Door Opening "X" Bars as Side Protection

[dickita15]

To Chris’s comment about the drivers wanting weight savings of the X bars, I saved plenty in gutting the right door to make up for the small about of extra tubing.
It is somewhat bothersome that this incident took the force in the door alone rather than using the crush structure of the rocker and floor. Given IT cage rules I do not know how to change that.

[Wreckerboy]

I'm glad that Rich Hunter is okay. Does anybody know anything about the driver that hit him? Chris built the cage in my Miata as well (which I unfortunately crash tested a few weeks later at LRP). I can't say enough good things about the quality of his work.

Earlier it was mentioned about drivers wanting the weight savings of x bars in the right side doors. When we discussed this as Chris was putting my cage together last summer, I thought (please correct me if I am wrong) that he mentioned that one of the advantages to NOT doing so was the straight load path gained from front to rear.

I understand that everything is a tradeoff, but but perhaps the best solution is a combination of the two or three approaches: the traditional X bar style arrangement as well as the NASCAR anti-intrustion design, as well as tacos. Yes, this will impart a weight penalty. The other thing to consider is the expanding foam mentioned here. The NASCRAP COT uses attenuating foam in the doors now. Does this sort of thing exist for our adaptation? I'm thinking that spritzing the inside of the tubes with the conventional expanding foam available at Lowe's is not a good idea...

[Greg Amy]

I'm re-quoting Sandro's photo, because this is a good illustrative example of Richie's/Chris' build. Note the driver's side full-up "NASCAR" on the left side; right side is a single-tube bar bisecting another bar to create an "X". Richie did not have a horizontal bar at the bottom.

I think something here is being overlooked. We should be looking at the car as a sacrificial anode in that the structure successfully absorbed the force of impact which allowed the driver to survive.

By your description of the force of impact, it sounds like the cage did a good job of absorbing the energy. Is there really a design that's practical in weight and material cost that can withstand any possible impact ? And how should it look after an incredible impact ? I wouldn't expect it to look like it did before the accident.

I suspect you don't understand the full scope of what happened to Richie's car. If Richie had been 180 spun around with the x-bar on the driver's side, he would be dead today.

Period.

There was absolutely ZERO space between the passenger side door and the exhaust tunnel. Zero. The passenger side door was halfway into the car, and only inches from hitting the driver, thankfully on the other side of the car.

A lot of people like to get into a discussion of "crush zones" and "energy absorption" and the like, but we don't have the tools to be able to quantify that. As such, it becomes more an "art" than a science. And without a survival cell, absorbing energy kinda doesn't matter. Granted, dying of a detached brain is just as dead as being crushed, but given the choice I think I'd rather take my chances with g-forces.

Finally, while this discussion centers around a crushed passenger side, my focus is how we should design a proper driver's side crash structure.

The design you show does appear to be a stronger way to make an X. I'm sure that at an 80 mph direct impact there would be some failure somewhere in that construction too.

Of course. But this particular door structure failed in tension, and failed in a way we cannot accept.

Let me make this clear: I am not hammering Chris' work. In point of fact, my Nissan NX2000 has a (highly more structural) x-bar design on the driver's side. But, my point is that the design as illustrated above in Sandro's photo can withstand exactly half the tensile forces of a true double bar.

Think of it this way: let's say you cut that "X" out of there and hang a car from it; how much force can it withstand? Only as much force as one tube. Why only one tube, you ask? Because its weakest place is in the middle, where there's only the cross-sectional area of one bar. If, however, you were to weld a plate across the face of that "X" it could withstand twice the load, because it's now being distributed among two tubes.

A "taco" gusset would not do the same thing, unless it were also welded across the face. The purpose of gussets is not to increase tensile strength but to support the tubes in a bending moment. For the purposes of the discussion at hand, two plates welded across the back and face of the "X" would be just as effective.

It is somewhat bothersome that this incident took the force in the door alone rather than using the crush structure of the rocker and floor. Given IT cage rules I do not know how to change that.

Well, as you know, the best thing would to be allowed to weld to the rocker panel. But trying to get that IT rule changed would be Sisyphian. As a compromise, I'm envisioning using the plate are rule to extend the plates as far towards the center of the door as possible, then welding tubes to that. Kessler always added a longitudinal bar at the bottom on my cars (similar to Sandro's photo, above) but I think we might expand upon that a bit more.

Does anybody know anything about the driver that hit him?

I saw Richie talking to him in impound, looked fine. Front-end damage on the 'Ta didn't seem significantly worse than other bad SM wrecks...that car seems to handle hits pretty well.

I am the one who built the cage in Richies car. I wish Rich had let poeple photo the damage as that is the only way we all learn.

I chatted with Richie about it, but he wanted to discuss it with you first. If you can talk him into letting one of his guys take some photos to post here (or you take some when you see it), I think we can all really learn from it.

Honestly, Chris, there was really nothing you could have done differently to the passenger side to affect a significantly different result; it was that hard a hit. All I'm offering here is a detailed discussion of the failure mode and how we might apply that to our driver's side going forward.

