Strenght of different tubing joints in certain places.

[javajoe79]

 

 I will begin this topic with a specific question about a certain tube joint in a certain place on a race car. In typical construction of a cage in a normal car, you will have a dash bar that connects the a pillars together from side to side. On alot of NHRA cars lately they have been using a method where the dash bar interrupts the A pillar bar and spans the entire length from door jam to door jam. You end up with A pillar bars that are two pieces with on piece on top of the dash bar coming down from the halo or all the way from the main hoop and one piece from the bottom of the dash bar to the floor.

 I know there are alot of smart folks on here who can help answer this. I am thinking that once this joint is welded up the strength of the joint is no different then if the A pillar was one piece and the dash bar was split into seperate pieces so that it still connected to the door jam. Please let me know what you guys think about this method and would it be legal in SCTA? Of course I would get the appropriate approval before using this method in SCTA.

 Here are some links to some pics.

https://scontent-a-ord.xx.fbcdn.net/hphotos-frc3/1452561_461359333973966_1171769291_n.jpg

http://s157.photobucket.com/user/straight30weight/media/goat22.jpg.html

http://i580.photobucket.com/albums/ss245/petec511/IMG_1261.jpg

[Joe Timney]

SCTA & ECTA do not tell you how to build a cage like NHRA advanced classes specs do, we just offer a drawing of a basic cage and tubing specs.. The examples you showed are very strong due to triangulation. Other than tubing diameter and wall thickness, the SFI chassis spec drawings are an excellent guide for building a cage. They offer various designs of driver location with respect to the cage. One of the things you will see is their attention to tying the A-pillar bottom tubes to the transmission cross member, to keep the pillars from collapsing inward in the event of a crash.  I would urge everyone building a car to buy their designs.

ECTA will honor any NHRA certified cage.

[javajoe79]

Good info Joe. Thanks.   I have access to the SFI books.   I am currently building a road race car for a customer and NASA does not want to let me do the cage like I described. It is not the typical way of doing the dash bar in SCCA or NASA so I am trying to convince them but they won't say yes or no, only give me an opinion that it won't be legal....  This is really annoying as you can imagine becasue I am mid build and they can't answer a question. If I called you up with a question about the cage on Kix's truck for example, you would have a yes or no answer not just an opinion. So here I sit waiting to hear back from someone that can say yes or no even though it was the head guy who told me this. Sorry for the rant...

[johnneilson]

Java,

SCCA and NASA (No Actual Specs Applied) will not answer yes or no. The people, volunteers cannot make that determination.
You can download the SCCA GCR on line for free. Get a 12 pack and tylenol and dive in.

On consideration is that these types of cars need much more driver side protection than say a Bonneville car. At Bonneville you don't necessarily have someone trying to "T" bone you.

At one point having more than 2 bends in the "A" pillar was illegal, then the halo designs came out and that rule is pretty much junk.

The pictures you show are perfectly safe from a strength view, logic is another story.

Also, the dash bar shown in the diagram above is bad, IMHO, having a bend in the middle creates a stress riser and a direct side impact will collapse it.


John

[javajoe79]

I have dealt with SCCA mostly on a pro level. World Challenge. They always had direct answers as they were paid staff. The guy I have been talking to is the executive director who the national office referred me to for this type of question. I am used to a chief technical director type who can make the call on the spot as to the legality of something and make it so. I just got an email back from them a few minutes ago and they gave their approval so I am in the clear now. The regional guy had already approved it but the national guy took issue with it for some reason. The two of them spoke and I suppose the regional guy talked him into it.

[dw230]

Does the SCCA subscribe to SFI?

DW

[javajoe79]

Some things SFI they go by but they have their own roll cage specs. For example they don't give a tubing thickness allowance when using moly tubing. They go by weight of the car. So for example this car I am doing can use 1.5" x .095" DOM but you can't use a thinner wall tube when you use 4130.

[johnneilson]

DW,

Good question.

I don't know for sure, it would seem that any organization would consult the SFI and then make up its rule book.

I do know that the SCCA in amateur racing went through a couple of cage design specs over the last few years.

I would not be surprised to see multiple specs in order to keep the old cars grandfathered in. Some of these older cars I have looked at and wouldn't let my Son drive a couple.

I seem to recall the 2 years on SFI belts replacement and flip flopping on the H&N spec requirements.

John

[floydjer]

Certainly looks to be an easier way to install/weld the top joints on a car w/ the roof in place.

[Peter Jack]

I've used that system on several oval track and road race cars I've built over the years because it allowed me to change the upper cage if the car was rebodied. I've always checked with the sanctioning body before I've done it and never had a problem even though it's unlike any cage diagram I've seen in any rule book. My own (not so humble) opinion is that it's at least as strong as a conventional cage and probably stronger as it allows one to eliminate some of the bends in the structure.

Pete