Geo

And therein lay most of the problem with this discussion. We're all making guesses.

RedlineMan

Holy Landslide, Batman! All this since lunch time!

924 - My understanding of the sternum strap deal is this. The driver slams the belts. The body bends and attempts to squirt through them, which pulls the shoulders back, stretchs the sternum, and SNAP! Sternum strap keeps the belts from separating and allowing the body through.

Oh... and before I forget. The Sternum Strap Lynching might be an old racer's tale too. Yes the belts stretch, but there is far more material behind the strap that below it, and that is where the majority of the stretch will take place. Mine rides at least 6-8" below my neck. The belts won't stretch that much, certainly not below the strap, and I won't compress that far down in the seat either, methinks.

Damn JCP... still testing me on that sub strap definition! It's a Pet Peeve of mine. Let's get this ironed out once and for all. I hope EVERYONE reads this so we will not be working under this misconception any longer.

What happens when you hit something? The first thing you do is slam into the belts. They have probably done 80-90% of their total work right in that split second, and then will hopefully keep you in relative proximity to the seat thereafter.

If the hit is severe enough, you will reach twice the limit of stress the neck can handle in 30 milliseconds! As the event unfolds, you will indeed be pushed down in the seat by the shoulder straps, but if I am correct in my assumption that 80-90% of the stress happens in that 30ms span, the submarine aspect will not be severe since most of the kinetic energy has already dissipated before the body begins to travel downward.

And there is the key. When our bodies travel downward in the seat, they do so in a very vertical nature. Sub straps did keep drivers from sliding UNDER the lap belt because they lay down to drive. The closer you are to horizontal, well, yes you stand to slide under the lap belt. To apply open wheel laid back seating position thinking to sedans where we sit so upright is erroneous to a large extent if my study and assumptions are correct.

Yes, you will travel downward in a sedan, and yes the stock seat will compress more. However, if my assumption is correct that most of the kinetic energy has already dissipated by the time this starts to happen to any real degree, the result would not be as catastrophic as people seem to think.

Now, a lot of this is supposition and surmise, but it seems to make sense to me. Guess I oughta enroll at Wayne State and find out for sure!

924RACR

Again, kudos to all for a REALLY great thread, gets all of us thinking about the most important thing - saving our butts!

The Sparco Circuit - very interesting info, thanks, but this exemplifies the beef that I have with most of the head restraint seats currently being marketed (Racetech seats showing similar designs, below): Head restraint only. No additional support for the shoulders in lateral.

In fact, it would seem that the Sparco Touring, though undesireable for possible vision obstruction, offers better shoulder support in lateral.

If you look at the Racetech 9000, you'll see what I mean in the difference in lateral support:
http://www.racetech.co.nz/new_template/seats/9000.html

Another pic, from the NA distributor - note that this seat retails for $1550:
http://www.racetech-na.com/products/9009/rt9009hr.html

Only the Viper seat offers the really good side impact support for the shoulders. This is what I've been complaining about. Maybe I should talk to the seat manufacturers, instead of just sitting here and complaining!!

Another thought - it may be that the head-only seat designs are only designed to support the head in high cornering loads, not in impact loading. That would explain the relative lack of support for the shoulders.

924RACR

More detail, this the email from Racetech (in response to my inquiry):

Hello Vaughan and thanks for the enquiry through our distributor.

You are correct in seeing the real benefits of the Viper seat. We had Dr
John Melvin give us the brief for this seat and the expected lateral loads
which can be expected in a 45G impact.

The beam and back mounting is unique in the world to our Viper seats and our
new model (9109HR) which has just been approved by the FIA. The shoulders
are also very square which supports the shoulder area well in an impact. In
a male most of the body mass is in the shoulder. These seats also have
energy absorbing foam in the vital areas hence protecting the body and
reducing the initial shock.

The theory behind a good seat is that 4 areas must be supported well and
kept in the same relationship to each other.

The thigh , Pelvis , shoulder and Head. A seat should not support the Ribs
as there is no protection with muscle and the vital organs are right behind
the ribs.

Our previous models of seats with side Head restraint are still better than
no head restraint but when these were designed the current technology was
not available.

I trust this helps in your decision making process and if we can be of any
more assistance please let us know.

Regards

David Black
Managing Director
Racetech Seats
New Zealand

924RACR

Re: the sternum strap deal - I heard this directly from the horse's mouth, mano-a-mano, when Dr. John Melvin gave a presentation in 2000 to Detroit Region SCCA... he's also a member of our PCA region, and quite active locally for someone so busy in the national safety scene. This presentation left quite a mark, and is in fact what I base most of my statements on.

But it gets better! (Don't you all wish you lived in Motor City?)

Next Wed. at our monthly Waterford Hills meeting, we are scheduled to have Tom Gideon talk about race safety. He is a race safety engineer with GM. I plan on grilling him about lateral impact and seats in particular!!!

RedlineMan

Vaughan -

You need to check out the Kirkey Full Contaimment seat. BIG lateral support for around a grand.

