Door bar construction

http://sphotos-b.xx.fbcdn.net/hphotos-snc7/s720x720/423454_3471653830329_1686988236_n.jpg

http://sphotos-a.xx.fbcdn.net/hphotos-snc6/165935_4397792623220_1850679661_n.jpg

What are some thoughts on door bars. A 1.75" sill bar is required so with a door X we end up with essentially three door bars. In the four door Impreza, I felt like it's hard enough to get in and out and having just the single door bar (plus sill bar). It is approximately 8 feet less tubing than bent V door bars and requires 8 less gussets in the cage, four less bends and four less profiles saving money and time.

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Grant Hughes

Sorry, having trouble understanding you. Just for clarifications sake

You are asking for opinions on a single door bar + sill bar vs bent v's and a sill bar?

Your second pic is how I did the bars in our Audi my son rallied. That is how I would do another rally car if I built one myself. I would use 1.75 for both bars anyway.

I think the X is just a bunch of compromises as well as a pain for ingress/egress. I believe the X is a mutant design from road race many years ago. Its only purpose is to re-inforce the upper strut mount many cars don't have anyway. If you tie the upper strut into the front A pillar then the X transfers that energy into the lower main hoop mount. The X allows a bit easier entrance than a straight upper bar would in a closed stock car. If ya crawl thru the window to get in you don't need an X...

The other option I like is to take the top bar and bend it down but much further forward. That allows the window crank to be used on many cars. It would touch at about 3/4s of the opening rather than 1/2.

Grant, Empty your PM's (you find any where to stream/listen to olympic soccer? NBC wants login info I don't have)

Done. I've been watching on the probably sketchy site, oleoletv.com.
Thanks for your opinion Gene! I think I'd heard you say that before as well.

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Grant Hughes

I prefer the single bar with a sill bar, both 1.75".


What rules are you building to that require a 1.75 sill bar?

Here's a mockup of the X and a single bar in my VW:

The X is good for cage triangulation and torsional stiffness. Not as great for secondary considerations like side intrusion and ingress/egress.

I think it was Carroll Smith (or maybe Smokey Yunick?) that said, "The trouble with drivers is they prevent proper triangulation of the roll cage."

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fliz
I prefer the single bar with a sill bar, both 1.75".
What rules are you building to that require a 1.75 sill bar?

I suppose it's not a sill bar required, it's just a single 1.75" continuous door bar. I just always do it as the sill bar.

I climbed in and out of the Impreza today fitting the dash. It was hardly noticeable compared to something miserable like Kern's BMW with it's well triangulated door bars and X.

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Grant Hughes

something like that would be great for me with an Rx7....

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First Rally: 2010 First RallyX: 2004 (a bunch)
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Last Updated, Apr 9, 2023

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heymagic
I think the X is just a bunch of compromises as well as a pain for ingress/egress. I believe the X is a mutant design from road race many years ago. Its only purpose is to re-inforce the upper strut mount many cars don't have anyway. If you tie the upper strut into the front A pillar then the X transfers that energy into the lower main hoop mount. The X allows a bit easier entrance than a straight upper bar would in a closed stock car. If ya crawl thru the window to get in you don't need an X....

Bingo, Gene. Glad someone else is getting this finally. Your analysis of the 2nd bar in the x is right; it was put in there to tie the front strut bar back to the floor. The 2nd bar does NOT act as 2nd stength member in side bars; in many cases, it actually tends to concentrate energy more into the very short center of the uncut throughbar, rather than letting it spread more through the whole bar; that is not good. So with an X and a sill bar, you have in essence have only 2 side bar members total, not 3; you DO have a place for welds to break and form bad pointy ends, in the weakest area of rally cages as they are now.

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starion887

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heymagic
I think the X is just a bunch of compromises as well as a pain for ingress/egress. I believe the X is a mutant design from road race many years ago. Its only purpose is to re-inforce the upper strut mount many cars don't have anyway. If you tie the upper strut into the front A pillar then the X transfers that energy into the lower main hoop mount. The X allows a bit easier entrance than a straight upper bar would in a closed stock car. If ya crawl thru the window to get in you don't need an X....

Bingo, Gene. Glad someone else is getting this finally. Your analysis of the 2nd bar in the x is right; it was put in there to tie the front strut bar back to the floor. The 2nd bar does NOT act as 2nd stength member in side bars; in many cases, it actually tends to concentrate energy more into the very short center of the uncut throughbar, rather than letting it spread more through the whole bar; that is not good. So with an X and a sill bar, you have in essence have only 2 side bar members total, not 3; you DO have a place for welds to break and form bad pointy ends, in the weakest area of rally cages as they are now.

Ok, so, the infamous "bent V" door X's...

What about them? They're two continuous doorbars, welded and gusseted in the middle. Besides e/ingress, how do they fair against two straight bars?

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Welcome to the cult of JVL drink the koolaid or be banned.

The dual bent vees that meet in the middle are better than the x. You have 2 true continuous bars all the way, and no single point of essentially one tube in the middle for force to concentrate. However, the issue with these that folks do not realize is that the strength of the connection of the length between the 2 bars in the center is very critical. If you just weld it with beads inside and out, or even reinforce it with the crazily thin .040 (1mm) FIA spec'd clamshell material, then there is a good chance to have the tubes separate; the way the forces work on this joint is to apply leverage on it and very readily separate it. If this joint separates, it takes very little additional force to rotate the 2 bars inward, and the 2 tubes are quite free to twist around their end connections and rotate inward into the occupants; that is very bad. I fuss at folks that they need to weld plating along the length of, and on the INSIDE of this center joint, at least 1/8" thick, and preferably wrapped over the top and under the bottom a bit, and welded all around. This is best place I can think of to add something to keep this joint rigidly together. There may be better methods and I would be glad to learn them; but this center joint has to be STRONG.

I agree with Mark. I'd guess the better plan would be to have the two bars be bent, run together for a foot or two then bend away to the terminating point. The parallell area gives more welding and plating, less twisting motion when hit and easier ingress/egress.

I think on the conventional race inspired X that if the x center was offset a few inches on each end instead of symetrical it might be a bit stronger.

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heymagic
I agree with Mark. I'd guess the better plan would be to have the two bars be bent, run together for a foot or two then bend away to the terminating point. The parallell area gives more welding and plating, less twisting motion when hit and easier ingress/egress.

I think on the conventional race inspired X that if the x center was offset a few inches on each end instead of symetrical it might be a bit stronger.

I know Sean Murphy did this on my old VW when he re-did the door bars. How much can we legally have the bars bent to make contact? Because doing something like the Mini Prodive has would be an ideal situation to get the best of both worlds? Long contact between the two bent bars, low center for easy in/out of the car. But I agree, that an X is only good if you have the front shock towers tied into the cage.



Interesting thing I saw in the article I pulled the picture from... they don't seem to run a dash bar at all on this car from the 3D model.

http://www.eurocarnews.com/238/0/0/6895/3d-modelling-helped-prodrive-optimize-design/gallery-detail.html

Billy,
No constraints on bending the bars in this case. The Mini bars don't touch so the gusset will need to do a lot of work. I would have siamesed the bars and then a gusset over them.

I'd still tun a sill bar btw, probably a 1.75 X2" or 3" box in 3/16".....did that on one of my cars and it later (different owner) soundly smacked a stump. Roll panel and door went pretty flat along the box tubing and that was that. Door still opened and closed...leaked a little wind but oh well.