Door Opening "X" Bars as Side Protection

[Knestis]

>> Dang tube has the potential to go THROUGH the driver.

Ooooh! You could take a core sample, count the rings, and figure out how hold the driver is!

>> But not all of us want to remove the glass. Problem not solved. ...

Take a look again at what we did. We retained enough room for the door glass on my Golf, although we have subsequently removed it under the "NASCAR door bar" allowance. We also did NOT gut the door, and we run the stock interior panels, to put more crushable stuff between the drivers and danger.

K

 

[Speed Raycer]

I can say for sure that I would NEVER race in a car with an X on the drivers side. Dang tube has the potential to go THROUGH the driver.

And a NASCAR style bar also has enough material to potentially to the same thing. The problem is that the impacts are exceeding the materials properties -even when installed properly (proper materials, joint prep, gap, penetration etc). Not that I'd like to see it anytime soon, but I'd like to see how a Nascar style bar would have faired given the same impacts.

Add the reinforcement plates to the X's and the potential is still there for the "Big One" BUT now two tubes will have to have to have their limits exceeded as you're still going to have the same impact force and potentially the same HAZ on the tube. I'm not entirely sure that an additional sill bar would help in the case of these types of hits as the rockers seem top be coming through pretty much unscathed.

I personally am not a big fan of the two bent bars as an X simply because there's enough material to flip inward ... I think someone mentioned like a sharks mouth earlier.. allowing the other car to enter into the cage.

From a builders perspective, if you try to offset the HAZ effect by offsetting the split bars, suddenly your labeled as a hack fabricator because you "can't build a proper X bar". Try to add the proper gusset to a 3 bar X and the customer screams about the 3 hours of labor it took to do it. Suggest an X AND a NASCAR style bar then people are concerned about too much weight as well as cost. Do a traditional "ladder" style doorbar and your back at the hack fabricator status cause you didn't do the cool X with the stamped gussets....

The wording on the rule needs to be well done so as not to limit the builders like the 7th/8th point rule has done. While you're at it, how about adding a provision to go through the B pillars ala NASA's rule so we can put an end to the S bends that are so popular in the NASCAR bars.

 

[trhoppe]

If we require two tubes in the door, a problem arises with reinforcing plates, as in yours: there's really no way to verify that there's two tubes in there.

Correct. But the tube running along the bottom is the "2nd" tube. At least I seem to think so.

-Tom

 

[Streetwise guy]

Just to chime in late in the game, My belief is the x without overlapping the two tubes is really just one tube, and should be treated as such. I have done lots of nascar bars for both roadrace cars and for our local ministock class, and I think the failure point will just move downstream, so to speak,if the doors are built sturdy enough. Our ministock rules require 3 bars drivers side, plated from sill to top bar with 12 guage, creating a very heavy, very strong assembly which is still attatched to the body of the car by two tubes welded to an assembly of 22 guage tin. I always spend almost half of the time and effort in caging a car in getting the mounting plates installed and welded to as many different planes as I can manage. I see cars in every class at every type of race I go to that have a lovely looking cage or roll bar which is not attatched to the car well enough to keep it from moving under any impact.

This has been an excellent thread, with lots of good ideas brought up. I think, though, it boils down to racers remembering, or choosing to believe, that at some point their incredible talent is going to let them down, and that cage you cheaped out on, or tried to save weight on, or figured you could do yourself with that 110v welder from Harbor Freight, is the only thing between you and a fender shoved firmly up your nether regions.

