-----Original Message-----
From: Jefrem Iwaniw <jiwaniw@iigo.com>
To: John Steczkowski <stecz@Crossroads.com>
Cc: 'John Coffey' <johncof@ibm.net>; Team. Net (E-mail)
<autox@autox.team.net>
Date: Tuesday, August 03, 1999 3:14 PM
Subject: RE: Adjustable Swaybars - One or Both Ends?
>Except for the fact that this thought doesn't take into account the
>fact that most (all?) swaybars use a "lever" as part of their
>twisting/springing/load-transferring activity, and by moving the
>mounting point in on only one side, or unequally, you are introducing
>asynchronous behavior into your suspension.
Yes. At first I did not think so, but now I understand. The easiest way to
see this, at least for me, is to think about what happens in a "speed bump"
condition, not in a cornering condition.
Consider that both wheels are to move the same distance when our perfect car
encounters our perfect speed bump. If both ends of the sway bar are
identically connected to the suspension, both end points of the sway bar
will move exactly the same distance. When this happens, the net effect of
our perfectly frictionless sway bar is now exactly zero.
To accept the hypothesis put forth by a previous post that it is OK to
adjust only one end of a sway bar, you would have to accept that the effect
of such a bar in a "straight-line speed bump" would continue to be zero.
If a bar is asymmetrically adjusted in the manner implied in the original
post, here is what would happen: Assume that the lever arm on the left side
is 9 inches. Assume that the right end was stiffened by reducing the lever
arm to 8 inches. Say the suspension is to deflect three inches when we hit
the speed bump. Each end of the swaybar would theoretically move through
the same arc having a chord distance of say three inches. The right end
with the 8-inch lever arm moves through 21.24 degrees. The left end with
the 9-inch lever arm moves though only 18.92 degrees. The result of this is
a twist of the working portion of the sway bar of 2.32 degrees. Therefore
there would be a resultant force upward on the left side and downward on the
right side. This means that the net effect of the sway bar in the
speed-bump condition is NOT zero. Therefore Jefrem is correct that you are
introducing asynchronous behavior into your suspension.
Yes, I know that in practice the resistance of the asymmetrically-tweaked
bar would cause the two sides to move different distances (inducing roll in
the car) when we hit the speed bump. This is the effect of the
asymmetrically-adjusted sway bar adding spring rate to one side and
subtracting it from the other. That is the point of this discussion.
In cornering, the total stiffness of the bar itself would be the same
corning in either direction, but the forces actually applied at the
suspension by the end links would be different. Therefore, the sway bar
SYSTEM would affect the car differently in right and left turns.
Variances in other parts of the car might make you want to do this on
purpose. But you had better know that the effect is there and how it works
before trying to use this for chassis tuning.
Phil "just have to think these things through" Ethier
Saint Paul Minnesota USA
Lotus Europa, VW Quantum Syncro, Chev Suburban
LOON, TCVWC, MAC
pethier@isd.net http://www.visi.com/mac/
|