kary993

Sorry John, I must be a bit slow today but I am not understanding your description . Can you explain differently?

Geo

Actually, IMHO there should be as few bends in any tube as possible (yes, I broke this rule with two tubes in my cage for what for me were compelling reasons). As such, side tubes (at the top) should have no bends. Every bend creates a weakness in the structure.

RedlineMan

Did we not recently discuss arhces?

Kary, your cage uses a "halo" tube to create the head and side tubes from one piece, instead of the more common side hoops and seperate head tube. Your side tubes - the ones right next to your head, running fore and aft - are flat in the horizontal plane. If a downward force were applied, they would immediately pull in on the next terminus point, which would be the a-pillar tube and main hoop joints. This "might" tend to collapse the structure more easily.

I am not sure I have ever seen a halo tube made with any arch in the side portion next to the driver's head. In this instance, the arch shape of the type of side tubes I use would distribute load DOWN and away from the point of force, and transfer it into the rest of the structure in compression, not tension.



It is just my gut reaction that this - unlike in a door bar - is a great place for an arch. An arch provides the properties you are looking for; Safe haven from forces of compression, and load distribution out into the rest of the structure. Then again, I could be splitting hairs. Just a theory.

Geo

John... I wouldn't call a simple bent tube an arch. The bottom illustration will not transfer the load like a true arch.

kary993

Interesting theory John. The guy who builds these cages (and I have seen a number of them) came from autopower and split off on his own after building them for many years. I discussed with him the strength advantages of various design points in my car as well as others I have seen. While I cannot do justice to his knowledge he seemed to understand and was able to articulate the strength of these various designs. I have also seen cars that have rolled a couple times just using a DAS bar for example, that did great and were much less sturdy in attachment and number of attachments. Also realize that this cage was installed with the top on the car not with the top taken off and reattached. I have also seen cars without knee bars running across and when hit on the side the A pillar strut collapses in regardless of the door bar design. There is also the weight trade offs..... Many trade offs .

I know you do a lot fabrication as well so I appreciate your feedback always but in general I think I (as well as others with cages) would need to fall off a pretty high cliff and land on the top of the roof to cave these cages in as you describe. Just a theory though

Adam Richman

Joe, are you entirely comfortable w/ how low the entire door protection you've laid out is w/ respect to how much of your torso is not behind it? For my sense of security, I want the door protection far from and as high as the bulk of my body - this also means that I run my seat lower than most folks my size. In my case, the lowest part of my door bars is the expanse about where your watch is and there is a tube gusset (2nd pic) that is coming up from there. A nice benefit of this is that the tube and rear gusset house the window net hardware so that w/ the padding in place, there is only the most minimal area to hit bare metal (and after my wreck, hitting a window net bar or mount was one of the bigger fears I had w/ version 2).

a. (for perspective, my left shoulder is mostly behind the taco shaped gusset from the main hoop to the door bar)


b. pointing out the tube that runs from the a-pillar to the door bar horizontal (not in the above pic.)


Also, if you are going to put an effort into improving the overall structure, how married are you the current cage itself? Door bar protection aside, the first thing I see is your foot and it looks very exposed from my vantage point. If it were me, I would put equal emphasis to adding at least a 7th point between the A-pillar tube and the firewall around your feet, adding a cross brace either above or below the steering column and adding some significant driver side protection. I would look at all three because I personally think they all carry equal importance AND, I'd do my best to create a common junction between them where they join at the a pillar tube.

If you don't have the clearance under the steering wheel, I have seen several cars that go directly over it and still preserve the guage pod - typically only cutting some of the shroud around the pod itself.

And if you decide that you want door bar protection that is relatively flat as opposed to something the moves outward, my thoughts would be to move it up higher than you have in your mock ups. I think you just leave far too much of your body exposed as that is laid out w/ the tape.

Darren

The guy who did my cage put the front cross brace over the steering column like this. I guess for many people this might cause problems retaining the gauges and not modifying the dash too much. My instructions to the installer were to make the cage safe and I'll work everything around that. With the cross brace under the dash it seems like it would be too close to my legs.

TD in DC

When track cars with full cages are rolled or wrecked, does anyone go to the trouble to analyze and record the performance of the cage? The discussions of cages make my head spin, and there seems to be merit to various different schools of thought. Since every cage will involve a trade-off of some type, it seems that it would be very helpful to see how various "compromises" performed in actual accidents. It seems like it would be helpful to the entire community if cage performance in collisions/accidents were analyzed and recorded. Is anyone doing this, even on an informal basis? If so, does anyone have access to this information?

