Do I need trailing arms on my custom IRS chassis?
 

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Greg, now I'm no expert, but I would assume not. It's an IRS. Why did they say it needed trailing arms? New cars, Vette's, Vipers, etc with IRS don't have trailing arms and my frame won't have any either. Don't think the Roadster Shop IRS chassis's uses one either.

That IRS looks good!

trailing arms?
 

I'm seeing it needs more direct attachment to the frame (the center section). Right now, it looks as if it is "hanging" only from the frame. You have to imagine all of the twisting force that a rear sees, live axle or independent. To me, I think you need a whole other "cradle" that the rear kind of sits in as well as the upper attachment you currently have. Maybe you have plans for that, but not shown yet.

Also, most independent style rears would have a toe link too. Unless you are going for something like the Heidts system. Notice the "trailing arms" on theirs and the cradle under the center section.
http://www.heidts.com/_uploaded_file..._irs_front.jpg

Also, how do you adjust for caster?
Fab work looks great.

Correct...mine will have that.


Greg, 65 LS1 T56 is correct about the toe link. Toe link bars are what will attach to the steering arm portion of your spindles. Which would be the equivalent of what the rack and pinion attached to on your front spindles. I've included a pic of an RS chassis with the toe link bar circled. Toe links or bars help with your cast when aligning the rear wheels and dealing with cast and camber.

Toe link is a bar that runs from the stationary section of the frame. Its to adjust rear toe on IRS, but since this is a Jag style LCA set up it should not be necessary.
The LCA appears to be attached to the steering arm mount on the ATS spindle. If the LCA was designed with a lower ball joint then you would need a toe link to keep the spindle from rotating.
The builder is the best person to ask. He's knows what he is doing. :thumbsup:

thanks 509...I type slow. LOL

On the trailing arm comment as related to the rear section (I assume he means differential). you should be fine, the diff mounting looks beefy enough as full rotational torque forces are not transfered through the half shafts.

yeah, I meant differential (the whole center that is fixed to the chassis). Greg mentioned another attachment that is not shown yet, I'd like to see that before changing my mind. You'll notice the lower differential to frame mounting on the Heidts as well.
The toe links are not required in this setup after I thought about it since it does not use a lower balljoint, so that additional degree of freedom is removed already.
Not sure how adjusting the upper single link would affect caster though, camber yes. The lower control arm mounting points on the knuckle would have to change too, right? Maybe it will just be set and fixed at a number?

Love the rocker arms though, that is very cool. Hopefully you put a "viewing window" in the floor pan to see it :unibrow:

Yes it will or should be set to a fixed number. Have fun adjusting. Do they even have a test set up to do rear caster swing?

I just looked, no caster specs on an IRS vehicles I can see. Its not applicable since its necassary when steering.

http://www.twf8.ws/new/tech/tip/setup/caster.jpg see if this helps you Greg.

If I'm not mistaken this chassis was in the Dominator booth ar Del Mar? I'm not an IRS expert, but Leonard is. If he says you don't need them...you don't.

Are those spindles just for mock up or is that the final product?

Heard that. It's good to become educated...to get beyond blind faith, no matter who you're dealing with. I'm sure a conversation with Leonard will reveal why he thinks the trailing arms are un necessary.
Looks to be a great project!

There are two questions to ask:

Is this a fully constrained system?
Is the setup strong enough?

The system is fully constrained as is. Some IRS setups use a ball joint top and bottom this allows for more adjsutments in the future. Toe, caster, camber. If you adjust the LCA to move forward then you will have more positive caster.

Without know material thickness and properties its hard to say if this is strong enough. I think that lower plate welded to a tube and bolted to the spindle needs some gussets. Also what car is that spindle from. That load path looks suspicious, is that the best place to attach the spindle?

My concern was the current way the spindle is now being used is not how it was designed to be used by the spindle manufacturer. The spindle on the Heidts rear end is doing the same as what you have here. But the spindle design from Heidt's is much different then how this spindle from another application is being used. That lower mount on the spindle looks like it would put a lot of undue stress on the hub bolting area of the spindle. My guess is you would have been better off to just have used an upper and lower ball joint on the spindle like the spindle was designed and built for.

My other thought is that you should have more faith in your builder. If your willing to take some analysis opinion of your project from someone on the internet. The comment on "Toe Links" to me is someone who has no idea. They are called tie rod ends. They are used on a car with Balljoints like a vette or modern IRS. This rear suspension is similar to a jaguar, kugal, or heidt's. That is why I was asking about whether spindle was a final piece or just used for mock up to design or set up for a final product. I under stand this project is still under construction and lot sof this may change before whoever is in charge says it's complete. I'm guessing but this chassis must be going under something else besides your cop car, because you seem to be putting a lot of effort into a custom chassis for this project when lots of people make great parts to bolt on a chevelle that would accomplish the same thing for much less effort and money.

