mentioned vectors, do you understand what one is? Do you understand how applying and changing forces relative to the CG of anything matters how it will react when the forces are applied? based on my third point, you don't.

So try this example. Same frig again but it's floating in space (LOL) but its stationary! You punch it and your punch lands exactly on at the CG of the frig, what happens? (Just the frig, not you) It will move in a direction parallel to your punch and it will not rotate at all. Now move the punch to the bottom of the same frig, now it not only moves away from you but it rotates too, so some of the energy of your punch is moving it away from you and some it spent rotating the frig while in the first case it wall went to moving the frig away from you.... OK now come back to earth and replace the frig with a car and your punches with four link bars.

So the bottom line is changing the force(s) direction and magnitude (also called a vector) with respect to the CG of an object with mass/weight such as a race car, will effect how that object reacts to the force(s) applied.

I cant' explain it any better.
 
Posts: 2145 | Location: Tewksbury, MA,USA | Registered: November 03, 2000Reply With QuoteReport This Post
DRR Sportsman
Picture of Boucher Jr
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This thread is awesome. Drr hasnt been this entertaining since Ed.

Sl, free Ed.

Didnt realize there was so many pollocks on drr. Its the only explanation.
 
Posts: 236 | Location: Il. | Registered: December 31, 2008Reply With QuoteReport This Post
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