[tech] swaybar question

[nealtovsen@yahoo.com (Neal Tovsen)]

> 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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