Thanks for the respect but I'm just a guy that uses common sense and smart friends to build what we can. I'm not trying to ruffle any feathers, You asked so I'm just sayin. Hopefully your builder has everything dialed.

I'm assuming Ironworks was referencing me as "some guy on the internet" even though we all are just that...my post was:
He is also correct, it is called a toe link, not a "Tie Rod" in the rear.
a simple diagram of an independent rear, though different in design than the Jag style.
http://www.sandsmuseum.com/cars/elis...suspension.jpg

I do agree that Greg should just trust his chassis builder as well. The work looks great.

So thats it from someone on the internet who has no idea.

I've heard of them called "toe links" for years. And so do some of these other people too.

http://shop.britishracinggroup.com/G...H111GTRTLK.htm

http://nitronracing.wordpress.com/su...-toe-link-kit/

http://www.dinancars.com/shop/R280-0...Toe-Links.aspx

And last, but not least for the Corvette guys.......

http://www.google.com/imgres?imgurl=...ch&um=1&itbs=1

Exactly, You might be the lead chassis designer for Chip Ganassi racing for all I know, No one has any ideas who is who, REALLY. All we have is screen name and a cool little picture. There are tons of guys who have been here for a while that we all find out are snakes in the grass years later. But my point is when you open up your project for the masses opinions, Your getting exactly what you asked for. The same idiots we share the road with, the same idiots who voted opposite as you, same people who do ugly things to certain cars that we like. There are tons of internet no it all's that have no idea about anything and once in a great while there might be a smart guy who gives you his opinion and all the know it all ponce on him. I did not mean any body in particular with my comment.

I really think these posts are a waste of time in the fact you cannot tell much from 3 pictures. And even if you could what is that going to prove when you go tell the guy doing the work what someone on the internet said. Pictures maybe worth a 1000 words but they give you no idea what is really going on during construction of a project, you have no idea what is what without really talking to the mastermind behind the project. Just like the saying goes you can't judge a book by it's cover, you also can't judge a project until it's complete.

I have never in my entire life heard the term toe links, So I guess I learned something new today. I wish you well on your project as I have heard you have had a rough go, but all I can say is you have to be on top of things or the same thing can happen again, don't trust anybodies work. Ask questions to be educated by the guy doing the work and keep asking until it all makes sense, if it does not make sense go ask some one smart who is willing to get involved. In a project car you connected to a guy for a long time with the quality of work they do. If you unknowingly pay for junk it will be with you until you cut it out and it will never be what it could have been. Picking a builder is like picking your wife, you better know exactly what your getting into. Because your going to be stuck for a long time with the person.

System will work, and as a DD, I would suspect you'd be fine after the diff is braced. My only concern on the functionality of the system is the rocker arm system. I can't really tell you if the loading will be a problem for the spindle without a ton more info and some expensive software. But the short link from spindle to rocker arm is likely to do funny things with your spring rates. If this was considered by your builder, or if you are working in a narrow travel range, then don't worry. Again, probably fine for a DD. If it's meant for racing or running an absolute ton of torque through, then things are probably going to break regardless of how much planning the builder did or what IRS system you go with. It is a pretty sweet looking setup though and kudos to you and the builder.

Toe link - because it controls toe in (or out)



If you want to see what happens when the spindle - carrier - axle yoke is not well designed -- look at this thread.


https://lateral-g.net/forums/show...28681&page=133



FYI -- 1800# '32 Fiberglass roadster - 450hp 383 stroker (mild) - 5 speed... 10' burn out - 3rd time (10'r) this happened -- and this is the SECOND SET of these... Now THIRD set is beefier as shown here.

I know at least one (or two) that will laugh at this, but these are words of wisdom in my book Roger. Your direct style is appreciated by many, even when it goes against the 'conventional' grain :thumbsup:

If your going to ask me a question I'm going to answer it. Don't ask a question you can't handle the answer to.

When you ask for free advice, you get what you pay for. And on the internet, lots of guys who have done nothing more then watch Nascar will tell you all day long how it really is.

Most people are only going to say nice things because that is what we are taught to do. The other 90% of people really have no idea what they are looking at. Except the nice welds and the parts are super cool.

