Inertial Seatbelts in an R10
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    Default Inertial Seatbelts in an R10

    Has anyone put inertia reel seatbelts in a an R10?

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    Where did you mount the reel?

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    Quote Originally Posted by AdelaideR10 View Post
    Has anyone put inertia reel seatbelts in a an R10?

    Where did you mount the reel?
    I could not be more serious in my remarks: please do not do this as this is a flawed type of belt. A fixed 3 point lap-sash belt, or, if you find adjusting a belt too bothersome, a so-called 'webbing grabber' design, are much safer. There's an old thread on this but briefly the problem is excessive belt stretch under emergency force loads. Peter

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    Cheers, I'll look into them. Still keen to know how people have mounted them if they have.

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    Default Inertia reel belts

    Hi,

    Mounted inertia reel belts in a 16. The unit sits on the floor with the belt through the pillar mounted loop.

    Haven't tested it in a crash situation yet, but suggest as the webbing is to Australian standards and the reel is manufactured by an Australian company to Australian standards, I am not too concerned.

    Make sure you attach the reel firmly in the horizontal plane or it will lock up.

    John E

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    1000+ Posts renault8&10's Avatar
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    You need to be a bit careful fitting inertia reels to pillars that weren't designed to fit them. Sure they look pretty and fit OK, but what happens the first time you really need them?
    KB


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    Default Belts

    The 16 came with pillar mounted loops so no problem. In the early days after market lap/sash belts were fitted to the pillar with a funny right angle device. Probably saved some lives even if not up to todys standards.

    John E

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    Quote Originally Posted by reno1151 View Post
    Hi,

    Mounted inertia reel belts in a 16. The unit sits on the floor with the belt through the pillar mounted loop.

    Haven't tested it in a crash situation yet, but suggest as the webbing is to Australian standards and the reel is manufactured by an Australian company to Australian standards, I am not too concerned.

    Make sure you attach the reel firmly in the horizontal plane or it will lock up.

    John E
    OK, to repeat an earlier post:

    The issue is not webbing strength but its length. The belt winds round & round a spindle & the locking is locking of that spindle. So you have a considerable length of belt between the end locked on the spindle & the other mounts. All nylon webbing stretches a bit under load & that stretch quantum on a long inertia reel belt means that you move forward more than with the shorter belt length that is stressed in the case of a fixed 3 point harness.

    Yes the former meet ADRs but that doesn't negate the above point (have a look at a picture of a dummy belted in with an inertia reel & hitting an air bag). They were introduced because John & Jane Dillbrain were too slack/incompetent when it come to properly adjusting a fixed harness & a poor automatic system ended up better most of the time than an ill-used superior system.

    Their failings were finally ameliorated by the use of air bags to get between your body and car bits as the belt stretched & then pyrotechnic tensioners that rewind the spindle to partly compensate for the stretch slack.

    As these features can't be retrofitted, you are best off with a fixed harness if you are willing & able to (tightly) adjust it properly. If you are not, then talk to Klippan about a so-called "webbing grabber" belt. As the name suggests, these have a device that clamps on to the belt where it comes out of the spindle or reel housing when its inertial trigger is tripped by an accident. As it grips the belt at that point & not down at the end of the belt on the spindle, it has the same stretch quality as a fixed belt.

    cheers! Peter

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    peter, logic would suggest that if this was a real problem, it might have been noticed some time in the last 30 years or so of intertia reel seat belt use, and addressed at a regulatory level. what are your thoughts on that point?

    i would think that the amount of potential slack caused in this way would likely be somewhat less than the amount of slack left by most people by not fully tightening a fixed belt.

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    1000+ Posts Haakon's Avatar
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    Speaking as an ex R10 owner and big fan, I'd suggest safety is not something you worry about too much. Or is that "something you try not to think about"?

    Intertia seatbelts are easier on their mounting points, as the loads are not as sharp in an accident. That's also why they're kinder to the human wearing them.

