I'm working on preparing my car for a cage build in two weeks and I'm back and forth on a door bar layout.

I was orginally planning to get the "nascar" style bucket for the driver side and a simple x-brace setup for the passenger side. Now I'm not sure if I really need anything more than a x-brace setup for the driver.

I currently use an open trailer to haul the car so losing my driver window would be a bit of a pain to deal with but that's not a deciding factor for me. I've read as much information as I could find on both designs and I'm still undecided.

I would appreciate feedback and thoughts. Thanks.

Here are a couple pics I found browsing sites:

"nascar" style bucket bars
http://www.vinnymac-online.com/Pics/door1.JPG

x-brace setup
http://www.vinnymac-online.com/Pics/door2.JPG

Nascar style would be MUCH easier to get in and out of. I had my cage finished recently and the x braces are a PITA.

Walter Ford

Built like REAL NASCAR bars, they would be just as hard to get out of because they would extend almost to the top of the door. I'm not sure that what we usually see in club racing fits the definition of "NASCAR bars".

There are ways of build the X bars that make them quite easy to get out of without losing too much of their added stiffness through the use of gussets:

http://www.bryanwatts.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=640&g2_serialNumber=2

http://www.bryanwatts.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=644&g2_serialNumber=2

Personally, if I were running in a Stock or Prepared class with a mininum weight, I'd run a combination of an X-bar setup to stop an impact and provide chassis rigidity with additional lightweight bent "NASCAR style" bars to provide additional impact absorption.

This is me speaking in my OPINION...

99% of "NASCAR" bars you see in club racing are not "NASCAR" bars as Brian alluded to. A true NASCAR bar probably weighs as much as Brian and Andy's complete cage.

The following is THEORY...

A few bars that are bent out to create a NASCAR bar are weaker than an X brace in several ways. One, there is no triangulation so therefore torsional rigidity is slim. 2nd, a bent out bar when impacted can bend the same amount in the oppsoite direction without ever impacting the A or B pillar. IE you are relying mostly on the bend strength of a couple of tubes to save you. A tube is weakest in bending.

An X brace is very torsionally rigid. Also, when hit from the side, the tubes are put in bending but they are also put in tension. They try to pull the A and B pillars together (which isn't going to happen) therefore they will not bend in towards the driver as much.

again my OPINION...

Why not do both? Use an X brace to create torsional rigidity and put a couple of bent out bars for impact. By doing this you create a crumple zone. Use thinner tubing on the bent out bars,too. Also, leave your stock door crash bar in place. Yeah OK this is all heavier but who is going home with their $20k prize after coming in first at a club race?

I like both:

http://www.nrubenstein.com/albums/album09/ncage4.jpg

X
"NASCAR" thingy
and stock brace

it's a miracle the car doesn't tip over. :)

Here is a cage in a GTI that is in the same spirit as brian's with the front of the X lower. Looks like it would hold up the windshield better than a conventional cage.

http://it2.evaluand.com/gti/images/mk3.2/cage08.jpg

What are the merits of having two V-shaped bars welded vs. an X made out of 3 pieces of tubing?

cheers,
bruce

the Nascar style is much stonger from a side impact than the x brace is. I use an xbrace on my passenger side but a nascar style on driver side. Also the nascar bar will move the point of impact farther away from you. Making it less likely to actually make contact with you. My father was in a really bad accident at pocono once in his GT4 Datsun 5-10 and after that our family wont drive anything that doesnt have nascar style impact bars. He didnt have them when he got hit in the drivers door but it was actaully far enough forward that the front hoop took some of the force and it didnt collapse completely. After that incident he says nascar bars are the only way to go. Cause all he can remeber is seeing a car coming at his door with the brakes locked up, and all he said he could think was that his x brace wasnt strong enough and that he wasnt going to be walking after that. He was fine, it hit a little further forware on the car but had it hit directly in the door it would have crushed it and cause some serious injury. Ill try to find some pictures of it. I know we have video but its from far away so you cant really see what happened to the car. but it was pretty much destroyed.

in my car we run Nascar bars, we have 3 bars, 1 striaght solid bar on the bottom right above the rocker, and 2 bent ones protuding into the door higher up. the car is difficult for some people to get in and out of. If you have ever met me youd know that i could get in through window without opening the first picture describing nascar bars.

Again i think its preference but the Nsacar bars may not be structurally stronger but since they move the point of impact out that can help alot, also on our cars BMW rocker panels are pretty strong. In my E30 there is alot of metal there which aids in stopping something from penetrating into the cockpit. So we have Nascar bars, a single solid bar spanning the front hoop to the Main center hoop, the rocker, and the stock bar that comes in the door. Also have foot well bars and a knee bar which helps keep the front hoop in place.

I always love these cage design debates, especially the NASCAR comparisons. How many 3600lbs club race cars do we have doing 200mph?

Unless you have a 600lbs cage, you simply can not be 100% safe.

Nick's picture looks like he expects to be hit by a loaded schoolbus travelling downhill without brakes.

I always love these cage design debates, especially the NASCAR comparisons. How many 3600lbs club race cars do we have doing 200mph?

Unless you have a 600lbs cage, you simply can not be 100% safe.

Nick's picture looks like he expects to be hit by a loaded schoolbus travelling downhill without brakes.
I've been thinking about a few small additions. :)

Edit: Besides, by the time I'm done this winter, I'm goign to have to put north of 200lbs. of ballast in the car anyway. That gives me a lot of freedom with a couple pounds of bars. :)

the Nascar style is much stonger from a side impact than the x brace is.

Based on what evidence? In ultimate strength, it would likely take 4 rows of bent bars to equal the "strength" of a set of X-bars. It takes some force to bend a bar, but not nearly as much as it takes to stretch a bar over it's length. I don't have the calculations in front of me, but I'm not sure that your statement would hold up.

Also the nascar bar will move the point of impact farther away from you.Now, THIS is true.

Making it less likely to actually make contact with you.How much study have you done to show this to be the case? Remember, those tubes are bent outward, and they may have been bent that way by a cage guy using a manual tubing bender. If a guy can bend the bar, surely a car at 80+ mph can bend it in the opposite direction in an impact? So, if the bars are bent outwards 12 inches, they can theoretically bend inwards 12 inches as well without every having to stretch or "tie into" the strength of the vertical bars of the A and B pillar.

Until someone actually tests this, nothing should be presented as absolute fact. While building our car, we actually put some thought into taking an old beater, installing "NASCAR" and x-bar braces on each side and ramming it to see how much intrusion into the cabin each design allowed. It would have been fun. :)

Obviously, other things need to be considered like impact absorbion...which is the reason I would recommmend a strong X to stop an impact and some lighter weight bent "NASCAR" bars to absorb some of the impact.

