[tech] swaybar question

[jdbubb@ix.netcom.com (Dan Bubb)]

OK! I'll try another approach to get my point across.

> > Summary; roll stiffness IS substantially proportional to spring rate.
(Dan)
>
> Yup...assuming other factors don't change...which they did in our example.
> The additional weight was used as a force on the additional spring to
> accomplish the same work. Ergo, same roll stiffness.(Neal)

Nope. Same roll ANGLE assuming the increase in spring rate is proportional
to the increase in weight. Same roll FREQUENCY, but NOT same roll STIFFNESS.
Stiffness isn't a function of the amount of weight being carried!
Deflection/roll angle is a function of roll stiffness and weight. Roll
stiffness is a function of spring rate and suspension geometry (geometry is
the same between 8V and 16V!)

As a side note, in response to your comment about work ,(that is pretty much
irrelevant) work is force X distance. So, if the distance is the same i.e
the spring is compressed the same amount, but the spring is stiffer i.e. the
force applied is higher, then work is greater!

If you put stiffer springs on the front of an 8V Scirocco will the front
roll stiffness increase? Yes! The entire car (as opposed to just the front)
will roll less for a given lateral acceleration, but because more weight is
transfered at the front it will understeer more or oversteer less depending
on the particular situation. Probably, in the Scirocco's case, the maximum
cornering force will decrease.
Now put a 40lb weight on top of the valve cover. Does this change the roll
stiffness at either end? No! The car will roll more, perhaps as much as it
did before installing the stiffer springs, because of the added weight above
the CG. But, the roll stiffness distribution hasn't changed. So, the car
will still understeer more than it did originally because of the stiffer
front springs, but now with the additional weight on the front tires they
wll be even more heavily loaded causing even more understeer. This is pretty
much the situation comparing 8V to 16V.
So, going from 8V to 16V it's probably safe to say that the front roll
frequency is close to the same between the two (although I can't think of
any relevance), but there is no doubt the roll stiffness has increased at
the front of the car and the fact of the additional weight only means the
roll angle is approximately the same. The additional weight doesn't
magically decrease the front roll stiffness nor change the front/rear roll
stiffness distribution!
As far as your confusion about my statements concerning the effects of
swaybars, I think if you go back and reread my comments IN CONTEXT you will
find I'm consistent.
Increasing roll stiffness (either with stiffer springs or with a stiffer
sway bar) at one end of a car will cause more weight transfer at that end
which in MOST cases will cause that end to have less traction. This may or
may not increase cornering capability depending on how the car was balanced
before the change.
Increasing the overall roll stiffness of a car without changing roll
stiffness distribution will reduce overall body roll, reduce adverse tire
camber (particularly in the case of the Scirocco which has virtually zero
camber gain!) and increase, perhaps minimally, maximum cornering capability.
Dan



--- Original Message -----
From: Neal Tovsen <nealtovsen@yahoo.com>
To: <jdbubb@ix.netcom.com>
Cc: Scirocco-L (E-mail) <scirocco-l@scirocco.org>
Sent: Friday, January 18, 2002 1:27 PM
Subject: RE: [tech] swaybar question


> > The springs create a torque (twisting force) about the roll center as
> > the car corners. So, you have a spring force acting at a
> > given distance
> > (moment arm) from the roll center that creates this torque.
>
> OK
>
> > For a given
> > roll angle the moment arm distance stays the same. If you increase the
> > spring rate the force of the spring increases, the torque
> > about the roll
> > center increases in proportion to the increase in spring rate.
>
> Yes, but my point is that, in the example we're talking about (8v to 16v),
> the increase in spring rate is offset by an increase in force (weight).
> Thus, it's moot. With the same swaybars on the front, the roll stiffness
on
> both cars is virtually the same. This, of course, presumes that the
increase
> in spring rate is proportional to the increase in weight, which probably
> isn't exact but close.
>
> > Summary; roll stiffness IS substantially proportional to spring rate.
>
> Yup...assuming other factors don't change...which they did in our example.
> The additional weight was used as a force on the additional spring to
> accomplish the same work. Ergo, same roll stiffness.
>
> > In practice higher weight coupled with proportionally stiffer springs
> > will give you approximately the same roll angle as long as
> > the center of
> > gravity height doesn't change. (and, of course, we all know the 16V
> > engine has a higher CG! Bad!)
>
> The "roll center" brings in a whole slew of other factors, but the bottom
> line is that the suspension design is the same in both cars, and the 16v's
> higher CG probably doesn't create a big enough difference for us to
concern
> us here...
>
> > But, the amount of weight being
> > carried is
> > greater (less grip) and the amount of weight transferred is
> > greater due
> > to the higher roll stiffness. (less grip)
>
> Huh? I'm not following you here. What wieght? Where? Transferred by what
to
> which? Grip?
>
> > I'll stand by my original anaylsis.
>
> Which? You used two...
> That swaybars add traction
> -or-
> Swaybars remove traction
>
> Neal
>
> > -----Original Message-----
> > From: Dan Bubb [mailto:jdbubb@ix.netcom.com]
> > Sent: Friday, January 18, 2002 10:48 AM
> > To: Neal Tovsen
> > Cc: 'Jeffrey Lowe'; pbureau@attbi.com; scirocco-l@scirocco.org
> > Subject: Re: [tech] swaybar question
> >
> >
> >
> > Neal Tovsen wrote:
> > >
> > > Sorry, but no. Higher front springs do not increase roll
> > stiffness if you
> > > also increase the load applied to them. A 600lb spring with
> > 600lbs on it
> > > will compress 1 inch. A 300lb spring with 300lbs on it will
> > also compress 1
> > > inch. Presuming VW made proportional changes to the springs
> > (which they
> > > probably didn't exactly, but more-or-less), heavier front
> > springs will
> > > compensate for the heavier engine while maintaining the handling
> > > characteristics. Swaybars do not carry weight, but they do
> > influence the
> > > transfer of it. The larger rear swaybar on the 16v makes
> > the car understeer
> > > less, which is appropriate on a car designed to be more of
> > a "sports car"
> > > than the 8v was.
> > >
> > The springs create a torque (twisting force) about the roll center as
> > the car corners. So, you have a spring force acting at a
> > given distance
> > (moment arm) from the roll center that creates this torque.
> > For a given
> > roll angle the moment arm distance stays the same. If you increase the
> > spring rate the force of the spring increases, the torque
> > about the roll
> > center increases in proportion to the increase in spring rate.
> > Summary; roll stiffness IS substantially proportional to spring rate.
> > In practice higher weight coupled with proportionally stiffer springs
> > will give you approximately the same roll angle as long as
> > the center of
> > gravity height doesn't change. (and, of course, we all know the 16V
> > engine has a higher CG! Bad!) But, the amount of weight being
> > carried is
> > greater (less grip) and the amount of weight transferred is
> > greater due
> > to the higher roll stiffness. (less grip)
> > I'll stand by my original anaylsis.
> > Dan
>
>
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