P.S. The discussion of H&N devices also make my head spin, but I installed my ISAAC device this weekend with the help of a friend, so hopefully my spinning head will not also snap.

kurt M

The problem with that type of testing is that it would be incomplete and mostly anecdotal. Without the energy involved data one cage setup might look better than another but only because it was subjected to less trauma than the other .

John, An arch with a flat spot as you have in your lower example will transfer some load to the ends but it will also bend at the curved points. You could add arrows pointing out at 45 deg angles at the two curved points. The amount of deformation will be same at the curves and at the ends. As the ends bow out and the curves bend tighter. It can be better than a longer flat run that is not under tension but not to the standard of a real arch. A true arch is completely, corectly, curved and only then does the geometric advantage come into play in full. A partial arch is still primarily a material based form in strength. Kinda like a “4” sided triangle with one of the sides being small. Looks like a triangle but the small change changes everything some.

M758

Adam,
Very high side door bars are nice for protection, but limit space to get and out. I realize I need to decided how much of one vs how much of the other.

For right now I am leaning putting in a X or something like that. From my stand point protection needs to be not a complete X, but more like and L. Shaped my legs and torso need the bulk of the protection. My arms on the other hand will be flapping around and in a side inpact should easily move. My legs are more fixed and much closer to front bumper of most cars anyway. Torso can't move with the blow so that needs most protection.

There fore I figure have the X high in the back were my torso is and lower in the front to cover the legs. I am thiking that it may be best to raise the forward part of the X higher than my existing single bar point.

Re... the Dash bar. It would be quite nice to add, but I think I will stay away from that for right now. Reason being is that an under steering wheel bar is to close to the knees and behind the dash unit requires complete dash removal. I have done that and really don't want to do that work again. Atleast not right now. Yes it is a compromise, but most everything is.

M758

Ok,
Here is door bar option E.

A little higher than before and requries cutting the exisiting door bar out.

My goal is the upper bar running close to the high point on my knee.


(note a-pillar gussets are not shown, but will be included per previous pics.)

Geo

And then, if I'm not mistaken, the strength is mostly centered around the axis. So, if you build arches in your race car if one of the legs gets hit IIRC it won't be much if any stronger than a straight tube. IOW, arches are great at supporting loads along the axis, but not angled loads along the legs. At least that's my understanding.

Geo

To protect your highknee?

There is another option of course for the dash bar. It takes careful planning and layout:



Here is a link to more pix:

http://home.earthlink.net/~geo31/Geo's_944_Cage.html

Caveat!: My dash tube requires it to be bent on both ends. Clearly that is weaker than a straight tube. But, like Joe, the only other option I considered was to eliminate the tube and that was obviously weaker than a tube with bends at both ends. BTW, on mine you will note it attaches at the same spot as the front top of the X (which I realize is out of the question for Joe).

Joe, I like option E the best. Even better if you add some sort of dash tube despite the fact it won't attach where other tubes do.

RedlineMan

Kary;

Certainly, your man has a lot of experience, probably far more than I. All I have is my gut reaction, farmer instinct, seat of the pants backside engineering. My reaction might not amount to a hill of beans in the final analysis, or maybe there is some merit in it. Your cage looks quite sturdy, and perhaps at least as important, space efficient!

Kurt, G;

I did not even stay in a Holiday Inn Express last night, so I have nothing for you in terms of engineering know how. I appreciate the input. Kurt, you threaten to set off my cerebral smoke alarm there. Obviously it doesn't take much!

But, back to Joe, since it is his thread!

Joe, I'm with G here and vote for option E. The one thing I would add is a piece that connects from the side hoop junction with the top of the X over to the a-pillar. This would dramatically increase the crush resistance of that door bar / side hoop structure.



Something like the green line. This could either be done by plating the inside of the cowl and doing a double tube, or doing a plate steel gusset. I would also look at doing the same between where the top of the X meets the main rear hoop and the door jam. Perhaps also a perpendicular tube brace as in this cage that ties the door bar into the center tunnel.

RedlineMan

Hey All;

Regarding the height of door bar protection, I prioritize thusly. My first priority is to protect the hips. A broken of crushed pelvis can be a very lethal injury, and is not a region of the body that will deform and resist impacts well. Next would be the main core of the torso (waist to ribs), as this is where all of your vital organs are. Above the rib cage is the last portion of concern for me, as it has it's own cage and is fairly resilient. Protecting this srea directly also has a great impact on ingress/egress. The first two areas I mention are also about at bumper height in a "normal" side intrusion.

Nothing is unimportant, but that is my priority list.