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.:thumbsup: 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.

[QUOTE=garickman;420665]There's a big difference between improving a known good setup, and just going off on an unknown trail for the experience.

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.:thumbsup:

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IRS race cars in the late 60's to the early 80's. There is nothing wrong with it at all, very tunable, and was mostly superseded by inboard suspensions for aerodynamic reasons.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.

The new vette and viper parts are :thumbsup:

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.

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.

No argument there!

Shiny Side Up!
Bill