View Full Version : 3 link Tech for dummies
Okay, I tricked you, I don't know squat about no three link. But it seems people kind of started a trend lately toward three links, when a year ago, almost nobody even knew they existed(besides you smart guys) Seems everybody kinda wants one, just like Wayne due front ends, and tubular control arms. I thought some of you suspension :geek: could show some descriptive pics and an explanation in Normal English. I have some what of an idea of what they are and have read a bunch, but I thought it would be good to get a firmer grasp on what they are all about in terms I and others can understand. Who wants to try first? :rtfm:
MoeBawlz
01-06-2005, 06:14 PM
Heres the 05' mustangs new 3 link setup. https://static1.pt-content.com/images/noimg.gif
the links here are short due to packaging and the need for a backseat in the production car obviously. i dont know squat about the math of a 3 link but you can place the 3rd link (upper link) anywhere on the axle.
I think Mean 69 is building one for his car... but im not positive. If you go to Corner Carvers there is a BUNCH of info on 3 links there.
baz67
01-06-2005, 08:28 PM
I guess we need to know what you do know before we cover theory you already understand.
Very and I mean very simply a three link has a huge advantage over a leaf style suspension by greatly lessening rear wheel hop under acceleration. It will also give you the ability to adjust ride height and rear spring rate. If designed properly it can be packaged in a Camaro easier than a four link. Is that simple enough.
Brian
baz67
01-06-2005, 08:31 PM
Moebalz, you are correct in that you can place the upper link anyplace on the axle. If place correctly you could run an open carrier, BUT when the forces reverse the car will pull in one direction under braking.
Brian
Well I know enough about them to understand most of it. My point of the post was to expose this for everyone, not for myself really. Just a good post with lots of good tech that people like myself(aka don't understand ROH, LSA, RSVSADG, ABCDEFG, type of terms and so forth) I have skimmed through herb adams suspension book, but I just thought with all the recent talk about three links, and that I noticed a lot of people have put a three link on there "to do" list that a good post like this might help
MrQuick
01-06-2005, 10:53 PM
Pody, put that number 2 after the mini tub...don't look at me,it will NEVER get done...
The most simple explanation and design can be found in Race car dynamics, and 2 books by steve smith: Paved track stock car technology and Building the PRO STOCK late model sportsman.
Wheel hop is reduced during accel is a plus due to anti squat but the likelyhood of brake hop is increased, a dampner or shock link can lessen the effects.
Optimal upper link (UL) is center mounted but not necassary. UL should be 18 - 20 inches long and mounted at a 5-7* downhill. Mounting point should be beefy and double sheer. Sheet metal mounts can be used if reinforced and/or tied into chassis or roll cage. Link itself can be constructed of 1 1/4" .219 wall DOM wall and tapped for 3/4" 16 pitch threads.
Lower links should can be 20 - 24 " in length, mounted double sheer, parallel with each other with no lateral angles. Constructed of 1 1/4" .095 wall DOM with 1" .156 wall DOM tapped for 3/4" 16 pitch threads.
3 links have been around for a long time but is not used due to the space required.Packaging is the hard part. Im very curious to see Marks design...no pictures yet.
MrQuick
01-06-2005, 11:20 PM
345's 345's 345's 345's...damn this jedi mind trick stuff is hard...what?
what are you doing still up? I am not a jedi, I am an Ewok....No wait, thats you, I must be Darth balls
touring67
01-07-2005, 12:54 AM
I too am eagerly awaiting Mark's design and to see some pictures when he is done. I know he's really busy at this time and it will be a while before that time comes but I'm sure we can wait.
Ok, so my books haven't arrived yet and I'm not old enough to have any great experience in this stuff so I'll demonstrate my ignorance. Why is it that the new Mustang can get away with a shorter upper link when we are usually forced to cut into the floor and backseat to make it 20 inches or so long?
However, what I think would be really cool was two narrowed bucket seats in the back with an 'armrest' in the middle where the upper link could go. The buckets could be modified (or the brackets) to fit in there and sheetmetal could span the gap between them to hide the trunk and create the 'hump' for the link mount. The seats would be narrowed of course to fit the minitubs that were just recently installed to fit the 345 mm wide fatties that are required to satiate the insane hunger for rubber we all crave. I think this would look spanking cool and custom. Of course there are other things such as seat belts to be modified to work and rollcages that would negate any reason for having back seats but hey, it's just an idea. Anyone like the sound of that?
dennis68
01-07-2005, 08:26 AM
Because the Mustang designers are not looking for an all out race car, just a well behaved street car.
Like anything else that is mass produced for the general public, compromise based on what "most" people will accept.
baz67
01-07-2005, 09:09 AM
https://www.pro-touring.com/forum/showthread.php?t=203 This is hiding in the archives.
For some interesting nightime reading https://www.pro-touring.com/forum/showthread.php?t=208
Brian
dennis68
01-07-2005, 09:28 AM
Yeah, we discussed this last nite, I wasn't going to contribute to a redundant thread except for the Mustang thought.
reduntant thread huh? Sorry for the redudnant post. its okay dennis I didn'[t really need you to contribute anyway :)
touring67
01-07-2005, 02:49 PM
Yes, I have read the archived posts and they are full of information but for the sake of my memory I went back and read em again. Some of my books came today and I plan to be reading for much of my time to get a better understanding of the concepts that are involved. As far as there being an old thread about this subject I'm not sure if it can hurt to dig up new or different information to post here or perhaps different applications of a 3 link's use.