I will agree this suspension does not need "toe links" as set up, but I really think the spindle as used in this design will be a weak link with the lower plate bolted to the spindle. I also think the cantilever arm could upon droop of the suspension go over center and and lock up the suspension when it is allowed to travel over center of the link. I also think that the positioning of the push rod on the spindle will limit your rear tire width unless your running like a 24" rear wheel. If that push rod link was connected to the lower control arm it would allow you to have a much longer link and allow you to run a much wider rear wheel. Plus the link would not be as apt to go over center on droop. I hope I'm totally wrong and look like an idiot when it is all done, but that is my opinion.

I'm done

The top link needs to be triangulated (like a vette) or an upper trailing link has the same effect. Something needs to take the brake reaction forces at the top of the spindle. Picture trying to rotate the spindle looking at it from the side, the lower link will resist all the force by twisting. It can't handle it.

Do what you want, but a viper and corvette both have upper links that provide fore and aft locating of the spindle (both use A arms). All IRS's I have ever seen have either triangulated control arms (a arms), trailing links, or trailing arms, or a combination thereof. Nobody makes an IRS rear with a single, unbraced upper link

I would take their engineering over a street rod builder.

I disagree that it will take load off the spindle. It has changed the loads, yes, but not taken them off. The lateral and fore aft loads are still applied through the spindle but now a moment has been added about the attachment points with now a shorter moment arm. In addition, the "vertical" load from the shock / spring has now been moved from the lower ball joint to the upper ball joint. However, the ATS spindles are 6061-T6 and OE Vette spindles are A356-T6. So you are gaining some strength and elongation there which is a big plus. Whether or not you'll have an issue depends on so many other things like vehicle weight and distribution, tire diameter, and on and on, that really no one can tell you for sure if this is an issue within pro-touring operating use.

Good to hear the push rod angles are being optimized. It was very hard to tell from the pics whether or not it could be an issue, but it looked like there was a good chance that at least you'd see undesired variation in spring rates.

I think the OP was mainly concerned with function, and not whether or not this was the optimum IRS style. It will work without toe links. Yes, most other IRS's have a toe link, but there are not many "swing arm" style IRS's out there, but there are some good ones. Check out the previous BMW X5 rear suspension for instance. Quite different from the OP's suspension and does have two upper links, but not really a toe link. Nor are the upper links all that effective at completely limiting roll / twist as they have rubber bushings.

Lots and lots of things that may or may not achieve ones goals.

Good luck to the OP and his builder! :thumbsup:

Not sure what you are getting at here. I wasn't talking about toe links. I said all IRS suspensions control the fore and aft movement of the upper part of the spindle from the top , think constraint of caster. All IRS suspensions also control the toe, whether with a toe link(like a vette or viper), or the physical layout of the locating arms like this design.

From the side view, the spindle as designed only resists rotation from the lower control arm. This is no way to design a performance suspension, unless the lower arm is super strong, because the forces will constantly be twisting the lower arm.

This design would be much better by spreading the upper link inner attaching point into two pieces, making it an A-arm. Same effect by using an upper trailing link.

Also, I'm not a big fan of modifying such a critical part as a spindle to use the steering arm location mounts as lower suspension mounts. Without obvious overkill design, it is foolish to do so without engineering analysis by someone familiar with the design and strengths of the original part.

This is what I was getting at. I agree it could be better designed for performance applications. That just didn't seem to be the intent of the original question.

http://www.pro-touring.com/attachmen...5&d=1334002712

http://www.heidts.com/_uploaded_file..._irs_front.jpg

http://i919.photobucket.com/albums/a...d/DSC00521.jpg

I prefer a short arm long arm configuation myself.:cheers:

Both of those setups have inboard brakes

Big difference in the spindle loads.

The lower is similar to a jag setup, and doesn't even have an upper link, it uses the axle as the upper link. A design from the 1960's, that wasn't known for great handling even back then, isn't something I would emulate for a modern scratch built performance vehicle.

I don't know who designed the other one, but it is not a modern, robust design. Fairgrounds street rod it is fine, otherwise, get something that incorporates the best design practices. Those IRS designs are the equivalent of updating a 30's solid front axle with an independent 50's design that uses kingpins. Or comparing a DSE front subframe to a street rod mustang II setup.

A bad IRS is worse than a good design solid axle.

