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Full Cage - construction challenges?

Old 01-19-09, 10:36 AM
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Full Cage - construction challenges?

I was originally going to post this as a follow up to the "Show Me Yours" thread, but figured that I shouldn't hijack it quite that much.

The question: when designing/constructing a full cage in an FC (SCCA ITS legal for the purpose of this discussion) what did everyone find to be the more difficult aspects of getting things to fit?

The background is that I'm finally determined to get a full cage in my car and start getting it to the point where I can at least begin to entertain going door-to-door racing. I have a couple people in mind for construction and I want have a specific design in mind when I talk to them.

One example: I'm a fairly big and leggy guy, so I have the have the seat fairly far back. This would seem to push the main hoop back (to give my head clearance) but how does that impact (sic) the design and strength of NASCAR style door bars, specifically where they tie into the main hoop? I have seen people do reverse bends in order to clear the back of the door frame, but I definitely want to avoid that if possible. Any thoughts on how to do that?

Other comments and ideas would be most appreciated.

-bill
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Old 01-19-09, 10:55 AM
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Bill,
All you need to do is to tie the door bars together vertically and down to a plate on the rocker/floor area. This will greatly strengthen the door bars and protect you very well in a side impact. Just look at how NASCAR cages are done and you'll see what I mean.
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Old 01-19-09, 12:48 PM
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ITS still limited to 8 pts. right? Those bars going to the floor would cause you to delete some forward protection. I would just tie them together and do whatever bends you need to get them in. I've seen the pretty tall guys get in FC's with the hoop in a place that only one bend was required though. You can do some things with the main hoop that will give you more room for a seat and door bars. The shoulder height harness bar can be bowed back and the legs of the hoop and can be pinched in to the maximum 10 degrees from the height of your shoulder. That will give you more room to send a bar into the door without hitting the jamb.

I would say seat choice is going to be the key.
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Old 01-19-09, 04:32 PM
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I'm 6'1" and I fit in my FC pretty well. I've also got longer lower legs (Can't drive stock FD's or pre-2005 boxsters because my legs are pinned to the steering wheel). Have a peek at my cage (bottom of page)
www.rxracing.com

-Trent
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Old 01-19-09, 06:25 PM
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Put the seat in place where your confortable with arm position & leg room. You may need a quick disconnect hub for your steering wheel including a spacer to suit to get the steering wheel away from your legs. If the steering wheel is geting to high upward you could always add a spacer between the steering shaft mounting bracket & the dash mounting surface. Just don't tell people what you did with the spacer because it may be deamed not legal. Once your happy with the seat location start looking at where your main hoop, horizontal (seat belts), diagonal & side protection needs to be for your comfort & safety. Keep in mind that you can get your side protection tubes in the way & whack the side tubes with your elbow. Get another experienced racer to support you effort.
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Old 01-20-09, 12:27 PM
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Thanks, Trent. I'll go have a look.

David: I already have a quick disconnect hub with a spacer. The wheel is in about the right position. But with my current roll-bar (a modified autopower) the main hoop is right behind/above the headrest of my Kirkey seat. It's just far enough away, but I am worried about clearance when I go to a full cage.

Thanks for all the comments.

-b
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Old 01-20-09, 04:02 PM
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Bill,

Cage wise the hardest issue was figuring out how to clearance enough room for my head with helmet to keep it as far away from the a pillar bar as possible. So my seat is bolted to the floor pan, we squared off the floor pan where it meets the tranny tunnel to make a bit more room

the autopower bar bolts to the floor pan as I recall, and a welded cage, ideally, should weld to the subframe cross member, rather than the floor pan. Much stronger part of the car, plus gets you 3-4 inches behind you. Once you do that you should have no issues with the main hoop being too close to your head.

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Old 01-20-09, 06:25 PM
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Nice seat/belt mount Silkworm.

When mounting your seat don't be afraid to tilt it in toward the middle at the top. Once you get on track you will never notice.

Another trick to get more room above the window for your head/padding/rollbar is to cut the body reinforcement parts that double up the structure in that area. You slot that panel and hammer it back close to the roof and window seam and you will pick up about an inch that you can put the cage into.

