Why?

[mattclow]

Ever wonder why? I do. Like why do seat belts have expiry dates but tires don't? For such an important item, everyone wins.

[Bill Baer]

The seat belt expration is based in some air force testing the shows a significant drop in the strength of nylon webbing when exposed tu UV light for a period of time (say 2 years or so).
While UV affects the neoprene in tires it's not as significant as it's affect on belts.

Per the S.F.I. :

"The rate at which the breaking strength of the webbing decreases with outdoor exposure is illustrated in the graph below. The webbing used in motorsports restraints is typically made with DuPont Nylon 6-6 or a similar product. According to the data, the webbing loses about half of its strength in one year. "

The Graph (not shown here) indicated ~20% stength after 24 months.

Reference: http://www.sfifoundation.com/seatbelt.html

[68camaroSS]

I don't know how this airforce test was conducted, but If this was the "real" purpose of the NHRA rule, as crash sensitive as the Insurance Institute for Highway safety which performs auto crash tests, and as safety conscience as the Dept. of Motor Vehicles is, why hasn't anyone picked up on this and made it a requirement to have the seat belts in your family car replaced or recertified every two years? How much UV light does a race car see parked in the garage or trailer 99% of the time, where your family car carrying your wife and kids is out in the sun every day?

[bottombulb]

OEM passenger car belts are made from a different material than racing belts.

[rayfin]

It seems to me that $$$ may have something to do with it.

[Bill Baer]

Originally Posted by rayfin

It seems to me that $$$ may have something to do with it.

Rayfin

Well that was my first thought also.
However after thinking about it for a while I think a bigger motivation was to protect the SFI from litigation (i.e. being sued)
Look at it from this perspective if you were the organization responsible for setting standards and it came to your attention that the driver restraint systems you were certifying potentially lost half of their strength after the first year and 4/5 of their strength after the second year then if you didn’t mandate their replacement after two years you have a serious potential to be found negligent if one of the restraints fails during an accident.

Now one could argue that most racecars don’t sit in the sun continuously and therefore the restraint systems may not degrade as rapidly as the testing shows however there may be some, in warmer climates that are outside almost continuously so to be conservative the SFI needs to plan for the (this) worst possible scenario.

As long as we live in a society where people try to sue every time there is a tragedy in motorsports there will always be a need for safety equipment manufactures and their standards organizations to continue to come up with higher and higher standards for safety and yes, we racers will pay for it, but it is we who will benefit from them and ultimately there may be just a few less of us who are severely injured or die racing.

[THE LEGEND]

Most local dirt tracks have a 5 yr rule on seat belts and they reuse them crash after crash.
Drag cars are 2 yrs and if you wreck after you are out of the car the next thing they do is cut your belts and take your helmet.
Go figure that one. I have no problem with it. I think the dirtdobbers are crazy.
Chip Johnson

[mattclow]

I was wondering why tires do not have expiry dates. not why seat belts do. A tire can sit on a shelf for 15 years and still pass tech.

[Bill Baer]

Originally Posted by mattclow

Ever wonder why? I do. Like why do seat belts have expiry dates but tires don't? For such an important item, everyone wins.

Well I think it has something to do with the fact that except for the 300MPH top fuel classes tire failures are pretty rare in drag racing. When the last time you saw a tire failure at the track? It wasn’t that long ago that we ran English moped tires on top fuel dragsters and until speeds got high enough that they wouldn’t stay on the rim (Remember Shirley’s crash in Canada) I know a lot of guys who have been running the same front tires for more than ten years some of them regularly going over 200 MPH. So far ( again except of for the fuel classes) there just hasn’t been a tire problem.

[Ron Gusack]

RJS told me that after 3 re-certs I have to buy new belts because the metal hardware has to be changed. I've heard of metal fatigue, but this seems excessive to me.