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davidfarmer

Cage DOOR-BAR design, FIA vs US

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davidfarmer

I'm just curious if anybody has any feedback. Here in the US of A, almost all racing series' now require double (if not more) "NASCAR" style door bars, with several vertical connectors tieing everything together.

 

elite.jpg

 

On the other hand, in Europe, almost every series runs the FIA style door bars, a simple X brace. Quite literally, two bars joined in the middle. Often they are gusseted, but stil you only get 1 bar at the intersections.

 

rollcage.jpg

 

I'm not debating which is safer, as I think it is fairly obvious that the NASCAR style would be much stronger. However, I wonder if the FIA style is simply safe enough. I'm all for safety, but I'm a racer, and I'm willing to take some risk. You hear about deaths occasionally, but it is extrememly rare compared to the number of actual racers in the world.

 

At what point is cage redundancy, head restraints, side nets, arm restraints etc more combersome and inconvenient than they are actually worth?

 

I guess the bottom line is this: If you are unfortunate enough to be T-boned by a car with a closing speed of 170mph, it is going to slice your car in half no matter how many bars you have.

 

Anyway, anybody have any thoughts??

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Greg Collier

The NASCAR design certainly gives the driver more room in the seat plus the additional impact area in the event a side collision. Obviously a 170mph T-bone would rip the car in half but at 60mph the NASCAR setup can definitely take some energy out of the blow.

 

The initial concept of a “rollâ€

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davidfarmer

I don't know that Nascar bars give you any more space. The X design sits low at your elbow, so it just isn't rubbing against you all of the time. Also, especially high NASCAR bars (like my installer put in my last car) made it very difficult to climb into the car. I mean it could seriously extend the amount of time to get out of the car in the event of a fire.

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leggwork

what racing series other than NASCAR require those style of bars? The X satisfies the two bar requirement of most. There might be another series that uses NASCAR bars but IIRC they are associated with the France family/NASCAR. The NASCAR bar specs aren't even public (that I know of), and you have to remember that they are tube frame cars and those bars tie into the tube frame. So, not clear that they are superior in a modified street car. Some say that if they are not designed correctly, then they can invert inwards as much as they are bent outwards and hence impinge on the driver space whereas the X must stretch and hence won't deform as much. There was a long discussion over on bimmerforums.com that discussed this.

http://forums.bimmerforums.com/forum/showthread.php?t=630102

cheers,

bruce

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davidfarmer

SCCA Touring (similar to our production classes) require NASCAR "style" door bars, extending into the doors.

 

SCCA Pro Racing, World Challenge (my old series) now requires 2 sets of door bars. They require Nascar-style bars extending into the door AND an X-bar running straight between the main and front cage supports

 

I'm still looking for ALMS rules for specific details, but FIA/ACO specs can be hard to find. Can't seem to find FIA Appendix J section 253

 

There certainly is no connection between SCCA and the France family.

 

And you are right, NASCAR "style" is what I'm referring to, no actual NASCAR-spec bars.

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davidfarmer

woo-hoo, found it

 

fia-cage.jpg

 

Here, the surprising thing is not only the limited space between the bars and the driver, but he mounting points can only be half the height of the door. NASCAR-style bars that many run here, extend up to the very top of the door.

 

btw, even NASA'a AI rules recomend NASCAR-style bars. The NASCAR reference was removed from the CCR this year.

 

I'm playing devils' advocate here. I am an advocate of a comprimise in the middle.

 

It is just funning watching the FIA GT or ELMS series on SPEED, and seeing these multi-million dollar Masarati's, Aston's, Lambo, etc with a simple, low-mounted X-bar in the doorway

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Sterling Doc

Just to clarfy - the attachment mut not be higer than 1/2 height of the door *opening* which could be near the bottom of the window opening.

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davidfarmer

ah, your right. I'm used to driving Corvettes which have frame-less windows. In other words, without the glass, the door is just the "door".

 

I thought that was a bit low.

