Let me see if I can save you a little time, Kevin, since I'm another geeky engineer and did pour over this quite a bit.
This may wax long, so take a deep breath, get a soda, and have a seat. LOL!
::Fires up the Robert Palmer MP3s::
Ok, first the basics about what we're trying to prevent by using traction bars. I'm sure you've all at one time or another felt the rear end of the truck stutter step and shake when you've made a hard launch. What you're feeling is called "wind-up" or "axle-tramp" and is caused by the axle loading and unloading the leaf springs around the axis of the axle.
What happens is that as the driveline transmits torque to the ground, the axle has to react in direct opposition to that - Isaac Newton decided that for us. That equal and opposite reaction causes the axle to rotate opposite to the direction that the wheel turns and as it does it bends the leaf spring into an "S" shape, arcing the forward portion of the leaf upward and the rear portion downward (see the diagram).
When this happens, the axle and differential rotate out of position and that changes the angle that the driveshaft meets the differential at. This can lead to u-joint binding and failure, pinion failure, spring failure, etc etc.
Eventually the energy stored in the “wound-up” spring has to be released. When this happens, the axle “snaps” back into place, usually lifting the tire off the ground when it does. As you can imagine, this isn’t particularly good for traction and can also damage other rear end components like the axle gears because of shock and movement. Again, not a good thing. So, in history or racing, some creative methods have been invented to reduce or eliminate axle tramp. These include everything from the simple – stiffer springs and snubbers – to the elaborate – 4-link rear suspensions. The two gizmos we’re most interested, the Calvert Racing Cal-Tracs system and the Rancho Torque Arms, lie in-between.
John Calvert came up with the Cal-Tracs system for drag racing. He raced in NHRA "stock" classes that mandated certain suspension components and tire sizes. Only bolt-on options are usable in these classes and prior to Calvert's work, that limited the class to stiffer leafs and snubbers. What Calvert came up with was radically innovative and I personally admire the simplicity and effectiveness of the piece.
Physically, the Cal-Tracs consists of three pieces - a connection to the bottom of the axle, a pivot around the front spring pearch, and a bar that links the two together.
The Cal-Tracs works by taking the rotational energy of the axle and using it to hold the spring straight. Again, the axle tries to move opposite the rotation of the wheel with equal and opposite the force of the wheel pushing against the ground. The Cal-Tracs takes this force from the bottom of the axle and transfers it forward. Part of the force is turned about the pivot at the front of the spring to push back against the spring itself and prevent it from winding up. The rest of the force is used, like a ladder-bar or 4-link, to enhance weight transfer. The downside here is that only part of the force is used and the lever arm is only as long as the front half of the leaf spring.
They work great. They're compact and hide inconspicuously behind the rear wheels and against the leaf springs. Great pieces of work.
The Rancho Torque Arms are originally from the Rancho 4x4 suspension setup and as far as I know, my truck pioneered their use on Lightnings. They're just an adaptation of the tried-and-true torque arm suspension components that are used in everything from road racing to offroading. I'd stop well short of calling them a "handling improvement" on the Lightnings, but they certainly work perfectly as a traction enhancer.
The Torque-Arms work by taking that rotational force from the axle and transferring it to the frame of the vehicle. Rather than working back against the spring to keep it from bending, they simply form a rigid lever against the axle's rotation so that there is simply no way the axle can wind up. All of the rotational force (multiplied somewhat by the offset of the tube mount from the bottom of the axle) is transferred via ~4' long torque tubes to the frame of the vehicle, which enhances weight transfer.
The tubes pivot at each end and their length is matched to the vehicle so that the rear suspension will continue to move through it's normal arc with no binding.
They work amazingly well. They're a bit more in-your-face and take up considerable real estate under the truck compared to the Cal-Tracs.
It's my opinion that the superiority of the torque arms come from two things - the length of the arms and the rigid (along the axis of force) mounting. They work basically like ladder bars without the downside of the ladders - the rough street handling. They're definitely not in the same league as a properly tuned 4-link, but I don't think many of our trucks are in need of that league either! ($$$$)
Anyway... that's my take on the subject.
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Later!
Jeff S.
NLOC #025, VP Gen 1s
Lightning #74 in '95 - Stroked and soon to be blown
Lightning #582 in '00 - Traded
1999 SVT Contour
1993 Probe GT -
15.36@89.7 stock daily driver
[This message has been edited by FMOS Racing (edited 12-03-2001).]