    But, it's an r10... If belt design has become an issue in a crash, you already have much bigger problems!!!

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    Quote Originally Posted by Haakon View Post

    Intertia seatbelts are easier on their mounting points, as the loads are not as sharp in an accident.
    is that a problem? i would hope that a 10mm 8.8 bolt would be able to hold the force of my decelerating body in a prang, given that high tensile bolts have a UTS of something over 100,000 psi.

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    If you think about it logically, the top anchorage point on the b-pillar has to withstand the force of the belt
    only with a fixed belt.
    In the case of an inertial reel system with the reel at the floor, the force on the top mount is actually DOUBLED!
    Vectors, you see..
    Imagine that top mount has a pulley hanging off it with a rope draped over it.
    Hang 100 KG off each rope. The pulley has to carry 200 KG
    No pulley, and you have only one rope with 100 KG load on the mounting.

    KEEP YOUR BELTS STANDARD!

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    steve, i dont think that is right.
    if you put a weight on a rope, and run a rope up through a pulley, and pull on the other end, there isnt actually any lever involved. it takes 1kg on one end to pull 1kg on the other end. i would think the force on the pillar mount is identical whether it is fixed there, or fixed at the inertia reel at the floor level.

    getting back to the initial question, the inertia reel normally is mounted vertically at the bottom of the B pillar, with a bolt going sideways into the pillar. the other end of the belt is mounted on a flat bracket, bolted into the floor just next to it. i think that would be quite a standard arrangement. i am sure you know this but i think the pillar mounting bolts have a spacer inside the pillar.

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    Icon7 Good to think about the issues and decide whats best for you.

    The most common fail is the attachment point at the vehicle chassis, all the fluff about high tensile bolts whatever, means nothing, when crash stress at that attachment pulls or tears the bolt through the chassis metal.

    The best you can expect is some energy absorbsion from the effects of the crash. That absorbed energy may help you survive with minimal injuries. Even a stretching belt does that too, provided it slows you down somewhat before your body meets a hard immovable surface. IMHO!

    Wearing a protective helmet in the car might help too, but in the end it is up to the individual to think their way through all these issues and decide for themselves.

    Ken

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by Steve K View Post
    If you think about it logically, the top anchorage point on the b-pillar has to withstand the force of the belt
    only with a fixed belt.
    In the case of an inertial reel system with the reel at the floor, the force on the top mount is actually DOUBLED!
    Vectors, you see..
    Imagine that top mount has a pulley hanging off it with a rope draped over it.
    Hang 100 KG off each rope. The pulley has to carry 200 KG
    No pulley, and you have only one rope with 100 KG load on the mounting.

    KEEP YOUR BELTS STANDARD!
    Wrong analogy Steve.

    The rope (seat belt webbing) is over the pulley (the upper loop).

    Both ends of the rope are secured to the ground (webbing secured to floor at buckle and webbing secured to floor at inertia reel)

    The "100kg" weight is forced against the rope on the inertia reel side of the pulley (the body forced against the seat belt by inertial forces).

    The force (now a kinetic force in virtue of the rope moving) is transferred by the pulley

    ... to both ends of the rope which are fixed (floor mount/ the inertia reel mechanism).

    .. The moving force of the rope (kinetic, energy of movement) is converted to an equivalent static force (because the rope ends are fixed) which is trying pull the rope attachments from their fixings (floor mount/ inertia reel mechanism )

    In fact there are equal static forces on both ends of the seat belts and a static force on the upper loop which is proportional to the "leverage" ie ratio of lengths of belt between the two end fixings.

    It's a classic mixed dynamics statics physics problem.