This is timely, as we've got a new car build going to happen this winter. I'm personally no longer a fan of the pure "X" bar on the driver's side, though I'm not clear exactly how far towards the "NASCAR" I'm wanting to go...

[RexRacer19]

This is timely, as we've got a new car build going to happen this winter. I'm personally no longer a fan of the pure "X" bar on the driver's side, though I'm not clear exactly how far towards the "NASCAR" I'm wanting to go...

Hey Greg,

This thread has lured me out of lurking...

That is a tough question/quandary that you have posed there. I am not sure if there is an ultimate solution here that is not a compete tank of a roll cage. My thoughts have always been "build it as best you can within reason, but there comes a point when, no matter what you do from a safety standpoint, the crash is just going to be too bad."

From the two schools of thought...The X style bar is structurally more efficient and increases the overall strength of the cage IMO. There is however, less metal there right next to the driver. The NASCAR style bars add more metal to the area adjacent to the driver, but are generally full of dead load paths. In nearly every example of a NASCAR bar shown in this thread, there is a nice mesh of tubes forming the side impact. BUT, that mesh of tubes gets attached to a single vertical tube in the front, and a single vertical tube in the rear mid-span. When having to take on an impact such as Richie's, The tubes that the NASCAR bars are attached to will be the first to deform/fail in a massive impact. Just like in Richie's crash, they will be in tension, which is less than ideal.

-Jeff

[ekim952522000]

<----Mike who is very interested in the discussion is getting a cage put into his ITR ITR next month and has to be worried about getting hit by 3200lb Supra's

I am thinking that a 3 bar door bar setup plus lower bar is going to be necessary on the drive side.

[Sandro]

The NASCAR style bars add more metal to the area adjacent to the driver, but are generally full of dead load paths. In nearly every example of a NASCAR bar shown in this thread, there is a nice mesh of tubes forming the side impact. BUT, that mesh of tubes gets attached to a single vertical tube in the front, and a single vertical tube in the rear mid-span. When having to take on an impact such as Richie's, The tubes that the NASCAR bars are attached to will be the first to deform/fail in a massive impact. Just like in Richie's crash, they will be in tension, which is less than ideal.

-Jeff

agree with what you are saying, but when I designed mine, I thought that bending, of the main hoop and a pillar bar would allow for some absorption.(the main hoop only has about a 2ft span where it isn't reinforced in another direction, and even less on the a pillar as I have a bar going to the firewall.) If I had added additional bars in line with the nascar bars to say the rear or the opposite b pillar, their would be zero absorption and in a hard blow my brain would probably fly out the passenger window.

My nascar bar also only has two bends( /-----\ ) on each bar not four as I see many do ( _/---\_ ), so a blow on the nascar bar will push the a and b pillars at 45*, not even relying on the welds to hold them in place, cause the bar will be forced into the a and b pillars, as opposed to the bars with four bends that you are now relying on the welds to hold the nascar bar to the pillars, putting the welds in shear when hit. Which as someone mentioned even when the welds are done properly the metal around them ends up shearing.

Please don't think I am trying to say my cage is perfect, just trying to give some insight to the thoughts I put into it, especially as I said my biggest fear is being T-Boned.

I personally think the passenger side should be able to give a little, so it reduces the g load in an accident but on the driver side you don't have that much room for it to give, until the driver begins to be crushed. So as Greg said I think on the driver side you need to accept the higher g load, instead of being crushed. That is also the reason I have a fully bolstered seat to reduce the chance of snapping my neck.

[RexRacer19]

Please don't think I am trying to say my cage is perfect, just trying to give some insight to the thoughts I put into it, especially as I said my biggest fear is being T-Boned.

I don't want to come across as a know-it-all either. As I have told some others, there is more than one way to skin a cat when it comes to these things. Both design types have merits and drawbacks. The important thing is to build/buy a cage that YOU will feel safe in and meets the standards of the GCR. These discussions are generally healthy and provide some insight for folks going through that process.

[spnkzss]

I don't want to come across as a know-it-all either. As I have told some others, there is more than one way to skin a cat when it comes to these things. Both design types have merits and drawbacks. The important thing is to build/buy a cage that YOU will feel safe in and meets the standards of the GCR. These discussions are generally healthy and provide some insight for folks going through that process.

I have to agree. I find it humorous that the first cage I had in my C car worked just how I needed it to. Then when I built the A car I had a whole different mentality of what I that was right and modified accordingly. THen I saw what you and Xian were doing and have another completely different mentality.

[Racer Chris]

...
Honestly, Chris, there was really nothing you could have done differently to the passenger side to affect a significantly different result; it was that hard a hit.
...

