No surprise, I guess, that these days I'm thinking about safety.

I have a 911 with a full cage, Recaro PP seats, fire system, emergency power cut-off and a window net. But I've had a Brey-Krause seat-back brace sitting in the garage for a while, now. I've always thought -- based on how it looks -- that there's a serious trade-off involved: it's a fixed piece of aluminum pointed right at my spine. So my question is whether it makes sense to add something like a 2-inch layer of high-density padding between the seat and the brace? (And if so, is there a source for this stuff?)

Second question is which side nets will work the best in a 911 with a cage. I've seen square ones and triangular ones, but I've never looked to see where they mount or which style makes the most sense.

 

I could not argue against it, really. This style of brace would be best utilized in the shadow of the seat's shape. By that I mean the "wings" on the brace would sit roughly behind the shoulder wings on the seat. This would directly support the heaviest part of the torso (shoulders) and also spread load down in the area of the seat corresponding to the lower back.

The flat HD foam (SFI spec 45.2) is available from BSR, and JAZ products also offers it. Behrent's sells the JAZ foam 1" thick 10x20" for $27.72. I'm sure there are suppliers on the west coast.

Well, the window nets and side nets are different in my book. Window nets keep stuff from going in out out the window (arms, stray car parts, track debris, etc). Side nets support the seat and driver. Side nets have been used for years by sprint car drivers to keep them in the open cockpits. Some smart guy thought to adapt them to sedans.

This first crude diagram is looking from the top. Note that the side net bends around the seat, and is somewhat pre-tenioned to support the seat/driver combo if there is any significant side shift.



The second diagram shows from the side. This would be my idea of an ultimate setup, using a full containment seat (like the Ultrashield RR Super Seat). The side net would support the seat high at the head halo, and also around the shoulder wings. This would support both the head and shoulders in case of a seat failure and/or the driver being spilled out, but not interefere with the arms that need to shift gears, wave at fans or pit tootsies (see Dal's avatar), etc.



These can work on both sides, and many NASCAR teams are doing just that. You would use a seatbelt latch on the front end of the side net to attach them to a dash bar on your cage or a point on the firewall. Note that some sort of "-ring" keeps the net in place on the seat. You can also still use a window net as well for the same reasons as before.

Full containment seat, H&N device, side nets. The ultimate setup for safety!

 

I had an e-mail discussion with an engineer at Recaro regarding seat back brace and their composit seats. Although he wouldn't come straight out and say it, he basically said that I should not use the brace with their seat. Basically, he said that the seat is FIA certified w/o the brace and you should not change anything from the way it was tested. The theory is that the composit seat is meant to flex a bit to absorb energy and the brace wouldn't allow that.

 

Hey Kim;

It boils down to whether or not you think flex and energy absorbtion is a good thing. If you designed a seat to FIA specs, it's not hard to figure what camp you'd be in. On the flip side, an FIA seat would never make it through NASCAR tech, and NASCAR and open wheel racing (whose cockpits are now quite similar in function) are state of the art right now as far as I'm concerned.

Testing has shown that the body can take tremendous stress as long as it is linear, and therefore the current thinking is NOT to allow any excess motion. If you follow that school of thought, and in regard to seat flex, then the FIA is going in the wrong direction on this point. It then follows that back braces would be fine for the solid school, but not for the "followers of flex."

Interestingly, side nets are not specific to EITHER camp, and will work regardless of what your position is. It seems obvious to me that given the flex the FIA likes, side nets would be extra helpful to that school of thought!

In the case of an FIA seat, and to follow the idea of flex, I'd be looking to create some sort of tube structure that would "catch" the seat if it flexed too far... or broke.

 

John etal,

Look at this.

You could 1) mount your seat to it for solid mount, 2) mount the foam to it then your seat for an inch of back whip, 3) mount your seat 3" from it if you like FIA flex theory. You can add a strap of plate in the shoulder area. You can mount your seat to it. You can mount it to the sill plate or mount the rear tubes to your sill tube. I think I will set up my car with the vertical tubes at about shoulder blade width and then the ultrashield bolted at the base. The tubes will be weled to my door sill tube and the interior tub tunnel. The top of the tubes will be welded to the harness bar. I can then weld a plate to the harness bar/seat back tubes to house the funny 4 belt HANS shoulder unit. So I will have a solid design with seat connected at the base. I weld my antisub anchors to that forward bar in that 20 degree range from the seat sub hole. Do you think I need to connect the back of the seat to the bars too? I'm the only driver ever so I can build to my specific fitment. What does your BS meter think of that design?

