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78targa's Avatar
 
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Cool Zuffenhaus - a rallye approach to cagework

There is definately an art to how cages are built. After going up to run the Targa Newfoundland with me this year, the guys at Zuffenhaus decided to take the rallye experience and apply it to cagework.

Keith and Aaron have several years of Grand Am experience where they have seen the results of cars into walls. Targa gave them a chance to see cars with more, ah...creative impacts. With that in mind they took a look at the car I am building and decided to make it as safe as possible for a potential impact from any direction.

We came up with a list of considerations. Sure you can build a jungle gym in a car and protect everything, but the weight penalty isn't worth it. So after much deliberating this was the list of tenants we used:

1) #1 protect the driver
2) use the cage to make a stiffer car (tie into all suspension points)
3) protect the fuel cell
4) don't worry about protecting the engine, but keep it out of the passenger compartment
5) cagework should impede vision as little as possible
6) keep the cagework as far away from the driver's head and knees as possible
7) keep the cage work as light as possible
8) ensure where cage meets chassis, the chassis can provide adequate support
9) build for possible impacts in all directions
10) understand the dynamics of an impact and ensure bends in the cage are properly reinforced and properly located


I'm sure there are more things taken into account, but this should give some idea as to the mindset while building the cage. #10 is an interesting point because I have seen alot of cagework that looks good, but when closely examined you've got to wonder why certain bends are where they are. All to often there is a bend where there shouldn't be and the cage could fold on itself in the right circumstances. Very scary.

Here are a few midway shots of the work they are doing. It is a bit radical from alot of track thought. Apparently they took alot of notes when looking over the factory Subaru WRX's we were running against.

This cage utilizes a "halo" system around the roofline to protect the driver. Think of it as a partial octagon.

I did ask for their permission to post these as I know they have done alot of research to do this. I thought fellow Pelicans, in particular the track rats would appreciate the art behind custom cagework.

Oh, sorry the pictures aren'tthe best. I think they are taking better ones as they document the build. Think of these as...spy shots...







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Casey
Road-rally, Targa Newfoundland junkie!!!
1969 RSR 3.4L PCA class GT-3 (in progress)...1800 lbs and dropping
Thinking of driving in TARGA NEWFOUNDLAND? Contact me and I can help answer your questions. The event is awesome!
Old 02-10-2006, 05:08 AM
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So far it doesn't look like you're doing anything dramatically different from anyone else. I'm not sure how you'd be able to actually "design" to those specifications without doing a bunch of FAE work first. There's an article on just this subject (Cage design for Rally Cars) in the most recent issue of "Racecar Engineering". Apparently the study was prompted by the spate of serious injuries and deaths which have affected the WRC in the last few years. I haven't read it through yet, but it appears that the problem of high-speed crashes from any direction (especially straight into the door) is a pretty complex problem.
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'69 911E

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Old 02-10-2006, 05:48 AM
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I've posted this before but it's still cool so I'll do it again. Here is a Subaru rallycar build, go thru the slides, tons of good pictures:

http://www.rally.subaru.com/rally/servlet/CarBuildingDetail?part=1&imageId=5
Old 02-10-2006, 03:54 PM
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I finally read through the excellent article in Racecar Engineering. It is certainly worth the purchase price of the magazine this week (as a bonus there's an excellent article on picking spring rates). Some conclusions...

1) Picking a Subaru as your only inspiration for your cage design may be to narrow of a focus since it was in a Subaru that Mark Lovell and Roger Freeman died in the 2003 US Championship Rally when their Impreza collided sideways at speed with a tree. It's not clear what if anything you are doing differently then was done in that car. Here's a picture of Lovell that shows some of the cage in the immediate area around the driver.


2) Here's an example of a Peugeot 206 from 2003. While the picture is from a Tamaya model, it gives you some idea of how the cage was laid out.

Here's another image of a complete tub with cage.

Unfortunately in 2005 Michael Park died in a Peugeot in 2005 Wales Rally Great Britain in a similar accident to Lovell's, so it's not clear if this style cage performed any better. Here's a picture of Park in his car.


3) Crush zones and load spreading is key. The door area in a rally car is especially bad since there is only about 30-35 cm between the outer door skin and the nearest occupant. How the designer manages that 30-35 cm's is key to the occupants survival. To give you an idea of the significance, check out the attached chart which was included with the article based on work done by some Cranfield Engineering students.

Basically, at 100G deacceleration -- You're dead.
At 80G's -- you'll have massive head injuries.
At 60G's -- you'll have a concussion.
(Note that there is some disagreement regarding the actual levels, but I think it's save to walk away here with an idea of the magnitude of the forces that we're talking about. Note that in other situations (such as Indy Cars), and if properly restrained drivers have survived over 100Gs.)