In the past, the simple X door bar design was not allowed in any SCCA road race car. The reason was that the perception of greater strength from this design is inaccurate. As noted, the door bars failed at the weakest point - a single bar crossing the center of the assembly. The rule should never have been changed, or at least only allowed such designs if significant reinforcements were added accross the weak point. I think the rule was probably changed due to lobbying of competitors who already had such door bars that had been overlooked for years, and one day ran afoul of a wise tech inspector who gave them grief. The X design may add a high level of stiffness to the chassis but doesn't provide good intrusion protection by itself.
Adding "taco" gussets would have significantly reduced the likelihood of complete failure of the door bar assembly, but only if the gusset material was in the range of .080" thick, similar to the minimum welded mounting plate thickness. An assembly with such gussets would have provided appropriate g-force attenuation, which is what we want to happen. The "taco" gussets shown with bell mouth lightening holes are not sufficient IMO, since the material thickness is not suitable for the forces involved in what happened to RH's car.

[Greg Amy]

In the past, the simple X door bar design was not allowed in any SCCA road race car.

Chris, I don't necessarily disagree with your technical points, but you are mistaken on the history of the rules. Prior to the 2007 change there was not even a requirement for a right-side tube. This is from the 2005 GCR spec for Showroom Stock:

A side tube connecting the front and rear hoops across the driver’s door opening is mandatory and across the passenger’s door opening is allowed (recommended).

It wasn't until the 2007 GCR that passenger side bars were mandated:

Effective 1/1/07 and permissible 10/1/05 two (2) side tubes connecting the front and rear hoops across both door openings are mandatory.

Finally, it wasn't until the 2008 GCR (per a 2007 Fastrack) that x-bars were approved as "two side tubes", precisely for the reason you describe (others had already gone beyond the prior rules requirements and built an x-bar where none was required, and didn't want it to be made illegal) :

NASCAR-style side protection or one bar bisecting another to form an “X” is permitted.

Greg

[tnord]

http://heddev.com/miata/product_info...8b15f21405e1d9

i'd be most interested in a critique of this cage. it's the only "cage kit" i'm considering for my next car.

[Sandro]

Solution:

mount a F1 monocock within an 8pt cage, its IT legal too

6. Any number of additional tube elements is permitted within the boundaries of the minimum cage structure.

[RexRacer19]

Since we are full on show and tell mode now...here are my last two IT car cages.

This is from my former, would be ITA CRX now driven by AJ Nealey.

[RexRacer19]

http://heddev.com/miata/product_info...8b15f21405e1d9

i'd be most interested in a critique of this cage. it's the only "cage kit" i'm considering for my next car.

Travis,

I am a fan of that cage kit. Having done a Miata myself, I really like how it mounts in and the configuration of the bars. I would maybe customize the driver's side door bar to suit me a little, but would hold judgement until I had all the pieces sitting in front of me.

$.02

[Wreckerboy]

http://heddev.com/miata/product_info...8b15f21405e1d9

i'd be most interested in a critique of this cage. it's the only "cage kit" i'm considering for my next car.

Travis - I looked at that cage when I had my car done by Chris last year. I'll be the nay sayer here on the Miatacage kit, but from a space usage viewpoint only. If you are tall the placement of the main hoop on that cage (just in front of the "parcel shelf") eats up a ton of space inside the car. I'm 6'2" and could not get sufficient head and legroom in any of the cars I say in with that cage installed.

As noted above, the cost difference between that and a custom cage is so little as to be negligable.

[Racer Chris]

Chris, I don't necessarily disagree with your technical points, but you are mistaken on the history of the rules. Prior to the 2007 change there was not even a requirement for a right-side tube. Greg
...

Going back a littler further in history...
At one time a tech inspector would look at all the roll cage rules if he saw an installation exceeding the mandate for a particular car. For instance - wrt the SS side protection - any additional bars would have to conform to the GT and Production rule that a horizontal bar and a diagonal bar bisecting the space below the horizontal were required. Two fully independent bars is stronger than the simple X. Adding a couple of vertical stringers would tie the two together very effectively.

[ScottL]

This may be a naive point, but does everyone here expect that it is possible to build a cage that can protect an occupant from a high speed side collision?

Isn't the primary purpose of a roll cage to defend against a rollover? I know it's a cage, but the strength is in the hoops (and their supports), right? Unlike the front and rear of a car, the sides have almost zero deformable mass to protect the occupants. An incoming car doesn't have far to go (nor much mass to move) before intruding into the cockpit.

Does the number of bars or their arrangement matter much in this kind of crash?

[Dave Patten]

I know the focus in the thread has been on effective side protection, but one of the areas that most road race cage designs seem to not offer is proper forward area roll protection on cars with a highly raked windshield. The rally cages pictured have a tube added into the side hoop from the top of the A pillar to the forward floor pad. This adds tremendous strength to the cage in a roll over or impact on the leading edge of the roof.

The SCCA cage design requires the side (or front) hoop follow the A pillar. Most modern cars have such a low windshield rake that it gives limited support at the A pillar/roof intersection. This added tube in the rally cage stiffens this point tremendously and is an addition that is worth considering.

[DoubleXL240Z]

Travis, I installed the Miatacages.com kit in a customers car, the fit and design were done very well. I was afraid that it would take more work to make the kit fit than actually bending it myself but it worked perfectly. I'll look to find some pics of it installed. definitely 2 thumbs up for the do it yourselfer. I average about $1800 for a cage so its not that far off from a custom cage though.