Its fine in the rules even for IT because that basic premis is 'anything for the cage/driver safety and comfort'
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Old 01-21-09, 10:07 AM
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Thanks guys, that's been real helpful.

-b
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Old 01-25-09, 01:52 AM
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Do you have to run NASCAR style doorbars? Is an FIA style cage legal? Could you do something like this?



through on the required gussets in the main hoop X, the door X, the brow to half lateral bar, and the A pillar reinforcement bar to door bar and your good.
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Old 01-25-09, 10:06 AM
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Hey Dazed -

The NASCAR bars are not required, but highly recommended. Having seen the results of side hits at speed (both from car-to-car as well as car into tree/barrier) I would like to get as much side impact protection as reasonably possible.

Your FIA design would not work for SCCA Improved Touring because they do not allow you to penetrate the firewall and tie into the front suspension. The rest of the design would would work, with appropriate modifications to the front.
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Old 01-25-09, 02:32 PM
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Ahh. That is a cage I drew up as kinda a "Rally car I would love to own" style thing, hahaha.

How do you stiffen the front struts in SCCA? Can you use triangular strut tower braces? How about gusseting down the tower to the frame rail? Can you reinforce in front of the tower?


EDIT: Oh yeah, the main thing to look at (that I forgot to point out) was that if you angle the main hoop back a little, and space it further back you can use the "cossie bars" (the little bars going from the half lateral to the main hoop in the upper left corner) to protect more around your head. This is really common in rally cars, 4 door (WRX, EVO) especially, as you can place the main hoop behind the B pillar, and then have the door bar tubes touching the body shell because you can easily weld all the way around the door bars.

Last edited by dazed_driver; 01-25-09 at 02:37 PM.
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Old 01-25-09, 09:40 PM
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Single strut bar only. No triangulation allowed. It is, afterall, an entry level class. The prep level is fairly limited.
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Old 01-26-09, 02:14 AM
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hmm. Thats kinda lame, but I understand.
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Old 01-26-09, 12:54 PM
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If you want to go to the sort of level of prep that you seem to be thinking about, then your have the SCCA "Production" class, where much more is allowed, but also much more money is spent.

Or you can go the NASA points route.

-bill
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Old 01-26-09, 02:47 PM
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Whats under production class? Production is the lowest rally prep class.
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Old 01-27-09, 06:17 PM
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First of all you will need to determine 6 or 8 point roll cage. IT only allows 6 or 8. No more. Also check with the region rules to see what else applies. If you are running in ITE things will vary. ITE is a Regional Class and therefore rules can be modified to fit the Region's needs. Here in Oregon we are allowed "Must meet or exceed 8pt" so anything is allowed. May not be if the car travels out of the Region.

SCCA also changed the Material list so the tube size is different, for the best. Determine the weight from the GCR to determine material size. Bigger thinner is better than smaller thicker for weight and strength. Use 1.75"x.095" instead of 1.5"x.125".

Also you will need to figure out door bars and how far you are going to go with the door skins. I prefer a "X" over "NASCAR" type bars. We are not allowed to add additional uprights from the rocker to the bottom of the bars like in a true Stock Car. That is considered a mounting point and not allowed unless your region allows it in ITE. Check with Region Tech.

If you do the "X" pushed out into the door skin you will gain a valuable crush zone between the seat and the door bars. Use sheet steel gussets to tie the intersection together for further strength. You can do a combination of both also. A very good option.

Down load the rules and take with you when you talk to the shops.
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Old 01-27-09, 06:41 PM
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cagedruss, did you ever hear about the Subaru rally cars going with smaller/thicker, like 1 1/2" x .120. In testing they found while it wasn't as strong as 1 3/4"x .095 (most likely in some metric form) it would bend more before it finally collapsed. They felt for the things they tend to hit it was a better trade off. I read it in Racecar Engineering a couple years back.

I still do all my sedan/road race stuff in 1 3/4" DOM though.
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Old 01-27-09, 07:59 PM
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I'll update my drawing later tonight with Rally America and NASA rally cage guide lines. RA uses more 1.75x.095 tubing, but NASA only requires that size for the main hoop. I'll highlight it for you guys.

My personal roll cage is a NASA cage.
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Old 01-27-09, 10:28 PM
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uh, as I cant see an edit button anywhere....

