Removeable Roll bars

["Bain, Bill" <Bill.Bain@domain.elided>]

Brian sends electrons out into the ether organized thusly: 

	Date: Thu, 28 Mar 2002 19:15:40 -0500 
From: "Brian Shorey" <bshorey@domain.elided> 
Subject: Removable rollbar w/for/aft brace pictures 

	A couple of people expressed interest, so some pics and a quick
write-up on 
the web: 

	www.employees.org/~bshorey/Rollbar.htm 

	Hope this helps somebody, 

	bs 

There are several ways to address the problem of mounting the roll bar
to the package shelf.  The basic problem is that the package shelf is
part of a "box" section with the lower metal stampings (remember since
the Spider is a unit body care there's no "chassis" per se) that has no
internal support and could collapse if the roll bar were to actually be
called upon to fulfill its intended function.  Alan Ward suggested to me
that one approach is to cut slots in the package shelf and the lower
stamping and weld vertical members in to provide a smaller. more rigid
"box" under the rollbar feet.  The shop that mounted my roll bar drilled
the holes to mount the bar, placed thick-wall tubing in those holes
welded item in place and then welded the reinforcement pads on the top
and the bottom. To the plate to the bottom of the car they welded "weld
nuts" so that the bolts could be dropped in from the top and bolted down
that way.  The kicker is that the package shelf metal and the lower
stamping are not quite parallel to each other so the tubes really should
be jigged up before welding to make sure that the bolts don't hang up on
the tubes. Of course the rear mounts under the rear window can use weld
nuts on the reinforcement plate so they can go in from the top as well.

The roll bar and cross brace to the foot well *will* add a surprising
amount of torsional rigidity to a Spider.  That's a "good" thing,
particularly if you're competing in a class whose rules don't allow
chassis stiffeners; however, like everything else, do not assume that
the auto will handle the same with the bar in and with it out.  From
personal experience, I can tell you that the Spider's "flexible" chassis
lends a certain feel and suspension "tuning", tire pressures, etc. are
subtly different.  Spend some time with the bar in the car on the street
and get used to it.  Last year my wife was driving our Spider with the
bar in, something that we rarely do since the top won't clear the race
bar and, with a rear suspension that was not set up properly (too stiff)
she too a turn near our house in her normal fashion, only to have the
rear end come loose because the chassis flex wasn't there to make up for
the excessive rear stiffness.  

Lastly, before anyone plunks down $$ for an Autopower race bar, talk to
a local race shop about having a bar made.  Check the rule book first.
The Autopower race bar barely meets SCCA Autocross rules, IIRC, and for
drivers 6 feet and over it may not be tall enough.  If I had it to do
over, I would have a bar made with a little "hoop" or raised part behind
the driver -- that seems to be acceptable under the rules (somebody
correct me if I'm wrong) and would lend a bit of helmet clearance as
well.

My $0.02. YMMV. 

Bill Bain 
AROC Atlanta 
'83 Spider 
'87 MIlano 

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