New Belts again

[gsbaker]

Found it: MIL-W-4088

Nylon, 1" wide, 0.045-0.070" thk, 2500# tensile strength. Here is a good example of how this webbing can be specified depending on the requirements.

We don't use the polyester so I can't help there.

[leggwork]

haven't done any research on their reputation, but RCI says that they will recertify a set of belts to SFI 16.1 one time for free (you probably pay shipping), so you can get 4 years out of the belts (or, I suppose, 6 years if you do it early in the year).

http://www.realtruck.com/productline/793/1..._belt_sets.html

cheers,
bruce

[planet6racing]

next set of belts, I'll be looking for polyester belts, not nylon. Nylon stretches 20% while polyester is at 7%. Think of the 3' belt from your lap to the harness bar - 20% is over 7" that you're moving forward in a frontal collision.
cheers,
bruce
[/b]

Yes, but keep in mind that, in an incident, the 20% of stretch in the nylon is used to decelerate your body. By changing to a 7% stretch, you decrease the amount of stretch used to decelerate the body and, by comparison, increase the chance of injury.

I know the polyester belts have been tested and accepted, so it is probably a minor point. But, I guess my main point is that, in this case, less stretch is not necessarily better.

[lateapex911]

Great point. In a recent and comprensive article in a motorcycling magaizine, they tested and compared dozens of helmets and analyzed the results with an eye to effective standards.

Amazingly, they found that the best helmets, which were those that imparted the smallest G loads on the head, were actually the cheapest. The ultra expensive helmets were probably able to protect the head in super high impacts, but the article suggested that those account for a very tiny part of the overall picture.

We don't hit walls in Indy cars. Our speeds of impact are lower. food for thought. Mr Baker? Car to comment?

[leggwork]

planet6racing,
that line of thinking is counter to what top safety experts like Joe Marko at HMS preach ... I believe the issue is that more stretch allows your body to get moving faster, then you come to an abrupt stop at the end of the stretch (which is equal in both webbings). I will admit that I don't fully understand the dynamics of these fast events.

cheers,
bruce

[leggwork]

Gregg,
I'm not an HNR expert, but I did sleep at a Holiday Inn Express last night ...

perhaps the experts could have just as easily directed you to
MIL-W-23561 WEBBING,TEXTILE,POLYESTER,LOW ELONGATION (May 1995)
instead of
MIL-W-4088 WEBBING, TEXTILE, WOVEN NYLON (Nov 1988)
(found these at http://global.ihs.com)

I haven't read them, but it looks like they are just specs on categories of webbing, versus something that says - this type of webbing is good for this situation. Is use in a parachute similar to use in a head and neck restraint (I don't know)? If you search the above link using "webbing polyester", you'll see lots of FORD and GM standards for seat belt usage. If you search for "webbing nylon" you don't see any references to seat belt usage.
Of course, the ultimate test is the sled and it sounds like the Link does fine there. Probably because the webbing lengths are so short, versus the length of harness belts.
thanks,
bruce

Found it: MIL-W-4088

Nylon, 1" wide, 0.045-0.070" thk, 2500# tensile strength. Here is a good example of how this webbing can be specified depending on the requirements.

We don't use the polyester so I can't help there.
[/b]

[gsbaker]

Actually, the experts suggested an alternative if the nylon webbing didn't work: Kevlar webbing. Zero stretch.

Somewhere around here we have a piece of Kevlar string about the size of dental floss. The breaking strength is 500#.

[planet6racing]

planet6racing,
that line of thinking is counter to what top safety experts like Joe Marko at HMS preach ... I believe the issue is that more stretch allows your body to get moving faster, then you come to an abrupt stop at the end of the stretch (which is equal in both webbings). I will admit that I don't fully understand the dynamics of these fast events.

cheers,
bruce
[/b]

Obviously, I'm not going to argue with safety experts (well, not here anyway!! ), but I am a trained engineer and a test engineer in polymeric composite materials, so....

It takes energy to stretch materials. Though the same amount of force may cause 20% stretch in nylon and 7% stretch in polyester, the actual g's on the body should be lower over the 20% stretch due to the increased travel...

Well, I think of it this way: crumple zones vs. rigid cars. They put deformable structures in the car for a reason...

The counter arguement is that the Polyester belts are well tested (I believe they have been used in production cars for years), so it really is a moot point. (so why do I keep prolonging it? )

In the end, I just installed a set of FIA belts. It was only $20 more than the SFI belts. I don't know if they are Nylon or Polyester and, frankly, I don't care. I just hope I never have to test them...