Also, for the guys who like FIA flex....doesn't the FIA mandate a firm ridgid seat in open wheel cars like an F1 car? Aside from some back padding what is the reason that ridid seat no flex is good for F1 but flexy seats are good for tintops? Is there something functionally different in the cockpit design that makes flexy seats work better in tintops? Looking at NASCAR/CART/F1/ all open wheel cars I think ridgid is the way to go. What do you guys think of that reasoning?

 

The FIA does NOT mandate a composite seat with no back breaker, er, brace.

Let me repeat that.....

THE FIA DOES NOT MANDATE A COMPOSITE SEAT WITH NO BACK BRACE.

Rather, the FIA has a set test (downloadable) and the seats are tested and homologated exactly as the manufacturers specify. Some seats are only homologated with side mounts. Some are only homologated with bottom mounts. Some are homologated both ways, but the seat manufacturers pays to have them tested both ways.

So, that said, to install a back brace is to void the homologation.

But you guys are right. There is a holy war not only about H&N devices, but also for seats. Choose your weapon wisely. I'd say if you have a FIA homologated seat, leave the back breaker alone. And of course, if you have a seat that is not FIA homologated, install the brace.

 

FBB;

That is certainly a tried and true style in tube frame race chassis. However, you can accomplish the same result with a lot less tubing.

You always have to remember that it is easy to add tubes... and weight. It is harder to come up with a smart design that accomplishes what is necessary, without being heavy too.

You could accomplish the same result (if you mounted solid) by utilizing the side sill and front lower cross tube for the front mount, and then mount the shoulder area of the seat back to your belt bar assembly, eh?

The sky is not the limit. More accurately, your imagination is.

 

What are we trying to avoid/prevent with the seat brace? Are they designed for 2 piece seats only or for racing shells as well?
Why is flex bad? Is all flex bad or the moderate flex that a FIA certified shell would allow?

There must be a way to find out the force that is needed for a FIA certified shell to brake (or come off it's sidemounts).

I am no expert but I am most scared of designing a safety system that actually puts me more in danger of serious injury just because I put together devices that are not supposed to work together.

 

Matteo, I honestly think both seat systems work well (just like the HANS, Isaac, and R3 work well as H&N restraints). It comes down to what you believe. There are those who believe the seat should remain rigid and those who believe that either the seat should flex and/or back braces are bad. Like all safey equipment, you have to decide what you believe.

Unfortunately many of these discussions become quite passionate because people must believe in their choices enough to trust them with their lives.

The best you can do IMHO is listen to the safety experts (there are 2 or 3 who are clearly at the head of the class), listen critically to people's opinion, and then try to figure out what choices and/or compromises make the most sense to you.

I guess this is a long winded way of saying don't worry about your choice. There are always compromises, but the aluminum seats are used every weekend in NASCAR and at short tracks all over the country as well as in road racing. Composite seats are used every weekend as well al over the world. While John and I disagree about seats I think we can both agree to tell you that whatever system you use, look at the whole system and use it accordingly. You should be fine with either.

 

I have a Recaro PP that had a manuf. date of 96. I installed the back brace last year before my first DE, can anyone explain the SBB with a FIA approved seat that is older than 5 years?

 

Hey G;

A very well reasoned and level response... for one of passionate persuasion!

Matteo - Geo is absolutely right. It is more down to configuring WHICHEVER type of seating arrangement you agree with properly than in which you actually choose. Each has it's encumbent needs, strengths, and weaknesses.

Geo (and others) does not like the idea of a seat back brace behind a seat that is designed to move. To restrain a seat that is suposed to move defeats the purpose; to absorb and disspitate energy. Further, it may impede the seat's motion in such a way that the seat becomes vulnerable to breakage; creating a fulcrum or point of increased stress that may cause the seat to fail catastophically. "Back breakers" as he is fond of saying.

I fully understand his reasoning, and cannot argue against it, at least on phylisophical grounds. However, I feel that a properly positioned and constructed brace will do nothing but further the ability of the seat to protect the occupant.

The real problem with seat braces is not the brace itself, but how it interacts with the seat given the attachment points available with the average cage. It is often very much easier to create an effective cage and brace system from scratch than to try and piece-meal one together from what is commerically available. Many belt bars are just too low to properly position a brace (let alone the belts!), which should be very near shoulder level to be most effective.

To me, the REAL issue regarding flex (FIA) seats is what happens when they do flex. The big problem is with offset hits. The seat will invariably twist and open toward the direction of impact. This will spill the driver out, and that makes the driver very vulnerable to whip effects and also not returning to a position inside the confines of the seat. The average alloy seat (one that is not heavily reinforced) will also suffer this same effect, the difference being that the alloy seat will bend and stay there for the driver to return to, while the plastic seat will spring back and possibly be ill-positioned to catch a recoiling occupant.