Cause all he can remeber is seeing a car coming at his door with the brakes locked up, and all he said he could think was that his x brace wasnt strong enough and that he wasnt going to be walking after that. He was fine, it hit a little further forware on the car but had it hit directly in the door it would have crushed it and cause some serious injury.That's all conjecture. You have no way of knowing whether he would have been better off with NASCAR bars or not. Perhaps the NASCAR bars would have bent inwards in the impact and injured him?

in my car we run Nascar bars, we have 3 bars, 1 striaght solid bar on the bottom right above the rocker, and 2 bent ones protuding into the door higher up.That doesn't match up with what NASCAR bars really are. IIRC, NASCAR requires 5 bars and mandates gussets at the junctions. NASCAR takes the approach of using a large mass of bars to keep the impact away from the driver...I'm not sure that directly translates into the 2-3 bars with a couple vertical bars that most folks define as "NASCAR" bars in club racing.

I always love these cage design debates, especially the NASCAR comparisons. How many 3600lbs club race cars do we have doing 200mph?

So who in American club racing has done the impact testing to prove that 2 bent bars is sufficient for an impact from a 2600 pound car going 160 mph? I'd rather take a look the cages that come from factory teams (BMW, Audi, etc) as well as Professional race teams with factory connections (Pratt-Miller, etc). You won't see 2 bent bars in an attempt to mimic NASCAR on their cages.

Nick's picture looks like he expects to be hit by a loaded schoolbus travelling downhill without brakes.

Looks can be decieving. His bent bars may be built from thin-wall tubing that is there simply to absorb some of the impact before it is stopped by the X-bars.

the Nascar style is much stonger from a side impact than the x brace is.

...

but the Nsacar bars may not be structurally stronger .

:confused

[QUOTE=txse46m3
Nick's picture looks like he expects to be hit by a loaded schoolbus travelling downhill without brakes.[/QUOTE]

Probably warranted. Alot of people have it out for Nick:evil2

Neil (just kidding!)

So who in American club racing has done the impact testing to prove that 2 bent bars is sufficient for an impact from a 2600 pound car going 160 mph? I'd rather take a look the cages that come from factory teams (BMW, Audi, etc) as well as Professional race teams with factory connections (Pratt-Miller, etc). You won't see 2 bent bars in an attempt to mimic NASCAR on their cages.



Looks can be decieving. His bent bars may be built from thin-wall tubing that is there simply to absorb some of the impact before it is stopped by the X-bars.
Oh no, same tubing spec. Up front, it ties directly into the dash bar, which I like. (Yes, it's low, but my seating position means that that bar is quite comfortably spaced.)

In back, i want to actually tie it to the x-brace because i'm a little concerned about intrusion there.

Until someone actually tests this, nothing should be presented as absolute fact. While building our car, we actually put some thought into taking an old beater, installing "NASCAR" and x-bar braces on each side and ramming it to see how much intrusion into the cabin each design allowed. It would have been fun. :)


Couldn't Steve J. have done some FEA analysis on this instead of doing an actual crash test? He seems like a smart enough guy to be able to do this and seems to have enough connections to get a hold of some software.

I have Simon H.'s cage in a solid model in Catia that I could further modify to have X intrusion bars with gussets vs a ladder bar design. Actually if someone here can do FEA analysis I could make three different setups. a) gusseted X bars b) ladder bars c) X and ladder bars combined

Our FEA guys here at work use Hypermesh but it seems like a somewhat crappy tool. These guys sometimes have trouble correlating the FEA stuff to actual sled tests. Anyway it would be cool to put an end to the debate with finite element analysis data.

Just a thought.

-Carlos.

Carlos - Would FEA be worth anything without modelling the chassis of the car as well? We aren't talking about a compete tube frame here, but rather a system that works together. The complexities of a modern chassis are rather hard to model from what I gather.

I'd put in $100 towards the "smash a beater" project. Perhaps we can get enough folks interested to cover the costs of someone with the ability to actually put this together?

I'd put in $100 towards the "smash a beater" project. Perhaps we can get enough folks interested to cover the costs of someone with the ability to actually put this together?
i'll bring the beer :D

Carlos - Would FEA be worth anything without modelling the chassis of the car as well? We aren't talking about a compete tube frame here, but rather a system that works together. The complexities of a modern chassis are rather hard to model from what I gather.

Good point. I was thinking you take the cage and define all the base plates as rigid points. Then you take a 2600 lb object of a defined dimension and slam it into the driver's side of the cage at a certain speed. Then you see what deforms further, x's or ladders, and compare how much better an X with a ladder performs.

We test our seats w/o having the entire vehicle in the model, frontal impact, side impact, rear impact (at different speeds) and other tests. So good enough for FMVSS requirements good enough for a bimmerforum debate? :stickoutt I don't know.

Carlos.

i'll bring the beer :D

Hold my beer and watch this! :lol

Hold my beer and watch this! :lol
That's the secondary "fun" segment of the experiment. ;)

We run NASCAR spec full cages. If you saw Joey Hand's car, he had NASCAR bars in his driver's door, so for Brian that's some justification about what a pro road race team runs. We really haven't had any problems with any of our drivers getting in and out of the cars, and use the M&R NASCAR blade type window nets, that drop down easily, completely out of the way.

As far as weight, we have had to add lead to every car we have built to be legal.

Hey David, I'll see your case of Stella, and raise you a case of Beck's :)

James Posig
JMT TrackCars
#231 GTS 2

We run NASCAR spec full cages. If you saw Joey Hand's car, he had NASCAR bars in his driver's door, so for Brian that's some justification about what a pro road race team runs.

Hand's car had both an X with gussets and a ladder bar.
-Carlos.

We run NASCAR spec full cages. If you saw Joey Hand's car, he had NASCAR bars in his driver's door, so for Brian that's some justification about what a pro road race team runs. We really haven't had any problems with any of our drivers getting in and out of the cars, and use the M&R NASCAR blade type window nets, that drop down easily, completely out of the way.

James - How do you define NASCAR spec? Does that refer to design? Tubing size? Rules requirements? I haven't seen anything in club racing that looks like this:

http://www.legendsofnascar.com/chassis2.jpg

That said, the cages in your cars have all looked quite strong, but I'm just not sure how NASCAR spec is defined when building cages into a unibody chassis. I'm not comfortable with the 2 (or 3)-bar NASCAR setup that most folks run in club racing. If it's actually built to NASCAR specs, it's been tried and tested. The X-bars have been tried and tested by multiple road racing teams and manufacturers in Touring Cars and LeMans type racing. Anything in between just seems like guess work as to whether it's adequate or not.

As for Joey hand, his car was built to Grand-Am rules. Grand-Am is owned by the France family, who also owns NASCAR. When PTG runs the same chassis in any other series than Grand-Am, they don't add the additional "NASCAR" bars that the Grand-Am rules require. Of the hundreds and hundreds of BMW Motorsport chassis in existence, my bet is that only the few that are run in GrandAm Cup and GrandAm Rolex have NASCAR door bars. You'll see as well that PTG retained the X-bars on those cars as well. IIRC, the bars on the PTG GrandAm cars don't even tie into the actual cage structure in the front and bottom, but rather are just welded directly to the sheet metal in order to meet the minimum rules compliance:

http://www.dtmpower.net/pictures/ptg_01_27_2001/dscn0737.jpg

Ha! Bryan beat me to it but I’ll leave it as I originally typed...

For the record J Hand's car came from the BMW factory with just the X brace on the door and no harness bars on the main hoop. PTG added the door bars and harness bars. Not all but most European Touring cars don't use either one. Interesting how we Americans like to add all that stuff. Maybe it is a hand me down from NASCAR?