Norm Peterson
01-09-2005, 11:16 AM
Why is it that the new Mustang can get away with a shorter upper link . . .The expected performance level utilized by the majority of owners lets Ford make compromises you would not do in a one-off custom arrangement or low production aftermarket kit. Forces them to do so, in the case of some details.
Ford is likely using relatively soft UCA bushings (or perhaps voided bushings) so that the angularity of a short 3rd link when the car rolls (think plan view) isn't adding lots of undesired loads trying to bend the link (and adding some rear roll stiffness in the process).
Even so, at least one magazine review has claimed to have noticed the limits of such a short link (I think they'd rather continue to skewer any stick axle design than attempt any explanations or make suggestions).
Norm
Norm Peterson
01-14-2005, 09:57 AM
Voided bushings it is.
Norm
David Pozzi
01-14-2005, 10:28 PM
Here is an article on the 05 mustang front and rear suspension:
http://content.sema.org/images/pdf/33625.pdf
mikehevans
06-17-2008, 10:15 AM
Anyone ever read Racing Car Design and Development by Len Terry? It hasn't got a lot to do with the chassis and suspension of American cars, but Terry worked in Formula and Prototype(LeMans) chassis development for a long time in the '50's,'60's and '70's and does an excellent job of explaining the whys and wherefores of suspension geometry. It is also a great aid to understanding how we got to where we are today in suspension design.
BillyShope
11-21-2008, 05:22 AM
Just adding a couple of comments to an old thread:
...BUT when the forces reverse the car will pull in one direction under braking.
Brian
This is true only at the point of locking up the rear wheels, which, of course, you don't want to do while braking. Jaguar used a 3link with severely offset upper link in the early C-Type Jaguars.
My site has a spreadsheet for 3link setup which provides equal rear tire loading while accelerating forward. If you insert the correct value for your CG height, the result provides 100% antisquat. But, if you "cheat" on your CG height entry, you can get a result for any desired percent antisquat and still have equal rear tire loading coming out of a corner. This, of course, was the goal of the early C-Type. (I keep saying "early" because, as you might know, the later C-Types had IRS. Many consider the Jaguar design the zenith in beam rear axle suspension design.)
http://home.earthlink.net/~whshope
Fluxion
11-23-2008, 12:11 AM
BillyShope, I was playing around with your 3 link calculator on page 18. I was wondering why the offset of the odd link can't be zero. I am just wondering what changes when you place the odd link centered on the rear end like in a Lateral Dynamics or Art Morrison 3 link rear suspension.
BillyShope
11-23-2008, 04:17 AM
BillyShope, I was playing around with your 3 link calculator on page 18. I was wondering why the offset of the odd link can't be zero. I am just wondering what changes when you place the odd link centered on the rear end like in a Lateral Dynamics or Art Morrison 3 link rear suspension.
When you center the odd link, you give up the advantage inherent to a 3link: The ability to dynamically cancel the unloading of the right rear during forward acceleration. With a beam rear axle, the driveshaft torque tends to unload the right rear (and, of course, load the left rear). The link loads are proportional to the driveshaft torque, so, if the odd link is offset correctly, it is possible to cancel the driveshaft torque effect for any and all values of driveshaft torque. Jaguar used the offset link in the early C-Type Jaguar.
So, why didn't Ford use an offset link on the Mustang? All you've got to do is take a peek at the Mustang underside and you'll see that there's a serious packaging problem with an offset link.
Some raise questions with regard to unequal wheel loading during braking, but this only comes into play as the rear wheels go into lockup, which, as I think I've stated earlier in this thread, is something to be greatly avoided in any case. Still, an outfit like Ford has to worry about legal claims after accidents, which, unfortunately, also affects design decisions.
http://home.earthlink.net/~whshope
Norm Peterson
11-23-2008, 07:05 AM
With an offset odd link, what happens to the rear tire loading due to roll caused by engine torque reaction and the rear suspension's proportion of roll stiffness? I know that's a big reason for the huge rear sta-bars sometimes seen on dragstrip cars and I don't see it going away entirely. Is rear roll stiffness something that can be used in conjunction with some other amount of odd link offset to advantage?
Norm
BillyShope
11-23-2008, 04:38 PM
With an offset odd link, what happens to the rear tire loading due to roll caused by engine torque reaction and the rear suspension's proportion of roll stiffness? I know that's a big reason for the huge rear sta-bars sometimes seen on dragstrip cars and I don't see it going away entirely. Is rear roll stiffness something that can be used in conjunction with some other amount of odd link offset to advantage?Norm
Norm, if an asymmetric suspension is used to cancel the driveshaft torque's effect on rear wheel loading, the car's roll stiffness distribution doesn't enter into the picture. In other words, the reaction to the driveshaft torque is taken entirely through the links and no roll deflection occurs.
http://home.earthlink.net/~whshope
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