tpi_roc

Hey guys,

I was reading some old posts and particularly ones where SteveSpohn was involved . I'm very interested in the physics of suspension, more specifically "anti-squat" and how to acheive it. How does lowering the trailing end of the LCA down 3 inches lessen squat? seems to me the forward movement and the torque on the tires is still going to shift weight to the back of the car, in turn dropping the rear? If anybody can tell me why a lower lca connection stops or lessens this I'd LOVE to hear the physics aspect.
Even MORE interesting to me is how a Torque arm can have anything to do with it? If I understand its pupose correctly its supposed to keep the axle (or housing) from rotating up or down, so how does an aftermarkt vs stock one do it any different?

Thanks for any serious replys!

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1985 Iroc-z, 14 second 305, new engine in the works.

tpi_roc

Even though this hardly glances my topic, I found it and figured it would be usefull to everybody here! Whether lowering the car, setting it up for drags, cornering, etc, here's some tips to save us some U-joints best case scenereo.
http://www.iedls.com/guide.html

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1985 Iroc-z, 14 second 305, new engine in the works.

AlkyIROC

Without going into pages of chassis theory all I can say is locating and using the "instant center" is what you're trying to do.

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IROCKZ4me

I'll go into it a little.

The "instant center" is the point where force is applied by a linkage.

In rear suspension applications, it is the point where an upward force is applied to the chassis through a linkage from the twisting energy of the rear axle. There can be more than one linkage pushing up in more than one place.

On an F body, the torque arm does double duty. In some aspects it replaces the upper rear control arms that these cars don't have. It also serves some of the same function as ladder bars.

Since you said you really wondered what the torque arm had to do with it I'll address it first.
It does much more than only stop (or reduce) axle rotation. It converts the energy from the axle rotation into upward thrust. As the axle tries to rotate it shoves the front of the torque arm up against the chassis. This is also what a ladder bar does, traction bars too. The point where the front of the ladder bar or torque arm is mounted determines its "instant center".
A shorter torque arm has it's front pivot point further back on the car. This moves it's instant center (the place it pushes up) back as well. The further back on the car the upward force (instant center) is placed the less squat you have. In fact if it is very far back at all the rear of the car will not squat at all but will lift. Moving the instant center forward allows more squat in the rear, but moving it forward also improves weight transfer from the front to the rear becuse it is pushing up more on the front. Moving the instant center up or down also has an effect on weight transfer. Up allows more weight transfer, because it places the instant center in better "leverage point" in relation to the cars center of gravity. It's easier to tip a glass of water over by pushing at the side of the glass near the top than it is pushing at the glass near the bottom.
So using a shorter torque arm to move the instant center back over the rear tires more, and mounting the front of the arm higher to raise the instant center to improve weight transfer usually works best. A more solid mounting, more solid bushings, and a stiffer torque arm transfers more of the axles rotating energy into lifting force applied to the body without absorbing or losing it because of flex.


You can read more about this in my reply to this post,
https://www.thirdgen.org/messgboard/...ML/003154.html

and in my reply to this post,
https://www.thirdgen.org/messgboard/...ML/003521.html

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Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"

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• TRW forged pistons/ceramic coated
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• SLP cat-back
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[This message has been edited by IROCKZ4me (edited December 06, 2001).]

tpi_roc

Ok I read your post here and your other two posts you made. Compairing the torque arm and the LCA's to ladder bars made it click. Much appreciated. But theres one thing I guess I just assumed wrong, I thought under heavy acceleration the pinion angle went negative (pointed toward the ground) instead it actually turns upwards? I thought it would follow the direction of the wheels.

Anyways, If it does go positive under acceleration it all makes great sense, THe torque arm pushes UP 3/4 of the way back on the body (if its a shorter aftermarket tq arm) raising it up and planting the tires. The relocation brackets drop the rear half of the LCA's making an uphill angle toward the front of the car, and under acceleration when the axle attempts to twist it just pushes UP into the lca's raising the car and planting the tires.

If i misunderstand anything let me know, but I think im getting it

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1985 Iroc-z, 14 second 305, new engine in the works.

[This message has been edited by tpi_roc (edited December 06, 2001).]

[This message has been edited by tpi_roc (edited December 06, 2001).]

Norm Peterson

. . . I thought under heavy acceleration the pinion angle went negative (pointed toward the ground) instead it actually turns upwards? I thought it would follow the direction of the wheels.. . .
Axle rotation is a reaction to wheel torque and is therefore in the opposite direction to wheel rotation.

Norm

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1979 Malibu w/some cornering tweaks and a few other interesting things

tpi_roc

Gotcha

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1985 Iroc-z, 14 second 305, new engine in the works.

johnsjj2

This may help on the pinion angle: At rest the tires are still. When you accelerate, the pinion wants to climb the ring gear. This makes the housing, or the pinion point up. I don't know how true this is, and I'm sure it is different for each car, but 4 degrees negative at rest is a good starting point.



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Joshua Johnston
1991 Z-28
350, T-5, K&N, Ported Vortec heads, Edelbrock RPM, Holley 750 D.P., HEI, 11.07:1 CR, Comp Cams Roller-.510"/.520"-282*/288* dur., Shorty Headers, Dual 2.5 Exhaust, Dynomax Bullet Mufflers, T&R Motorsports custom air intake, Bald tires

IROCKZ4me

That's pretty much true for a drag car (or Saturday night special) so you have near 0° pinion angle or so while under hard acceleration.
If you set up a regularly driven steet car with that much negative pinion angle you may have drive line vibration when driving at part throttle and decelerating and your Ujoints will have a shorter life.
For a "real" street car somewhere between 0° and negative 2° is usually best
Norm Peterson had it right,
rear end housing rotation is the equal and opposite reaction to the force from the wheels rotation

Apeiron

Opposite, but not equal.

IROCKZ4me

originally posted by Apeiron:
I didn't write the laws of physics, I just have to live by them. LOL

Newton's Third Law of Motion:
"For every action there is an equal and opposite reaction."


For every pound/foot of torque aplied to the rear wheels trying to turn them forward, that same excact force is trying to turn the rear end housing backwards. Equal and opposite.

arthur

Also, making the TQ arm shorter will apply more 'lift', as it doesn't have as much 'leverage'. Though it cannot lift as high. Kind of like using 4.10 gears as opposed to 3.08s.