PDA

View Full Version : 4-link (from old site)



chicane67
08-16-2004, 12:25 PM
69speed
Registered User
Posts: 10
(5/16/04 1:27 pm)
Reply 4 link suspension
--------------------------------------------------------------------------------
It's almost time to install my rear suspension, but I'm having trouble finding what I want. Seems everyone has a 4 link for drag racing, but none I've seen for sale seem suitable for a PT car. I've noticed on different cars on this sight a long panhard bar, but all I see for sale are the short ones that mount over the diff. Please help. Where do I look for a parrallel bar 4 link that will work well for my 69 camaro?

SSWANAB
Registered User
Posts: 16
(5/16/04 2:26 pm)
Reply Re: 4 link suspension
--------------------------------------------------------------------------------
Check with DSE. They have done a couple including the "Mule". They should be able to help.

Ralph L
Moderator
Posts: 3241
(5/16/04 2:44 pm)
Reply
Re: 4 link suspension
--------------------------------------------------------------------------------
I don't think DSE did the 4 bar on the Mule, but they have duplicated it. They are coming out with a 4bar kit soon, but I'm not sure when. Here's a link: www.detroitspeed.com

Also try AME, they sell a "kit" to build a parallel 4 bar but it is more for street rods, and you will have to modify it for carving corners. www.artmorrison.com
Ralph
Project Fantom Expected Completion - May 2005
My Tahoe - "Black Mamba"
Rendering of Project Fantom

parsonsj
Registered User
Posts: 1611
(5/16/04 4:45 pm)
Reply Pics of my modified AME 4 bar
--------------------------------------------------------------------------------
Here's a link to how I modified my AME setup.

Pics of modified AME 4 bar

John Parsons


69speed
Registered User
Posts: 11
(5/17/04 7:49 am)
Reply Thanks
--------------------------------------------------------------------------------
Thanks for the input guys, that helps alot. Most everything else for my car has come for DSE so I will be sure and check with them first. I never thought to ask them because they don't advertise the rear kit.

Nutsy
Registered User
Posts: 65
(5/17/04 8:04 am)
Reply Re: Thanks
--------------------------------------------------------------------------------
Let me know if you find anything out from DSE on the 4-link setup. I am VERY interested in it myself.

Thanks,

Trevor

Mean 69
Registered User
Posts: 23
(5/18/04 10:42 am)
Reply Why a parallel setup?
--------------------------------------------------------------------------------
Just a question for you guys, but why the motivation to go with a parallel link setup? By going with a converging setup and positioning things correctly, you can get nice anti's as well as a well defined roll axis. Granted, the parallel setups are available commercially, but there are far better ways to go for cornering applications. Just curious.

JP: Nice fabrication skills, is this a business for you, or just a hobby? Clever bracket for the PHB.

Mark

Nutsy
Registered User
Posts: 66
(5/18/04 12:11 pm)
Reply Re: Why a parallel setup?
--------------------------------------------------------------------------------
'Scuse the nOOb questions, but what is a converging setup? also what are "nice anti's"?

Mean 69
Registered User
Posts: 24
(5/18/04 2:06 pm)
Reply Clarification....
--------------------------------------------------------------------------------
Sorry 'bout that.

Anti's refer to anti-squat, and anti-lift (for a rear suspension). Basically, it is a predictor of how the suspension will react to torque, there is no relevance for a steady state condition (stopped or constant velocity). These figures are very important, and are relatively easy to calculate. For anti-squat, you need to know the "instant center," which is an imaginary point about which the suspension will rotate. This is found by determining the point where the upper and lower control arms intersect when looking at the side view of the car. You just draw imaginary lines to find the point. (The strange thing about a parallel link setup (side view) is that the IC is indeterminate, at least I think it is). Next, you draw a line from the contact patch of the rear tire forward and up to the centerline of the front axle. The point where this line intersects a vertical line needs to be at the same height as the center of gravity of the overall car, David P and I found that about 18 -19" for a typical lowered first gen Camaro is about right. If the IC falls anywhere on this line, you have 100% anti-squat. Above the line is greater than 100%, below is less.

