Door Opening "X" Bars as Side Protection

Greg Amy said:

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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.
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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.

More examples, all from Euro rallying...



This was the primary inspiration for the Pablo II-spec cage



This one has an additional bar that I wish in hindsight I'd added - from the rear terminus of the top door bar back to the strut tower.



A US-prepared rally car, pre-gussets.

K

For folks looking for impressive safety cages for production based cars I suggest looking at the Australian V8 SuperCar roll cages. There is a lot of good ideas, one being cross bracing the floorpan. We all assume the floorpan is stiff and only really pay attention to the side and top sections.

I keep a file on roll cages that I see pics of on the net. Many of them have influenced the design on my Volvo 240 (cage goes in this winter, finally).

jerestahl said:

The attached photo was my interpretation of how to build some protection into a door bar and to meet the idiotic SCCA 8 point cage attachment rule which is the 1st rule that needs to be changed to improve driver safety.

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I couldn't agree more. I'm not sure what the logic is with limiting the number of roll cage attachment points. It only seems to limit safety by reducing load paths.

Racer Chris said:

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

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

http://heddev.com/miata/product_inf...id=35&osCsid=b354913a13d93cf9668b15f21405e1d9

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

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.

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.

Had to split this up because of image rules...

This is the ITB Civic that I am currently building for myself.









I was happy with, and felt perfectly safe in the CRX cage. I wanted to try some things differently on the new car and made some changes in the door bar and rear bracing areas to both add some extra strength and maybe loose a little weight in the right places. My philosophy has always matched what the pictures that Kirk posted of the euro rally guys. (The GT cars are similar too). That is, to try my very bestest to make all the tubes connect at nodes that are supported by at least one tube in another plane with no dead load paths. Also, I feel that the cage itself should be its own structure that can completely be strong on its own without being welded into the car. That way, any energy from an impact, regardless of where it occurs, gets distributed throughout the cage and it's mounting points. This is easy to do in the rear half of the car, but it gets hard up front due to the rules as they are written. The cages are safe, I think, but could be a little better up front with more attachment points.

rsportvolvo said:

I couldn't agree more. I'm not sure what the logic is with limiting the number of roll cage attachment points. It only seems to limit safety by reducing load paths.

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One benefit is that spending mega bucks on dampers is pointless, as the chassis is an undamped spring of sorts....

tnord said:

http://heddev.com/miata/product_inf...id=35&osCsid=b354913a13d93cf9668b15f21405e1d9

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

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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

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?

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.

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.

...and i forgot to mention that when i put in my seat, I put it as far to the right as possible - gained about 3" in additional distance from danger, which might someday be very appreciated.

K

tnord said:

http://heddev.com/miata/product_inf...id=35&osCsid=b354913a13d93cf9668b15f21405e1d9

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

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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.

Wreckerboy said:

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.

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i wondered about that. i'm 6'3'' so i'd likely have the same problem as you, but i'd never sat in one so it was hard to say.

looks like i'll be going the custom route.

Greg Amy said:

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
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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.

Greg Amy said:

At yesterday's NARRC Runoffs at LRP, ITA Integra driver Richie Hunter spun in West Bend, a very fast sweeper corner leading up to the bridge. He stopped driver's right (normal line is driver's left), with the passenger side of the car facing oncoming traffic and the two front wheels in the grass. As he sat there, perpendicular to the traffic, two or more cars passed by safely before another car t-boned him directly in the middle of the passenger door.

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Not quite as described here...Hunter was still moving and was not off course during impact...only one car got by - and that was BARELY...but the video is proof of the intensity of the hit.

[ame]http://www.youtube.com/watch?v=eDpUjcQe92c[/ame]

What happened to the video?