Full Cage Design Question

[MyTurbo3.6]

I am having a full cage fabricated for my 911 and my fabricator is not happy with my request for removable door bars.

I would appreciate any thoughts/recommendations regarding a safe/functional removable door bar design. The car is a multi-function vehicle and door bars are not acceptable for normal non-track use. I have no issue having a permanently welded sill bar and dash bar but not the door bar.

Any help/pictures would be greatly appreciated

Thanks in advance

[David]

The SCCA Solo rulebook under roll bar standards states: "If one tube fits inside another tube to facilitate removal, the removable portion must bottom on the permanant mounting, and at least two bolts must be used to secure each joint. The telescope section must be at least eight inches in length."

[addictionMS]

People I have talked to are more worried about the potential of smacking your head on the bar above the door, even in a low speed hit it could kill you.

Be sure you head can not hit that bar.

Good luck

Jim

[Yargk]

Originally posted by addictionMS
People I have talked to are more worried about the potential of smacking your head on the bar above the door, even in a low speed hit it could kill you.

Be sure you head can not hit that bar.

Good luck

Jim

How is this accomplished? I was seriously considering running a cage on the street and I am aware of the dangers. I thought some really great safety padding with high energy absorption would be safer than my head hitting some other hard stock piece of the interior. What else could/should be done to help the safety of a cage in this respect?

[jyl]

I don't have personal experience with rollcages but I have researched them a fair bit and I do have personal experience with automobile accident investigation. Based on that . . .

I think you should consider having everything forward of the roll bar detachable, unless you plan to wear a racing harness and helmet while driving on the street.

With stock three-point belts, you'll move a lot in a serious accident - enough to slam your head into the sun visor area, headliner, upper door sills, etc. I've seen films of dummies in frontal and rollover crash tests and they move around much more than one would expect. Considering how small the cockpit on the 911 is, in the right rollover you could even smash your head onto the passenger side of the cabin.

Striking your head on a bare rollcage would be like being clubbed hard with a metal baseball bat. Striking a foam-wrapped rollcage would be like getting clubbed hard with a foam-wrapped baseball bat - still damaging.

At least look into the most protective padding, not the nice soft stuff but the expensive hard stuff (e.g. see Safety Devices' website).

I started a thread about rollcages in the AX and Racing Forum and there were some good responses on this issue, especially see the one by TRE.

I am planning a rollcage for my 89 Carrera this summer and am leaning toward a rollbar with a removable front cage section for this reason. And if I can't find a way to protect my kids who sometimes ride in the rear seat, I'll abandon the idea.

Edit: Of course you can sustain head injuries from striking the stock interior too. But many of those surfaces are either flattish (e.g., windshield), deformable (e.g. roof panel), or padded (e.g. door panels). Sort of like getting clubbed with the flat side of a plywood sheet. Hurts but not as bad as getting clubbed with a 2x4.

[addictionMS]

I think John hit the nail on the head....it is not so much the hardness as the shape and proximity to your head. It is impossible to put a cage in without taking away head room.

one way to solve it would be to put in one of those PVC pipe cages we saw so many of a while ago on an other thread here. They will not protect you, but they are soft enough not to kill you :-) (if you don't remember the thread or were not a reader at that time, these were fake cages for the all show and no go cars, mostly imports, if you know what I mean)

I just suggest you be careful and think about where your head will hit,

Jim

[Wil Ferch]

Then again...Jeep Wranglers have factory roll-cages with factory applied padding for the rear seat passengers....same risk there I would imagine. If you accept this premise, then retain the full cage but put in high quality and hi-density foam padding for the front section.
---Wil Ferch

[Dantilla]

I drive my NARP 944 on the street quite a bit with a full cage.

Door bars- My car is no more difficult to enter/exit than before the cage was installed. The door bars are low enough, and you still have to drop your fanny down into the race seats. Made no difference.

Headache bar- After having the cage installed, I have found myself tightening the shoulder straps on the harness quite a bit tighter to prevent my head from being able to contact the bar. It has firm padding, but I'm aware that I have a steel pipe in close proximity to my head when I drive. Before I installed the padding, I actually practiced quickly grabbing my head so that I would break my wrist before my skull.

I have been told I have a pretty thick skull......

[Ove]

MyTurbo3.6,

Consider if anything can be done to lower your front seat(s). I had a pair of Momo racing seats in my car for a few months. In the Momo seat I was sitting 2" to 3" lower than I am now with the regular 911 seat.

If you can get the seat down, your head will be less likely to hit the front part of the cage.
A 4pt harness will help a lot to keep you in the seat. However it may not be very practical for everyday use.

I have a Heigo roll cage for my BMW. The side bars are fully removable, and this works very well. To remove the bar you twist it to remove the pre-load (like on some strut tower braces), then remove one bolt for each end. Takes 1 minute for each side bar.

I would not go for a removable front cage, public roads are not safer than any racetrack in my opinion. Besides, on public roads you may hit a car coming in the oposite direction. A roll bar only will not be very helpful in that situation.