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    1000+ Posts Kim Luck's Avatar
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    One of the many reasons I bought a brand new R10 in 1967 was the fact that it was fitted with front seat-belts. I believe that at that time only some French cars sold in Australia were fitted with them as standard. Having seen with my own eyes the after effects of collisions on occupants NOT wearing seat-belts, and having viewed an American film called Signal 30 I felt they would be a nice thing to have in my car, stretchy or not. In fact, their stretchiness is not as much as you would think, because modern vehicles have load limiting devices simply because the belts don't stretch enough after the pre-tensioners fire. As for the ridiculous notion that somehow inertia reel belts put more strain on everything, Rob's post pours water on that. The dynamics are the same for both inertia and fixed belts as soon as the inertia reel locks.
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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    Quote Originally Posted by alexander View Post
    peter, logic would suggest that if this was a real problem, it might have been noticed some time in the last 30 years or so of intertia reel seat belt use, and addressed at a regulatory level. what are your thoughts on that point?

    ** Um, it was. Enter airbags, pretensioners & (as noted elsewhere) load limiters to ameliorate belt forces. And yes, to pick up a later point, a fixed belt will transit more quickly imposed force on your torso than an inertia reel stretching more & temporally spreading the load but it also greatly increases your chances of imposing more forces by way of hitting various hard objects as you move too far forward (relative to the car) before your inertia is overcome. **

    i would think that the amount of potential slack caused in this way would likely be somewhat less than the amount of slack left by most people by not fully tightening a fixed belt.
    ** I agree; & so did the regulators. That was my "Dillbrain" point. BUT, we are talking of diligent, skilful AFers, not members of the great unwashed. If one is willing & able to adjust a fixed belt properly then, in an airbagless car, it's the safest option. As an aside, in my one toy without a 4-point harness, the R8, I retighten the lap/sash after a km or so owing to seat cushion compression.
    As another aside on mounting points on the B pillar: I'd recommend a through bolt with a spreader plate on the outside of the B pillar & a crush tube around the bolt. **

    cheers! Peter

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    peter, i can see the sense of all that you are saying, but just to clarify my comment, i meant that if intertia reel belts were observably inferior to fixed ones, it is surprising that the difference between belt types was not addressed at a regulatory level.

    the existence of airbags, pretensioners, etc i would view as a response to the limitations of seat belts generally, not interia reel belts specifically. as between the types, it seems there are several factors affecting which belt will have the best outcome, and my intuition is that there is no clear winner, but that the difference between them is likely neglibible when used correctly. my observation of people, however, strongly suggests a very low understanding of fitting a fixed belt tightly, and that would be my biggest concern.

    i second your comments about the pillar bolts. i think the availability of correct bolt kits was canvassed here not too long ago. i do recall that it did involve a spacer tube for inside the pillar, and one would hope any sentient being would realise the need for suitable load spreading plate on the outside! that said, i note that an 80kg body declerating at 10g, exerts a force of 800kg. i would think that such a load spread over 3 mounting points wouldnt present too many structural challenges anyway.

    the top mount for the fixed belt in my lotus is a nut on a plate, set in the fibreglass... yes, i does make me wonder...
    Last edited by alexander; 15th August 2012 at 02:58 AM.

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    [QUOTE=alexander;1091903]peter, i can see the sense of all that you are saying, but just to clarify my comment, i meant that if intertia reel belts were observably inferior to fixed ones, it is surprising that the difference between belt types was not addressed at a regulatory level.

    ** it's not as if reel belts are total crap, just relative crap and differences between individual well used systems were over-ridden, as i understand things, by consideration of the dillbrain factor**

    the existence of airbags, pretensioners, etc i would view as a response to the limitations of seat belts generally, not interia reel belts specifically. as between the types, it seems there are several factors affecting which belt will have the best outcome, and my intuition is that there is no clear winner, but that the difference between them is likely neglibible when used correctly.

    **i agree that airbags had their case anyway(i'd retrofit them in a flash if i could) but pre-tensioners are not applicable to fixed belts.
    i'd be curious to hear what your intuition has specifically to say about the comparitive-stretch point.
    as another voice on this, hop into your newsagent and browse the "dog and lemon guide". it's basically a guide to buying used cars but has some interesting articles at the front**

    my observation of people, however, strongly suggests a very low understanding of fitting a fixed belt tightly, and that would be my biggest concern.