Europeans like to attach the shoulder harness to the rear deck area. Most cars I see in American club racing attach it to the "harness bar" on the main hoop just inches behind the driver seat. My guess for the Europeans doing it that way is so that in a frontal impact the harnesses stretch to prevent your insides from pulverizing from impact. Anyone care to chime in? Same principal as the stitching on harnesses stretch on impact. This is why they are re-usable after a wreck, just send em back to get re-stitched.

An FEA model of a cage within a production car (i.e. a unibody stamped sheet metal frame) is next to impossible. The cage relies on a significant amount of its strength from the sheet metal chassis. Have fun modeling that. We have done some FEA a LONG time ago on some individual joints but it just wasn't worth it. We actually make scale models of our cages and do torsional rigidity tests on the models. However this is only testing the tubing structure itself and not accounting for the sheet metal chassis. Some of the results were very interesting.

So anyway back to the point... NASCAR bars or door x braces. Nobody on this forum can prove which is better. Well let me rephrase that. Plenty of people on this forum can prove which is better but nobody here has the financial backing or time to do so. So searching here for the answer is not going to get you a result. You will however get a bunch of peoples opinions though. Our basic philosophy here is to design for torsional rigidity and let safety be a result of a well-made structural cage. We also tend to follow European Touring car trends, as those cages are, one, built inside unibodies and two, usually built by the Factories with FEA and actual crash test analysis. Remember, NASCAR cages are bound by a different set of rules, i.e. the cage is the chassis so the design is going to be different.

This has been done before but would be fun to see people do in Club Racing. Do an x brace on the driver side so that bars DO NOT intrude into the door. Then skin the door with aluminum and fill the big door cavity with expanding foam. Light and good impact absorption there...

I have been following this as I am right in the middle trying to do the drivers side bars. I am working on an E30 chassis on which I pretty much copied from the M3's that ran in the touring car series back in the day. I would like to go with the 'X' style bars in a plane but cannot because I suffer from a little thing called too much meat and potatoes. After installing the Evo XL seat I cannot keep the plane.

The design I have been looking at is what is done in the current Porsche GT3 cup cars In that the 'X' is still in place but the meeting place for the four bars is offset about 2". None of the bars have bends and there are large square plates on both sides acting as gussetts. They are straight to the main and forward hoops. With this design wouldn't an impact have to spread the whole cage apart to allow the bars to come inward?

They are straight to the main and forward hoops. With this design wouldn't an impact have to spread the whole cage apart to allow the bars to come inward?

No, the bars could still bend inwards before having to move the A/B pillars...that said, it seems a better solution to me than pre-bending the tubes (i.e. creating a failure point) in multiple places (4 per bar on most of the setups I've seen).

I have been following this as I am right in the middle trying to do the drivers side bars. I am working on an E30 chassis on which I pretty much copied from the M3's that ran in the touring car series back in the day. I would like to go with the 'X' style bars in a plane but cannot because I suffer from a little thing called too much meat and potatoes. After installing the Evo XL seat I cannot keep the plane.

The design I have been looking at is what is done in the current Porsche GT3 cup cars In that the 'X' is still in place but the meeting place for the four bars is offset about 2". None of the bars have bends and there are large square plates on both sides acting as gussetts. They are straight to the main and forward hoops. With this design wouldn't an impact have to spread the whole cage apart to allow the bars to come inward?

I don't have a pic of our GT3 Cup car at the moment, but the door bars come together and actually form a pyramid(pointing outwards) with the gussetts. I think Steve J. has posted a similiar pic recently.

I don't have a pic of our GT3 Cup car at the moment, but the door bars come together and actually form a pyramid(pointing outwards) with the gussetts. I think Steve J. has posted a similiar pic recently.

That is what I am talking about!!! I figure if it were in todays 996's and 997's it couldn't be too bad:dunno

Something like this:

Something like this:

I like that setup. Maybe I'll have my guy build my door bars in that fashion.

I'm running the X style of brace in my POS as installed by our good friend at Izzy's Custom Cages. You're welcome to take a look at it anytime to get an idea of positioning with a seat installed. Even though its on an E30, the seat relationship should be comparable. Ingress/egress is pretty good too. I feel pretty safe with how its done. (should be as I'm not going fast enough to hurt myself)

Based on what evidence? In ultimate strength, it would likely take 4 rows of bent bars to equal the "strength" of a set of X-bars. It takes some force to bend a bar, but not nearly as much as it takes to stretch a bar over it's length. I don't have the calculations in front of me, but I'm not sure that your statement would hold up.

Now, THIS is true.

How much study have you done to show this to be the case? Remember, those tubes are bent outward, and they may have been bent that way by a cage guy using a manual tubing bender. If a guy can bend the bar, surely a car at 80+ mph can bend it in the opposite direction in an impact? So, if the bars are bent outwards 12 inches, they can theoretically bend inwards 12 inches as well without every having to stretch or "tie into" the strength of the vertical bars of the A and B pillar.

Until someone actually tests this, nothing should be presented as absolute fact. While building our car, we actually put some thought into taking an old beater, installing "NASCAR" and x-bar braces on each side and ramming it to see how much intrusion into the cabin each design allowed. It would have been fun. :)

Obviously, other things need to be considered like impact absorbion...which is the reason I would recommmend a strong X to stop an impact and some lighter weight bent "NASCAR" bars to absorb some of the impact.

That's all conjecture. You have no way of knowing whether he would have been better off with NASCAR bars or not. Perhaps the NASCAR bars would have bent inwards in the impact and injured him?

That doesn't match up with what NASCAR bars really are. IIRC, NASCAR requires 5 bars and mandates gussets at the junctions. NASCAR takes the approach of using a large mass of bars to keep the impact away from the driver...I'm not sure that directly translates into the 2-3 bars with a couple vertical bars that most folks define as "NASCAR" bars in club racing.


yes ours arent true nascar style bars and you may be right about them being able to bend inwards but an x brace has welds in the middle which arent weak but are weaker than a solid bar. meaning at the center of the x brace you run the possiblity of them crushing and bending there where the bars are welded to each other.

its all theories, as we havent done testing, but i guess someone whould have to test which takes more force to bend. you could build a set of bars and put them in a press and see what bends more. a Nascar style set up or an x brace. I think welds are a weak point in the x brace. those straight tubes also are just as likely to bend than one thats already bent.

Does anyone know if it takes more force to bend a Single Bent piece of tubing or a straight piece of tubing. Also remember with the nascar bars they are all tied together by bars inbetween the horiziontal bars which can increase thier strength. Since the impact would need to bend 3 bars instead of 1 or two.

alot of people seem to think the bent bars will bend against those bends and back in. this might be true but what makes you think a straight bar with a weld in it wont bend inwards either? Im not saying he would of been safer with nascar style bars im just saying he thinks he would of felt safer with them.

i like that Porsche cup cars setup thats pretty interesting.

