[alfa] Notes on Roll bars in Spiders

["Bain, Bill" <Bill.Bain@xxxxxxxxxxxx>]

If the bar isn't high enough to keep your noggin off the pavement while
you're in inverted flight, it's not high enough to use 5 point
harnesses.  Russ Neely (I think) once mentioned that he is able to raise
his top over the Autopower race bar by doing something with the bolts in
the top brace -- if you replace certain of them with clevis pins, you
can unpin the frame, raise the top and then clevis pin the top frame
back together, or something like that.  Maybe he can elaborate.

I can't speak for every roll bar out there, but adding the Autopower
race roll bar certainly stiffens the rear of the car -- with the roll
bar bolted in my S3 Spider lifting one side of the car at the rear
brings up the other side to within about 1/4" of the side with the jack.
Without the roll bar it's at least a couple of inches difference,
although the off side does still come up in the air when you jack up one
side at the rear.  It stands to reason that the bar would add more
torsional stiffness across the rear.  The effect on the front would
likely be much less, if any, but I have been advised that one can get
the same net effect as the chassis stiffener by installing a bolt-in
for-aft brace from the roll bar top to the passenger side foot well.
The virtue, is of course, that while a chassis stiffener might not be
legal in a particular class, the fore-aft brace might well  be.

Series 2 Spiders are very definitely less twisty with the top up --
that's an old trick used back before folks got worried about roll bars,
etc.  Probably holds for all Spiders as the top frame "knits" the car
together to a degree once it's tensioned.

If you are putting a roll bar into a Spider, you *must* figure out some
way to reinforce the area where the bolts go through the box section
behind the seats.  The extended box section may well not be strong
enough to take the twisting side loads if the car rolls over (the roll
bar is first stressed on its side, then its top).  Options include
drilling the holes through the box section large enough so that black
Iron pipe can be welded in place between the backing plates to spread
the compression load once the backing plates are welded in place and the
bolts go down through the iron pipe.  The problem is that the box
section is not quite square, so some trial and error in fitting and/or
making a jig up would be needed to get the fit right.  Another option
might be to cut a slot in the upper and lower sections of the box
section just inboard of the bar's mounting holes, place 1/4" weld steel
sheet in the slot and weld it in place top and bottom to create a
smaller fully boxed area.  After it's welded in place, you can grind the
edges of the sheet flush, etc.

One note on the backing plates.  It's been mentioned that you have to be
careful of the main battery cable when you drill the hole.  It's also a
*real good idea* to bullnose or round the edge of the backing plate that
is closest to the cable so that the edge of the backing plate doesn't
saw its way through the cable's insulation. 

Lastly, the bar must be installed metal to metal.  The carpet will allow
the bar to lever against the bolts as the carpet compresses and the
bolts could fail. 


Let's be safe out there . .  . 

Bill Bain 
AROC Atlanta 
'83 Spider 
'87 Milano 
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