[chrisp]

Just make sure that the bolts that hold in the door bars are in double shear. Meaning, they are going through three pieces of metal with the piece being impacted (door bar) either being the two outside pieces (where the bolt head and nut face would contact) or the single piece sandwiched in between the other two pieces. For example you could have two tabs coming off the roll bar and a single tab on the end of the door bar. Have the single tab inside the two other tabs and have the bolt going through all three pieces. That's double shear.

[Wil Ferch]

Plus...NEVER run a 4 point harness..on the street or on the track. At least a 5 -6 point.
VERY dangerous if you have the lap belt come up around soft tissue areas of your body,...you need the extra restraint to keep the lap belt down around your pelvis...your natural pivot point.

---Wil Ferch

[Lothar]

There is some good advice here. I probably can't add much more. However, I think you need to think of a full cage, harnesses and your helmet as a package.

Either a cage alone or 5/6 pt. harness alone (meaning one in the absence of the other) could be deadly. Never run a harness without at least a roll bar. Your head will become the highest point in the car in the event of a roll-over and subsequent roof collapse.

In a violent collision, you'ld be surprised how people get thrown around like a rag doll and where their parts can come into contact with surrounding structures. Having a roll cage around your head without a harness to limit travel and a helmet to protect on impact is a grave situation in a collsion. For that reason, I have chosen not permit the use of the standard lap/shoulder belts in my car with full cage during those occasional street drives. I won't require a helmet (would look really stupid driving down to the grocery store), but all passengers will wear the 5 pt harness.

If the rules allow for a roll bar rather than full cage, this would be a better compromise if you plan to drive on the street.

Once you go full cage, you are far more track car than street car. I have not seen a removeable front section that looks easy enough to install/remove/repeat to be pratical.

[jluetjen]

It doesn't matter how much you tighten your 5 or 6 point belts. In an accident (even as slow as 30 mph) you'll learn three things.

1) You won't have any more control over your head or limbs then a rag doll would.

2) Seat belts stretch in accidents, they're supposed to. If they didn't; wearing seat belts wouldn't be any different then having an H-shaped piece of steel shoved into your chest. The stretch (between a few mm to a few inches) slows down the deacceleration of the body to a survivable rate.

3) The human body (especially the neck) will stretch. In spite of wearing a 6-point, 3 or 4 inch wide belt system and being fully reclined in his car, Paul Tracy's head hit his steering wheel (an arm's length away) when he crashed at Indy once. The conclusion: if you have a full cage, LOTS of padding is required at a minimum, especially if it is in front of you (which is normally where your momentum will carry you, as opposed to a Jeep where the padding is on the side bars and the bars behind you,). Better yet, a Snell SA approved helmet.

When it comes to safety, you'll only have one chance to find out if you did it right or not.

[Wil Ferch]

John:
My earlier reference to the Jeep Wrangler was in the context that there are rear seat passengers that must be accounted-for in an accident...and that the car must meet minimum street safety standards. In that context, the Wrangler has a roll bar with padding...meaning...at least have the same ( or better) type of padding for your front 911 occupants when running a full cage.
--Wil Ferch

[Dantilla]

I agree that the roll cage I installed to protect me could also kill me.

That being said, if you knew you were going to be in an accident, would you rather be in a Porsche with a full cage, padding, kevlar race seat and five point harness, or a motorcycle?

[HawgRyder]

Of course..I choose the motorcycle....for the avoidance factor (best not be there when accident happen)...LOL
I think the whole idea of a cage is to surround you with steel in the event of an accident.
The second point is to keep you in the middle of the cage....if you get to the outside or the edge...that's when damage occurs.
So...complete harness...maybe the helmet (with restraint straps)...and lots of padding on the bars...maybe even Kevlar suit....just to get groceries?.....overkill to the extreme....besides...the trunk is full of safety cell and fire equipment....no room for grocery bags.
Take the plush-mobile with the 4000 cubic foot trunk.
Save the P-car for the open road.
Bob

[Ove]

MyTurbo3.6,

Here's a very nice cage: http://www.homestead.com/redlinerennsport/OBrien1.html
It takes up a minimum of space by being as close to the car's body as possible.

[MyTurbo3.6]

Thanks for all of the great advise…you never let me down.

The cage is nearly complete so I thought I would post some pictures. For the time being, I have decided to only have the lower door bars and will add some form of removable upper door bars in the future.

The car has been chemically stripped and will be powder painted after the bodywork is finished…the stripped metal looks rustier than it really is. I will post additional pictures as the project progresses (fuel cell, remote oil tank, Big Reds, coilovers, etc.)

[Randy W]

Looks good, My Turbo3.6. I agree with everyone who has responded who has actual experience with having a roll cage in a car they drive to the track.

1. Comply with the rule book when having your cage built - do not bolt or weld it to the floor.
2. Use the best fabricator and materials you can afford.
3. Have the side bars placed as low as possible or make them removable if you must.
4. Pad the bars within 2 feet of any part of you or your passengers body with dense foam designed for the task.
5. Wear a 5 point harness at all times cinched tight.

If you crash on the way to the track you will be better protected than anyone else on the road.