I guess someone is going to have to build a cage get in a car and run into it at about 60mph and see.

yes ours arent true nascar style bars and you may be right about them being able to bend inwards but an x brace has welds in the middle which arent weak but are weaker than a solid bar. meaning at the center of the x brace you run the possiblity of them crushing and bending there where the bars are welded to each other.

its all theories, as we havent done testing, but i guess someone whould have to test which takes more force to bend. you could build a set of bars and put them in a press and see what bends more. a Nascar style set up or an x brace. I think welds are a weak point in the x brace. those straight tubes also are just as likely to bend than one thats already bent.

Does anyone know if it takes more force to bend a Single Bent piece of tubing or a straight piece of tubing. Also remember with the nascar bars they are all tied together by bars inbetween the horiziontal bars which can increase thier strength. Since the impact would need to bend 3 bars instead of 1 or two.

alot of people seem to think the bent bars will bend against those bends and back in. this might be true but what makes you think a straight bar with a weld in it wont bend inwards either? Im not saying he would of been safer with nascar style bars im just saying he thinks he would of felt safer with them.

i like that Porsche cup cars setup thats pretty interesting.

I guess someone is going to have to build a cage get in a car and run into it at about 60mph and see.
It's simple. An X bar runs a basically straight line between the A and the B hoops/pillars/whatever. Ergo, any incursion into the driver area requires one of three things: 1) weld failure, 2) tubing stretch, or 3) for the A/B hoops to move.

With the "NASCAR" bars, you have the additional variable of extra tub length (no stretching needed), extra bends, and less intrinsic support from the A/B pillars. Neither solution is perfect, but I would definitely choose the X if I had to pick one.

Yes Brian, that pic shows how the x is done as I have seen it. What is interesting is that I do not remember that third bar running horizontal nor the two vertical ones. I like it though.

Another thing to consider is rally car construction, they for the most part use a x style door bar and have to worry about intrusion much more and trees are just a bit narrower then cars which will focus the impact.

This topic has been posted to death guys. Please DONT call anything being used in BMWCCA as Nascar Bars...I've only seen one car actually use nascar bars with a BMW body and its a "baby" bmw which is basically a mini nascar with a BMW styling and a 1300cc motor ;)

People have done FEA, its useless to be honest. Anyone can make FEA do whatever they want. Usually the only person who knows FEA is worthlessis the person who made it...especially when we're dealing with doens of unknowns.

And to be honest, if you are not an engineer, your "factual" based opinions mean as much to the discussion as if I were to suggest you how to practice Law.

Only comment i'll add (since this has literally hundreds of posts in archive) is look at GT level racing around the world, let me know how many of the "ladder" bars you find on production ENGINEERED cars. Only place is as an extra cautionary measure, like in GA.

(running out now i'll try to post more factory car pics showing xbraces dominantly being used, if not all)

http://www.supercars.net/carpics/2984/2005_AstonMartin_DBR94.jpg

I'd put in $100 towards the "smash a beater" project. Perhaps we can get enough folks interested to cover the costs of someone with the ability to actually put this together?


I'll be happy to do the welding, and I have a mountain to throw the car off of while we drink David's beer.

Chris

I'll be happy to do the welding, and I have a mountain to throw the car off of while we drink David's beer.
Chris

I think you want to smash another car into the beater not throw it off a mountain. I own a beater that could be used. Oil burning, rusty azz E30 325is that by some miracle still runs. Groans like crazy too so it has quite the personality. Somebody dial up Mythbusters. :D

Carlos.

You'll need IDENTICAL cars, in identical condition, with Full cages installed, only different being the door brace.

You'll need 100+ people or so with $100/ea to do it right to get even semi acceptable results...and thats if you can replicate the crash exactly, which would require a crash facility, anyone got any connections?

Steve - You're missing the point. Obviously a single example isn't scientifically valid, but it would be fun as hell.

Don't worry i'm not missing the point :) I''ve been part of several "car bashings"

8 engineering students with thier own fully equipped raceshop, over 4 years...produces some fun stuff :)

I think you want to smash another car into the beater not throw it off a mountain. I own a beater that could be used. Oil burning, rusty azz E30 325is that by some miracle still runs. Groans like crazy too so it has quite the personality. Somebody dial up Mythbusters. :D

Carlos.

If you involve those guys we'll be shooting it off the mountian from a cannon. I was thinking of using trees as the impact zone, more "worst case" than another car that would have some give on impact.

Chris

If you involve those guys we'll be shooting it off the mountian from a cannon. I was thinking of using trees as the impact zone, more "worst case" than another car that would have some give on impact.

Chris

Chris were you in the IP car that was in the school the Road Atlanta club race weekend? I remember your car had some nice fab work done to it. Yeah I vote you build the cage! :D

Maybe I can drive down the beater to NC for Thanksgiving (I'm going to Asheville) and you can get started on it ASAP. heh, heh.

-Carlos.

I was just looking at some International cage designs, before even reading this thread and was wondering similar things.

If DTM, BTCC, WTCC, Aussie V8, etc, are using the X bars, they certainly can't be that bad, granted they don't have quite the Horrific crashes that we see everyweekend in Nascar. I think part of the design comes from the difference in the type of wrecks.

Although, this video will show the type of Wreck that can occur in Road Racing
http://www.youtube.com/watch?v=9dIX6Wei2d4

Forunatly everyone was Mostly OK, but the question is how much which bars would help if this impact were on the Drivers side.

Another question comes back to why do only US cages use Cross bars and support right behind the drivers seat? When many International cages, including BMW Motorsport come with what I call an Open Cab design, where there are no bars in the Center of the car, some even Halo the entire roof all the way back to the C pillar, then go down from there.

Standard BMW motorsport chAssis are built to be generic, they are designed to be finished by the user so it can fit exactly into the class its being raced in.

Guys, also realize nascars are tube frame cars that weigh substantially more than most roadrace GT class cars.

The crashes have much more going for them, more weight, higher avg speed, etc.

A lot different then a carbon hybrid/monocoque, or a steel unibody.

Just to add...

Bryan and few others already hit on it but Grand-Am requires those extra "NASCAR" style bars be installed in the car. Only there for that reason.

The welds on the Motorsport cage held up perfect in my 134mph accident with the Watkins Glen guardrail at the top of the esses. Hit the right front/right side and only tubes bent at mounting locations where the whole unibody was smashed in. Welds in the x-brace were noticably stressed and not one showed evident signs of cracks or damage.

Just to add...

Bryan and few others already hit on it but Grand-Am requires those extra "NASCAR" style bars be installed in the car. Only there for that reason.

The welds on the Motorsport cage held up perfect in my 134mph accident with the Watkins Glen guardrail at the top of the esses. Hit the right front/right side and only tubes bent at mounting locations where the whole unibody was smashed in. Welds in the x-brace were noticably stressed and not one showed evident signs of cracks or damage.

You don't happen to have any pictures of the post-crash cage, do you?

I'd suggest looking at the Motorsport E46, E36 and DTM sections, here:

http://e30m3performance.com/tech_articles/cage_symposium/cage_symposium.htm

Chris were you in the IP car that was in the school the Road Atlanta club race weekend? I remember your car had some nice fab work done to it. Yeah I vote you build the cage! :D

Maybe I can drive down the beater to NC for Thanksgiving (I'm going to Asheville) and you can get started on it ASAP. heh, heh.

