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aqn@panix<img src=/i/dc.gif border=0 width=35 height=15> wrote:
> The short form: I have an Auto-Tech front stress bar, and
> the Whipple QR rear stress bar. I am not removing them
> anytime soon.
> HOWEVER. If I was looking to do mods to a stock VR6, A3 or
> Mk4, I would leave stress bars until the very last, after
> springs+shocks, after tires, after lightweight wheels, after
> air filter+chip, after cams, after exhaust.
>
> Paul Andrews <emosound@erols<img src=/i/dc.gif border=0 width=35 height=15>> wrote:
> > I'll play devil's advocate here; the following is *my opinion*.
> > A car's chassis can never be stiff enough. Does your car creak going over driveway
> > entrances at an angle? In a perfect world, the chassis would be one solid block of
> > weightless something, with infinite rigidity. In the real world, weight, cost, safety
> > crush zones, etc, all have an effect on stiffness.
>
> Good points, but you're wrong. |-)
Which part?
> Seriously, I would agree that stiffer is better (or so my
> wife said). I agree that a deflection of one degree at the
> shock/strut tower's top won't make the doors inoperable,
> but may result in one degree more or less of camber or toe.
> A one degree change in camber or toe is HUGE; it is a change
> that one can DEFINITELY feel.
> The question is, does the body flex that much WITHOUT the
> stress bars?
I dunno, it's hard to hold the camber gauge on the wheel when the car is moving. :-P
The real question is, is the stressbar worth the $100 or so that it costs for the X amount of
added stiffness that I can feel? For me, it is, and I think enough of it to recommend it. If
it cost $1000, no way, it's not worth it. Other things make a bigger difference.
> > If the Mk 3 cars were stiff enough, VW wouldn't have spent any money to stiffen the Mk 4
> > cars.
>
> If the Mk4 is any stiffer it would be called a BMW, and
> costs as much. There may be many reasons why VW did what
> they did. I don't claim to know the answer. I definitely
> would wonder whether VW stiffens up the Mk3 purely for
> performance reasons.
>
My guess is they stiffened the Mk 4 so it will rattle less! They want to have the car feel more
expensive than it is, feel like a BMW or Audi. Better handling is a side benefit.
> Going over curbs, dips, bumps etc. also produce twist/flex
> along the length of the body, not just side to side. How
> do stress bar prevent such lengthwise twisting?
>
They don't. But, they can reduce movement between mounting points on one end. Not a perfect
solution, but for the money, worth it to me, at least. An 8 point welded cage would be better,
but it's not practical, or cheap.
> Furthermore, how does a point-to-point stress bar prevent
> the shock/strut towers from twisting, or prevent the body
> shell from "parallelograming"? Indeed, are all of them
> stout enough to avoid being compressed like an accordion?
>
See above.
> Such being the case, I still question the validity of stress
> bars, especially the front one, in an A3/Mk4 car.
I don't, but then I autocross my car, so I'm willing to spend my money for what I think helps.
Bottom line, is it necessary? Probably not. The rear makes more difference than the front, but
for the minimal weight and money the bars represent, they're worth it.
> > As far as the removable bar goes, I have only seen pics, but it looks like it mounts
> > halfway up the rear strut tower. This likely reduces the effectiveness quite a bit vs a
> > bar mounted at the top, where the force is applied.
>
> The Whipple QR stress bar mounts about 3 1/4" lower than
> where an Auto-Tech stress bar mounts, 12" up from the hatch
> floor:
> http://www.gti-vr6.net/library/suspension/Whipple_QR_bar_inst/p3110698_measuring.jpg
> So it's 12" versus 15 1/4". It's clearly not as effective
> as the Auto-Tech bar, but I do not know how to quantify it.
> I do not know if it's "quite a bit" less effective or
> "somewhat" less effective or "a little bit" less effective.
>
That's a better pic (or just a better install) than what I have seen before. Other pics, like I
said, had it lower on the tower. I can't quantify it, either, but it seems to me a solid bar at
the very top would be better, purely for stiffness. How much......?
> One aspect where the Whipple wins hands down is that it
> allows me to regain all of the hatch's space, which is
> important to me when I need to load/unload four wheels/tires.
Perfect reason to get it.
> > That said, it's a beautiful piece of fabrication that solves a
> > problem of stiffness vs practicality for most people.
> It's a good conversation piece among gear heads! |-)
And a civilized conversation at that!
-Paul
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