This is a NASA cage. (although it does need a sill bar as well... I forgot to put it in for the picture)


Rally America Cage.

The green is the 1.75x.095 tubing. Everything else is 1.5x.095. Its all DOM. ERW is NOT allowed. CDS is.
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Old 01-28-09, 09:57 AM
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X-bars vs. NASCAR

Hey Russell,

The thread got a little hijacked, but what the heck.
Originally Posted by cagedruss View Post
Also you will need to figure out door bars and how far you are going to go with the door skins. I prefer a "X" over "NASCAR" type bars. We are not allowed to add additional uprights from the rocker to the bottom of the bars like in a true Stock Car.
Interesting. I've always heard that NASCAR bars were the way to go if you could fit/afford them, but your comment makes a lot of sense. I still can't help but think that using a NASCAR design with three bars (a sill bar and two door bars) would be at least as strong as an X, but a lot heavier at the same time.

If you do the "X" pushed out into the door skin you will gain a valuable crush zone between the seat and the door bars. Use sheet steel gussets to tie the intersection together for further strength. You can do a combination of both also. A very good option.
Could you elaborate on this? Are you just taking about a combination of gussets and having the penetrate the door?

Thanks,

-bill
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Old 01-28-09, 12:54 PM
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Yes, I heard about the Rally Teams using the heavier wall tubing for the extra strength. It is really hard to compare the two series and structural cages between the two. The odds of hitting a boulder or 20" tree is rare in Road Racing. The FIA cage has many years of development with a little help from the Attorneys like all sanctioning bodies.

Roll cages are designed to keep the passenger safe by having crush zones built into them. The Average Pro Rally Car has panels designed to absorb the energy before it even gets to the cage. The biggest weakness is the door bars in the FIA cage. X is flat and has no strength from a side impact and is using just the tension aspect of the tubes, not compression. The span is rather large and has a greater area of failure under heavy impacts with non-movable objects. The X affords its greatest strength in a frontal impact and lets the energy pass through the bars to the rest of the cage.

The NASCAR style bar is stronger on a side impact due to the amount of bars and uprights. But a true NASCAR style bar has uprights welded to the frame.

The image is from the bottom view of the bars. Since we have rules against attaching those tube because of the purity of the rules our NASCAR bars have to take the impact across a much larger span. Don't take me wrong, 3 tubes tied together with multiple uprights is pretty good. Many people actually do that. They will run 2 bars and attach 2 uprights and call it good. Some will even have a bend that bends inward to reach around the B pillar close to the driver's seat. Its all a matter of playing the odds.

Here is how I do NASCAR type bars. Not the best but better than just 2 bars. I and my Engineer friend does not believe in having Door Bars running uphill to the main hoop like some people do. He says something about frontal energy absorption plus it looks wrong. I have to agree. I have never seen a Pro Car series use them like that.

On the X pushed out to the door question, the only pic I have is this one. Notice the center of the X is pushed out to the door skin and then gusseted using sheet steel. That loads the side impact to the uprights because the center can't push in and the bars are trying to be compressed. It also allows for the doors to be gutted as per SCCA IT rules.
[IMG]http://img.photobucket.com/albums/v390/cagedruss/Past%20Projects
/Alfa%20Jeff%20Z%20vintage%20SCCA/al7.jpg[/IMG]
OK, I am not saying this is better or worse than the SCCA NASCAR bars but I like it and so does my Engineer's computer program. No, you can do both like the image below.

Best of both worlds.

On the statement about cost. It doesn't take any more time to charge what some shops charge if you add the gussets to the "X". Actually I prefer to do the NASCAR bars because it is easier. I really can't say anything negative about what other shops charge. Take it if you can get it.
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Old 01-29-09, 07:18 PM
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In my case, my cage was the 3rd cage my builder built, and the first to the IT rules spec. I used him cause I knew him, trusted him, and saw the quality of his work, but my car was one of his first. We went with 2 parallel nascar style bars. I love the x + nascar combo in the picture above, I wish we had done that, but in the end, I'm satisfied with the level of safety built into my car for the kind of racing I'm doing.

PaulC
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Old 01-30-09, 01:45 AM
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On the X+nascar, is the X pushed out and gusseted to the NASCAR bars? Or is it straight?
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