 

[DoubleXL240Z]

I've got to post again!!
First, as a cage builder I agree with both Scott and Streetwise(don't see/know your name) many drivers don't want to spend the money or weight to do it right. Nascar style bars will be stronger than an x. 3 bars will be stronger yet.
But, let me digress for a minute. Half of this thread is people trying to build the strongest cage possible. The other is drawings of door bars that are trying to cheat the "physics" at work in a crash, while being legal. and trying to put a 6foot plus driver in a 5 foot something car. Sorry Travis!
The simplest way to figure this out is too look at a car that is almost designed from the start for side impact and that is a stock car. 3 or even 4 door bars are the norm. Also starting a main hoop halfway up the drivers back is not safe. It should start at the floor, and have a cross bar as close to the floor as poss. parallel with the belt bar. Try to build as close to 360 degrees around the driver as possible.
Double door bars with a third made out of 1.50x.063 would meet the GCR and only add about 5 lbs to that side. Additional tubes do not have to meet minimum dimensions. Also a petty bar from the center of the belt bar to the base of pass. side a-pillar would "help" keep that bar from caving in on a right side impact.

 

[rsportvolvo]

I recently stumbled across this. For those looking for additional ideas please see the BMW E36 Super Touring car pictures located here:

http://www.m42club.com/forums/showthread.php?t=4749

This car was designed and built at the pinnacle of Touring Car racing. The rollcage picks up every key suspension point and the load paths are such that the tubes are not in bending (as much as possible). The only addition I would possibly make is a Petty bar from the top of the main hoop above the driver's head to the bottom of the passenger side down tube (i.e. base of A-pillar tube). Volvo used this type of Petty bar on the 850 Super Tourer.

 

[rbucchino]

Examples of simple design change

These crashes both happened in the last two weeks. The "X" design split just like Richie's, the simple NASCAR design held! Althouth I would not recommend that simple of a design, it did it's job. There was also significant damage to the rest of the chassis, it was deemed repairable.

 

[Speed Raycer]

Sorry.. apples to oranges. Same speed, angles of both cars, etc? Doesn't appear to be. I see the rocker is still intact in the Nascar bar... the rocker's demolished in the X bars exterior pic.

Althouth I would not recommend that simple of a design, it did it's job.

And so did the X bar. The job of the safety cage is not to save the chassis. AGAIN material properties can be surpassed no matter what the design is and how well it was designed/installed.

 

[rbucchino]

The impact was very similar. The lack of damage to the rocker is due to the bars absorbing most of the impact and preventing intrusion. I think this is what we all are hoping for. Check out the photo below of where the energy went, the front was similar. I am just hoping we all can learn from these examples.

This also why when designing a cage, tubes have opposing tubes, not offset like this!

Scott, I also agree about surpassing the materials strength. There are a few different DOM types to choose from, some, even though legal, I wouldn't want to use.
Further more the "X" failure seems to be equally due to design, weld heat, and high impact. The Miller website just had an article about heat and suggests that alot of welders
tend to use too much heat during MIG welding. For example when welding multiple joints on the same tube, each one should be allowed to cool before welding the next. This would definately make a difference. I would like to see what weld failure analysis shows about the properties of the material being altered due to the welding heat. My bet is that when two welds done in succession on the same tube, are causing excessive crystallization around the weld heat zone. Exactly where the break occured on the "X" design.
The BMW shown in the link had nice gussets as well as impact absorbers. Somebody should see if the four gussets would be considered legal in SCCA.
Randy

 

[lateapex911]

The BMW shown in the link had nice gussets as well as impact absorbers. Somebody should see if the four gussets would be considered legal in SCCA.
Randy

I would think it would, as, IIRC, the rule limits it to two gussets per joint, and as there are two joints at an X bar, that's four gussets.

 

[Speed Raycer]

The impact was very similar. The lack of damage to the rocker is due to the bars absorbing most of the impact and preventing intrusion.

For one aspect of this threads debate (X bar design vs Nascar Style), that doesn't really cut it. "Similar" doesn't help and you're assuming that the Nascar bars prevented the impact from reaching the rocker. The X bars rocker appears to mimic the contour of the failed bars meaning the NCBs rocker should be doing the same thing yet are untouched. Not the same hit to make this an apple=apple.

I'd like to see how the X bars hoop joints held up.

