RE: stiffening spiders

[Chris.Prael@domain.elided (Chris Prael)]

Thanks, Alan.  That makes me much less ignorant.  

That sounds to me like 90% of the stiffening effect is in re-enforcing
the panels to which the steering mounts.  (Have you ever watched the
panels flex while someone else moves the steering wheel back and forth?
The flex is a bit alarming, 1/4 of an inch, or so!  This is a much of a
problem in the Sprint as it is in the Spider.)  

I have been thinking about a welded reinforcement of the panel, just on 
the driver's side.  The enthusiasm that you and others have expressed 
confirms my speculation that this would be a significant improvement.  
What I had not considered is that it might be more effective to do the 
passenger side, too.

I still think that the rest of the structure is more ballast than
improvement.  Though it might compensate for the inevitable sagging of
the floor pan with age.

chrisp

From: Alan Lambert <gerard@domain.elided>

> Hi, thanks for the response--The stiffener bolts on to the car at the 
> rear trailing arm nounts, and at the front three bolts (on either side)
> that hold the steering mechanism on. Crosswise, the stiffener bolts (to 
> itself) two crossbars, front and rear. The stiffener is made of 1" square 
> cross section steel tubing, with fastening plates of thick steel. It adds 
> torsional rigidity because any twist applies a moment action to the front 
> plates, which then transfer the force to the steel tubing. It greatly 
> reduces torsional flexibility.
> 
> Hope this helps.
> 
> On Wed, 30 Jun 1999, Chris Prael wrote:
> 
> > What you say has some truth, though the ignorance has been acquired from
> > the list.
> > 
> > Care to be a little more informative?
> > 
> > chrisp
> > From: Alan Lambert <gerard@domain.elided>
> > 
> > > I'm afraid Chris is speaking on a subject of which he is ignorant. First, 
> > > the stiffener does not bolt to the floor pan, Second a friend of mine who 
> > > is a competent Alfa racer drove my Spider through only a couple of 
> > > corners at some speed (on the street) before he asked me "do you have a 
> > > stiffener installed?" He asked because the car was so much more rigid 
> > > than Spiders usually are.
> > > 
> > > I'm not trying to flame, but I have a problem with inaccurate advice 
> > > being send the the list, some of whose members will believe it.
> > > 
> > > 
> > > On Tue, 29 Jun 1999, Chris Prael wrote:
> > > 
> > > > > From: Jack Nasielski <jackn@domain.elided>
> > > > > 
> > > > > There must be a few people who have tried the spider chassis stiffener.
> > > > > Please share your experiences.  Did you install it yourself?  Who
> > > > > supplies these things? (I saw one in the centerline book for $425).
> > > > > 
> > > > > thanks-
> > > > > jack
> > > > 
> > > > I have never tried one of these, nor would I!  They are a shuck.
> > > > 
> > > > If you much about structures, it should be obvious that any "bolt-on"
> > > > device will add a lot of weight and do very little stiffening.  
> > > > 
> > > > It is simply a matter of leverage.  Alfa already built extra weight
> > > > into the floor of the 105/115 chassis to stiffen the Spider.  Any
> > > > structure that you bolt to the floor pan will have an even worse
> > > > strength-to-weight ratio.  
> > > > 
> > > > You can produce a useful improvement in torsional stiffness by careful
> > > > design of a roll cage that is welded to the car. But the car will be a 
> > > > single seat race car, not a street machine.
> > > > 
> > > > These chassis stiffeners probably make great ballast, but that will not
> > > > improve the car's performance.

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