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trackboss

All the upper level race cars I have seen that only use straight tubing for the door bars on the driver side also have an impact absorber of some kind attached on the outside of the bars. The WC cadillacs are one example. That being said, one could argue that it is not safe in side impact to use those bars without the impact absorber. As an alternative, "nascar" bars that extend out towards the door skin are used.

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davidfarmer

World Challenge only allows manufacturers (ie GM) to use energy absorbing setups.

 

As far as I can tell, FIA cages require no energy adsorbing door material, just a simple bar.

 

Here is a minimalist example. This the the new GT3 Corvette Z06R. I'm sorry, but I think a 550hp car with an ALUMINUM frame needs more door protection than this. If there is an energy absorbing pad, it is mounted inside of the door panel, and would be ripped off if the door were to come off

 

z06r.jpg

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leggwork

yeah, it looks like the marketing dept had more input on that door bar design than the engineering dept...

 

cheers,

bruce

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davidfarmer

anybody else have any input?

 

I did just get confirmation that World Challenge now requires cars to have BOTH Nascar-style outter bars, AND an inner set of X or parallel bars going straight from the front to rear down-tubes. I guess this second part is to cause the "stretching" acton described above.

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Mike Hurst
.... Some say that if they are not designed correctly, then they can invert inwards as much as they are bent outwards and hence impinge on the driver space whereas the X must stretch and hence won't deform as much. ......

 

This is spot on.

 

Unless you have a massive assembly of door bars and studs (like NASCAR), the straight bars are safer because they will be immediately loaded in tension upon impact.

 

Curved bars will bend, not be loaded in tension, and not have much strength until the bar has traveled a fair distance towards the driver.

 

Best solution is to have good impact aborbing structure outside a set of straight tubes

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davidfarmer

the big problem is that for the Club racer, there is no off-the-shelf energy absorbing material available. Even at the SCCA Pro level, they won't let self-builders use this material, as they don't feel they have the technical resources to come up with something truly better than more bars.

 

As an engineer, I'm not convinced that straight bars are better than curved door bars. While I understand the argument, it still will take a tremendous amount of force to invert a curved set of doorbars, and you would likely have several inches of travel between impact and the driver. While it might take even more force to stretch a straight set of bars, you have literally ZERO margin of safety before it hits the driver.

 

It would be nice for someone with the resources to do a thorough Finite Element Analysis of this, and more importantly SHARE it with the public!

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Mike Hurst
the big problem is that for the Club racer, there is no off-the-shelf energy absorbing material available.

 

Yes there is: The complete, stock door structure is a good and tested energy absorber.

 

The complete stock door with straight bars behind it is superior to the one or two curved bars and a gutted door....this was reported to me, from research, by the FIA institute.

 

Once the curved bars are kinked or bent by the intitial impact, they have almost no strength or resistance from traveling towards the driver. Steel tubing has very little strength in bending compared to strength in tension.

 

If you use curved bars and a gutted door, use at least 3 bars (preferably 4), and tie them together with vertical studs. (like real nascar bars)

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white_2kgt
the big problem is that for the Club racer, there is no off-the-shelf energy absorbing material available.

 

Yes there is: The complete, stock door structure is a good and tested energy absorber.

 

The complete stock door with straight bars behind it is superior to the one or two curved bars and a gutted door....this was reported to me, from research, by the FIA institute.

 

So, you are saying this,

IMG_9206.jpg

 

Is stronger/safer than this,

IMG_9509.jpg

 

ha

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Mike Hurst

So, you are saying this,

IMG_9206.jpg

 

Is stronger/safer than this,

IMG_9509.jpg

 

ha

 

No, (please read my post again), that is not what I am saying.

 

Your car would be safer if your door bars were straight, and you left the door structure complete. The door in the first photo is not complete, structural inner door panel has been cut off.

 

With only the outer door skin between an impact and the door bars, the bars are easily dented or bent early in the crash event. A dented or bent bar is greatly reduced in it's ability to resist further bending, but denting a bar does not significantly reduce it's strength in tension.

