Wow, Phil, I think you're right, and that I've been wrong about this for
years.
My Formula Ford had an adjustable rear swaybar where only one side was
adjustable. But it was a blade-type adjuster, as opposed to adjusting
the lengths of the two arms. The arms stayed the same length, but the
arms were allowed to bend different amounts.
I think this type of swaybar really can be adjusted on one side. But I
have to admit you make a very compelling argument that a swaybar that
adjusts by manipulating the lengths of the arms must be adjusted
symetrically. It never occured to me to think about the speed bump test
before.
Josh
Phil Ethier wrote:
>
> -----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/
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