This is where a good side net system can really pay off. These seats WILL spill the driver out in the direction of impact, and having a good side net system in place to restrain the driver at the point he threatens to leave the seat makes all the difference.

I am of the feeling that the "cacoon" type cockpit of an open wheeled car is the safest environment. No room for unrestrained movement = no excess energy created by that unrestrained movement. A sedan ups that by providing more protection by having a roof and body around it. The absolute state of the art is to buy a carbon fiber cacoon and install it in your sedan chassis. Such things actually do exist, but they are understandably a bit pricey.. somewhere north of $10 large!

What you see in NASCAR is an attempt to create that type of fixed cacoon inside a sedan body. Solidly mounted seat with huge thigh, shoulder, and head fences that DO NOT MOVE are the state of the sedan safety art. NO excess motion is allowed. This has been proven to be the safest environment.

Some of the containment seats you see now will offer you quite a portion of that cacoon idea while being mounted solely to the floor. Obviously, the more solid the mounting the better, and yes they still will benefit from side netting as well.

The only real problem with cacoon type systems is that they can be extremely restrictive to vision, and ingress/egress. Simply solidly mounting a full containment seat in a normal floor fashion can offer some challenges, let alone full halo-ing and side-netting.

I personally don't feel there is any doubt which type of seating arrangement offers the most safety. Whether you can rationalize such a system in your recreational vehicle is quite another matter.

In the end, as Geo said, it is really down to doing it right, HOWEVER you choose to do it. For most recreational purposes, a well done FIA flex seat will offer what you need. If you feel you need more, you will have to give up something for it.

The art - and SCIENCE - of compromise is alive and kicking at every turn!

 

I just don't want that damned thing pointed at my spine whether the seat is composite or aluminum.

I don't agree with your conclusions (I know you knew that), but I won't make a holy war out of it. Each person can (and should) draw their own conclusion. We're probably all a little right and a little wrong no matter which way we decide.

Actually, I have to correct this. The movement (which isn't unrestrained) does not create energy, but rather absorbs it.

I definitely don't draw the same conclusions here either. But that's cool. I honestly don't feel it's a matter of either of us (or anyone else) being right or wrong. Shoot, I'm not an expert. I'm just another monkey listening to the experts and non-experts and trying to make sense of it all.

 

I know that we cannot forcast what will happen in every individual circumstance, but that in general is what seats that are only anchored at their bases do in a crash, no question.

No, energy is not created. However, kinetic energy builds as a function of time. The longer an object remains in motion, the more kinetic energy builds. That is quite the raison d'etre behind the creation of the hydraulic Isaac Device, I would imagine. This absorbing of energy you embrace is actually creating a greater whiplash effect because it lengthens the time span of movement. The less time the body spends moving, the less whiplash effect it will have to sustain. I am an idiot with math and such, but I believe this is bio-mechanical fact. Where's Gregg?

Indeed, I am in that boat too. However, this is not just me hypothisizing. Based on my own studies, I am spreading the gospel (acurately, I hope) of the two people on this planet that seem to know the most about this stuff; Hubert Gramling and John Melvin. It sure aint coming out of thin air, or my measly brain!

 

George and John

thank you very much for your help and advice. Here is the deal. My car is a daily driver and I find myself in th land of compromises...

First off a cage is not practical at all. So a roll bar will have to do and I was thinking about getting a DAS weekender.

With that I feel that an ISAAC could be a better overall fit than a HANS. I read all the threads and came to the conclusion that HANS would perform best as a part of a whole system designed to perform in certain ways (Hans seat, hans harness, seat brace, full roll cage etc.) like in NASCAR or F1.
ISAAC seems to be an easier fit in a 911 cockpit, without having to sacrifice much in terms of safety. I do not need any homologation, my car being a DE car.

As per the harness it seems that the consensus has fallen on a 6 point belt system.

Nomex suit, gloves, balaclava and a fire extingushing system are given.

So I think that with my Recaro Pole Position this could be a homogeneous set up that, albeit with some compromises, could provide a good level of safety.

What's your opinion?

 

Do you have a picture? I think I get it. Does your design mean it is O.K. to leave my seat mounted at the shoulders bolted thru the aluminium and then bolted at the front cross tube and

1) leave my tailbone portion of the seat not connected to the cage and free floating or
2) just bolt the tailbone part of the seat to the floor via some fab'ed up little mounts or
3) make a rear tailbone tube from the doorsill tube to the tunnel and mount the seat tailbone area to that?


Thanks!