 

There is a common misconception that a well built roll cage is impervious, (The cage in the mustang is a very nicely built cage), but in a major impact, those door bars will act more like flexible steel cables than a rigid structure.

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white_2kgt
No, (please read my post again), that is not what I am saying.

 

Your car would be safer if your door bars were straight, and you left the door structure complete. The door in the first photo is not complete, structural inner door panel has been cut off.

 

 

With only the outer door skin between an impact and the door bars, the bars are easily dented or bent early in the crash event. A dented or bent bar is greatly reduced in it's ability to resist further bending, but denting a bar does not significantly reduce it's strength in tension.

 

There is a common misconception that a well built roll cage is impervious, (The cage in the mustang is a very nicely built cage), but in a major impact, those door bars will act more like flexible steel cables than a rigid structure.

 

Ok, I thought the 'bar' you were refering to was the stock door bar. I see now you are talking about the stock ungutted door AND an X. However, it may be 'stronger' I also believe you have entered the realm of diminishing returns. When I was researching door bars I felt the benifits of the NASCAR style door bars outweighed the drawbacks. The extra room added by them helps in ingress/egress in an accident (I've been upside down in that car now, and it was nice not to hit anything on the roll over) not to mention the added room if someone does hit you. I'd have to see actual test preformed using the same material and the same type of impact. My guess there wouldn't be much change in the results.

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Mike Hurst
Ok, I thought the 'bar' you were refering to was the stock door bar. I see now you are talking about the stock ungutted door AND an X..

 

 

Actually, the set up of paralell horizontal bars with vertical studs is superior to the "X"...and the FIA now knows it. The X tends to yield and fail near the center. The newest homologated FIA cages have 2 complete seperate bars instead of one continuous and one split bar.

 

The X was designed with torsional stiffness of the chassis in mind, not side impact protection.

 

Most FIA rules require the stock door structure, or a very specific (and expensive) aluminum / carbon composite "sandwich" impact panel.

 

True "Nascar" bars are good, but I've seen some cars with only an single curved bar and a gutted door, and that is not good, nor is an X with a gutted door.

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white_2kgt
True "Nascar" bars are good, but I've seen some cars with only an single curved bar and a gutted door, and that is not good, nor is an X with a gutted door.

 

This is actually a NASA rule, you can't gut the door w/ just an X, you have to have bars that extend into the door (aka NASCAR bars) and NASA requires at least '2' bars to consider them NASCAR style, this was last years rules, I hear they removed the refrence to NASCAR but I haven't looked at the 07 changes yet.

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davidfarmer

the key there is gutting the door. If you want to leave the door intact, then the x is fine if I remember correctly

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FocusTed

Here's a cage for a World Challenge Focus.

 

MVC-010S.JPG

 

here's the CAD drawing of the cage.

 

focus_cup_cage1.JPG

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davidfarmer

that cage is no longer legal for world challenge. You have to have BOTH the Nascar bars and straight bars, UNLESS Ford has designed an approved crush structure (no, the OEM single bar doesn't count).

 

Not that SCCA is likely to check it, however.....

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trackboss

I see a business opportunity for someone to build crash structures so we can run straight bars and mount the structures between the door skin and cage. Much like the cadillac WC cars. I for one would rather build cars with straight bars and just have to attach a crush structure.

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davidfarmer

I think many have tried, but due to extreme differences from maker to maker, SCCA Pro in particular has chosen not to accept them, UNLESS it is basically a factory racecar (Porsche Supercup, Viper Comp Coupe etc).

 

That does not mean they aren't good, just that there isn't adequate testing data to show that they are better than ton's of ductile steel.

 

I've tried to get some insight from GM Racing (who HAS done tons and tons of testing, and is basically the force being the Drivers' net mandation), but they no longer return my calls. My brief period as a GM race-winner has been long forgotten

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