Do I need trailing arms on my custom IRS chassis?

[onevoice]

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.

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.

[ProTouring442]

Originally Posted by onevoice

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.

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



Shiny Side Up!
Bill

[preston]

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.

[onevoice]

Originally Posted by ProTouring442

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



Shiny Side Up!
Bill

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?

[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.