analogmike

Hi,

I had some additions done on my '73 911 roll cage to make it SCCA legal. I added a door bar to each side to make an X pattern. I also added two down bars on the driver's side from the bottom of the X to the sill for extra strength.

I added a bar on each side from the front hoop to the firewall (inner fender) which is also a good idea on any cage.

Those came out great.

I also added a dash bar which is required for a GT class car, but not an IT class car. Unfortunately it is only a few inches in front of my knees, and directly in front of them, with the high density foam installed. I have read previous posts about pros and cons on these bars (mostly cons). I am thinking of cutting it out before my first race in a few weeks.

Some pictures are attached.

Should I get out the hacksaw? Redline Man???

analogmike

attachments did not seem to make it, try again

paradisenb

I have a knee bar like yours and I think about it every time I get in the car. I think its possible to move that bar up under/behind the dash. I was looking at Jack Lewis' early 911, IIRC his is moved up and under.
Tht is what I want to do. I do not like the bar so close to the knees. I think the belt stretch enough for my knees to hit it in a crash.

I also think it is worth cutting the dash to move the bar forward and higher. Another mod.

jrgordonsenior

From my recent 996 build. Doesn't your knees go under the bar?

analogmike

My knees don't go under the bar as my seat is up pretty high and I sit pretty far forward. And my bar is a few inches lower than yours. Your bar looks fine.

Tom W

My bar is up even higher than where John's is. With the stock dash completely removed, it provides the 'frame' for the edge of the dash and is the support that the steering wheel is attached to.

RedlineMan

Hey;

As with anything cage related, there is a lot going on here.

First off all, the purpose of the bar is to provide side bolstering for the cowl/door post and door bars in case of a t-bone. That is their main purpose in a structural sense, although they do tie the open ended side hoops together down low and keep them from bowing under compression. In a full built car, they make a nice place to anchor the steering column, and can also help in fastening in a dash panel.

It is nice to have them as low as possible to give as much protection toward the feet and legs as you can get. Balancing that is them GETTING IN THE WAY of the legs, or being proximate enough to be impacted. Considering in the "average" forward impact, your hips will travel at least 4" forward, you ideally need to put them in the right spot so you will go under them if moving straight forward.

What is fouling you up here Mike is the positional limitations of the exisiting cage structure. Your side hoops terminate at the sill quite far back, out from under the dash. This forces the straight knee knocker bar right out near your knees. You'd have to do some fancy, um... footwork with the tubing to run it back under the dash and yet have any structural integrity for its intended purpose. Unfortunately, I'm not liking your chances of improving this situation much. I'd cut it out if it wasn't required.

What also jumps out at me is the rather haphazzard placement of the door bars. The front lower diagonals are indeed a good idea, particularly on an early 911, to reduce the possibility of wheel/suspension component incursion into the footwell. Unfortunately, the door bars and the front lower diagonal do not form one node as they mutually intersect with the side hoop. This is a lost opportunity to create far more strength in the entire area. If you had what I refer to a "geometric x door bar" (projecting outward), the lower diagonal becomes the critical pathway for diverting side intrusion away from the opccupant(s) and sending it forward in compression into the sill. In your case, with a "flat x", these diagaonls would be loaded in tension, and without the node this tension will pull on the unsupported area of the side hoop above where the lower diagonal attaches, not directly on the lower diagonal and then the sill by default.

What this is all leading up to is that in an overall sense, I think you have reached (and now passed) the point where the base architecture of the existing rudimentary cage will prohibit you from getting more focussed job-specific tubes into their proper place. Unfortunately, this largely diminishes their effectiveness. Mostly all you end up with is added weight more than increased safety.

kurt M

I am not a fan of the below the wheel knee bar. My unlearned thinking is the chance of a frontal with your legs making it into the bar are greater than the chance of a hard enough side impact that brings the bar into play.

Tom W. Your car looks like the sister to mine in ways. The dash for one.

I went a little off the norm for the foot well protection on the drivers side. There is a leg board on both sides and I reinforced and tied in the rocker area to the steering rack reinforcement area then ran a down tube that ties in to the cross tube at the triangulation node. Keep things out of the leg area and resists a wheel coming through the footwell some.

Juan Lopez

Mike,

Mine is built into the dashboard, the bottom part of the dashboard is my knee bar. Come see it at Lime Rock for some ideas.

Juan

stownsen914

There was a thread over on Pelican on this a few months ago. A few posters did not see the value in a knee bar, especially if it is located too close to the knees and could cause injury in an impact. As much as I'd hate busted knees, I think I'd hate even more having a nasty side impact (especially a T bone) in a car without a knee bar, as the cockpit could collapse laterally. A scenario like that could cause all kinds of terrible injuries ...

Scott

kurt M

All true but is the bar or lack of the bar the weak link? Is the seat, harness and other systems up to the task of a hard side hit? The lack of a bar might be the least of you worries.