-Carlos.

Yep I was there. I asked the tech guys to look at it. I think that was you? The new shop needs to get done first, wait till March.

Chris

Well I am in for a little testing... I can built the cages in the beaters :) Let<s find a big parking lot and T-bone cars....

Well I am in for a little testing... I can built the cages in the beaters :) Let<s find a big parking lot and T-bone cars....
I'm in for a hundred bucks. :) Heck, I'll even travel up there for the tests...

Who else is in? Come on folks!

im in for a hundred too and down to help with it

I see the logic in thinking the X bar design is strong because it would be difficult to stretch the tubing rather than bending it as folks consider only the portion of the cage that is inside the doorway. However, if a ladder bar design is supported/braced with straight bars that lean outward from being welded to the steel rocker panel (permitted only in Mod) to meet those bent bars and tie each bar together as well, to bend the ladder inward toward the driver would force those outward slanting bars to shrink....which is even more difficult than stretching tubing. Plus, if the bars at the front and rear of the ladder are triangulated into other sections of the cage, they would very likely be unable to move outward upon impact, so that even those bent ladder bars that protrude into the door would basically have to shrink to be bent so far that they could go all that additional distance to the driver. I know for my own peace of mind driving a car with 4 lb fiberglass doors, I GREATLY prefer the additional safety of the ladder design in my car to an X brace right directly beside my seat/leg/hip. The point has been made that we are NOT driving 3600lbs NASCAR machines, but that works to our favor rather than detriment if you consider the likelihood that our lighter cars are MUCH more likely to be knocked into a spin or out of the way than crumple the cage upon impact due to being so much lighter. Lots of things to consider, so I don't think there is any answer that fits every case in CR since we have so many wild variations on how things are done in the different classes, chassis, and in some cases to fit drivers that don't fit the common Race Driver stereotype!

However, if a ladder bar design is supported/braced with straight bars that lean outward from being welded to the steel rocker panel (permitted only in Mod) to meet those bent bars and tie each bar together as well, to bend the ladder inward toward the driver would force those outward slanting bars to shrink....which is even more difficult than stretching tubing.

Those bars could still bend and never need to shrink or stretch. That said, the more mass you add to a NASCAR type setup, the more likely it is to not bend. Then again, at what point does additional mass make the NASCAR bars so rigid that they don't absorb any impact as they are supposedly desgined to do? Without testing, it's all pretty much a guess.

Here is a cage in a GTI that is in the same spirit as brian's with the front of the X lower. Looks like it would hold up the windshield better than a conventional cage.

What are the merits of having two V-shaped bars welded vs. an X made out of 3 pieces of tubing?

cheers,
bruce

Hey - that's my car. :)

We went with that door bar design because there was no consensus as to whether a simple X - with one continuous bar and two segments forming the "second" bar - actually constituted the two continuous bars required by the SCCA GCR for Improved Touring cars. There's no doubt with our design, built by Competition Cages in Hillsborough, NC.

You'll also notice that the structure "pyramids" outward a little, gaining room for the driver. We left the door structure intact however, as well as most of the door panel, to provide crushable structure between me and the world. A downside of massive NASCAR-style door bars is that NOTHING moves in a side impact, so kinetic energy gets used accelerating things laterally - including the driver.

More at it2.evaluand.com/gti/build4.php

EDIT - I'm not special enough to be able to post images or links so this doesn't make as much sense as it might otherwise...

Those bars could still bend and never need to shrink or stretch. That said, the more mass you add to a NASCAR type setup, the more likely it is to not bend. Then again, at what point does additional mass make the NASCAR bars so rigid that they don't absorb any impact as they are supposedly desgined to do? Without testing, it's all pretty much a guess.

I would describe the outward angled bracing bars as triangulation of the ladder bars with the steel chassis so that both the ladder bars and the chassis would have to bend in opposite directions for the ladder bars to move inward and this would cause the steel chassis of the car to have to stretch to permit this action. That's my perception, but you are absolutely correct in it being a big guess without SIGNIFICANT testing and elimination of other variables (Welding Quality? Material hardness? Consistency of installation? etc.) Let's hope and pray that NO ONE in CR ever learns that his/her cage lacked anything!

I did not realize that NASCAR intended the bars to do ANY absorbing of the impact as I thought they were intended to be very rigid to protect the driver compartment from external objects intruding into the limited space for the occupant (no crumple zones intended as far as I've heard....but then I haven't been paying too much attention to any of their crash test reports either). :)

welded to the steel rocker panel (permitted only in Mod) !

ooopppss sounds like I will have to watch this on my KP car;-)

Hey - that's my car. :)

We went with that door bar design because there was no consensus as to whether a simple X - with one continuous bar and two segments forming the "second" bar - actually constituted the two continuous bars required by the SCCA GCR for Improved Touring cars. There's no doubt with our design, built by Competition Cages in Hillsborough, NC.

Chris Schimmel did my cage, as well. (www.competition-cages.com) I can't speak highly enough of his work and intrinsic knowledge on cage design.

When I had mine built, Chris and I talked about "NASCAR bars" and he explained to me that unless it was significantly reinforced, with an X-bar, that they were much less safe.

Interesting that the other thread: "HMS Cages" by Seb showed NASCAR door bars. As HMS is the official safety consultant for CR, and Joe Marko's work with NASCAR and other racing organizations is well known, maybe he should be consulted on this debate. His wealth of knowledge in safety is immeasureable.

We'll be sticking with our full NASCAR spec cages, built by a NASCAR shop with over 40 years experience in building cars and custom fabrication. They built the cars for Jeff and Ward Burton early in their career, and we know where they are today.

James Posig
JMT TrackCars
#231 GTS 2

Chris Schimmel did my cage, as well. (www.competition-cages.com) I can't speak highly enough of his work and intrinsic knowledge on cage design.

When I had mine built, Chris and I talked about "NASCAR bars" and he explained to me that unless it was significantly reinforced, with an X-bar, that they were much less safe.

I'm dropping my car off with Chris this weekend :D

I too am going with and X-bars. However. I'll be doing so with the addition of a bar that will run parallel with the bottom off the door. I had planed to add gussets at the "X" but that may not be permitted by the NASA/Spec E30 rules. I'm hoping it will be allowed. I like the idea of the added strength to that area.

My car was dropped off for cage yesterday. I went with a driver's side door bar design similar to the pic previously posted of the Porsche GT3 cage. It's a modified X with additional horizontal bars above and below that are tied in with verticals. The point where everything comes together is angled out toward the exterior skin of the car. The passenger side just gets an old school gusseted X.

I did not realize that NASCAR intended the bars to do ANY absorbing of the impact as I thought they were intended to be very rigid to protect the driver compartment from external objects intruding into the limited space for the occupant (no crumple zones intended as far as I've heard....but then I haven't been paying too much attention to any of their crash test reports either). :)

I don't believe NASCAR intends the bars to do any absorbing either, which is why they require the door bars to be so substantial. However, I always hear cage builders and racers recommending "NASCAR" bars in our club racing cars because of the energy absorption...yet I don't know of any who have actually tested this.