I really wish there was a way to sled test this. Same cars, same impacts etc. Although I'd miss all of the internet debates on either "side" Things are always learned. I think the main thing we've all learned here is to gusset the crap out of joints and hopefully to drop the coin on a little more tubing when it comes to cage time.

Heading over to the miller site

 

[Grumpa]

Scott,
I haven't seen anyone mention a particular type of material for gusseting a cage. Gussets in my cage are nonexistant and that will be dealt with now that my season is over. My question is what gusseting is better - flat stock or round tubing? The tube is obviously more time consuming to fab correctly, but are the benefits worth the effort to triangulate with tube?

 

[Speed Raycer]

Really depends on the joint access. If you're not able to get 360 deg. access- use some flat stock

You want to use at least 16 ga. with 12 ga or 1/8 as your max (whatever is closest your tubing thickness). Use some cardboard or 20/22 ga as a template to get your angles correct. Whenever possible (wrt access, time & budget), use a wrapped gusset. Same thing, use a template and then make the final version.

Might be a good time for a thread about gussets... I'll work something up after the weekend if someone else doesn't start one first. I actually get to race for the first time this year so I've got my hands full!!! :026:

 

[Racerlinn]

Looking for opinions. I like the basic structure of the X bars I have and feel that they can be effective. I don't want to take a cutter to what I already have installed, so I am considering adding an additional pair of bars to the existing cage. Pic below, the black bars are existing, the blue are what I am considering adding. I have not gutted my doors as I still have the windows (which I want to retain) in behind alumimum inner door skins. The blue bars would extend minimally into the door cavity, not as a true set of NASCAR bars as many see and do. They would have the "pup tent" tensile bend outward as described originally by tGA. The gap between the new blue bars and the X bars at their center would only be a few inches.
Thoughts?

 

[spdmonkey]

Added weight would be an issue potentially, but otherwise if done properly It would be stronger and you would save ALOT of time grinding welds off. Ask me how I know....

db

 

[Racerlinn]

Added weight would be an issue potentially, but otherwise if done properly It would be stronger and you would save ALOT of time grinding welds off. Ask me how I know....

db

Dave, I'm far from a 10/10th's build, I'm not concerned about the weight.

 

[seckerich]

Steve a much easier upgrade would be to add a parallel bar top and bottom to the existing X. This would tie the bars and add side protection. 2 bars about 24" long should do to basically box the X in.

 

[Racerlinn]

Steve a much easier upgrade would be to add a parallel bar top and bottom to the existing X. This would tie the bars and add side protection. 2 bars about 24" long should do to basically box the X in.

Issue there is entry and egress, especially on the drivers side. A bar along the top would make my gymnastics a lot more difficult getting in and especially out of the seat.
I also like the idea (whether it is proved out or not, I'm no engineer, nor did I sleep at a Holiday Inn last night) of the bar being in "tension", ie. pointed out towards the door. The tubes would only have a single bend, at the "apex" in front of the current X bar cross. The ends would not have bends, they would weld straight on to the front and rear main bars. Of course a side impact would have to be "perfectly" perpendicular to spread equal force to front and rear tubes, but even an offset hit would seem to initially push more energy into the main hoops before getting to the X bar.
Any one else???? Please?

On edit: I also would like the new bars to be down at Miata bumper height.......just sayin....

 

[jimbbski]

I've been following this thread since the beginning and have learned a few things, just to late to incorporate them into my cage build. I had the bars bent by a pro but did the cutting, fitting, and welding myself. The holes in the gussets were put there for looks and not weight savings. Please feel free to comment as I know I'd get some if I asked for none.

 

[Doc Bro]

I've been following this thread since the beginning and have learned a few things, just to late to incorporate them into my cage build. I had the bars bent by a pro but did the cutting, fitting, and welding myself. The holes in the gussets were put there for looks and not weight savings. Please feel free to comment as I know I'd get some if I asked for none.

IMO I think you need a vertical bar in the area of the steering wheel on both sides to strengthen the A pillar if you go on your lid. That span looks long and the bend angle looks steep.

R