Edit: I just saw the linked picture, and I stand corrected, that is obviously a recent rear axle. Explorer maybe? It is however very different from the OP design. The linked pictures show a lower control arm that is VERY wide to take the loads involved. The inner mounts of that arm are about twice the diameter of the brake disc, probably 18-20" apart. The lower arm attachment to the spindle is also spread apart what looks like a brake disc width, call it 10 inches, and the attachment of the arm to the spindle is very close to the axle center-line, minimizing the moment. In short, that arm is designed to take the loads I was saying the OP design isn't. Certainly not the same case as using a modified front spindle with the steering arm mounts as the lower arm attachments.

well you said it....
lol :thumbsup:

Another view of a single, untriangulated upper arm, IRS design, showing the massive lower control arm necessary. Notice the wide design, the reinforcements, and how the axle centerline is close to the outer spindle attaching points. All missing from the OP design.

All to handle the massive power of a t-bird. :rofl:

Chroming it or using rod ends is just putting lipstick on a pig

A ground up design should be based on the best handling performance vehicles around, not a design for a relatively low power car in which comfortable ride was probably at the top of the wish list.

Of course, Jag moved the brakes outboard later...

http://img171.imageshack.us/img171/6...quokjeerzu.jpg

Shiny Side Up!
Bill

Wow those setups with a wide frame lower arm and trailing links look like bind city.

So many of these different IRS setups seem so hokey. I agree with the other poster who said, in essence, why wouldn't someone just go with what's known to be the best setup ? Upper, lower a-arms using ball joints and a toe link (can also be done with a lower arm in a non-ball joint arrangement that uses the 2nd link as kind of a toe link, you see this on some race cars. I don't like it as much as you can't tune the toe curve).

I see a lot of things I'm not fond of in the OP photos, but putting that upper pushrod link (ie all of the shock load) on top of the spindles UBJ is incredibly dangerous. No way is the spindle supposed to see that type of load. That pushrod needs to be brought down to the LCA. IN addition to Ironworks concerns about length and binding etc. It should be easy enough to do, just have to get it around the axle but there is articulation room there.

And it was still a piece of crap :rolleyes:

The point is that EVERY IRS doesn't handle better than EVERY solid axle. It doesn't make sense to take production car designs and translate them into a performance vehicle without knowing the REASONS for the original design. Many current IRS designs in production cars are done for ride considerations, or low floorpans, or other packaging reasons. With the exception of the the Viper and Corvette, and a few others, they are not designed around anywhere close to the HP we are talking about either. Does anyone actually think a Jag design from the 60's, or an Explorer, or a T-bird are suspension designs to be emulated for a 500+hp trackable car?

A spinning chrome Jag rear looked cool in the back of a t-bucket 40 years ago, but thats not what we are building is it? :thumbsup:

Then again, most of the parts we are using were not designed for the HP, torque, cornering ability, etc that we put them through.

Corvette utilized the half-shafts as the upper link through the C-4

Jag used the same basic suspension through to the new millennium.

We upgrade leaf sprung cars (hell, that dates back to the model T), trailing arm/solid axle (on GM cars from 1958), truck arms (yeah, they were meant for the HP we use), etc. So to say that one of these rears is, by the nature of its original use, somehow automatically unsound is... well... unsound.

The Jag unit is essentially a Dana 44 (that coveted rear also used in the C-4 'Vette), and the basic design is sound. With a little careful ingenuity on the part of the builder, and with a mind toward things like Roll Axis, it can be a very good unit. Will it be the absolute best in handling when set next to an all out 3-link? Probably not, but I bet it will give a better ride.

All suspension systems are a compromise. The question is, what compromises are you willing to make. In some cases, ride is the compromise, in others, all out cornering will be. Pick your poison.

For the OP, I suggest checking out the IRS forum: http://irsforum.boardhost.com/viewforum.php?id=1

Add to that a lot of research.

For me, I plan on going Jaguar IRS with trailing links that pivot on the same axis as the lower Dogbones.

Anyone want to buy a nice Currie-Ford 9" set up for a '69-'72 GM A-body?

Shiny Side Up!
Bill

http://www.lmp-engineering.de/cms/up...Suspension.jpg

Some food for thought.

lower inner is single mount, huge difference.

I like that sway bar set up though.

I agree with Vince. According to the above pic, you do need trailing arms. But, that's only because it's a single mount attachment with the lower control arm and it has no upper control arm or attachment point. With Greg's setup, he has both, upper and lower control arms. As with mine, I have no trailing arms because I have both, upper and lower control arms. The same as a C5/C6 Corvette. Obviously there's more than one way to skin a cat.

There is a upper arm in the pic look again.

Dave, that looks more like a tie rod for adjustment of camber to me. I would assume that single rod isn't a control arm. But, hey...what do I know.