Do I need trailing arms on my custom IRS chassis?

[ProTouring442]

Originally Posted by onevoice

And it was still a piece of crap

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?

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

[dave96dcm]

Some food for thought.

[Vince@Meanstreets]

lower inner is single mount, huge difference.

I like that sway bar set up though.

[214Chevy]

Originally Posted by dave96dcm

Some food for thought.

Originally Posted by Vince@MSperfab

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.

[dave96dcm]

There is a upper arm in the pic look again.

[214Chevy]

Originally Posted by dave96dcm

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.

[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.

[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