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Roll bars redux
To Dean's point, the area underneath the parcel shelf is an open box section and SCCA and AROC have been concerned for some time that the top of the open box section would deform from the lateral loads put on it in a roll over situation since the initial load is lateral as the car rolls over. The obvious solution is brace the box section by welding in reinforcements. The most common way is probably to use "black iron" pipe as reinforcing tubes between the backing plate on the bottom of the "chassis" and run the bolts though the pipes. Since the pipes are in compression between the plates on the roll bar and the backing plates, the top of the box section has a much smaller likelihood of deforming as the lateral loads differentially act on the sides of the roll bar. There are probaby a dozen other ways to achieve the same reinforcement goal, but an unreinforced rollbar is defintely NOT a good idea.
Most street bars are designed to let the top close over them. This means that for many drivers they will NOT be high enough to keep the passengers' heads off the pavement when the car is in "inverted flight." A street roll bar does not have a diagonal cross brace. SCCA and AROC consider one a neccessity to reduce the potential for the bar to deform and collapse. In a side impact with roll over, if one side of a street bar were to become "tucked in" from the initial impact, it could collapse, with disasterous effect. Many "street" bars are made from thinner materal of a smaller diameter than the sanctioning bodies would allow (The AROC Competiton Code gives material types and dimensions). The lack of height, plus the lack of a diagonal brace, and the sometimes questionable choice of materials, would give me pause concerning their utility as a safety device -- better than nothing, I guess, but it's not clear how much better.
The "race" roll bars with diagonal braces will not permit the top to be closed, which rules them out for most street Spiders, although IIRC that Russ Neely of AROC figured out a way to replace some of the bolts in his top frame with clevis pins so he could unpin the frame, hoist the top over the bar and then pin it back together. It worked with the Autopower race bar, I'm told.
Lastly, a rollbar should ALWAYS be padded appropriately. The Snell SA standards incude an impact test for the helmet hitting the roll bar so it's not merely an abstract possibility. Autopower makes fancy vinyl covered padding for the street bar, but the other alternative is to use the foam paddiing that is ubiquitously seen in race cars. Whether the padding would affect the ability to close the top, I don't know, but the risk of whacking your noggin on an unpadded hunk of steel is significant and probably greater than the chances of a roll over.
As far as installation goes, most Bosch Spider owners who have put a roll bar in report that although it's tight on the passenger side, they do not have to relocate the ECU. I did not with the Autopower race bar I have in my '83, but the street bar may be narrower than the race bar, which would put the foot of the bar in the tangle of wires, fuses and relays just outside the ECU brackets.
If you're still wanting a street bar, the best thing to do is to find a race car fabricator (Mike, I'm sure, knows of one) and have the bar custom made of appropriate materials and mounted properly. Unless you're VERY good at metal fabrication, and welding, a proper mounting job is not something for an amateur -- the box section is NOT square, but IS trapazoidal in both the forward and lateral dimensions, whcih makes getting the reinforement tubes into the right spot, lined up and properly welded a non-trivial task. Also, the main power cable from the battery to the starter is in the way and can be easily nicked as one is drilling.
Hope that helps!
__________________
Bill Bain
AROC Atlanta
'83 Spider Veloce
'03 Mazda Protege5 (Red - zoom, zoom!)
ex - '87 Milano Silver (RIP)
Last edited by bill_bain; 08-22-2004 at 01:10 PM.
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