Do I need trailing arms on my custom IRS chassis?

[dave96dcm]

I'm under the understanding that any "arm" that is parallel to the axle and connects the spindle to the frame above the axle centerline is a upper control arm, if it is below the axle centerline it's a lower control arm, if it is in front of or behind the axle centerline and is for controlling toe it is a tie rod "or toe link". If it is perpendicular to the axle centerline it is a trailing arm or "swing arm". That could also be upper or lower. Shape/size/number of attachment points don't matter, that's what it would be called. Or at least from my experience.

[214Chevy]

Originally Posted by dave96dcm

I'm under the understanding that any "arm" that is parallel to the axle and connects the spindle to the frame above the axle centerline is a upper control arm, if it is below the axle centerline it's a lower control arm, if it is in front of or behind the axle centerline and is for controlling toe it is a tie rod "or toe link". If it is perpendicular to the axle centerline it is a trailing arm or "swing arm". That could also be upper or lower. Shape/size/number of attachment points don't matter, that's what it would be called. Or at least from my experience.

Sounds good to me Dave. Hey, no arguing from me. What you've just stated to me sounds very true and educational. All I know is my IRS will not have trailing arms. Now, I did speak to my builder yesterday and he said that they changed some things up. I doubt he may have added trailing arms in that change, but we'll see. From when I say the initial setup back in February, it didn't and wasn't getting any control arms.

[onevoice]

[QUOTE=garickman;420665]

Originally Posted by preston

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. /QUOTE]


If everyone went with what is known to be the best setup, then nothing better would ever come along

There's a big difference between improving a known good setup, and just going off on an unknown trail for the experience.

Originally Posted by garickman

I have no idea how this set up will perform, but if it fails, I will look at it as a learning experience rather than a failure.

You have to keep in mind that a suspension failure can be more than a learning experience, it can be a death experience. Make it safe and experiment all you want.

[onevoice]

Originally Posted by dave96dcm

Some food for thought.

This is an almost exact copy of the suspension that was used on many, many IRS race cars in the late 60's to the early 80's. There is nothing wrong with it at all, very tunable, and was mostly superseded by inboard suspensions for aerodynamic reasons. Dive and squat adjust by moving the trailing link forward attachments, toe is adjusted at the lower arm outer rear attachment, camber at the upper link. Camber curves are easily adjusted, but it lacks an easy way to change toe through suspension travel, something that many designers would like.

The weak point about the OP design can be seen easily in this illustration, as the OP design is essentially the same thing but with a lower arm that is restrained from fore and aft movement by two inner mounting points. Imagine this suspension with no trailing arms and a lower H shaped or box arm. The only restraint of the torque of the spindle is by the twisting of that lower arm, something that is not desirable, and is accounted for in the various OEM designs in this thread by having a very stout and wide based lower arm. The easier, stronger and lighter way is to spread the load between a lower and upper arm, ie like a vette or viper, or a modern racecar, or the trailing arms seen in this design.

[onevoice]

Originally Posted by ProTouring442

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

The new vette and viper parts are

Originally Posted by ProTouring442

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

The half shaft as the upper link isn't the problem I was concerned about, I was more looking at how the upright controls torque inputs, and for that, the vette used upper and lower trailing links. The C3 used a trailing arm.

Originally Posted by ProTouring442

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 only pictures of current performance Jaguars I can find (which incidentally are 500+ HP) use upper and lower A-arms, with a toe link, as is the current state of the art. There is nothing wrong with an old design, as long as you keep in mind its limitations, and incorporate fixes in the new usage.

[ProTouring442]

Originally Posted by onevoice

There is nothing wrong with an old design, as long as you keep in mind its limitations, and incorporate fixes in the new usage.

No argument there!

Shiny Side Up!
Bill