Originally Posted by bart:
Here is a better angle, but I still don't understand if this it the 5th shock.
Bart
Your first picture showed it. It’s tied from the top of the birdcage to a tab on the chassis at about a 45 degree angle. I don’t see it in the second picture. There’s no spring associated with it (coilover). I assume what it’s doing is dampening the lateral load that the ladder controls when you slam into the cushion. The chassis is still going to move sideways until all the slack is out of the ladder, but dampening it slows that down for a split second. And since it’s mounted at that angle, it splits the dampening in half, so it’s an even more slight adjustment than you might think. Tying it to the top of the birdcage instead of the side probably also has an affect. Creates leverage to plant the RR due to the car’s lateral momentum?
Whereas the "main" or "usual" shock is oriented close to the vertical and approximately at 90 deg. to the axle, and is most effective in dampening wheel motion in bump and rebound, the "5th" or auxiliary shock, by virtue of being oriented at about 45 deg. is more effective at dampening chassis roll motion.
If the valving of the main shock were stiff enough to provide the same roll dampening as is provided by the auxiliary shock, it would be too stiff to allow the needed compliance for good tire performance.
Originally Posted by Frank Reiner:
Whereas the "main" or "usual" shock is oriented close to the vertical and approximately at 90 deg. to the axle, and is most effective in dampening wheel motion in bump and rebound, the "5th" or auxiliary shock, by virtue of being oriented at about 45 deg. is more effective at dampening chassis roll motion.
If the valving of the main shock were stiff enough to provide the same roll dampening as is provided by the auxiliary shock, it would be too stiff to allow the needed compliance for good tire performance.
What Frank is saying here is correct. With the current car design the chassis suspension (torsion bars, etc.) on the rear is mounted below the vertical center of gravity. Since the suspension is the only means of controlling chassis roll (until the jacobs ladder locks up, that is) it must be stiff enough to limit the rate of said roll, which potentially makes the suspension too stiff to maximize tire contact/weight transfer, etc. This 5th shock appears to allow some control of the roll rate while keeping the suspension as soft as possible. Kind of like installing an adjustable rate anti-roll bar. Probably not a bad idea, but all I need is to have to buy another 4-600 dollar shock.
By the way - coil-over suspension suspends the car at or above the roll center which adds some anti-roll itself.
Originally Posted by Tim:
What Frank is saying here is correct. With the current car design the chassis suspension (torsion bars, etc.) on the rear is mounted below the vertical center of gravity. Since the suspension is the only means of controlling chassis roll (until the jacobs ladder locks up, that is) it must be stiff enough to limit the rate of said roll, which potentially makes the suspension too stiff to maximize tire contact/weight transfer, etc. This 5th shock appears to allow some control of the roll rate while keeping the suspension as soft as possible. Kind of like installing an adjustable rate anti-roll bar. Probably not a bad idea, but all I need is to have to buy another 4-600 dollar shock.
By the way - coil-over suspension suspends the car at or above the roll center which adds some anti-roll itself.
Tim Simmons
I really appreciate these topics about the technical side of open wheel cars. Frank and Tim made interesting comments about the fifth shock helping to control the roll center of the chassis. I was wondering if the fifth shock would work similar to the QRP CL2 bird cage that had a small coil spring in it's assembly that was connected to part of the W link, I think it was created to help prevent a bind and keep a true arc in the roll center? Many sprint car sanctions banned this birdcage early last year and I was wondering if it's the same idea presented in a different way.
Originally Posted by jonboat15:
I really appreciate these topics about the technical side of open wheel cars. Frank and Tim made interesting comments about the fifth shock helping to control the roll center of the chassis. I was wondering if the fifth shock would work similar to the QRP CL2 bird cage that had a small coil spring in it's assembly that was connected to part of the W link, I think it was created to help prevent a bind and keep a true arc in the roll center? Many sprint car sanctions banned this birdcage early last year and I was wondering if it's the same idea presented in a different way.
As to the location of the roll center, that is determined solely by the geometry of the locating links, in this case by the geometry of the Jacob's ladder. The auxiliary shock functions to control/dampen roll movement but has no influence on roll center location.
The reason that the spring linked ladder connection fell out of favor, as I understand it, was because of very erratic handling when the spring failed.