In the end, I guess I prefer to go with what has been proven in "built on a chassis" sports cars (including factory teams like BMW that DO crash their cars and perform FEA on them) for years and years. I don't see a single NASCAR style door bar in any of the BTCC, ETCC, DTM, ALMS, ELMS, or FIA race cars...in fact, the only place NASCAR door bars show up in sports cars is in club racing, World Challenge (the same folks building these cars as club racers for the most part) and Grand-Am (NASCAR owned). Different strokes for different folks.

I don't believe NASCAR intends the bars to do any absorbing either, which is why they require the door bars to be so substantial. However, I always hear cage builders and racers recommending "NASCAR" bars in our club racing cars because of the energy absorption...yet I don't know of any who have actually tested this.

In the end, I guess I prefer to go with what has been proven in "built on a chassis" sports cars (including factory teams like BMW that DO crash their cars and perform FEA on them) for years and years. I don't see a single NASCAR style door bar in any of the BTCC, ETCC, DTM, ALMS, ELMS, or FIA race cars...in fact, the only place NASCAR door bars show up in sports cars is in club racing, World Challenge (the same folks building these cars as club racers for the most part) and Grand-Am (NASCAR owned). Different strokes for different folks.

You may be right. Unfortunately, I just don't feel as comfortable (mentally and physically) with the X brace since I'm actually touching the part of the car that would be the first solid thing another car might hit with a side impact. The ladder bar design gives me much more room, makes getting out of the car significantly easier/faster, and I know the bars would have to bend several inches before my body is hit too. If I had more room in the cockpit, I would likely have a hybrid design that utilized both X brace and ladder bars (like the PTG car in the photos). :)

Does anybody even know what the Nascar rules are for the doorbars? I thought the rules weren't public information. If I'm correct that it's not public information, how does anyone here know what a real Nascar doorbar is?

I had planned to get my door bar made like the doorbars from TriPoint (Randy Pobst's car) so I thought I would add this picture into the thread:

http://www.we-todd-did-racing.com/wetoddimage.wtdr/wMTE3MDUzODZzNDEzZGZkMzF5NTQx.jpg

Does anybody even know what the Nascar rules are for the doorbars? I thought the rules weren't public information. If I'm correct that it's not public information, how does anyone here know what a real Nascar doorbar is?
It's a matter of looking at what the NASCAR cars have. What they have it's what's allowed.

I'm with the X brace with gussets...BMW Motorsport, Porsche, RRT and others use that as does many touring car cage fabricators including high dollar factory pro teams that have the funds to R&D for production based unibody type GT cars (not tube framed stock cars)...although it's interesting to see the different types of designs done around the basic x-bar structure, i.s the Aston's vs. say the porsche cup varient

You see a difference in the circle track approach because they are made for a specific set of rules. The ladder bar approach works well when all cars in the field have the same frontal height which gives a narrow area needed to reinforce. Nascar also deals with the fact they go faster in trains than most racing series and the odds of getting hit in the drivers door when all you do is turn left are a lot higher than any other type of racing series. The x-brace approach is the strongest way to reinforce a unibody car, but by physical nature has less "meat" or surface area to dissipate a square strike to the drivers door. So if you want safety, use a ladder design. If you want the best chassis structure, use an x-brace. Maybe there is an acceptable compromise in the middle.

The point has been made that we are NOT driving 3600lbs NASCAR machines, but that works to our favor rather than detriment if you consider the likelihood that our lighter cars are MUCH more likely to be knocked into a spin or out of the way than crumple the cage upon impact due to being so much lighter.

The weight point was more about the energy delivered by a car hitting another, not a propensity for a spin vs. crumple arguement. My point was that a full 5 horizontal bar setup is a red herring when considering that the total energy of a car that weighs 2900lbs and is traveling 90mph (average lap speed for tracks out here, it seems) is roughly a third of a 3600lbs car averaging 190mph. Nevermind that the t-bone incident risk level is vastly lower in road racing than in circlejerk...er oval racing. When is the last time you saw a NASCAR race that DIDNT include a side impact crash?

One other note...it is my understanding that tubing is strongest in compression, not tension...something to consider when looking at nascar bars which much be compressed to be moved into a driver.

You see a difference in the circle track approach because they are made for a specific set of rules. The ladder bar approach works well when all cars in the field have the same frontal height which gives a narrow area needed to reinforce. Nascar also deals with the fact they go faster in trains than most racing series and the odds of getting hit in the drivers door when all you do is turn left are a lot higher than any other type of racing series. The x-brace approach is the strongest way to reinforce a unibody car, but by physical nature has less "meat" or surface area to dissipate a square strike to the drivers door. So if you want safety, use a ladder design. If you want the best chassis structure, use an x-brace. Maybe there is an acceptable compromise in the middle.

It would be really cool if the rigidity difference between the two in a unibody was quantified, even if only in a single model/type chassis.

I'm with the X brace with gussets...BMW Motorsport, Porsche, RRT and others use that as does many touring car cage fabricators including high dollar factory pro teams that have the funds to R&D for production based unibody type GT cars (not tube framed stock cars)...although it's interesting to see the different types of designs done around the basic x-bar structure, i.s the Aston's vs. say the porsche cup varient

Those guys do not always choose the safest route. Often they choose the lightest. An x-brace may have a foot or two less tubing....

I had planned to get my door bar made like the doorbars from TriPoint (Randy Pobst's car) so I thought I would add this picture into the thread:

http://www.we-todd-did-racing.com/wetoddimage.wtdr/wMTE3MDUzODZzNDEzZGZkMzF5NTQx.jpg

That's an attachment point. Hope you're in mod.

My car was dropped off for cage yesterday. I went with a driver's side door bar design similar to the pic previously posted of the Porsche GT3 cage. It's a modified X with additional horizontal bars above and below that are tied in with verticals. The point where everything comes together is angled out toward the exterior skin of the car. The passenger side just gets an old school gusseted X.

Hint...check cage rules. Might want to change the pass side.

No more freebies for competitors!

Edit: Not a saftey thing, not a legality thing....

The weight point was more about the energy delivered by a car hitting another, not a propensity for a spin vs. crumple arguement. My point was that a full 5 horizontal bar setup is a red herring when considering that the total energy of a car that weighs 2900lbs and is traveling 90mph (average lap speed for tracks out here, it seems) is roughly a third of a 3600lbs car averaging 190mph. Nevermind that the t-bone incident risk level is vastly lower in road racing than in circlejerk...er oval racing. When is the last time you saw a NASCAR race that DIDNT include a side impact crash?

One other note...it is my understanding that tubing is strongest in compression, not tension...something to consider when looking at nascar bars which much be compressed to be moved into a driver.

Good point(s).
I tend to agree about the compression vs stretching theory.....At least I HOPE that is the case as I really don't want to EVER find out that those bars might permit another car to hit ME!

I've seen plenty of accidents over the years. Actually, using either design is OK, it’s the seat mounting that's important. Remember, there is a driver in the seat. In 2005 a Z3 was hit in the drivers side at turn one at Mid-Ohio. A 997 was running at full tilt and the Z3 was stationary. The "NASCAR" bars held but the seat broke loose. This resulted in the driver suffering some broken bones. That was probably the hardest hit in the drivers door I've ever seen. What this comes back to is that most of the cages I've seen always hold up in an accident.

