Seat Belts

[Ken's 57]

I know this topic has been discussed extensively here on the forum but here goes anyway.
I already have a pair of fully restored light blue static belts with GM buckles and always intended to fit these into my FE once the mechanical rebuild was complete. This is now pretty much done although I'm now leaning towards inertia reel belts because no matter what belts I put in, it's not original and they are an easier belt to wear.

I have just spoken to a licenced seat belt/restraints company in Gosford NSW and he informed me that the rule of thumb is that static belts are what should be installed in older cars because the maximum force exerted on the B pillar is only one ton where as with inertia reels it is a maximum of 1.5 ton force.
I know many of our members have fitted both types so my questions are:

1. Is it correct about inertia V static in older cars in NSW? Is there a way of finding out? You would think as a professional this bloke would know his stuff.
2. Are inertia reels a tidier look?
3. Can I have some opinions on this please? 

Cheers, Ken

[Harv]

G'day  Ken,

I think that the seatbelt technician is using an old rule of thumb, or something someone told him years ago. The loading on the B-pillar is dependant on how many mounting points the belt has, not whether it is retractable or not. A retractable belt normally has a bolt on the floor near the B-pillar, a bolt in the B-pillar at shoulder height, and a bolt in the floor near the transmission hump. All three bolts share the load (not necessarily equally). A static belt with 3 bolts will be near identical loading as a retractable belt with 3 bolts. A static belt with only two bolts (like the old sash-only belts) will increase B-pillar loading.

I am not aware of any B-pillar loading requirements in NCOP, VSB5 or the Road Traffic Reg. If anything, the guidance leans towards inertia reels. VS5B indicates that:
"Some registering authorities may require retractor type (inertia reel) belts to be fitted for all additional outboard seating positions and this should be checked with your local authority before proceeding. In those States or Territories where retractor belts are not mandated it is strongly recommended that they be installed.".

I have certified static belts in the FB, and engineered retractable belts in the EK (both in NSW).

There are ways to decrease B-pillar loading, rather than use Frankenstein bolts. One way is to hole-saw a 1" hole in the B-pillar inner skin, then insert a reinforcing plate (long and thin, but larger surface area than the head of a Frankenstein bolt). The plate is held in place with some temporary fishing line, then pop riveted to the inner skin. The sash guide covers the 1" hole. This is how my FB was done.

Static belts look more period correct (they were a NASCO option), though are painful if the car is a daily driver, or if you have kids in the car regularly.

Cheers,
Harv

[GMHwagoon]

     l am looking at putting the centre rear  retractable belts out of commodore in my wagon

    the belt comes straight out of the parcel shelf from the reel  down over your shoulder to the buckle
 
    on mine l will be  putting  reel inside onto the wheel arch   then up through the window ledge behind the rear seat

    over the shoulder down to the waist

 1. can anyone see a problems with this l might encounter
 2. the anchor point will be inside the wheel arch with appropriate plates
 3. up through the window ledge with a plastic or smooth metal guide like on the parcel shelfs have

       thanks greg  (fcwagoon)


 

[Harv]

G'day Greg,

That's pretty much how I did my wagon. I copied the way that Ed Ho did his wagon a decade ago  .



Some issues:
a) Whilst not prohibited, some engineering signatories refuse to accept 2nd hand belts.
b) There are minimum sizes for the reinforcing plates. Some engineers will not accept Frankenstein bolts on the C-pillar.
c) There are specific locations (dimensions) for the floor bolts and sash guide. Some signatories don't care, as long as it looks right. Other signatories are fussy about the dimensions (per NCOP or VSB5).... my engineer was fussy. I did a lot of measurements, photos and a write-up for my wagon... can email you a copy if you want it (kinda like a seatbelt mini-Guide).
d) Gotta avoid the seat latches (at least in an EK... not sure how an FC wagon latches).

Cheers,
Harv

[ardiesse]

Ken,

I'm about to go all physicist on you, and dispute this notion of maximum force exerted on the B-pillar.

When an object is accelerated (or more to our point, decelerated), the relevant physical quantity is the impulse.
Impulse is the change in momentum, that is, mass times the change in speed.
The impulse is independent of how quickly the object is accelerated, it only depends on the difference in speed.

For example, when you gently brake a car to rest from 30 mph (say) and run into a concrete wall at 30 mph, the impulse imparted to the driver is the same in both cases.  A gentle stop doesn't hurt, but running into a concrete wall is usually lethal.  What gives?

Impulse is also equal to the product of force and time. A gentle stop involves low forces, because it happens over a long time period.  Running into a concrete wall involves very high forces, because it happens in a split second.

Collisions are "impulsive" events, in that they happen almost instantaneously.  Remember the famous photos of a golf ball at the moment of impact?  It's squashed down to something like half its normal diameter.  The force acting on the ball at the moment of impact is for most purposes infinite.  So it with vehicle occupants in a collision (and here I speak from experience).  The forces are very high, and very brief.

Back to the B-pillar thing.  If you define a maximum force on the B-pillar, then you are also defining a minimum duration of collision (which is directly proportional to speed and driver mass).  The real world is not so neatly deterministic.

Let's say that a B-pillar attachment is restraining 50 kg of driver.  One ton is ten thousand newtons.  If you make the totally arbitrary assumption that the crash involves constant deceleration, and let's also say that the speed before impact is 36 km/h (= 10 m/s), then

F=mass x (change in speed)/(change in time), giving
duration of crash = mass x (change in speed)/force, which gives
duration of crash = 50 x 10/10000 = 0.05 seconds.

But if, instead of the deceleration being constant, it follows a triangular pulse shape, the peak force is doubled.  Or if the deceleration is a half-sinewave pulse, the peak force is 1.57 times the uniform case.  This is my point - in a crash, you don't know what the function of deceleration versus time is, and you have no way of working out what the peak force is.

Rob

[GMHwagoon]

thanks for the pics harv

      The ek pillar is a lot wider  at the point  where the bolt goes in in your pic 
       allowing of the belt to be in a nicer position , lower and back over the shoulder
       l had the reel sitting on the wheel arch like in the pic on my fc wagon and it   passed the engineers check.
       now l want to put it inside behind the cargo wall onto of the wheel arch .
       go up through the window ledge  straight over the shoulder .

[Stewy]

These would be what I would do. courtesy of CoolFCwagon. 





Cheers Stewy   

[Ken's 57]

Many thanks Harv and Rob. I've printed off your earlier post detailing the way to avoid the "Frankenstein" pillar bolts Harv. Really helpful..cheers! 

Is there a licensed business in Sydney who can fit and certify/engineer either style of belt? I prefer not to do this one myself. I'll still see the fellow in Gosford of course but am happy to go further afield if I'm not entirely comfortable with what he proposes. Thanks again.

Ken 

[Harv]

Is there a licensed business in Sydney who can fit and certify/engineer either style of belt?

Try this website for a list of NSW RMS Authorised Restraint Fitting Stations:
http://roadsafety.transport.nsw.gov.au/cgi-bin/index.cgi?action=authrestraintfitting.form

These stations can install and certify the belts. They issue you with a small certificate - not an engineers certificate.

You can enter your postcode, and find one close to home. Ring around and check for prices, and whether the individual station will do the type of work you are after.

Cheers,
Harv

[Ken's 57]

Thanks Harv.