bob_dallas

Got a brand with a picture or a weblink that demonstrates the install of these belts? I think I'm following you but don't want to make assumptions here... Is this strictly a formula car application or also valid for sportscars?

SundayDriver

These are what I currently have, becasue that is what came with the car:
Crow Formula Car Belts

These are described as being for formula cars and sports racers - note that neither the lap belt nor sub is adjustable, except at the buckle. They do not work well in a passenger car with movable seats, but would probably be OK for fixed seats in production cars. Clearly a very bad choice if youi need to fit a different person. There are others that are similar but have traditional adjusters, at least for the laps.

The sub mount is shared with the lap belt, so it is much like a parachute harness. Note how the subs thread through the small metal guide on the lap belt, then a loop on the end slips over the shoulder belt for attachment.
Now for my car, add arm restraints, very tight belts and a small cockpit plus the HANS and it is a major production to get strapped in.

Bryan Watts

After getting accustomed to the Formula Car style belts, that's all I like to use any more. They both prevent the lap belts from riding up and prevent submarining...not to mention the fact that they are a lot more comfortable for your family jewels. I've even seen the Formula Car style belts mounted like a traditional 6-point, and they seemed to work just fine (i.e. the lap belt wouldn't move up no matter how much tugging you did to the shoulder belts).

924RACR

John - you're quite right. In my case, having an aluminum Kirkey, I was able to have the luxury of just cutting new holes in the side (seat was designed for a 5-pt harness) and run them under the padding. That would be a bigger concern with a CF or fiberglass seat, though I think I would just cut into that stuff anyway.

Sorry, I can't describe the mechanism that causes the chest compression; I can only guess that it's simply a direct result of the amount of force that must be applied by the shoulder straps to halt the body. With the additional travel allowed by the 5-point single sub strap, the shoulder straps must then exert more force to stop the upper body. F=-kx, and so that determines the compression (not that the ribcage would necessarily function as a linear spring, but you get the point).

Bob - this information is primarily focused on sportscars, as all the testing results that are covered here and were referenced were from sleds with NASCAR and C5R cages, not formula cars (though the same lessions for the belts apply). Side impact is a much different issue in a formula car due to cockpit design.

I like those Crow belts - much better layout. Willans makes a similar setup, only they're even nicer, in that the sub belts are adjustable by the driver.

bob_dallas

Thanks - that helps. I could actually use those in my car because the seats are fixed mounting. Definitely more food for thought...

bob_dallas

Re: 6 point mounting in a sports car. Here's a link to Schroth's thinking. More information in the .pdf linked at the bottom of the page.

From what I understand Schroth does a lot of sled testing and safety research.

http://www.schroth.com/produkte/raci...points_009.htm

RedlineMan

Here's my surmise on the chest thing, and the mechanics in general.

Think about the shoulder straps for a moment. If you drew an imaginary straight line from the latch to the mount point on the cage, it would go right through your pelvic area. If your torso were thrown into the belts as would happen in an impact, there would be downward compression on your torso trying to move it toward that imaginary line. That is the first part of the equation.

The second part is that because your hips are below the lap belt, your legs project outward below the lap belt and have fairly high mass, and your spine is flexible, your hips will rotate forward with the lap belt as a fulcrum.

If you combine the downward compression of the shoulder belts on your torso with the forward rotation and outward projection of your hips and legs, you get the formula for sedan type submarining. This is probably not as directly dangerous as in a formula car, but is still problematic.

There are a few items that mitigate this scenario.

- One is how padded the seat is. How much extra downward travel does your seat allow? If it is a stock seat, it could be substantial. In a race seat not nearly so.

- Two is what type of sub you use, and how is it set up and adjusted? A single sub will stop you, but it is out quite a ways from pelvic contact and might also catch some other "vital" equipment on the way. A double sub adjusted tightly and mounted rearward will catch the hips sooner like a cradle. This will stop the forward rotation and projection of the hips and thus the downward path of your torso, and once the hips stop the load will be transferred back up into your torso and shoulder belts.

Once again, how low the lap belt rides is also a factor. The lower it is, the less body mass there is below it to roll forward.

I therefor think the chest compression mentioned is in the vertical plain, not the horizontal as most people probably think.

Make sense?

924RACR

No, my understanding is chest compression is as measured normal to the chest/spine.

SundayDriver

That is what I thought was said, much because of the 2" travel is where the strenum breaks. That sounds like compression.

The only think I can think of is that the 5 point allows the lap belt to move further upwards, which provides more slack for the shoulder belts. Assuming he was talking about a standard g load, then it would make sense that a looser shoulder harness means more impact and more compression. (I am guessing, because I can't see a clear connection between that and chest compression, but sure would like to know.)

924RACR

Right, and yet another reason to give those belts just one more tug before they drop the green!!!

I've added a page to my website with pics of this net (in place, though not yet fully installed):
http://vaughanscott.com/construction/safety.htm

Dave in Chicago

One of the companies I worked at in years gone by produced webbing, like that used in belts. As a manufacturer, we were required to test the thread we made, the webbing itself, and any devices sewn from the webbing.

Picture a loop of webbing wrapped around a 4" thick solid steel bar. Now pull on this webbing with a motorized little crane device.

You would not believe:

A) The stretch you get before breaking
B) The deformation of the steel bar as you yank it to 7000 pounds

Yep, webbing stretches a bit. Seems good for modulating our deceleration. Best to let it do its job by strapping in tight.