Traction bars/Lift bars, how do they work?

[spyder_xlch]

I understand the use of them on leaf springs to control axle wind up, but how do they work on the Vega or more importantly to me, the Monza? With 2 upper and 2 lower control arms, or a long torque arm and 2 lower control arms there's no way the axle can wind up.

[TopNX75]

Lift bars aren't really designed to "prevent" axle wind up. They are really designed to take advantage of it.


The idea of a lift bar is pretty cool actually. It uses the axle's spin to force the tires into the ground. (coincidentally liftintg the body up against the tires).

With the stock suspension on most cars, when you hit the gas the rear end SQUATS down..

This is how it was explained to me, and it really makes sense (i think)

Stand on a SCALE at the rear bumper of your car and push DOWN on it. Your weight (or the pressure on your feet gets LIGHTER.... This weight reduction happens to the rear tires the SAME WAY...

This is a rough way to explain that the downward pressure on your rear tires actually DECREASES when the rear end squats...

Now standing on the scale at the rear bumper of the car, LIFT UP ON THE BUMPER....

Your weight on the scale INCREASES DRAMATICALLY!

Again, a very rough way to describe that the weight placed on the rear tires with lift bars installed, increases dramatically,,hence the better traction.

As the weight transfers from front to rear, if the rear squats, some of that transfer benefit is lost..

If the rear of the car is lifting with "lift bars" the ONLY thing that the body can be pushing down against (to lift up) is the rear tires!!

What a theory! Who invented these things??!!

Cool stuff, hope this info helps!

Sean

[cjbiagi]

This type of traction bar on a suspension like ours isn't going to work that well because of exactly what you said, there is very little axle wrap to take advantage of. The only way they would work is to have the snubber right against the control arm to take advantage of the very small amount of wrap. I think you are better off using improved bars and bushings and maybe playing with the angles of them.

[AusRs]

i actually wonder whether the lower control arm repositioning brackets that the 3rd gen f bodies use would also work on a H body seeing as the suspension is similar
i KNOW that they worked on the 3td gen !!!
bottom setting was fantastic traction BUT a little to much oversteer for the corners
mid setting was decent traction and decent cornering
top setting was stock position !

http://www.thirdgen.org/techboard/attac ... angle2.gif

[spyder_xlch]

I did alittle looking around and did find out why they work. I'm not good at explaining things and would have to make some drawings to explain it better (which I plan to do and will share with Spohn performance too). Basicly the lower control arm on our cars is pushing forward when the axle tries to rotate on acceleration. Relocating the rear mount lower gives more of an upward motion on the front of the control arm helping to lift the chassis. The lift bars you see for sale basicly lower the rear of the lower control arm. You are buying a lower control arm and a relocation bracket all in one package. It's totally unnecessary to buy the whole set up to get the advantage. I've come up with a few other ways to accomplish this, they have all probably been done before. I'm not claiming to be a pioneer or anything like that. I never really looked into how they work and now that I have an idea of the principle I have an idea of what could work. I'll do some drawings and post them later.

[spyder_xlch]

I'm no artist but here's some quick drawings. Keep in mind these ideas have probably already been done in some form or another. I'm not trying to take any credit for coming up with a new idea. I've just never seen lift bars explained before and came up with these to help explain how they work or atleast my theory on why they work. The "slapper" style traction bars commonly used on leaf spring suspensions would work in a similar way by stopping the forward motion of the lower control arm and converting it to an upward motion when the rubber snubber hits the control arm. Again, just my theory.

[chevyart]

good explanation on the rear end squatting and loosing traction. ever notice a leaf spring car taking off or doing a burnout. the rear does the opposite of squatting. It pushes the body up therefore putting downward pressure on the axel, giving more weight on the tires, giving more tire bite. the chassdis experts call this anti-squat, really. just thought i would tell you guys that info. PS I have a chev II with slapper bars, run right against the spring eye(no space between) and the car launches like a raped ape Chevy Art

[SunbirdMan]

But the torque arm does the same thing doesn't it? It tries to pick up the front end at the transmission, trans ferring weight to the rear tires. That's assuming that the built in slop of the stock T/A bushing is replaced.