Anti-squat is important to predict how the rear supension will react when you throttle the car. With 100% anti-squat, ALL of the energy that is being fed back into the car will be directed through the suspension links, NOT through the springs. In a perfect world, this would mean that the car would launch without compressing or lifting the rear end of the car. It also means that none of the energy that you want to move the car forward is being wasted in motion through the springs. If you have more than 100% anti-squat, the rear of the car will actually want to lift (or will lift) under acceleration, in this case the tires are actually being driven into the ground and can create additional traction, which is a good thing. Nothing is free though.

If you think about it for a while, you come to the conclusion that you can make the anti-squat larger by making the convergence point of the control arms closer to the rear axle( and higher). The problem you will run into is one of potential brake hop. The "length" of the imaginary arm that defines the IC is called the Side View Swing Arm, or SVSA. Literature suggests that if the SVSA of a rear suspension is too short (i.e. less than 42 inches (Herb Adams), or less than 60" (Millikan)), you are at risk of violent brake hop.

Anti lift is defined by a similar calculation, but takes into account the percentage rear braking bias, and the geometry is a bit different.

Now, if you look at the suspension links from the top (Plan) view, some other interesting geometry possibilities arise. I spoke of the roll axis, which is a really important aspect of the rear suspension if you are going to drive fast safely. The roll axis defines how the rear of the car will steer under suspension roll, yes, it can and will steer the car. If things are setup wrong, you could be visiting the wall of your nearest racetrack very easily. The roll axis is defined by the intersection of the rear and front "lateral restraint" points. For a link setup, the rear lateral restraint point is defined by the Panhard Bar, or Watts link (or by the intersection of the upper control arms in the case of the quadrabind- Chevelle - late model Mustang 4 link setup). Here's where it gets interesting for the front or a parallel link setup. Normally, the forward restraint point is found by determining the intersection of the lower control arms, but if the arms are parallel, then there is no intersection in Plan view. In this special case, the roll axis angle is the same as the lower control arm angle, in side view.

So what's the big deal? Maybe not so obvious, but the prefered roll axis inclination angles down from the back of the car to the front (side view). In this case, the car will have roll understeer, which is alot more comortable for a driver to deal with than roll oversteer. If the axis slopes upward from the rear to the front, roll oversteer will occur. The steeper the roll axis, the more the car will steer in body roll (i.e. in a turn, when you want it to be stable...). Simple! Make the roll axis level to the ground, then roll steer will be minimized!

But!!!!! If you do that, with a parallel link setup, you are forced to keep the lower control arms parallel with the ground. Easy enough. Now think about the desireable anti-squat again. If the lower arms are parallel, and you want to have a decent amount of anti-squat, you will need to lower the forward mounting point of the upper control arms pretty steeply in order to make the geometry work. Again, easy enough. The catch? The good ole SVSA all over again, doing this makes it really short, and the car will be prone to brake hop.

A different approach is to make the lower control arms converge in plan view. This way, you can have a clear definition of the front lateral restraint point, and the rules for the roll axis definition change, possibly for the better. With this approach, it is possible to get 100% anti-squat, a SVSA of over 60", and a downward sloping-roll understeer roll axis. How do I know? Because I laid it out this weekend in preparation for doing this on my car.

That's a mouthfull, I think I babble as much on paper as I do in person! Anyway, I hope that helps a bit.

Mark

Ralph L
Moderator
Posts: 3258
(5/18/04 3:49 pm)
Reply
Re: Clarification....
--------------------------------------------------------------------------------
Mark,

I think the reason all of us are going with or considering going with a parallel 4-bar rear suspension is because that is what Stielow did on the Mule, and us suspension newbies don't really know of any other capable rear suspensions, that are "easily" replicated. The Mule is also "proven" to handle very well, and Mr. Stielow is a very well accredited builder, all of these things lead us towards following in his footsteps.

