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.