    ** my case was always premised on diligent and competent use by the relevant AFer. one thing that has astonished me with some supposedly "enthusiast" users of 4-point harnesses is how they do not maximally tighten the transverse belt and then adjust the verticals to be tight but not pulling the transverse one up off the pelvis. the result of slack transverse and overshortened verticals? transverse section whack in the middle of all the squishy and rupturable abdominal stuff**

    cheers! peter

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    Can I point out to those who suffer from a bit of myopia that the webbing used in ALL seat belts is the same width, 50mm, has the same stretch factor and minimum breaking strain. When an inertia belt locks, which is faster than the blink of an eye, (actually 13 milliseconds,) it becomes a fixed seat belt. Please try and get your head around that fact!
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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    Quote Originally Posted by Kim Luck View Post
    Can I point out to those who suffer from a bit of myopia that the webbing used in ALL seat belts is the same width, 50mm, has the same stretch factor and minimum breaking strain. When an inertia belt locks, which is faster than the blink of an eye, (actually 13 milliseconds,) it becomes a fixed seat belt. Please try and get your head around that fact!
    Whilst I agree about the locking of the inertia reel.

    The 12mS delay allows the body to move forward considerable distance in a rapid deceleration accident. The seat belt stretch allows the body to move forward even more.

    Hence the addition of seat belt pre-tension in modern cars which reduce the lock-up delay and the grip on the body.

    A fixed tightly fitted correctly worn seat belt is probably better. Preferably a three point type or four point harness. However human nature is to be comfortable and fixed belts often are not adjusted correctly.

    In older cars it's sometimes impossible to reach necessary controls when wearing a tight seat belt.

    So inertia reel and pre-tensioned belts may be a compromise. But they still better than a loose fixed belt.

    Here is a link for those interested in the physics.

    http://hyperphysics.phy-astr.gsu.edu/hbase/carcr2.html

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    Damn Yanks! Can't they use metrics? They are still not the worlds best users of seat-belts, anyway! I calculate, Rob, that in 13 milliseconds at 60 km/h you will travel 216mm distance before the belt locks. If that is the case and I'm not sure exactly how much a belt stretches anyway, if the car is going to stop in the 305mm (1ft) distance advertised it means the passenger is brought to a halt inside 89mm! Food for thought! (P.S: in any collision, a driver becomes a passenger)
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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    Quote Originally Posted by Kim Luck View Post
    Damn Yanks! Can't they use metrics? They are still not the worlds best users of seat-belts, anyway! I calculate, Rob, that in 13 milliseconds at 60 km/h you will travel 216mm distance before the belt locks. If that is the case and I'm not sure exactly how much a belt stretches anyway, if the car is going to stop in the 305mm (1ft) distance advertised it means the passenger is brought to a halt inside 89mm! Food for thought! (P.S: in any collision, a driver becomes a passenger)
    Your body is not travelling at 60kph when the belt locks. So your calculation is not valid.

    Your body acted upon by a g force of deceleration. That's why the belt locks due to change in inertia.

    It's a far more complex calculation and frankly I'm happy to accept that modern technology is best. Without looking up my kinematic formulae.

    l

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    1000+ Posts Kim Luck's Avatar
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    Rob! Steady on! I'm not sure who's laws of physics you are quoting or whether I missed something in class. I'm fairly sure through observation most passengers seem to be travelling at the same speed as the vehicle they're in. The passenger does not begin to slow down until after the belt has locked and begun to apply a decelerative force to the wearer, surely?
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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    where does this 13ms number come from?

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    1000+ Posts Kim Luck's Avatar
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    http://www.nointrigue.com/docs/notes...1carsafety.pdf

    Robmac came up with 12 ms from somewhere too.
    Last edited by Kim Luck; 16th August 2012 at 04:26 PM.
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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