Bill Birney wrote:
>
> Hello all listers.
>
> > RE: . . . an anti sway bar can make jacking or wheel tuck worse. . . .
> >
> > I disagree.
>
> Sorry, got to jump in here (I'm a bit of a lurker normally, but this is
> something I most definitely know about).
>
> DO NOT use a anti-roll bar on the back of a Spitfire!
>
> To control 'tuck in' you need a way to stop the two wheels acting in
> concert, the anti roll bar does the opposed, stops the suspension acting in
> opposite directions. So when one wheel tries to drop, the other is acted on
> to follow, ie as one wheel tucks under it will actually apply a force to
> move the other wheel in the same direction.
BIll,
Drooping is a passive thing the active part of wheel tuck is the motion of the
loaded wheel being forced up into the bodywork. Without
anything to compensate, the unloaded wheel will fall down and in the process,
TUCK UNDER. The camber compensator counteracts this.
But the rear anti sway bar also performs somewhat the same function. The
loaded wheel forces the sway bar up as well and carries the
unloaded wheel with it. The down side of this action is the unloaded wheel
doesn't have an opportunity to drop and thus loses
adhesion. So while it doesn't work as well as a camber compensator, it does
perform somewhat the same function.
>
> You can use a modification of a anti-roll bar however, here we call them a Z
> bar (I think it's probably pretty common terminoology). They are just a
> anitroll bar shaped as a Z (obviously) rather than a rather square U!
>
> They are mounted so that one corner of the Z is ahead of the axle line, and
> one behind. Now, when one whell tries to tuck under, it actually applies a
> force on the other to whell to push it up into the wheel arch, against the
> spring. Newtons laws then take over, a return force against tuck in is
> applied to the original wheel, and so tuck in is reduced.
Z-Bars were declared illegal by the SCCA back in the 60's. I haven't really
paid attention to the rules since to determine if they are
still illegal, but in theory they should be very effective. But to do their
job they need to be preloaded with a fairly significant
amount of force. That makes their installation somewhat precarious.
>
> Stiffens the hell out of the rear suspension though, all the aftermarket
> changes tend to.
Indeed, and in most instances, the result is ok, but it depends on what you are
trying to accomplish.
>
> That's all, I'll go back to my corner no and be quiet.
Don't be shy, speak your mind when you have such astute input!
Joe
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