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Old 08-22-2017, 08:00 AM
JRas JRas is offline
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Default Cage Design

Hey guys,

Looking to get a cage installed in 3-weeks and want to iron out the design. Planning on continuing HPDE once the car is running and doing maybe TT in NASA.

X-bars, is it worth having them do two bars continuous (bending) vs the traditional x setup?

FIA bars, any issues with NASA/SCCA?

No halo bar

Trying to decide what to have them do off the rear strut towers, low on main hoop or high?
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Old 08-22-2017, 08:46 AM
Def Def is offline
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2 bent bars is much stronger in an impact. You're deforming twice the material in the center of the X, and are not loading a weld very heavily like a single bar X has to.

I would go high on the main hoop for connection to the rear strut bar, that provides much greater strength in a roll over. Basically attach them on the outer portion of the flat top part of the main hoop (top of the B-pillar to roof connection in car).
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Old 08-22-2017, 06:23 PM
JRas JRas is offline
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Quote:
Originally Posted by Def View Post
2 bent bars is much stronger in an impact. You're deforming twice the material in the center of the X, and are not loading a weld very heavily like a single bar X has to.

I would go high on the main hoop for connection to the rear strut bar, that provides much greater strength in a roll over. Basically attach them on the outer portion of the flat top part of the main hoop (top of the B-pillar to roof connection in car).

That makes sense thank you

I saw some pictures of the cup cars starting to protrude into the door panel. seems counter-productive to the x bar design and starting to get in the realm of the nascar style.


this is for a civic but the design seems solid
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Old 08-22-2017, 06:52 PM
Def Def is offline
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You want the X to go as far out as possible. The Cup car design has it right. 2 bars would provide more protection at a tiny weight penalty.
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Old 08-22-2017, 07:28 PM
JRas JRas is offline
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Quote:
Originally Posted by Def View Post
You want the X to go as far out as possible. The Cup car design has it right. 2 bars would provide more protection at a tiny weight penalty.
The bars at the rear of the door appear to get that S bend though



here is another cup car designs from Porsche
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Old 08-22-2017, 11:14 PM
Joe D Joe D is offline
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I did my car a lot like the cup car design, but I had the X meet with bends welded around where they meet and then boxed in. The X can provide a stiffer chassis. Boxing in around the X is very strong

The thing I don't like about NASCAR bars is you generally have a long distance that is unsupported. I did a lemons Sentra with NASCAR bars but plated the rocker panel and added 3 braces from the NASCAR bars. It's also really hard to avoid the S bend without going through the B pillar with either type of door bar.

Also, make sure all tubes terminate so the load path goes into another tube or the chassis. You don't want tubes welded more than 3" away from each other.

Another thing to consider is adding FIA rollover tube. It triangulates the A pillar and prevents it from collapsing in a rollover.
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Old 08-23-2017, 07:09 AM
Def Def is offline
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It's always better to have the material out away from you rather than having everything straight. I guarantee you it takes more energy to move that Cup car design with the S curve in the back of the X door bar to the seat, vs. a straight X that's maybe 1" from the edge of your seat.


Maybe the straight X takes more ultimate load to fail, but at that point, the door bar is already up your butt and you're likely severely injured.
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Old 08-23-2017, 08:29 AM
gills gills is offline
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If you're only going to have one rear strut member it needs to be high on the main hoop, just like Def stated.

Things move in a proper crash. Give yourself SPACE, again, like Def stated. Get the bars as far away from you as possible into the door. If you have S-bends, they can be supported by having verticals like in a NASCAR style cage and then ultimately tie it into the rocker panel or rocker cage member if you have one.

With Joe D's cage description you could fortify it even more by having a vertical running to the vertex from the rocker panel. If I were to build a new cage right now, I would do this method.

The biggest benefit of NASCAR bars is protrusion potential. They are usually skinned and provide a ton of space. And correctly done, they don't have S-bends and tie into a straight lower member that runs along the rocker.

Don't be scared of going through the unibody B-pillars. They are pathetic on an S-chassis anyway. Take a good look here from my old car/cage (where I would now change quite a few things):

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Old 08-23-2017, 09:17 AM
Def Def is offline
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Yea, I don't know why more cages don't put a large notch in the b-pillar seam to get a straighter shot for door bars. Then weld all that together (if rules allow). The b pillar is flimsy, and you get way more strength tying it into a cage tube than leaving it intact and out of the path of a tube.
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Old 08-23-2017, 05:30 PM
Joe D Joe D is offline
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Def,

Totally agree. Always make everything as far away from the driver as possible.

When I did the Sentra I actually came around the lower part of the B pillar with the nascar bars. The door striker was between the two bars and the they came all the way out to the door skin. Then added 3 supports to the rocker. We built a brand new car due to a side impact in the left front wheel area that moved it over a foot. It only had to be one foot back or so and the driver could have been seriously injured. It was an easy decision to go with nascar bars.
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