In 2006 we had a car that was in an accident at M-O. The driver survived but the real problem was the seat mounting and placement of the crotch belt. The seat broke off one of the bolts and the crotch belt cut into the seat about 6". This was because that belt was mounted way too far back. It’s my fault for not changing this when we bought the cars.

Luckily, the car had the stock steering column in it. This is the second time I've had a car that benefited from this. We had 330 run head on into the wall at about 130mph. The rack moved back about 8" but the steering wheel stayed in place. The M-O crash moved the rack back about 6". Again, the steering wheel stayed in place (even though the column was collapsed). Some people put in a solid shaft, which is a bad idea. It's just a spear ready to go through your heart. The stock steering in a BMW (at least in an E46) is more than sufficient for racing).

What have I done to the car to make is safer? Well, I moved the crotch belt anchors into their proper place, reinforced the seat sliders, tied in both seat rails with a plate of aluminum, installed and made the window net spring out of the way (when released). Every time I’ve had a car in a major accident, I learn a little bit more. I really look at cars now and I have noticed that they usually have a cage built like a tank but the seats, window nets, seat belts and padding are mounted improperly.
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Grand-Am does mandate the “NASCAR” style bars and I’m actually fine with that. The last two 330’s that I built had the three “NASCAR” bars installed. They ran out to the door and made it easier to get in and out of the car. Trust me, there will be a time when you might want to get out of a car in a jiffy. Having an X brace makes this more difficult (especially when you are wearing a HANS device). The cars we currently have, have an X brace (along with the NASCAR bars). Both cars were 2 door BMW’s and the one without the X brace was definitely easier to get out of. There is some young punk that posts here from time to time who has driven both cars and he will probably not agree with me as he is not old and can get into just about everything. As for the rest of us, we need all of the help we can get.
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You can engineer whatever you want for a cage in your particular car but there is a reason why there are rules out there regarding cage design. You can rip on NASCAR all you want, but they are not as dumb as you might think. Actually, in the next year or so, I bet Grand-Am will mandate the crushable structure that required on all of the DP’s and is installed on the Crawford GT car. This is on the driver’s side and is designed to collapse in the event of a side impact. Again, the rules have changed.
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I take this a bit more serious now. When you are on the radio with someone and you have no idea if they are alive until they finally respond, it’s a life changing moment. Those were the longest 10 seconds of my life. After that moment, I cried for about 5 minutes. I am 100% responsible for the safety of the driver in that car. If I cut corners and the driver gets hurt or killed, I’ll have to live with that for the rest of my life. Grand-Am works with the NASCAR tech center and they have much more engineering know how than I do. If they tell me that I need to make a change, I’ll believe them and do it.
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ISome people put in a solid shaft, which is a bad idea. It's just a spear ready to go through your heart.

Seems like the steering wheel would serve to spread the load a bit...

You can rip on NASCAR all you want, but they are not as dumb as you might think.

Heck, I'm usually the guy defending NASCAR around here. I'm just suggesting that NASCAR builds cars from the ground up, so building a "smaller" version of their door bars doesn't necessarily transfer...especially when we don't see the trend towards NASCAR bars from the guys who do specilize in building race cars out of "street" cars.

There is some young punk that posts here from time to time who has driven both cars and he will probably not agree with me as he is not old and can get into just about everything. As for the rest of us, we need all of the help we can get.

I liked getting in and out of the car with the x-brace more actually. It kind of guided you right into the seat. The other one felt awkward getting in and out. :stickoutt But yes the one without the x-brace was obviously easier to get in and out of.

Re: Energy absorbing structures

I think you'll see this introduced in the future for most race cars. As you said, DP's have it, as do the C6.R's and WTCC BMW's and I'm sure many others.

I think you'll see this introduced in the future for most race cars. As you said, DP's have it, as do the C6.R's and WTCC BMW's and I'm sure many others.

I'd love to see them become more popular, to the point that you could simply buy a panel of a certain size and thickness and install it in the door of any tin-topper.

Tubes are definitely stronger in tension than compression. Once you start getting any sort of yielding on a tube in compression, it pretty much folds at the same stress(i.e. a small part of it goes plastic). A tube in tension distorts much more material before yielding. The other bad thing about compression is that you typically end up with some bending as well, so this only further reduces the tube's strength by making the highest stressed part of it deal with a complex stress.

Structures isn't my specialty, but from what I've learned looking at a few "efficient" structural components, I'd say that the X-brace uses the much smaller mass of steel in a much more efficient manner. The typical NASCAR door bar structure seems to have quite a bit more mass and material to absorb energy. It's hard to say which would be the strongest in terms of absorbing the most crash energy before it intrudes into the driver's space, but I'd be inclined to think that the X-brace with gussets would. Once the NASCAR bar starts yielding, the extra space it has before it reaches the driver won't be worth much since it probably already "shot its wad" and it has a much smaller cross sectional area subjected to stresses, and any that is likely has already gone into plastic deformation.

Those energy absorption "energy management" devices have been in racing for probably 15 years+, fortunately we are benefiting from much better technology that gives us extreme energy absortion in short distances (with composites, advanced plastics/foams/etc). I currently have a design madeup for my e46 project which uses an "energy management" device that goes between the drivers Xbrace and into the door shell. Its a fairly common design, with composites enclosing several layers of alum honeycomb with a foam outer shell. If godforbid there is a side impact on the drivers side, where the driver is closest to the incoming load/force, the energy will be dissipated through this device, into the cage and unibody. Even with my seat probably 12" away from the outside of the door skin, nothing short of a direct battering ram hit should penetrate into the cockpit.

Most people are are missing a big point...we're talking side loads midpoint on a tube, not longitudinal. If there is an accident that is pushing a tube directly into itself, thats some pretty spectacular crash that could only happen if it was getting hit head on by a semi and had a semi hitting it from the back as well. If anything it'll be a broad side impact (wall) or a Tbone type incident, which spreads the load out across the door, plus some. Unless someone has a battering ram, you won't get many point loads in car crashes...thats why when you see crash tests they are walls and barriers, not metal spikes. Thats also why most cars in the last 5-8 years have purpose built crumple zones built into the unibody...this is what makes some brands safer than others. The design that goes into how energy is dissapated is pretty intense, and there are some pretty hardcore simulation programs for aiding in these designs.

My problem with nascar "STYLE" door bars is they introduce a huge failure point, and thats because there is a tube between two points that is longer than the shortest distance...which means it'll fail. We are talking about fairly thick walled tubing here, but take 3000lbs at even 50mph, and spread it across the door, you get quite a bit of force trying to push on tubes that have "give" inherent in their implementation. Having an X brace creates a structure that can absorb energy, yet has a higher "ultimate strength" if you will, and with the pyramid porsche design, it can take a HUGE impact, even fairly direct ad hold up very well.

