Tech thoughts. Was: The Cheapest Sway bar!

[Dan Bubb <jdbubb@ix.netcom.com>]

Just some thoughts about sway bars in general.
The type of steel used for the swaybar will have little impact on the
bar's STIFFNESS. From 1010 low carbon steel to 4130 chromolly the
material stiffness is always right around 30,000,000 psi. So, going to a
high alloy steel will not make the bar stiffer.
OTOH the material has to have enough strength. If the stress put on the
bar by the application surpasses it's yield strength the bar will take a
set. The stress is a result both of the geometry of the bar's layout and
the bar's cross section and requires calculation for each case. 1010
steel has a yield stength of ~60 ksi whereas 4130 is ~220 ksi. So, if
cheapass 1010 (hardware store grade) doesn't cut it there is lots of
room for improvement.
Also, cross section has a big impact on bar stiffness. In general, open
shapes eg, C's, U's, T's, I's are torsionally weak. Closed shapes such
as squares and rounds are stiffer for a given cross sectional area.
Personally, I think the application Ron & Ben have come up with is great
because it gives us the ability to change rear roll stiffness very
easily and cheaply i.e. put on a bigger bar of the same shape; stack two
bars; put on a square tube; bigger tube; make end adapter plates and
mount a round tube. Not stiff enough? Go up in diameter or wall
thickness. No complex bending or brackets requires. And, of course, NO
BINDING!

As far as the front bar is concerned, attaching the bar directly to the
strut has two advantages.
1. The end of the bar will move as much as the wheel. So, for a given
amount of chassis role the bar will twist "X" degrees. If the bar is
attached halfway out on the A-arm, for the same chassis role, the bar
will twist half as much. So, it is effectively half as stiff. Attaching
the bar directly to the strut give the maximum bar twist for any amount
of chassis roll.
2. Attaching the bar to the strut removes miscellaneous deflections from
the system. eg. deflection of the a-arm in bending and deflection of the
a-arm bushings will reduces swaybar twist for a given amount of chassis
role making the bar less effective.
The issue here would be how do you attach the bar to the strut, allow
for steering lock, and clear the driveshaft? Sounds like another test
for Cheapass Ron to me.
Dan
PS. Does anybody else think the front swaybar chassis mounts are a POS?

Ben Channard wrote:
> 
>         The touted advantage of the Shine bar and by extension, Ron & Ben's over
> Neuspeed et. al. is that the former design doesn't bind.  Personally, I'm
> very impressed by the Cheapass design and am eager to hear feedback from the
> racers (autox and road).
> 
>         So now, can you come up with a Cheapass front bar?  Surely one of the giant
> bars from a 4000lbs car/truck could be adapted to ours?  One interesting
> tidbit from the April GRM regarding the E30 chassis M3 (1st Gen): "The front
> anti-roll bar was linked to the struts instead of the lower suspension arms,
> giving the bars double the effect."  I know there is the RWD vs. FWD issue
> but the BMW and VW both use Macpherson struts in front so can someone
> explain how attaching to the strut is better than to the control arm and
> whether this can be exploited in our cars?  Kudos, guys.  benton-----
>

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