I know(atleast I've read) there are some good results to be had with triangular 4 bar. Also, a decoupled torque arm setup(I might have messed up the name) like Vince Asaro has on his El Camino looks like it is very good. And people can always fall back on good 'ol fashioned IRS.

I was planning on going with the parallel 4 bar because I felt it would be the easiest suspension setup to get measurments and specs on. I'd love to try something different, but I don't have the ability to design it.

Could you please email me? I'd like to pick your brain a bit if you don't mind. ralphl@pro-touring.com
Ralph
Project Fantom Expected Completion - May 2005
My Tahoe - "Black Mamba"
Rendering of Project Fantom

Edited by: Ralph L at: 5/18/04 3:53 pm

parsonsj
Registered User
Posts: 1614
(5/18/04 5:57 pm)
Reply 4 bars
--------------------------------------------------------------------------------
I went with the 4 bar from AME because it was the best compromise of handling, strength, looks, and ease of installation. Would I use something else today? Maybe so.

Katz Tsubai and I worked to lower the roll center by moving the PHB below the axle centerline. You can see the results in the link above. (I'm only a professional in my dreams).

We are going to do some more work to tweak the geometry a bit once I've gotten accurate measurements at ride height of where everything is. Anti-squat is on the list to measure and possibly improve. I think somebody might make themselves a nice living with an easily packaged torque arm suspension that works in some of these older cars.

jp




awr68
Registered User
Posts: 703
(5/18/04 10:28 pm)
Reply Re: 4 bars
--------------------------------------------------------------------------------
I went with a 4 bar because jp told me to. Seriously though after deciding I wanted a coilover based suspension and seeing some early pics of II Much it was an easy decision what I wanted to use. It might not be the ultimate suspension, but for a street car that sees the track from time to time it will work plenty good, it's quite adjustable and yes it has the cool factor too!!

For pics of my install open the '68' folder.
Anthony
'68 PT Camaro

SteveN 69 69 69
Registered User
Posts: 463
(5/19/04 12:06 am)
Reply
Re: 4 bars
--------------------------------------------------------------------------------
I saw this while looking for rollbars, it looks like a cool itemwww.swracecars.com/street_rod_4bar.asp
Steve N
69 Camaro RS , Hugger Orange , LT1/T56 , Chassisworks NoFab clip
www.pbase.com/steven69/69camaro

Nutsy
Registered User
Posts: 67
(5/19/04 7:18 am)
Reply Re: 4 bars
--------------------------------------------------------------------------------
Mark,

Thanks so much for the explaination. Can you tell me if there is a book out there that explains all these things with some pictures as well? I need to see what you are talking about in order to fully understand it.

Trevor

katz
Unregistered User
(5/19/04 12:30 pm)
Reply my two pennies
--------------------------------------------------------------------------------
I agree with Ralph as far as why many people wanting to use 4-bar setup. I too respect Mr. Stielow. His white '69 and Red Witch got me interested in pursuing my career. I don't agree with everything he does, but just like I can't design what I really want at AME, I'm sure he has reasons.

What Mark (Mean 69) is saying is true. From engineering design stand point, there are many susp. configurations that are superior to 4-bar and some can be made to fit under stock sheetmetal. My '65 Riviera came from factory with 3-link & PHB at axle height and still has enough room to seat two grown-ups in the back seats. It may be tough to do with 108" WB (Riv is 117"), but O1mrquick is currently working on fitting a 3-link in F-body.

That said, unless you're super-serious about competition and winning at tracks is your primary concern, 4-bar can be made to work to satisfy majority of PT people.

