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 Post subject: Main Hoop rules question
 Post Posted: Mon Feb 01, 2010 11:50 am 
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Joined: Thu Jul 16, 2009 3:27 pm
Posts: 3
Location: Tufts University
Hello,

We are cutting out our current main hoop to bend and weld in a new, taller hoop to meet the rollover requirement however we have a question on 3.3.4.2 about the main hoop. Our chassis, including the main and front hoops, is made out of 1" 4130(mostly round tubing, some square). We see in the third statement of the referenced rule section:

Quote:
The Main Hoop must extend from the lowest Frame Member on one side of the Frame, up, over and down the lowest Frame Member on the other side of the Frame.


but then later in this same section we see:

Quote:
On vehicles where the Primary Structure is not made from steel tubes, the Main Hoop must be continuous and extend down to the bottom of the Frame.


This suggests to us that if the hoop/chassis is not constructed from steel, the hoop must be the lowest point of the frame. Our car is all steel so we do not think we need to do this. It would make the retrofitting of our car much simpler and stronger as well due to the minimization of cuts and rewelds needed.

Since our structure is all steel, is it within the rules to extend the main hoop to tie in to the top of the frame rails without having to cut out the current piece and go through again?

Thanks!


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 Post Posted: Thu Feb 04, 2010 9:42 am 
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Joined: Tue May 16, 2006 11:34 am
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The short answer to this team is "Yes. You do not have to cut into the Lower Frame Rail."

When we say "The Main Hoop must extend from the lowest Frame Member on one side of the Frame, up, over and down the lowest Frame Member on the other side of the Frame" then the Main Hoop can sit on top of the lowest Frame Member. It does not have to go through the lowest frame member!

If you are cutting out your current Main Hoop and adding a new one to increase the height of the Main Hoop, I suggest you follow the procedure from the SCCA's GCR. (link below)

"The following procedures are approved for modification to roll bars/cages that do not meet the two (2) inch required minimum: The old main hoop may be cut off near the chassis mounting and a new main hoop of equal tube size or a section of equal tubing size may be added, and inner tube(s) must be used to mate all sections together. All braces must be minimum distance from top of hoop per Section 9.4. All welding for this modification must be arc welded (min.). The inner tube(s) must be rosette welded three (3) places near top and bottom, see figure 21."

The idea is that the existing Main Hoop is cut off somewhere between the Upper and Lower Side Impact Members. The new Main Hoop must be the same OD and wall thickness as the old one, typically 1.00" OD x 0.095" wall, and the two tubes butt together properly. The joining is via the rosette welds to the inner sleeve AND the butt weld between the old tube and the new tube. If the team has a problem obtaining a length of tube of the correct OD (0.81"), I would accept sleeving on the outside with a length of tube of 1.00" ID. You would still need 3 rosette welds through the sleeve above the join and another 3 rosette welds below the join, plus a 360 degree weld between the sleeve and the tubes at each end of the sleeve.

This information can be found in the SCCA GCR at:

http://cms.scca.com/documents/Club%20Rules/09%20GCR/2009GCR.pdf

Appendix G, 9.4.7

-Michael Royce


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 Post Posted: Sat Feb 13, 2010 7:04 pm 
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Joined: Thu Jul 16, 2009 3:27 pm
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Location: Tufts University
Thanks for the help. On the document defining the required rosette welds, we saw that the holes drilled in the hollow bar should be 1/2" wide. Since that guide is for 2" diameter tubing and we are using 1" diameter tubing, what is the minimum size hole to drill?

Thanks a lot,
Andrew


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 Post Posted: Wed Feb 17, 2010 9:12 am 
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Joined: Tue May 16, 2006 11:34 am
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The holes identified as 1/2" in the GCR can be somewhat smaller for 1" tubing, but must be of adequate diameter to get good penetration of the weld into the inner tubing. Use your best judgment.

-Doug


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