And as for the steering...collapsable columns should be MANDATORY. They are not expensive, and are super easy to install with a cage (which everyone has). Not only do you have Tilting and telescoping features, but you obviously have 2-8" (depending where your telescoping is set) or compressable shaft.

http://www.jaffster.com/E46M3/9-28-06/main/p9270001.jpg


Also, lets just make something clear, I am happy many people are giving thier input about this, but quite frankly, unless you are trained or somewhat factually knowledgable on the topic, declare that with every reply...because you might as well take legal counsel from me, I can make it sound like I know what I am talking about too ;)

This is NOT an easy topic where we can say, "here is the answer," however for those educated in engineering (formally educated, as this is advanced structural engineering) theories and experience in implementing similar designs can help determine the best method. There are literally hundreds of variables that play key roles in determining the cages/chassis strength and where it will fail. If you design in the failure points you can predict more, and therefore know whats going to happen much more likely then if you just build it to "hold its form." I'd much rather wrap myself in 2 feet of foam, then 1" of metal to protect me from getting hit by a sledge hammer.

Xbrace w/gussets FTW. :)

Note: Gussets should be made between all these tubes and the A and B pillar, even if they are very small sheet metal gussets, it will substantially raise the failure point of that tube ripping away from the main hoop and front A pillar. These are legal in every class, as I have yet to see any racing series/body mandate/restrict the use of gusseting internally in the cage. I'd much rather rely on a tube failing from catastrophic tension, then rely on 1.5*pi weld bead.

Tubes are definitely stronger in tension than compression. Once you start getting any sort of yielding on a tube in compression, it pretty much folds at the same stress(i.e. a small part of it goes plastic). A tube in tension distorts much more material before yielding. The other bad thing about compression is that you typically end up with some bending as well, so this only further reduces the tube's strength by making the highest stressed part of it deal with a complex stress.

Thanks for clearing that up...I was having trouble wrapping my mind around the concept of tubes being stonger in compression especially since there's no way that a tube is ever going to have a perfect compression force on it in the real world. Like you said, a crash would in some way put a bending force onto the tube, and once it starts to bend, it loses all sorts of strength.

All of you are wrong. Here's the perfect solution. Have your wife go to Europe for a week and leave you with the kids. Get the kids to bed early, drink a bottle of merlot and sit on the couch cruising the internet. Here in my leather couch, I only need the side support of a pillow. I doubt a car will hit me (it's not impossible) so I will live on the edge. As for living on the edge, I just hope I can get 2hrs of sleep. If I do, then I consider myself lucky. I understand why this young punk would disagree with me. I too had an older sister. I have a feeling that he was beat up too and taking it out on his elders.

Even more interesting. Take a look in the Latest EVO magazine at the Aston Martin that was run at the 24 Hrs of Nurburgring in GT3, It only has 1 door bar! But it looks like it has a very large side impact structure built into the door sill/chassis.

All of you are wrong. Here's the perfect solution. Have your wife go to Europe for a week and leave you with the kids. Get the kids to bed early, drink a bottle of merlot and sit on the couch cruising the internet. Here in my leather couch, I only need the side support of a pillow. I doubt a car will hit me (it's not impossible) so I will live on the edge. As for living on the edge, I just hope I can get 2hrs of sleep. If I do, then I consider myself lucky. I understand why this young punk would disagree with me. I too had an older sister. I have a feeling that he was beat up too and taking it out on his elders.

Was that directed at me? :rolleyes

While I think its an interesting topic, there is really no easy answer.

My personal fear and intuition is that if I got T-boned at HIGH speed right smack in the side of the car, I would not want a straight X-type bar 5 inches from my flank where my lungs, heart and femoral vessels reside.

Even with the best welds, there are a pair of bars there that do NOT cross the entire span of the doorway and could break loose and end up puncturing my body.

I'd rather the bars were a few inches farther away. Yeah, its a gutt feeling, I can't back it up with Cray Super-computer analysis, but its just the way I feel about it.

I find the discussion of how professional series build their cages also a bit muddled for the simple reason that we rarely know the rules, priorities, goals and values of the builders of those cages.

From an engineering standpoint, I'm pretty sure that the straight bars, not the curved nascar ones offer the lightest weight, and most direct stiffness per pound in design, so from a lightness standpoint, and rigidity standpoint, they are the best... I think they're used for those reasons, not because they're the safest. Those teams want to win, and the drivers are not going to say "I won't take my paid ride in this car unless you weigh it down with more cage"

just my 02 cents

Thanks for clearing that up...I was having trouble wrapping my mind around the concept of tubes being stonger in compression especially since there's no way that a tube is ever going to have a perfect compression force on it in the real world. Like you said, a crash would in some way put a bending force onto the tube, and once it starts to bend, it loses all sorts of strength.

Even with perfectly flat plates pushing on perfectly square ends of a tube will cause some bending stress. There will always be some part of the tube that's weaker than another, so as soon as it yields/strains just a bit more than another part bending stress is introduced(because the tube is not perfectly straight wrt the compressive stress anymore).

The outward bends that everybody seems to like for getting the NASCAR bar tubes away from their body extensively weaken the tubes compared to an X-brace(given the same material, thickness, diameter etc.). So yes, you'll have more deflection before it gets to you, but since you make it easier for the car to essentially yield the tubes to a very low amount of strength, is it really helping the situation with bending them out from you? I don't know if it does or not, but it'd be something neat to test if we had the resources.

Also, lets just make something clear, I am happy many people are giving thier input about this, but quite frankly, unless you are trained or somewhat factually knowledgable on the topic, declare that with every reply...because you might as well take legal counsel from me, I can make it sound like I know what I am talking about too ;)


This is a discussion forum - and you aren't exactly some master of structures with decades of experience, so just let everybody be. You've mentioned this over and over again, when it really goes without saying that most people won't have the formal education to really explain their thinking, but that's why this was posted on BF.com and not some engineering forum(of which I can't stand most).

This is a discussion forum - and you aren't exactly some master of structures with decades of experience, so just let everybody be. You've mentioned this over and over again, when it really goes without saying that most people won't have the formal education to really explain their thinking, but that's why this was posted on BF.com and not some engineering forum(of which I can't stand most).

I agree, and never said I have the answer, in fact I know I don't have the answer. I was merely making sure readers were taking everything with a grain of salt, b/c its all heresay basically. But, if we're taking the bars out of context, and most people here seem pretty confident they know exactly how car crashes apply loads, its a pretty easy problem...however the fact that its being added to a structure thats originally designed to be hit from the side WITHOUT a cage also needs to be considered. Street cars get tboned millions of times more than racecars, and they are designed (well the good ones anyways haha) to be able to take a fairly heavy side impact. The big difference with racecars is the driver is more heavily constrained, so technically we want more of the car to absorb the impact, b/c there is more room. We don't have worry about the driver full coming out of the seat, or hitting other parts of the car...wehave to consider the opposite:Parts of the car intruding into the cabin. Since we have the unibodies A, B and firewall protecting the driver without the cage, you have to consider where loads are directed in a side impact. Unless you hit a gaurdrail sideways, its fairly unlikely you'll have a point load onto the door bars.

The engineering forums usually are annoying to post in, but there are definitely a couple good small ones I observe to get some good info from people who do have decades of experience.