Billy Shope;GM F body torque arm?

[V Remian]

Billy, could you tell me if the torque arms that go from the rear end to the trans on F bodies do anything other than control "wind up"(or wind down under braking) ?
Can they also influence squat or rise?

[Ed-vancedEngines]

I am not Mr. Billy, but I can tell you that it does.

Torque Arm suspension modifications are a different sort of animal and are different form of suspension technology but still using the same laws of physics.

They still utilize what we call an Instant Center, but moving it and adjusting it is different. Also ways to control rotation around rear axle is different.

Let me see what Mr. Billy has to offer before I run my mouth anymore. Despite he and I not agreeing on many things, he is very intelligent and knowledgable. This I know.

Ed

[BillyShope]

Thanks, Ed.

Page 27 of my blog

http://home.earthlink.net/~whshope

has a spreadsheet for determining the IC location for a torque arm. Pages 4, 11, and 28 help in making sense out of the results.

[1989TransAm]

Timely subject for me. I'm getting ready to play with the torque arm on my 1989 f-body. Any one with a rule of thumb or practical experience of what works best. Car is 90% a street car. Was thinking of shortening the stock length maybe a couple of inches. I believe the stock length is 42 inches. Thanks ahead of time

[af2]

Timely subject for me. I'm getting ready to play with the torque arm on my 1989 f-body. Any one with a rule of thumb or practical experience of what works best. Car is 90% a street car. Was thinking of shortening the stock length maybe a couple of inches. I believe the stock length is 42 inches. Thanks ahead of time

That link above you is pretty direct!
Read the thing and you will be amazed!

[Ed-vancedEngines]

There are many companies making aftermarket Torque Arms for your car. Many of those are no different suspension wise except are made to be stronger.

I like the ones made by Steve Spohn and Spohn Engineering and those made by Brian at Madman Racecars or Thunder Racecars in Louisiana best. The one made by Wolfe Racecars is similar to that one of Spohn Engineering but for much more miney.

S&W Racecars Torque Arm for your car is 12 inches shorter than the fatory one is. All of the good ones are shorter than the fctory ones are. BMR has one that doesn't look bad too. The Global West ones are in my opinion junk.

If you do buy an aftermarket Torque Arm do not buy one that is a replacemnet for the factory one. You do not want the Torque Arm appliying torque the the transmission like the factory does.

Most everyone that sells Torque Arms also sells adjustable bottom control bars and also pieces yoou can use to modify the rear of those bars mounting positions.

Steve Spohn races a Gen 3 car himslef. Brian at Madman or Thunder Racing builds and tunes his bars to his customer's cars.

Ed

[1989TransAm]

Thanks Ed. I knew of some of the torque arms you listed but was not aware of some of the others. I will look into them.

I slowly read the link above. It is one of those things I will have to read through 3 or 4 times for all of it to fully sink in. Thanks for the responses.

[Mike Peters]

Am I missing something here? I don't own a car with a torque arm suspension but, correct me if I'm wrong. Doesn't the rear mount of the torque arm on the housing attach above and below the axle centerline? If so, doesn't that mean the I/C is dictated by the location of the front mount of the torque arm and the lower outside trailing arms have nothing to do with the I/C location? The forces of the housing rotation are directed through the torque arm like a ladder bar, correct? .

[Ed-vancedEngines]

You are correct. Almost. Eaqrlier I said the Torque Arm Suspensions are using the same laws of physics but we apply them different, or something like that.

The torque arm is applying all force originating from a central or center part of the rear axle housing. The outside of the housing is where the tire friction resistance is and it is the outer parts of the housing that will react to that force by pushing forward on the lower bars.

I know it doesn't make sense at first. In real practile usage with the same torque arm, same shocks and the only change is the mounting ht of the rear of the lower bars, by changing them to be lower in the rear it will give a harder hit on the rear tires. Go figure lol. That is waht raer re-positioning brackets are made and sold. They make them bolt in or weld in.

Ed

[Mike Peters]

Thanks Ed. I appreciate the insight. I assumed the lower links acted with force vector you're describing but, assumed the I/C was dictated by the front mount location of the torque arm. The lower span of the torque arm would still have a force vector acting upon the launch characteristics though possibly not near the influence of the lower outboard trailing arms. Seems like this could be a source of suspension bind due to the unequal lengths and plane differences, no?

[BillyShope]

In an earlier post, I simply referred to a spreadsheet at my site which calculates the IC position. But, of course, the spreadsheet doesn't give any explanation.

The IC of a torque arm suspension is located at the intersection of a vertical line through the torque arm contact point and another line through the pivot points of the lower links. So, as Ed pointed out, if you lower the rear pivots for the lower links (or, for that matter, raise the front pivots), the IC will move up. This means more anti-squat, or, as Ed put it, a harder hit on launch.

[Mike Peters]

Agreed. Just like the SSM bars for the factory 4-link cars. Does the force transmitted through the lower span of the torque arm not come into the equation? Is it negligible because it is located on the centersection of the housing?

