Mokesta, please read what I wrote rather than dismissing it simply because I'm asking questions. I agreed fully with you that any single point will be a 'balance'. What I'm questioning is the total force exerted on the point. I've yet to see anything explaining why/how there is a total increase in the force exerted by arresting the same force (ie your body).

Sorry if I appeared to be dismissing you. Not intended.

There is no increase in total force on the car from catching a soon to be mushed corpse with a 2" belt. The additional load in the top of the B-pillar is equal and opposite to the load applied at the sill where the belt is anchored.

If you picture the B pillar as being flexible and the seat belt reel is locked. Now imagine you pull on the part of the seat belt that goes over your chest (sash). For every 10 cm you pull the belt out, the B pillar will compress 5 cm due to the pulley effect of the upper mount. As we know from the principle of leverage, a halving of the movement equals a doubling of the force applied.

In the end it is the same as a block & tackle. The foce balance is the same. A pulley at the top holding up a weight at the bottom. It just allows you to pick up a weight heavier than the tension you apply to the end of the rope.

M

Nice diagram on the previous page. I finally understand what you are all talking about, forgot that intertia reel belts are mounted to the floor and not the B pilar.

I do have a question though as I think the force diagram is wrong and I may be completely wrong (most likely! ):

In the bottom diagram with the interia reel belt, if T is the mass of a moving driver in a crash, isn't the force exerted on the B pillar still just T and not 2 x T? I don't understand how you get 2T forces when the floor is not pulling against the B pillar but actually it's the driver's weight against the B pillar and anchored at the floor.

I don't see how the top diagram and the bottom diagram differs in the force T as T is constant. There is no force T being pulled by the floor to in actual fact aren't the forces of the bottom diagram T/2 and T/2 because T is being distributed to 2 belts not 1?

So your saying that if I can't lift an engine, if I hang a rope from the ceiling, loop it around the engine and pull on the rope again towards the celing (similar to what's being said above) I will double the force lifting the engine?? doesn't make sense unless I am mistaken...

I am stumped (but it is rather early in the morning )

_________________
Lillee - 1969 Morris Mini K

Thought I might throw something else into the debate.
These early 850's did not come with seat belts. So, were the "B" pillars modified to allow the fitting of seatbelts or........were they just added and therefore simply by having a seat belt has the stuctural integrity of the pillar been brought under question???

_________________

I've seen only one mini in my life that was fitted with barrel bolts (bolts that go all the way through the pillar with the big ugly bolt head on the outside).

I have forgotten specifically when seat belts became compulsary fitting in all new cars. I have a feeling it was around 1964. In anycase, manufacturers knew it was coming and had to make the engineering changes prior to that mandate.

I also remember seeing some early cortinas and minis with the bolt through the B piller, but all the minis i have ever owned (that includes a couple of sliding window 850's) had engineered mounts.

I think the engineered mounts were mandatory some years before the seat belts were made law.

I do clearly remember the hue and cry when the belts did become law and the wearing them the same. I remember people claiming medical exemptions etc, vocational exemptions and lots of people strapping razor blades to the belts in case they were trapped in a burning car or the like.

I'm not sure when they started either but the sports850 was built late '62 and it has themounts in the door pillar for the belt , I have seen the big bolt through the B pillar on some , might be time to ask the people on the earlier end of the 850 register and see if we can pin it down .

_________________

Now my head hurts

_________________
Cheap, Fast, Reliable. Choose two.

Here's another sketch:



This one should answer the load on the ceiling question.

Quote: "So your saying that if I can't lift an engine, if I hang a rope from the ceiling, loop it around the engine and pull on the rope again towards the celing (similar to what's being said above) I will double the force lifting the engine?? doesn't make sense unless I am mistaken... "

You are not mistaken. You will lift 1/2 of the engine weight but have to lift it twice as far. See case #4.


Cases #1 and #2 are the seat belt analogy. There is still just 100 kg worth of tension in the rope/belt but the termination point determines the load at the ceiling.

M.

Ya see that's where I'm thinking the analogy doesen't quite fit. A few things: the inertia reel isn't a fixed point, even though the reel locks the belt tightens (considerably) around the reel, with the net effect being a moving anchor point. Secondly, the belt stretches (considerably). These two points together are the reason you can still whack your nose and/or chest even though the belt locked.

Last thing to consider - even if the force on the B pillar mount greatly increases in the case of the inertia reel (as opposed to static), this is actually of unknown impact unless we also know the maximum design loading of the B pillar mount. Anyone know what it is?

Ahhh!!! Eureka! i get it now!

great drawing skills by the way, the facial expressions do it for me

_________________
Lillee - 1969 Morris Mini K

Yes but the car becomes the weight of the driver as it pulls the same amount equal to the weight of the driver. Every action has a equal and but opposite reaction

_________________
Lillee - 1969 Morris Mini K

So I guess I'll just fit a roll cage and harness!!

Boy what did I start. Good discussion though, It highlights the difference between body shell structures.

Gig

_________________
67 Deluxe - Red and white
69 Deluxe - Sugercane Grey

But those diagrams all show an extra weight added, being the person lifting, AND the 100kg mass.

You are in your seat in the car. No extras are added.

_________________
Cheap, Fast, Reliable. Choose two.

A car coming to rest from xx kmh in four feet (1.1 metres) with enough force to push the powerplant into and under the cabin with say an 80 kilo body mass strapped into a seat against the body deformation with that pulley mechanism is the extra weight.