NEHA

Hi all,

I have taken pictures to try to document how the different cage designs have resisted the crashes we have seen at Okemo 2.
The pictures are here (they also include the pictures of my cage build): https://plus.google.com/photos/10690173 ... 2789019105

I'd like to have the opinion of the tech experts on what they think of the bolt-on cage that was in the Neon and the other cage in the BMW.
I think it's good to discuss this now while it's still fresh in our heads.

Manu

Not a tech expert, but I do agree it would be a good conversation.

Speaking with David (Neon) at Okemo, I believe he said that he would not be going with a bolt-in cage in the future.

I did notice that there were no supports going forward to the strut towers and the cage was pushed through the windshield.

Did the cage do its job? Yes... would it have done its job if the impact was forward more? Don't know.... I see David drinking more than one free beer at the beerfest that night to take care of some pain if the tree was at the driver's door.

Kevin (drove the Rabbit) brought up an interested observation. If there was a seat brace (middle of the back of the seat to the harness bar), would this type of impact actually push the brace into (through?) the seat?

Steve
VW Golf with American Flag on roof... or red VW Jetta when the Golf is broken

I didnt spend much time studying either cage after the impact. Don may have, but as we all know he isnt likely to log on and share his observations here.

I would like to make a couple comments though.

The cage in the Neon remained surprisingly in tact for the minimal cage it is. Meaning it did a good job of maintaining the occupant space and not collapsing. The impact moved the whole cage forward. I did not see if the main hoop floor mounting points were still in the floor and the floor accordion-ed, or it tore out.

The side bars in the BMW tore part way thru at the gusset welds. I am not sure what the tube material was made from and any steel will eventually tear like that under those conditions but mild carbon steels are a lot less likely to do so than harder steel alloys like Chrome-Moly (4130). Mild will deform more easily and stretch more under the same circumstances but is less likely to shear off at a weld, becoming an occupant hazard in in and of itself. That is a lot of the reason for recommending 1020 to 1026 steels (or its equivalent) for cages. Much softer and it stretches too much and much harder and it becomes brittle. There is more to it than just this including the fact that many rules that permit 4130 also permit it to be thinner (and therefore lighter), and 4130 really needs to be annealed after welding (hardly ever done except in very high level cages such as dragster cages) to normalize its crystal structure.

Cages are all at their poorest in terms of protection during a side impact between the main hoop and a-pillar. This is partly due to the very limited room between the occupants and the cage to absorb energy and partly because of the fact that the side bars (those between the main hoop and A-pillar) are not braced across the interior of vehicle (since we need to sit there). Various attempts to improve this by bending the side bars out into the door voids can be tried, but depending on how the bends are achieved and how they tie into the main hoop, A-pillar and sill bars they not be any more effective than a straight bar in terms of absorbing a side intrusion before it reaches the seats. I think a possible strategy to improve this is to add straight cross braces below the seats, either completely across the car between sill bars, or sill bars to the tunnel. This would reduce the tendency for the floor under each seat to collapse on a side impact and instead force much of the energy absorption to occur by the tunnel between the seats or by a combination of both sill bars deforming in the came direction.

One thing I noticed about how my cage moved so much was that the mounting point of the main hoop on the floor actually pushed all the way to the ground. I can grab a picture this afternoon for a visual. This cage had a 6" plate on each side of the floor, bolted through, and welded into the car. The floor pan pulled all the way to the ground.

Another thing Allan noticed was that the factory crash bar at the front of the rear seat, across the floor (its a 2" square tube across the car) is actually where the tree stopped (or, I guess I stopped).

Rabbit Farmer wrote: Speaking with David (Neon) at Okemo, I believe he said that he would not be going with a bolt-in cage in the future.

The only reason I ran with one in the first place was because it was already in the car. Won't run another one. Though this was a bolt in cage that was welded in. Not sure what the result would be if it was only bolted.

Also, If anyone wants to see pictures of a specific part of the cage, car, etc., let me know and I'll take some before it gets scrapped...

3rdgendennis wrote: Also, If anyone wants to see pictures of a specific part of the cage, car, etc., let me know and I'll take some before it gets scrapped...

It would be great if you could take pictures of the mounting points. Also if I remember well your door bars were bolted too at the front, I'd be interested to see how these connections held up at the bolting points.
Did any other weld fail besides the one that was behind the driver seat?
Do you know what size tubing was used and what the weight of the car was?

All this will be very valuable information as we don't have (thankfully) many opportunities to document such incidents.

I believe the rear support was the only weld that failed (the only one I've seen so far). The weld only failed after the mounting point deformed quite a bit. I never put it on scales, but It weighed somewhere around 2300#. Tubing was 1.5"x.095". Not sure on material, or if DOM.

I've often wondered the " what if" in a caged car- this pointed out my fear. Put in all the bars you want- its still only attached to a piece of 20 gauge sheet metal.
The cage did its job- the floor pan couldn't.

sdwarf36 wrote:I've often wondered the " what if" in a caged car- this pointed out my fear. Put in all the bars you want- its still only attached to a piece of 20 gauge sheet metal.
The cage did its job- the floor pan couldn't.

That's one thing I don't get, why is it allowed to have plates on the floor pan?
Every plate on my cage is on the chassis frame (my floor pan is just balsa wood and fiberglass anyway!).

The pictures from this weekend remind me of the last time I drove at Ascutney...

You are one very lucky person Dave! You will never catch me in a car with a Bolt-In cage!!

Nick's cage seemed to do its job from the pictures. Anyone remember what the door bars of my tube frame did when I hit the tree sideways? NEVER mix ALLOYS with Mild steel. That should be a rule for next year.

I think it would also be wise to add a rule regarding how the vertical components of a cage are tied into the chassis. Specifically stating that the lower needs to be sunk into the inner rocker and plated, or needs sufficient welded points to vertical structural components of the chassis..

https://drive.google.com/folderview?id= ... sp=sharing

Photos should be linked above.