[Ed-vancedEngines]

Mike as you pointed out, The bottom ataching point is above the axle centerline and the lower attaching point is below the axle centerline. BUT BARELY.

Many people do not take this into any consideration with 4 link or ladder bars or 3 link suspension. Leverage Means a lot. A typical 4 link will have the rear attaching point of the top bar a few inches above the axle center but will have the attaching point of the bottom bar several more inches below the axle center.

Consider the axle center as a pivot point;
The further away from the pivot point you put attaching points, the less leverage the twisting center will exert on that point of force. It will move quicker but with less force. I.E. Bottom bar of a proper 4-link or bottom bar side of ladder bar or bottom bar os 3-link.

Again consider center of axle as a pivot point;
Now the attaching points are much closer to center than the previous example I.E. Top bar of 4-link or 3-link. The force exerted on that closer in to the center attaching point for bolts, will be much greater and will move slower as the axle is trying to twist in the suspension joints.

Now again consider center of axle as a pivot point;
Bottom attaching point is far from the axle center but the top attaching point is somwhat close to the axle center, I.E. Ladder Bars. The torque force exerted on the top part of the ladder bar is not very great with little movement and the bottom force exeted in the axle twisting motion is tremendous pushing it as a solid bolted on part to swing radically upward as axle rotates.

Lastly we have out little forgotten Step-child of Rear Suspensions the Single Torque Arm [Which I do like once the mods are done and better bars used] ;
Rear top attaching point is barely above axle center, so when axle tries to rotate not much force or speed is exerted on that attaching point. Bottom raer attaching point is just slightly lower than axle center, usually near the lower part of front axle section. Not much torque force is exerted on the bottom section, either but more than the top section, The solid mounted Torque Arm willo move as one with the rotation of the axle center section, but not with as much leverage force on the lower section of it, like a ladder bar would have.

Anyone forgot the Lower Bar on the Torque Arm sYSTEM?
nOT ONLY DOES MOVING THE MOOUNTING POINT OF THE BAR CHNAGE THE EFFECTIVE ic WHEN YOU LOWER IT IN THE REAR YOU ARE TAKING SOME OF THE TWISTING FORCE LEVERAGE AWAY AND TRANSFERING (Caps) that same force back into the Torque arm because if one suspension member loses leverage over the other that one will gain an increased leverage advantage. BUT with the now higher IC because of the lowering of the rear of the bottom bar the movement it willl exert will be a quicker action.

I hope I am not further confusing you in all of this.

Think Instant Center. Think Bar leverages. It is all the same thing whether we are talking about ladder bars, 4 links, 3 links Torque Arms, as far as how certain laws of physics actually control it all, we just need to learn new tricks to stay in the game as technologies change.

Ed

[BillyShope]

It should be understood that both the torque arm and ladder bars attach solidly to the rear axle housing. Once attached, they become, as far as the rest of the car is concerned, a single "hunk" of material. In other words, it's the same as if they were one continuous piece of steel. But, it's obviously impractical to make the housing and torque arm (or ladder bars) as a weldment, for it would be impossible to fit it under the car. So, the torque arm (or ladder bar) has to be bolted to the housing. But, the actual attachment points are totally unimportant. The torque arm, for instance, could have a crazy "S" shape and attach to the housing 3 feet above the centerline. So long as the front of the arm remains in the same location, the effects on the car are unchanged.

I hope that's what you're saying, Ed. I couldn't follow you.

[Mike Peters]

I followed Ed perfectly. I guess I do have a question of the leverages imparted by suspension links with different spreads. Suppose I had an axle I could twist by hand with a bar welded on the end for my hands and suppose I had attachments welded to the axle of different lengths which represent the different spreads of suspension link attachements. The bars bolted to these attachments were the same and were parallel to each other. It seems to me I could impart more leverage force through the bar that was closer to the axis of rotation, no? I agree the bar with the longer attachment would have a harder initial hit due to the relationship of the attachment on the chassis as well as distance away from axis of rotation but, the energy transmitted through the bar would not be as great. I also understand that suspension links bars have much different acting forces on the chassis with different spreads both chassis-side and housing-side. Wider spreads hit harder due to distance away from the axis of rotation and the additional distance between the bars on the chassis mounting points. However, this is also contingent on the attachment points on the chassis and since we can't keep the same relationship of bars with different spreads to the chassis, we're comparing apples to oranges. The outboard suspension links on a torque arm suspension would have the leverage advantage over the lower span of the torque arm due to the mounting angles and attachment points on the chassis.

Mr. Shope, I'm not sure I understand the "it doesn't matter the location of the torque arm mounting point on the housing" philosophy. I would think there has to be different forces transmitted due to different mounting relationships. I don't see how it can't matter. Maybe I'm just thinking how 4 links are affected by different housing spreads and assume there are different leverage ratios if the housing mounting points of a ladder bar are wider or narrower. To me, the bar angles of a wider spread vs. a narrower spread would impart different force vectors on the same common chassis mounting point.

Dang, I just read what I posted and it's hard for me to understand. Hope you can. This is interesting to me so, thank you for trying to enlighten me.