Setting up and finding proper spring/anti-roll bar rate goes a long way. It's just more difficult to get it right due to some roll bind, and you'll have to give up some of the good stuff (anti-squat, mostly). We proved that with a shoebox with very mild IFS (172" FVSA, 12-deg KPI) and Triangulated 4-bar. It sure isn't the fastest car through corners, but we got it to go through cones faster than a stock LT1 Corvette. It had less than desirable anti-squat, but it ran 12.6 @ 116mph, which isn't too bad for any street car rolling on low-profile street radials. And it still has pretty good ride quality due to relatively soft springs (Ride frequencey 103 Hz front and 88 Hz rear) and the design of IFS (good SVIC location and small scrub). There are many ways to improve it a lot, but I'd be happy to have a daily driver that runs mid 12s and hangs on corners better than a stock '88-'96 C4.

I'm neither recommending or discouraging the use of 4-bar. If you're just getting started on your project, there are alternatives so keep your eyes and mind open. Not everything you see in AME catalog is what I consider as good setup. I'd say same goes for what you see in magazines, even if Mr. Stielow did it. There are always compromises people have to live with. Read what Mean 69 said carefully, and understand what you'll be giving up. 4-bar, IMO, is still a viable option if packaging is your big concern (backseats and stock trunk).

If you already have 4-bar in your car, don't get discouraged. It won't be the ultimate setup, but it can be made to work well. Mule proved it (I honestly don't have a doubt, but I'd like to see lap time or something). II Much will do the same.



Nutsy
Registered User
Posts: 70
(5/19/04 12:39 pm)
Reply Re: my two pennies
--------------------------------------------------------------------------------
I wish there was a place to go that would give a really good graphical description of all available options, give the pro's and cons of each so that i can make my mind up. Thoughts?

katz
Unregistered User
(5/19/04 1:04 pm)
Reply re
--------------------------------------------------------------------------------
Milliken's "Race Car Dynamics" book has all graphical explanations, but it's rather expensive and it's hard to justify the cost unless you're looking for lots of engineering equations and formulas.

Fred Puhn's "How to make your car handle" has similar graphics in it. Haven't read it personally so I don't know how good the rest of content is. But the price is about what you pay for a large pizza.

Mean 69
Registered User
Posts: 25
(5/19/04 2:38 pm)
Reply Reference Materials
--------------------------------------------------------------------------------
Concerning the literature, I'd start with Herb Adam's Chassis Engineering, I bought my copy off of the shelf at the local Barnes and Noble, a very easy read and does a very nice job at describing a fair amount of what is happening. I highly recommend it.

Carroll Smith had a number of books out that go a bit deeper into detail, and he has a pretty fun writing style to boot. Tune to win is a good one, but his emphasis is on real race cars, as in open wheels, so there is limited practical application to our dual duty cars. Still, a ton of good stuff.

Alan Staniforth (sp?) has another good book that I really like. He is a brit, and has a wonderful writing style, and comes at things in a bit of a different angle, gives you a new way to look at what is going on and helps to firm up the concepts. There is a section on lateral weight transfer in his book that I think is brilliant.

The bible is Milliken's Race Car Vehicle Dynamics. You can get this book through the SAE website, poke around on google for a link. It is a textbook written style, and a bit harder to read. I would consider it to be an upper level undergraduate/graduate level reference. I keep this book on my nightstand and read it in the middle of the night when I wake up thinking about what I want to do next to the car!!!!

Basically, if you are really interested in this stuff, read everything you can get your hands on, there is alot of it out there and you can learn a ton. Of course, when I learn something new, I quickly realize how much more I have to learn.

Katz: Are you sure about those frequencies? Are you talking about something to do with the springs themselves, or the natural oscillation of the front/rear of the sprung mass?

Lastly, I don't disagree with Katz or the others at all, the four bar systems can obviously be made to work great despite their theoretical shortcomings. My emphasis is towards going fast as stink, on the race track, as "safe" as possible. I am by no means a race driver (but learning....), and with the performance potential of the cars we build, the last thing I want is a surprise, at speed, that I can't overcome. I'd rather have the limit of performance on the race track be me, rather than my car.