[cjbiagi]

You need some "give" in the torque arm bushing or you will end up with a binding condition. As the rear end and suspension move up and down, it changes the distance between the rear end and the trans. This is why there is a slip yoke at the front of the driveshaft. Without some type of allowance for this change there will be a bind. Some torque arm mounts use a different type of bushing that actually interlock and slide back and forth to allow for this movement. I think the later F bodies use this type of mount. So for us, on a street car at least, the rubber bushing is probably best. Don't forget, with the length of a torque arm there is a lot of leverage available.

[SunbirdMan]

Yeah, I'm aware of that binding issue. Another reason Energy suspension doesn't recommend using all poly on the street. But some people go with rigid T/A mounting. It still applies though, i believe, that the T/A will do what matt is designing.

[spyder_xlch]

Don't give me credit for the design Roger, I just figured out in my head what was going on and put it in drawings to help me understand it better and to explain it. I'd like to take credit for the designs and pantent them but I'm sure they've been done before in some form or another.
The torque arm has somewhat of the same effect but to a lesser degree I think. It does help with wheel hop and does plant the tires better than the 2 upper arm design but it's not as instant or as effective as the pics I drew. The stock design works great for what the cars were intended to do but we all know most of us push the limits or far exceed the limits the factory had in mind. The drawings I made are more of a ladder bar set up, or atleast the same concept as a ladder bar set up. I just realized that and haden't thought about it when I drew those.
The torque arm is long and provides a lot of leverage but I think the reason these drawings I drew would be more effective is because the forward and reward forces are triangulated into a more centralized location. The upward force where this occurs is more "violent" if you will. The harder the suspension tries to lift on the chassis, the harder the tires get planted.

[cosvega76]

I'll see if I can copy an illustration or two later on this, but this is the theory on rear suspension geometry:

Looking at the side of the car, draw imaginary lines through the pivot points of the control arms, or through the center of the mounting point at the rear axle and bushing at the trans for a torque arm. Where these two lines intersect is called the instant center.

Where the instant center is in relation to the vehicle determines how the rear suspension will react during the launch. Normally, the instant center on a production vehicle is in front of the front bumper, causing the car to squat at launch.

Now, draw an imaginary line from the contact patch of the rear tire to the vertical centerline of the front wheel, at the horizontal height of the Center of Gravity for the vehicle. Rule of thumb places this height roughly at the engine's camshaft height as installed in the vehicle. This is called the neutral line.

Compare the instant center point to the neutral line. If the instant center is below the neutral line, the car will squat. If the instant center is above the neutral line, the axle will separate from the body, planting the tires harder.

There is a lot more to this theory, as where to place the instant center to control how hard the tires are planted, but this is the basic premise.

Why lowering the rear pivot point of the lower control arm works is because the instant center has been moved rearward, and at or above the neutral line.

Chuck

Chuck

[AusRs]

honestly think a H body will always squat while it has a torque arm trying to pick up the complete front of the car !anti squat is never going to happen !

[hammerdown7]

When I was autocrossing the Monza a number of years ago, when running slicks, I had severe wheel hop when leaving the starting gate. A friend of mine who is a Chrysler suspension engineer fixed the problem by shortening the torque arm. It was connected with heim links to a 2X2 tube which was mounted cross ways 3-4 inches behind the front seats.
Dick

[spyder_xlch]

Since the F-body shares the same basic rear suspension we can benefit from what they are doing. I haven't looked into it yet but I bet if you go to their message boards and just read what they have done you could learn alot. It's all about geometry and physics. Not my strong points in school but the geometry and physics of a suspension is pretty basic stuff. Sometimes it's trial and error but alittle understanding of why something works helps you figure out what has to be corrected to make it work better.