Disclaimer: I'm not an engineer, and I didn't sleep in a Holiday Inn last night. I'm just a safety concious 911 driver (and sometimes racer).
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'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
"Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman
Old 02-12-2006, 12:18 PM
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Casey; Forgive me dragging this thread down a rat-hole about door protection. You're right that the cage pictured definitely has some stuff on it that's better then your average bolt-in 911 cage. The whole design around the A-pillars with the extra gussetting at the bend into the roof bars, and the extra Y where the A-pillars meet the roof look like an excellent strategy for improving the car's roll-over protection.

Have you also considered gusseting the cage to the shell along the A-pillars and roof?

It would be great to see how these guys fill in the rest of the tubes. Keep up the posting!
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'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
"Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman
Old 02-12-2006, 03:12 PM
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Thanks John,

Good insight and comments as always. I guess the major difference with this cage is the lack of a traditional front hoop. the Y at the top of the a-pillar looks simply massive in person and the pictures don't do it justice.

Cory, nice link. They do a much better job of documenting each step that I am doing. Must be nice to be a factory team though.


Those rally impacts are truely scary and honestly for the speeds they are going and their surroundings...not sure what kind of cagework would be the best protection.

Side impact is definately a concern. With the cage we are building the distance from the driver's head top the cagework has been improved with the use of the extra space the fiberglass roof supplies. They are adding a bent X above the driver for additional rollover protection.

Side-impact... We are still working on that one, but the use of doors without panels helps to allow the cage to be as far away as possible (cage bends into door pocket). Not sure of a better system than a gusseted X for the bars.

John, that chart on injurys...not sure if it is entirely accurate. Either that or I am #$#^% lucky! We impacted a rock going backwards over 120 kph... the car only moved 10 meters or so once it hit... My helmet was cracked from hitting the main hoop diagonal. yikes.


Ok, more pictures hopefully to follow this week. Thanks for the ideas!
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Casey
Road-rally, Targa Newfoundland junkie!!!
1969 RSR 3.4L PCA class GT-3 (in progress)...1800 lbs and dropping
Thinking of driving in TARGA NEWFOUNDLAND? Contact me and I can help answer your questions. The event is awesome!
Old 02-12-2006, 05:07 PM
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Yeah Cory, I agree. A lot of cars just do a straight X on the plane defined by the A and B pillars. While better then a single bar torsionally, it doesn't provide much buffer in a door intrusion. I definitely think that arcing the bars into the door space is an improvement. In addition to the extra "crush zone", as the bars collapse inwards the should transfer a lot of force against the A and B pillars.

Between the article in Racecar Engineering and this thread on the 911 forum, I'm still kind of fixated on how to improve the intrusion safety in the door area.
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'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
"Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman
Old 02-12-2006, 06:02 PM
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Don't under estimate the strength of a X in a flat plane. Mass for mass, the X is stronger than bent tubes. Bent tubes are already longer than the shortest distance between two points and may bend much sooner than a flat plane X. IOW the failure mode of bent tubes is to bend inward. In order for the flat plane X to fail either 1) the tubes are literally ripped from the cage and if the force is that strong the driver is dead anyway, or 2) the force must be strong enough to stretch the tubes along their length (where they are strongest) before bending. Again, that much force and the driver is going to be dead anyway.

True NASCAR bars get their strength from mass. Just look at how much material is in a set of true NASCAR bars. Also, true NASCAR bars attach the verticle elements to the chassis for added strength. Oh, and NASCAR bars are NOT an arch and even so, most impacts would not be square againts the door anyway.

In the end, any monkey can build a strong cage by adding mass. A truly beautiful cage is one that provides maximum strength and chassis stiffness with minimal mass.
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Last edited by Geo31; 02-13-2006 at 06:12 PM..
Old 02-13-2006, 07:10 AM
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George! good to see you (again) online - reading you alot lately, lol! (keith from rennlist)

The main difference between this cage and the road course cages we build (and Geo has seen pictures of those and I believe is in agreement with their strength and efficiency) - is the somewhat octagonal halo that is pushed WAY up into the roof. After being at Targa Newfoundland in the fall, it occurred to me that a rollover onto a rock in a good road-course cage would still be bad news for the drivers heads. There aren't enough large protrusions on a racetrack (like a small boulder to roll upside down on top of) to necessitate that kind of protection. Sure, cars end up on their roof, and conventional cages hold up just fine, even with barrel rolls. - it was the increased possibility of rolling over onto a rock that concerned me about road-race cages in that particular environment.

So, we looked at some of the solutions of the rally cars present. They seem to favor a tighter halo, higher into the roof, with almost polyhedron-esque facets leading down to the more or less vertical pillar bars. Additionally, they have a lot of extra spaghetti, and many places to scramble your mental eggs, and as mentioned, really poor side impact protection.

We are marrying our road race cage experience with more overhead protection, the SENSIBLE bits of the rally-style semi-octagonal halo. This got the roof structure up and away from Casey's head, and allows us to put some crossing tubes up there to eliminate foreign object entry in to the cockpit.