Mark

katz
Unregistered User
(5/19/04 3:19 pm)
Reply re
--------------------------------------------------------------------------------
Oops, my mistake I mixed up cpm (cycles per minute) and Hz (cycles per second). Sorry! I guess "relatively soft" may be misleading too. Those frequency figures are about the same as factory late-model sports cars. Spring rate is 575 on 0.69 ratio front, and 250 rear.

I agree about Herb Adams' book. That's the first book I read too. It's probably the best book for beginners. I didn't think it has detailed diagrams of 3-link, etc. like Milliken's and Puhn's, but it's been a while since I read it so I could be wrong.

Also agree about differences between pure racecars and dual-purpose cars. I think majority of PT people's emphasis is on the latter.

Nutsy
Registered User
Posts: 71
(5/19/04 3:53 pm)
Reply Re: re
--------------------------------------------------------------------------------
Thanks to all for the great information. I am going book shopping this weekend!

Trevor

68Protouring454
Registered User
Posts: 178
(5/20/04 4:38 am)
Reply Re: re
--------------------------------------------------------------------------------
katz, thanks for all your helpfull posts, its great reading post from guys like and and mean 69.
i was wondering how the s&w 4 bar crossmember looked for use in a pro touring 68 camaro?? is the 2x3 crossmember enough on a street driven car?? if it does look good, what would you use for coil overs and panhard bar on a 68 camaro, thanks for all the help you always provide
jake

Mean 69
Registered User
Posts: 26
(5/20/04 11:26 am)
Reply Wheel Rates
--------------------------------------------------------------------------------
Katz: Makes sense, and I agree, it seems like it is a bit rigid, especially up front. Still, a good solid built car can tolerate a firm suspension, but when you get the rattles and the like, yikes! Wheel rate in the front is over 300 lb-in, so that is pretty tightly sprung, but not outrageous by any stretch. This is in line with what most of the real performance oriented late model Mustangs are running, with the very poor camber characteristics they possess in Mac-Strut form, they really need to resist roll.

I would love to drive that car on the track, how cool would it be to run Willow Springs in a 55 shoebox!!! With the A/C on of course, it's a little toasty out there in the summer...

Mark

katz
Unregistered User
(5/20/04 6:12 pm)
Reply re
--------------------------------------------------------------------------------
Jake,
Thanks for the kind words. But the truth is I only chime in when I feel like it (and when I have time to surf the net). I used to be more active, but I don't feel like sharing info more than necessary anymore. That's what gives AME the edge in street rod industry, and you never know who's reading this forum (I'm not talking about DSE, GW, Hotchkis, etc - I know they know what they are doing). Besides, there are many other individuals who have wealth of knowledge, like Mean 69 and David Pozzi, so I'll let them do the typing

Anyway, I've never seen S&W 4-bar setup. Any link to pics? Generally, 2x3 crossmember (I assume 0.120 wall) would be sufficient, but I guess it depends on the design of 4-bar. Make sure you tie it to the front subframe with connectors. You'll have to fab PHB yourself. The most stuff you see on the market aren't really suitable for handling use. Try to duplicate the PHB used on DSE-built Firebird, HTH's kit, or JP's II Much. Coil over choice is up to you. If money's no object, I'd pick Koni or Bilstein. Penske coil overs are awesome, but probably way too overkill for a streetcar.

Mark,
Yeah, it'd be a kick to go around road courses in a '55 Chev, wouldn't it?

Unfortunately, it wouldn't happen with our car. The car is no longer what it used to be. It now wears show-quality paint job, and is stuffed with huge speakers, leather interior and all unecessary stuff (to me anyway). It'll weigh at least 400 lb more when it gets back on the road. It's a show car now.

If it was my own car, I'd have left it as a beater and drive the hell out of it on tracks and whatnot. Oh well. A couple of guys and I are trying to talk Art into building another one - a car that he can drive hard without worrying about little dings and scratches.

