Seatbelt weight limit?

[AdamW]

I've just read on a US website that in America, car seatbelts are only required to restrain a person up to 215lbs (15 stone 5 lbs... or a tad under 100kg)

I can't find any legislation for the UK or Europe, but I'm just wondering, if the US, renowned for it's less-than-svelt proletariat, has such a low requirement, is the legal limit for belts going to be any better in this country?

Obviously, in this case a requirement is a minimum requirement so hopefully the manufacturers have a higher design requirement. Otherwise, I reckon about 50% of the guys here would be either right on the limit or exceeding it.

 

[oilman]

If you have a belt able to restrain heavier people, it becomes more hazardous for lighter people as the deceleration rate provided by the belt will go up. If it could cope with a 35st body, the poor 8st one would get a near dead stop (maybe literally.

 

[kendor]

Have seatbelt specifications been relaxed a bit in the advent of air bag technology?

 

[Steve]

The actual belt itself can probably take way more than 100kg. It is the fixing to the chassis and the winding mechanism that needs beefing up, these are the weak points.

I think a lot of modern seat belts also dont provide dead stop, but have a cushioned stop, which lets a bit of the belt out as you push against it during a crash, so you dont break any ribs or backs etc lol. This also reduces the stresses on the fixing points slightly - less decelleration = less force.

 

[securespark]

As DIYnot's resident 125kg personage, I'm now worried!!!

 

[AdamW]

As DIYnot's resident 125kg personage, I'm now worried!!!

Being a mere slip of a man at 110kg I don't exceed the limit quite so much...

But seriously, being the macho, burly, pie-munching, beer-swilling DIYers/tradesmen that we are, I thought it worth pointing out because I reckon there must be a lot of 15-stone plus guys here.

EDIT: I've tracked down the legislation on our seatbelts. They don't seem to specify a design mass, but they do lay down some very specific dimensions. See section 4, "specifications". This is an old reg, but I've checked the ammendments and they don't list any mass for a design requirement or aim.

Perhaps any mechanical engineers would care to stick the design into ProE and do some simulations to tell us what this baby can take?

Which reminds me, a mechanical engineer for a crane/hoist company told me that mechanical engineers, like all engineers, will design and test everything above it's mandated limit. In his particular case, they designed everything to take twice the load, tested it to 1.5 times the load. So, presumably even with a 215lb mandatory rating the seatbelt will be tested to 320lb and designed to 430lb...

What happens when you're REALLY fat?

 

[securespark]

You break the seat belt. Take it from me, I know...

 

[empip]

A couple of facts from ROSPA.

Seat belt pretensioners tighten the webbing in a crash to remove the slack in the belt and this helps to reduce the occupant's movement and distribute the load over the whole body.

Some car seat belts are fitted with load limiters, which have been developed because of the relatively small risk that seat belts may cause occupant injury from the restraining force. They respond when the belt is applying a large restraining force, and release a small amount of belt to compensate. The load that the belt applies on the occupant is kept below a threshold, above which the risk of injury would be higher. This is an important consideration when elderly occupants are using the seat belt, as the aging of bones makes them brittle and increases the risk of injury

Some roughish safety factors ... Here. A non-independently verified site, but does contain some useful info.

At college, Engineering ? Usual caveats apply :- Interesting... for some eg. 'How stuff fails..' Some pictures and calculators ...

 

[AdamW]

They are clever things though, aren't they?

I had never noticed until the other week, but seatbelts respond to acceleration in lateral directions too. So, if you corner quickly, the seatbelt locks and stops you sliding around in the seat. Presumably it's really there for side-on collisions, but it's pretty useful nonetheless.

 

[Steve]

My seatbelt does something REALLY annoying. there is a junction on a country lane near my house, where the road comes to an end and at the end, it joins a "more major" road at 45 degrees, so to look left, you have to lean forwards and look thru the rear left door. But its going uphill to this junction, so despite the decelleration not being major, the seatbelt still locks up so i end up sat there going back and forward in my seat until the seatbelt unlocks, i must look like im having a fit to anyone passing

What happens when you're REALLY fat?

friction between rear end and seat keeps you on the seat i guess

 

[securespark]

I remember the static belts in my Mum's Triumph Herald Estate.....

Back then, inertia reel seat belts were like todays ABS with EBD....!!

 

[Softus]

If you have a belt able to restrain heavier people, it becomes more hazardous for lighter people as the deceleration rate provided by the belt will go up. If it could cope with a 35st body, the poor 8st one would get a near dead stop (maybe literally.

Hmm. Yes. This makes sense. I suppose that if a feather was being restrained by a seat belt, then, in an RTA, it would be decelerated so quickly that it would be completely pulverised.

 

[oilman]

A feather wouldn't have a problem, it's strength to weight ratio is immense, but if you have an 8 stone not too strong person things would be very uncomfortable.

 

[Softus]

What's fascinating here is that you actually believe you know what you're talking about.

Did you study Newtonian physics at all, or this a new brance of science in search of the grand Oilmanian Unified Theory of Matter?

 

[oilman]

What's your problem softus, you seem to be very insecure in that if you don't agree with something I write, you get offensive and personal. Do you have another forum name too, by any chance?