Cage X design

I am not trying to start a debate so much about the actual X design of a door bar, but a related question regarding the evolution of the design as it applies to the rest of the roll cage.

So the old school version of a door x was to use one straight tube and 2 cut tubes to form the x like this,



But more recently the design has evolved to integrate 2 uncut tubes either by bending and gusseting 2 V shaped bars like this,



Or crossing 2 uncut tubes and gusseting them like this,



It is basically agreed either uncut version is stronger than the old design correct?

My question is why are the newer designs not used in any other cage x's other than the door bars? I understand the main hoop and roof have different loads than the doors but with proper gusseting shouldn't either of the newer designs still handle loading in most all directions better as the node cross section is much beefier?

There are no "reasons" for anything anybody does excpt fads and this "creativity" thing.
All is rationalisations all after the fact..much luike you "reasoning" about suspension and spring rates on the other thread..
people do it cause they want to, and talk shit why its better.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

This would probably make way more sense if this wasn't in text. Your sarcasm and double reverse sarcasm are confusing me.

Logic isn't logic because reasoning is a fad and nothing is ever measurable or scientific and engineering development is fantasy and whim. I'm guessing your solipsistic ranting is in jest but I don't honestly know what the point was this go round? Generally behind that veil you haven a real point you are making.

I thought cage structure was to help you not die?

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timiacobucci
This would probably make way more sense if this wasn't in text. Your sarcasm and double reverse sarcasm are confusing me.

Logic isn't logic because reasoning is a fad and nothing is ever measurable or scientific and engineering development is fantasy and whim. I'm guessing your solipsistic ranting is in jest but I don't honestly know what the point was this go round? Generally behind that veil you haven a real point you are making.

I thought cage structure was to help you not die?

Ultimately. and i say in the meantime it should be saving your car (bodyshell) life since we are all privateers..

I am dead serious...people choose some postion of something that "strikes' them, and decide on whims and then defend tyo the death many "debate" their way to "enlightenment"..Nope.
Some debate "to win points"..

Most people merely "assert" their stomach grumblings and call it reasoning..then argue..

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

So then are you saying all these designs will work and it's splitting hairs?

My first cage I did the 1st design, my second I did the 2nd shown.



In my opinion the 2nd design is easier to do. The most difficult parts for me doing a cage are the severe angle notches. My notcher doesn't work over a certain angle and its more difficult to get the tubes to fit up properly.

The only other tubes left on a cage with an extreme angle are the a-pillar bars. Eliminating 6 'difficult' notches, down to just 2.



As far as whats safer, I dont really know if it is.... but the idea behind the 2nd being safer is that the tubes tend to break about 1/2" up from the weld. If there's no weld the entire way around its more likely to break in front or behind you instead of in the middle right where your mid section is.



Edited 1 time(s). Last edit at 02/25/2015 08:55AM by czwalga.

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timiacobucci
So then are you saying all these designs will work and it's splitting hairs?

I'm not John, but I definitely believe that's the case.

The folklore surrounding the 1-solid, 1-split-bar X is that the welds could fail, and take a core sample of one of the meatbags inside.

The folklore surrounding the "parallel bent bars" is that the gusset/weld could fail, which lets the bars pivot inwards on their ends and allow lots of intrusion.

The "crossed bent bars" seem to be new-er-ish, require more labor, and may sacrifice some internal space.



The bottom line is that, if a weld fails in your cage, you're going to have a bad time.

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KF7RWG
http://www.utahrallygroup.com

We do more cars with a single bar than an X (plus will bar always.) There's a big discussion on this I started a year or two ago. Titled "door bar designs" I believe.

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Grant Hughes

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NoCoast
We do more cars with a single bar than an X (plus will bar always.) There's a big discussion on this I started a year or two ago. Titled "door bar designs" I believe.

Ya I read that whole discussion, that's the reason I said I wasn't trying to get into a big debate over the actual merit of the design so as to not rehash all of that. I have read on other road racing type forums about failures from side impacts and the classic x failing. Again like Aaron said if welds fail you in trouble despite the design, I think the last design is the best in that case, even if the gusset welds fail you still need to rip through 2 bars despite the welds... in the middle anyhow, but at least you've got 4x welds at the outer ends to support all the load in the middle at that point.

Sidetracking though, my question really was why not use either of the last 2 designs for the roof or main hoop? Especially considering like Steve said they are easier to fabricate well. Following that weld strength is relative to gap and gap to fitment, easier to fit, easier to make a strong weld. Obviously the roof and main have a more uniform 90 degree x vs the harsh angle of the door bars but it's still a valid point to consider. I just like that there are 2 full bars, or 3 in the main if you have a solid lateral harness bar in it.

Has anyone seen this done before? Does it pass tech?

The difference between the door bars and the other X's is that the door bars are protecting from intrusion, the main hoop and roof X are used to triangulate a square to prevent deformation.

One is loaded from the side, the others are loaded from the end.

I see that but the roof still has intrusion function in a roll over and does the cut up x really sustain side loads in the main hoop better than a gusseted node with 2x the cross section? I'm not sure what to think I'm just wondering if it's been done.

I haven't done the 3D modeling to be able to speak 100%, but looking at the forces, I think the "cut up X" is still better.

The roof does have intrusion...but that is not it's MAIN function...the crash into a tree on your roof is not the most common crash, and you also have the two half laterals helping with that load. The main purpose is to absorb/transfer a frontal load hitting the top of the A-pillar. If you have a gusseted, bent tube...all of that load is transferred through the gusset, which would tend to tear it.

With the cut X, the tubes should be perfectly straight, and matched end-to-end...so the force is transferred straight through the weld to the tube on the other side. It is also required to be gusseted, to help transfer.

The cross-over has to bend the tubes, which will reduce their strength in compression, making them more likely to bend.

That makes perfect sense and completely answers my original question. Thank you.

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timiacobucci

Quote
NoCoast
We do more cars with a single bar than an X (plus will bar always.) There's a big discussion on this I started a year or two ago. Titled "door bar designs" I believe.

Ya I read that whole discussion, that's the reason I said I wasn't trying to get into a big debate over the actual merit of the design so as to not rehash all of that. I have read on other road racing type forums about failures from side impacts and the classic x failing. Again like Aaron said if welds fail you in trouble despite the design, I think the last design is the best in that case, even if the gusset welds fail you still need to rip through 2 bars despite the welds... in the middle anyhow, but at least you've got 4x welds at the outer ends to support all the load in the middle at that point.

Sidetracking though, my question really was why not use either of the last 2 designs for the roof or main hoop? Especially considering like Steve said they are easier to fabricate well. Following that weld strength is relative to gap and gap to fitment, easier to fit, easier to make a strong weld. Obviously the roof and main have a more uniform 90 degree x vs the harsh angle of the door bars but it's still a valid point to consider. I just like that there are 2 full bars, or 3 in the main if you have a solid lateral harness bar in it.

Has anyone seen this done before? Does it pass tech?

strength of a welded joint is a function of the linear inches of weld in the joint.. Fit presumed to be correct.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Well yes, I was trying to not make this more terribly complicated but when you take all of the weld issues into account it's really not the weld joint and gusseting that it the issue. The larger heat affected zone relative to a bigger gusset joint will always be the weak point and failure point in most tubing faluires, if you can weld anyways. Which was part of the reason I was thinking the non linear part of the gusseted x in say the main hoop wouldn't really be the weak point it would appear to be in direct side loading, the thing is the HAZ in the not quite straight tube is still going to be. Likely weaker than a straight tube with a smaller weld.