Roll cage in tomorrow...final choices

[JohnJL]

My SC is going into Bond Roll Bars tomorrow morning for its cage install. This car will be tracked exclusively. Bond is FIA and CAMS certified.

I have some final choices on the cage. My primary consideration is safety. I won't be going out to the suspension points for class reasons.

Firstly, with respect to side-impact protection... When speaking with Peter @ Bond today he stated there wasn't much point going with an X (as seen here...)

...unless I was hooking into the front suspension points. He said
1. it made exiting the car in an emergency too difficult
2. the load transfer to the adjoining points was the same as in a single bar and
3. you sit so low in a 911 that most side impacts he's seen transfer the load at the sill and there isn't much to hit the driver directly

Here's their typical 911 side protection...




Any opinions or expert advice, particularly from engineers or people who have seen extensive damage (unfortunately) is much appreciated.

[Wil Ferch]

I would prefer the "X" brace and would go further to suggest a brace of "tacos" welded as webbing between all points of intersection....

do a search on roll bars..as there a thread on this lately....with talk also of the side bars. I think it was a rally-inspired thread...can't recall the title. Maybe in the racing/autocross section too.

- Wil

[tc-sacto]

The scrutiners' at my SCCA license class this weekend failed a 911 for only having a single bar. They let him take the license class, but wont sign off for him to race until he has dual side bars. You may not be racing with SCCA, but some day you may sell the car to someone who will and not having the right safety equipment could be a deterrent to a potential sale.


Duhhh...just saw your in Sydney....never mind. Don't know your class rules down there.

[JohnJL]

This is a mock-up of what I am sending along to Bond. They have a good reputation so I feel a little weird debating design with them...they don't even take walk-in business anymore. You need a 'referral.' Most of their business is rally stuff.

Maybe I'll use the excuse that the car will be going to the US (likely at some point) so it needs to have the "x".

I did search on "roll and side" but didn't see what I was looking for. I also went back through some recent "RCE" mags...I thought there was a recent article...

[Craig 930 RS]

I have to agree with Bond, however take a look at my 930 and a Cup Car at the track for ideas:

[Craig 930 RS]

[jluetjen]

Originally posted by Wil Ferch
I would prefer the "X" brace and would go further to suggest a brace of "tacos" welded as webbing between all points of intersection....

do a search on roll bars..as there a thread on this lately....with talk also of the side bars. I think it was a rally-inspired thread...can't recall the title. Maybe in the racing/autocross section too.

- Wil

Wil, I think that you were talking about this thread, right?

1. it made exiting the car in an emergency too difficult

I believe that this comment pre-supposes that you'll be able to open the door. If you're going out the window, I don't know how either design will be a bigger hinderance then the other. Most of the US racing organizations (such as the SCCA mentioned above) presume that you'll be going out the window, either because the door doesn't open, or because they door was pinned shut before hand as is often the case in Production classes.

2. the load transfer to the adjoining points was the same as in a single bar and

I'm not there on this after running a number of FAE analysis. Yes, the cage is attached to the floor in the same places, but the X design is definitely stronger then just a single bar when torsionally stressing the chassis.

3. you sit so low in a 911 that most side impacts he's seen transfer the load at the sill and there isn't much to hit the driver directly

Maybe. Maybe not. I haven't seen enough 911's post crash. But a quick walk around the paddock with a tape measure will tell you where most of you're competitors's rams (I mean bumpers ) are located.

Two conclusions that I drew from the work that I did on the earlier thread:

1) If you add a second bar, you have at least doubled the intrusion protection for no other reason then you have twice the mass and twice the weld area. Adding a 3rd bar increases it by 50% and so on. This is the simple reason why NASCAR cages have 3 or 4 rows of bars.

2) It's much better to have the bar bent out into the door area, and braced some how in 2 dimensions. I've read that the racers in Aus like to keep their cars closer to showroom stock then we do in the US. I noticed that you still have your door panels on your car and so such an arrangement may not fit. But bending the bars out into the doors does two things:
A) It causes intrusion forces to be to be spread out to the cage structure at right angles to the intrusion. This loads the bars in compression which is preferable to tension. So even though you may be getting T-boned from the side, the forces into the cage will be such that they try to spread the main-hoop and front down-tube apart.
B) It provides very valuable space for the cage to collapse before it comes in contact with the driver.

Disclaimer: I'm a salesman, not an engineer. If harm comes to you because of my comments, it's your fault for believing them, not mine for writing them.

[Wil Ferch]

That's it !!! ...

I think a thorogh "read" of this will prove beneficial to JohnJL

- Wil

[Todd Simpson]

Are you attaching to the A pillars, B pillars or under the dash?

I have a welded in 6 point "copy" of a cup car age in my '71.



When I'm driving I can feel play between the knee bar and the dash. While the car is a lot more stiff than it was stock I wish the cage was tied in under the dash and to the roof pillars.

[obrut]

john,

i have a bond cage with their single side bars. my car is mainly used for tarmac rallies where you get in and out all day and the single bar is a bonus in this regard.

however, i have also lowered both of my seats so that the seat sides (and my hips/legs) are lower than the bar and pretty much also protected by the sill. my nav'rs seat is also as rearward as possible. we feel pretty safe with this setup. plus, i'm 6'1" and i now have no headroom issues when wearing a helmet.

you're welcome to do a test sit in my car if you like.

[eimkeith]

I'd have to disagree with Bond as well. The X will strengthen the door hoop in the event of a rollover (at the dash bend). It is not hard to get out of (especially in a fire situation!) unless you are joint limited in a way that makes it difficult to even get into the car.

And, it is better in side impacts. Put a sill bar down there between the front and main hoop baseplates as well.

[JohnJL]

Hi Wil, thanks I read it and all the attached links.

Ryan, where are you located? I live in Mosman, work in CBD.

Hi Tod, nice cage. WHat's that color & finish? I think I have the same carpet too...

John, thanks a lot for your detailed response, its very much appreciated. Yes, they seem to be more picky about the "stockness" of the class. Tying into "b" pillar, for instance, is disallowed. Though I have seem most people doing it anyway and not getting caught.

I have printed out a bunch of those Cup car pics (inc the Kelly-Moss car with the side impact damage) and left them in the car for Bond...the truck just took the car away and I should have it back next week!

[obrut]

john,

car is usually in alexandria. i work in the cbd and live close by.

what class/competiton are you prepping the car for?