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      07-27-2019, 10:06 AM   #7
Michael9218
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Drives: 2007 Z4 M Coupe
Join Date: Oct 2012
Location: Woodstock, GA

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Cage designs differ for many reasons that you need to consider.
1. Chassis design - this will dictate what is needed and how to make it fit. Two seaters like the Z4 and Miata/MX5 often need the main hoop to terminate on the shelf behind the driver. Structurally, it's a better place to terminate the main hoop and also may be needed to set the main hoop behind the driver.
2. Rules - rules obviously have a great impact on ones cage design...if you're going racing.
3. Anticipated use and risk tolerance - There does not exist a safe cage. More cage is not necessarily safer. Dale Earnhardt died because NASCAR chassis' are too rigid. Energy absorption is key to survival. Defeating engineered crumple zones can make the car less safe. Having bars run through the firewall to the front strut towers is a good example of this. This is done to stiffen a chassis at the expense of safety (also note that there is no requirement to run bars through the firewall in CAMS). So there is definitely a balance. Understand what you are trying to accomplish before you simply build a birdcage in your car.

Looking at the CAMS cage rules, they look pretty reasonable. The amount of cage depends on the class you plan to run. But looking at the rules, I think it would be pretty easy to build a modular cage that can be added to later. Mine would definitely be easy to make compliant. The only issue may be the main hoop not coming down to the floor behind the seat if I need to add more door bars. I suspect I could add a plinth behind the seat. My cage builder told me this was not an issue as he's done this before and builds cages for SCCA, NASA, and BMW CCA compliant cars.
https://www.cams.com.au/docs/default...sn=7721ed27_10

Of course I have pics of my cage:

Easier to see raw without paint from the cage builder. Note that rather than run the down bars to the frame rail, we brought the frame rail up to the down bars by building the box (aka, plinth) that also serves to create a structural mounting point for the shocks for the option to use coilovers. This also makes a good mount point for a strut bar and diagonal in the downbar plane. Looking at the robust C pillar and roof structure, we felt is wasn't needed on this chassis, but could easily be added if required by rules.


The seat is bolted to the cage for additional structure.


Personally, I'm more terrified of side impact than rollover so we added a single diagonal door bar terminating into a plinth that can be used for the front hoop if added. A single diagonal door bar doesn't impede ingress/egress. BMW Club Racing here in the states only requires a single door bar (most run more). It looks like CAMS also only requires one depending on class.




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