I don't think Art will ever take the '55 to any kind of racing event, but stop by at our shop if you have a chance to come to Seattle area. He'll be happy to take you for a ride in the car. He was planning to do Power Tour this year, but looks like it's not gonna happen.

ryans67deuce
Registered User
Posts: 8
(5/20/04 8:48 pm)
Reply Here's the link
--------------------------------------------------------------------------------
Katz,

Here's the link to the S&W 4-bar:

www.swracecars.com/street_rod_4bar.asp

I'm curious of your answer too.

JP - any chance you can post a pic of your PHB & rear sway bar for us??

Ryan

parsonsj
Registered User
Posts: 1615
(5/20/04 10:03 pm)
Reply Pics of PHB and rear sway bar
--------------------------------------------------------------------------------
Ryan,

Just click on my sig and go to the rear suspension section on my website. I've got a couple pics up (pretty big too) that are decent.

jp


68Protouring454
Registered User
Posts: 180
(5/21/04 4:26 am)
Reply Re: Pics of PHB and rear sway bar
--------------------------------------------------------------------------------
thanks katz, ryan posted the link, as well as steve on the 1st page. again thanks for the all suspension help from you guys, mean69,katz, jp,david, sorry if i missed anyone , i love reading about suspension, cause i have no idea!!!! lol
jake

katz
Unregistered User
(5/24/04 4:42 pm)
Reply re
--------------------------------------------------------------------------------
Bars look kinda short, but other than that, it looks like a typical 4-bar setup. Also check the diameter of those bars with them. 1" OD x 0.156" wall DOM is typical (and bare minimum). Long bars need to have bigger OD. If they give you a choice, get the longest bars you can. You can always shorten them if packaging doesn't allow long bars. If it's 1" x 0.156" with 5/8 x 3/4 rod ends, you can just cut the bars and re-tap the threads.

Mean 69
Registered User
Posts: 31
(5/26/04 11:35 am)
Reply Tube source?
--------------------------------------------------------------------------------
Katz, where do you guys get your DOM tubing? I am looking for some 1" and 1.25" OD, 0.125" wall tubing, none of the local places carry it. I can get the thinner wall stuff, but not this thickness.

Mark

katz
Unregistered User
(5/26/04 1:33 pm)
Reply re
--------------------------------------------------------------------------------
Mark,
We get all of our steel tubes from EMJ (Earl M. Jorgensen). I'm not sure if they deal with retail customers.

www.emjmetal.com


When I need something AME doesn't have in stock, I get stuff from these guys.

www.onlinemetals.com

They don't have DOMs, but they have Delrin, 2011-T3 hex aluminum (for anti-roll bar end links, etc), bearing bronze, and other usuful stuff. And it's local to me, so I get my stuff fast.


Here are links to a couple of other places that I'd try when need arises.

www.metalexpress.net
- They have thick-wall DOMs like 0.188 and 0.250.

www.aedmotorsport.com
- Never dealt with these guys yet, but they have all sorts of materials for race car construction, including 4130 streamline tubing and some Ti round bars and sheets. They have some thick-wall DOMs.


Also, Chassis Shop sells random assortment 10lb box of 4130 tubes for $25. Comes in handy for fabbing small stuff.

www.chassisshop.com


If you know of other good sources, please let me know.

P.S. Have you had a chance to watch the video clips I posted a couple of days ago? The thread title is 'Slalom video clips' and is in open discussion forum (probably somewhere in page 2 or 3). Many people here don't seem to show much interest unless it's about 1st gen Camaros

Mean 69
Registered User
Posts: 32
(5/26/04 4:38 pm)
Reply Thanks!
--------------------------------------------------------------------------------
Thanks for the links, I will poke around in there and see what I come up with.

I just watched the Tuna boat, it is still just too darned cool to think about that car actually handling well. Nice shots, thanks for the heads-up.

Mark