924RACR

Yeah, I think we chatted about that seat on a previous post - and yes, it's nice, meets the requirements. I just wish it were FIA cert - would feel a little more comfortable about it then...

fatbillybob

You know on the racetech seats mentioned earlier, for the viper there may be some other design parameters that we can all benefit from. I'm only 5'5" and with a helmet I hit my head just checking mirros on the roll cage in the vipers! This hapens to me on many low slung converted streetcars like Ferraris. The best cars for cages are big boxes like the old E36 BMW chassis. Anyway, what do you guys do when you have a bar 2" from your head? You are going to get a headache thats what. I think that sometimes due to the low rollevoer chances my odds are better for less head trauma without that bar by my head. Now th viper seats limits your lateral head movement. I'd like to try that seat and see if my head hits the bar now. What do you guys think of that issue?

fatbillybob

what is harnesses doubled back through the buckles look like?

What is a petty bar?

Adam Richman

"What do you guys think of that issue?"

I think it sucks The Spec Miata's have the same issue. Even at 5'7" I still felt like I was in a headache waiting to happen and this cage was rather optimized for this clearance issue. One of the things I have seen done by a builder to ease this is how they mount the bar from the A-B pillar and reinforcing that B Pillar-Main hoop with a tube gusset. It doesn't buy you a ton but it does move the bar out to a degree. Obviously, floor mounting the seat as well as moving it closer to the transmission tunnel will also help with these sorts of issues but in a lot of cramped cars, it just doesn't buy you that much more room. If there is room to do so, changing the rake of the seat (rearward down) can give you more head clearance (unless it poses other issues w/ the main hoop). The problem with the seats may end up being fitment - I know that some OMP seats won't fit in the Miata whereas the Momos do. I would imagine that the full retention seats would be an even more difficult fit.

Funny, we floor mounted my seat in the CRX and I have a good 8" to the roof panel from my helmeted head.


Petty bar (pg. 1 man ) - " Petty bars, (and I understand them to originally came from running a diagonal from the b pillar on the driver side to the a pillar on the passenger side on the roof - irrespective of the root, the current type is what I am talking about) the bar running from the main hoop to the psgr. footwell when mounted to the top of the main hoop, it is a.) providing no appreciable rigidity (its how many feet long?) and b.) it becomes a very easy bar to hit on a psgr. side impact with your head. If you must have one (and many folks do), for safety's sake, run it from the cross bar to the psgr. side footwell."

Harnesses doubled back would be threading them through forward (as they loop over the bar) and then taking the material back through the rearmost slot one more time (going the opposite direction so you can pull it snug) - it should be very tough to get it through but the belts won't move once done.

Edit: for clarification

RedlineMan

Actually...

There has been a change in thinking in the last few years regarding tube placement and proximity to the occupants. It used to be that you got them as far away as possible. Now there is a movement to actually bring some of them in toward the occupants to create a safety cocoon that can be enhanced to provide even MORE safety.

Your first thought is that these tubes are hard and you're going to crack your skull on them. Makes logical sense. However, what has come to pass is that sled testing has shown designers that using the tubes as a safety cell around the driver will actually increase safety. In an impact, the driver will quickly hit one of these tubes (properly padded of course!), thus decreasing the amount of kinetic energy created as the body travels through an otherwise unimpeded path. It also allows the designer to place tubes for increased rigidity in places where they are beneficial to both.

Here's perfect example on an Ice Racer I built.



The diagonal brace shown here from the main hoop to the side hoops is such a tube. The side hoops are the weakest area because there is such a long expanse of hoop unsupported by any bracing. These diagonal braces not only dramatically brace the side hoop, but also create a perfect helmet containment fence. They are far enough away to not even be noticed, but only allow the head to move about 5" before striking them.

Of course, you might get your bell rung by them, but the looming spectre of unimpeded movement and possible basilar skull dislocation is the alternative.

Personally, I'd choose the headache!

M758

Yeah in some strange way is probably better to have the bars closer.


Example.

Bang your head on the wall starting with your head 2" from the wall. Hurts doesn't it.

Now try it with your head 8" away from the wall. Seeing stars yet?

RedlineMan

Hey M;

Somebody offered that on a previous safety thread. I thought about it for a minute then, and came up with a qualifier. Try it this way.

Stand one foot from a wall and fall forward. Then stand 5 feet from the the wall a fall again.

The difference is that by falling you are only picking up the velocity and kinetic energy that gravity provides, -vs- using muscles to accelerate or slow the head out of proportion to the distance involved. Seems my revision might give a more linear idea of the force multiplication.

Geeez... I almost sound like an engineer?!

Adam Richman

I see how you guys are thinking of it but I tend to disagree. It is a reasonable assumption that cages (DOM tubing not F1 tubs) will deform with the right (err. wrong) load and angle. I want a dash bar that is far away from my knees, I want a top front hoop far away from my head, I want my door bars way out from my body. I don't want a series of comprimising bends to get it this way but that's where I want these in realation to my knees, head, arm/head. I don't want to have a Petty bar running along-side my head from the main hoop to the floor so that I have something close to hit - I'd hope that "most" hits would keep me from getting that far but if not, I'd rather rely on a net or seat-type vs. a bar even w/ SFI padding. I also think you have to look at how deformation to the cage could affect egress. I am no expert on any of these matters so this is speaking to my comfort zone vs. sled test results.

RedlineMan

Sure Adam;

If you've got room, get it away. If you have a compromised area, like the one I pictured, why not use it to double your advantage? Far greater stiffness, and improved occupant retention to boot!

Keep thinking of it this way. If the obstruction is not far from you, you will not be able to accelerate enough to have it hurt so bad.