complexx

Good input, thanks. My plan for the driver side impact tubes is to do an X brace, but have it extend into the door in the shape of pyramid on its side (similar to the new gt3 cup car brace). I'll have the builder add either 2 or 4 gussets where the X bracing tubes meet like on the gt3 cup car as well. I'm hoping it will not intrude on the driver like this. We'll see when we speak with the builder.

This was the intent of my idea before I asked, but I wanted to see what you all thought before I stated it.

Geo

Actually, while I'm a proponent of the X door braces, IMHO if you aren't going to keep the X in a flat plane you may as well go the full NASCAR bars route. The "bent X" loses the rigidity of the X in a flat plane and it also now is composed of tubes that are no longer the shortest distance between two points, thus reducing their strength.

M758

I agree with Geo on this.

The X works best when in the same plane as the side of the cage. If you must bent it outward in to the door I would go with a more Nascar style set-up.

One way compromise is if you put an extended X in the doors then below the X, put a single tube from the main hoop to the front support in the plane. Then tie this bar in to the extended X in the center with a short 12" or so vertical tube.

complexx

I see what your saying about the bent X bracing. However, I'm not convinced that a nascar basket will withstand a side impact any better than a gusseted pyramid (or bent X brace) will.

I'm really not a fan of the nascar methodology. It seems that the basket would require many more tubes, more weight, and from what I've been told, would actually give way before a basic X brace would.

I'm still not sure what the best method for this side impact protection is.

complexx

Like this? I love MS PAINT

M758

Yep,
The bottom bar is straight and in one plane and the X and short tie bar are angled a bit.

Lefty's Deceiver

I prefer the NASCAR style (about the only thing I like about NASCAR) because it gives you more room and you get to remove a door panel and glass which compensates for the cage weight. Also, they just look safer.

Cory M

Here is another take on 944 door bars. The door is gutted and the X is bent but has upper and lower bars attached to the X at the bend with vertical bars. Very robust and offers the driver more room than a flat X, probably heavier than Nascar bars though. Tall people would have a fun time climbing in and out.

The car isn't mine, I just snapped a couple of pics at an event. I was very impressed with the workmanship on the cage, which was done by Hergeshiemer Motorsports in CA. It was fully TIG welded and all the tubes were bent and fitted exceptionally well.

RedlineMan

Good Lord!

What is that guy worried about on track... cement mixers? Talk about over built!!! Of course there is nothing wrong with a little excess in the name of safety, but holy cow!

Anyway, I dissagree with the criticism of the bent X idea. I understand the basic premise of the argument against them, but I think it is over simplifying it and that the reality isn't quite that dire. The factory is almost ALWAYS a very good reference for what is keen. They have done a gussetted "pyramid X" in the Cup Cars for years. Yes, it is a compromise to ingress/egress, but not a drastic one. A poorly rendered NASCAR bar is worse in my opinion, and the vast majority you see in sports cars will fall under this heading.

Complexx, I think you are spot on in your thinking regarding the NASCAR way. They rely on factors not found in the normal sports car cage to be effective, namely being massively OVER BUILT. This has been discussed before, and I'm sure a search for "NASCAR door bars" would work well for you.

Cory M

I thought it was overbuilt too and I don't think I would have included the top bar, either way it is another take on door bars and is obviously very strong. It also had an X on the main tube rather than just a diagonal and harness bar. I looked over the cage very closely and can say that the work by Hergeshiemer was top notch. I think his last car was totalled going into a wall and he apparently didn't want to take any chances this time!

Geo

For the record I'm a fan of the flat plane X because I think it's the strongest solution, mass for mass.

I agree that most RR NASCAR bar set-ups leave a LOT to be desired.

As for the bent X, my reasoning is, if you're going to compromise the X, you may as well commit to good NASCAR bars and really gain some room. That room is VERY tempting. My car is tight with the flat X (but workable for sure). When I sit in a car with NASCAR bars (our Sentra SE-R that's being converted to SCCA EP for example) I'm jealous of the room it provides. I think the bent X is the worst of both worlds instead of the best. It compromises the strength and rigidity of the flat plane X and doesn't give you the room of the NASCAR bars. To sum it up, I guess I would say if you're going to not take the advantages of the flat plane X, you may as well go all the way and take full advantage of the space provided by the NASCAR bars.

bruinbro

With the bent X, doesn't a side impact cause the X tubes to spread the body apart due to thier shallow angle with relation to the door plane? A small out-of-plane force equates to a huge in-plane force. The action would be similar to an over-center latch.

Bro

tinman944

I am a huge fan of the X Bars bent out
Even if the bars where bent one degree it would be stronger in a side impact.
easy to test
take a piece of tubing and lay it across two bricks now jump up and down on it.
now take a bar and put a one degree bend in it and do the same test. it will not bend.

Geo

Not exactly a valid test. The straight tubes are not anchored in your example. Also, hit those bent tubes from an angle rather than perpendicular to the base of the pyramid. Will it still be stronger? I don't know for certain, but would love to see some really good FEA on this.

M758

Too bad my job has changed. Afew years ago I could have run a simple FEA model of this stuff for some real answers. Now I no longer have access to the FEA programs at work.