Going this route resulted in a bend in the A pillar in a less than strategic place (as Geo can attest to - he's got good cage sense). We solved it by gusseting in a couple of planes. Visually massive, but efficient in terms of material, and strong as-executed. Keep in mind, this is a Targa cage, for a crazy pilot that doesn't have a normal man's fear of rocks and cliff faces. Normal insane road racers get the less-is-more, tried and proven design we build.

The cage will become to resemble our road-race cage more and more as it nears the floor pan.

Stay tuned, we'll continue to not notice the "spy" cameras in the shop as the cage is filled out...
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Old 02-13-2006, 05:29 PM
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Hey Keith. Always good to run into you. One of these days it has to be face to face over some beers.

I actually have been kind of admiring the treatment at the top of the a-pillar.

Cool stuff.

Not that anybody cares necessarily, but Keith is one of the few people in the country that I would trust to build me a cage.
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Last edited by Geo31; 02-13-2006 at 06:02 PM..
Old 02-13-2006, 05:59 PM
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- before the few beers, of course ;^)
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Old 02-13-2006, 06:08 PM
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Cage

I happened to catch this thread and later on that evening a special on the top 20 drivers of all time on ESPN. Without commenting on their choice of drivers, (I do think they blew it by not including Mark Donahue). I couldn't help but notice that this cage is identical in roof design, corner attachments at the roof and laterals at the main hoop to one used by Richard Petty in the mid 70's. The shot inside Petty's car was very clear and his cage matches this one to a "T". Its also similar to a short track cage used for Saugus Raceway built for Ron Hornaday Jr. by Speedway engineering of Canyon Country, CA in the early 80's.
I guess it just goes to show that everything old becomes new again.
I don't know the guys designing this cage but if you can you might want to access the design for Petty's cage in the mid 70's or contact speedway engineering (They currently build NASCAR truck and Winston West set ups) Yours is a twin to both of these earlier designs.
Randy

Last edited by Kart54; 02-14-2006 at 10:19 AM..
Old 02-14-2006, 10:15 AM
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Re: Cage

Quote:
Originally posted by Kart54
I guess it just goes to show that everything old becomes new again.
We have a similar truism in the art arena. Naturally, it also seems to pertain to the field of design.

I'd love to see some pictures of the aforermentioned antiques after this cage is completed.

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Old 02-14-2006, 02:36 PM
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Bending of X-bars:

http://www.914club.com/bbs2/index.php?act=ST&f=2&t=46255&st=20

About 3/4 down the page.

After looking at the pic for a while, it seems the center of impact was further aft than the cross point of the bars, but they bent closer to the dash ie. NOT in to the drivers torso. I wonder if they were made to encourage bending forward of the seat.
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Old 02-14-2006, 06:28 PM
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I looked at all the pictures and most the bars look pretty good but (and I am not an engineer) I would have thought that a straight bar between teh "b" pillars would be a good idea to firstly shorten teh distance of teh harness and thereby reducing teh possibility of stretch in teh harness as well as stopping teh seat/s from going out through the back of teh car if in the event of an accident tehy became loose dislodged or broke free of the mounts.

My humble two cents worth.

Michael
Old 02-14-2006, 07:09 PM
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That picture is interesting. What horrifies me is that the forward upper connection appears to be severed.
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Old 02-14-2006, 08:17 PM
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I looked closer, and it definately tore some, it does not look like it goes all the way thru though:

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Old 02-14-2006, 09:01 PM
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geez - I was there all weekend and I missed that hit...
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Old 02-15-2006, 04:31 AM
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To me it looks like a black tie-wrap wrapped around the bar. If it had severed like that, I would have expected the bar to bend in given where the impact seems to be, rather then staying perfectly aligned as the picture showed.
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Old 02-15-2006, 06:50 AM
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John, good catch! I agree it looks like a black tie wrap on that cage.


Side impact definately seems to be a tough area to tackle in building a safe cage. Geo31, in regards to your comments about a flat X, I found an article at nissanperformancemag.com that discussed the matter briefly. Their cage builder's comments:

"For side impact protection, we used an x-brace design on each side. We believe an x-brace is safer than "NASCAR bars" because the x-brace's bars will not bend in the event of a side impact without "stretching" the metal. The distance "NASCAR bars" are bent outward away from the driver is also the distance they can be bent towards the driver before the force of the impact starts to stretch the tubing."

found at: http://www.nissanperformancemag.com/february05/nasa/

Interesting arguement against a bent X but I still think that a well designed bent X would allow for both strength against side impact as well as increase the distance between the cage and the driver.

They also talk about adding bars to the outside of their x-brace, but I can't see this as being overly beneficial. I would rather put that extra mass into a unified piece.
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Casey
Road-rally, Targa Newfoundland junkie!!!
1969 RSR 3.4L PCA class GT-3 (in progress)...1800 lbs and dropping
Thinking of driving in TARGA NEWFOUNDLAND? Contact me and I can help answer your questions. The event is awesome!
Old 02-15-2006, 07:19 AM
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