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Author Topic:   Brake Chain
A&M Motorsports
Dirt Maniac

Total posts: 117
posted May 10, 2005 10:56 AM  
Can some of you nice folks please explain the theory of using a 5th arm and a brake chain. Just wondering?????????????

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Artie Perilloux
A & M Motorsports

Kromulous
Dirt Forum Champ
Total posts: 796
posted May 10, 2005 11:22 AM  
Were going to run this deal this year, a Pull bar and the lift arm, some call it a torque arm. Anyway most cars just run a chain to the chassis off the lift arm, because rules only allow 5 coils, and the unsprung weight.

My theory or view on it is, that the lift arm is better for braking because its biased, or offset to the right of the CL of the chassis, and its further fwd than the pull bar.

Evidently it allows you to drive it harder in the corner, hit the brakes to make the corner, but when you hit the brakes the chain pulls down on the chassis to keep it loaded. A pull bar alone will unload the tires once you hit the brakes.


wfoondirt
Dirt Forum Champ
Total posts: 505
posted May 10, 2005 11:30 AM  
I assume you are asking as opposed to using the third link to control braking.

It basically comes down to IC location. A high/rearward IC creates anti-squat which in turn aids in forward bite. The downfall to large amounts of anti-squat is that it causes wheel hop/unloading under braking. By putting the brake chain on a fifth arm you are effectivly moving the IC forward and reducing the amount of anti-squat that the car "sees" under braking. Basically it has a similar effect as floating the brakes except it also decouples the decell forces. Make sense?

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted May 10, 2005 11:42 AM  
a longer pullbar will also help with the 'wheelhop' encountered under breaking.

Our car has a long pullbar that mounts by the tailshaft so it is actually furthur forward than the lift arm would be. We ran the pullbar/brake arm setup last year and it worked well. Driver said it really helped the car enter harder. this year we are running a 2 way pullbar and did away with the brake arm. So far he is really happy with this setup, he said it is smooth on entry.

A&M Motorsports
Dirt Maniac

Total posts: 117
posted May 10, 2005 11:55 AM  
quote:
Originally posted by wfoondirt:
I assume you are asking as opposed to using the third link to control braking.

It basically comes down to IC location. A high/rearward IC creates anti-squat which in turn aids in forward bite. The downfall to large amounts of anti-squat is that it causes wheel hop/unloading under braking. By putting the brake chain on a fifth arm you are effectivly moving the IC forward and reducing the amount of anti-squat that the car "sees" under braking. Basically it has a similar effect as floating the brakes except it also decouples the decell forces. Make sense?


Yes I understand now. The next question is how can I determine the most effective length of the arm and will the attachment points for the chain ever have to be moved to adjust for changing track conditions.


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Artie Perilloux
A & M Motorsports

[This message has been edited by A&M Motorsports (edited May 10, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted May 10, 2005 12:04 PM  
On our car it was easy because of the x in the frame. The bar could only be so long and still clear the x I want to say about 36" long. Then the chain was vert from there to a mount on the frame. You wouldnt really ever need to move it.

wfoondirt
Dirt Forum Champ
Total posts: 505
posted May 10, 2005 12:19 PM  
Imagine a line from the contact patch of the rear tire to the CG. If the IC falls on that line you will have 100% anti-squat (suspension neither raises nor squats on accel). Anywhere above that line and the anti-squat is >100% and below <100%. Ideally you would like to have your IC for braking just slighly above that line or ~125%-150% anti-squat. The IC for a torque arm is at the attachment point to the chassis. 32-38" is the average range of length of the torque arms that I have seen and should be close for you situation. You probably won't be able to tell a difference in small changes in torque arm length because the braking forces on dirt are relatively small.

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