Question about seat belts

[the_dude]

Hi folks,

I was looking into replacing my driver side seat belt with one that doesn't have electronically controlled tension (based on speed and G forces) and can be manually pre-tenssioned (you pull it out completely and then slowly bring the belt back until desired tension is reached). Just like the one on the passenger side.

I was looking at the service manual and saw that there are two types of belt assemblies. Type A and type B. Type B has an extra connector (besides the one for the pyro) which, I'm guessing is used for tension control.

Did I get this right? If so, can type A be manually pre-tensioned and what would be its part number?
Could I use one from an older BMW maybe? What do I look for?

Any help would be much appreciated!

I have a 2024 MT.

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[i3igpete]

Unfortunately can't directly answer your question.

I've also found the factory seat belt to be slightly annoying on the track. What I've seen other folks do is Slide the seat all the way back, do a quick yank to trigger the centrifugal lock, then keep holding tension as you slide the seat forward. Sometimes takes a few tries to get the tension just right.

 

[Z4m40i]

Unfortunately can't directly answer your question.

I've also found the factory seat belt to be slightly annoying on the track. What I've seen other folks do is Slide the seat all the way back, do a quick yank to trigger the centrifugal lock, then keep holding tension as you slide the seat forward. Sometimes takes a few tries to get the tension just right.

This is what I do also. I’m not a safety expert, but I run a Simpson Hybrid S when doing so. I’m under the impression that locking the belt removes 3 major safety functions for 3 point belts:

1) the belts ability to stretch and decelerate the body
2) the ability for the body to roll on the right shoulder and into the airbag.
3) the usefulness of the steering airbag.

 

[the_dude]

Unfortunately can't directly answer your question.

I've also found the factory seat belt to be slightly annoying on the track. What I've seen other folks do is Slide the seat all the way back, do a quick yank to trigger the centrifugal lock, then keep holding tension as you slide the seat forward. Sometimes takes a few tries to get the tension just right.

Thanks for the input. I've used this before but I'm switching to bucket seats and I'll be using 3-point until I manage to put in a roll bar + straps

 

[the_dude]

This is what I do also. I’m not a safety expert, but I run a Simpson Hybrid S when doing so. I’m under the impression that locking the belt removes 3 major safety functions for 3 point belts:

1) the belts ability to stretch and decelerate the body
2) the ability for the body to roll on the right shoulder and into the airbag.
3) the usefulness of the steering airbag.

Locking of the belt is the whole point of the belt Thanks for the response tho

 

[Gabe]

Oh. This is somewhat my topic (trauma surgeon)

DISCLAIMER: this is theory. In practice things are not this dramatic unless you actually crash.

In a very basic way The OEM seat belts are designed to stretch up to a point and then lock. The reason for that is because there is a ton of energy that needs to be dissipated out BEFORE he lock happens.

why? Because otherwise your body would be absorbing all that energy from the get go and your organs and bones will be crushed under the force.

In a 4,5, or 6 point harness there is no pre tensioning of the belt. Everything is static. So how is the force dissipated there? Along the additional belts over a much higher surface area and the neck is restrained with a HANS style device.

I know a lot of people tracking the cars with OEM belts do that locking belt trick. In reality it helps a little by keeping you in the seat and not sliding around, but also -In the case of a major frontal crash, organ and bone injury risk is greater because a lot of the energy normally dissipated before the lock takes place will be instead dissipated by the body and the cervical spine.

Do what you choose with that info.

 

[the_dude]

We're getting a little sidetracked here. All I wanted to know was if the belt I have in the car can be exchanged to one without the electronic pre-tensioning

Oh. This is somewhat my topic (trauma surgeon)

DISCLAIMER: this is theory. In practice things are not this dramatic unless you actually crash.

In a very basic way The OEM seat belts are designed to stretch up to a point and then lock. The reason for that is because there is a ton of energy that needs to be dissipated out BEFORE he lock happens.

why? Because otherwise your body would be absorbing all that energy from the get go and your organs and bones will be crushed under the force.

In a 4,5, or 6 point harness there is no pre tensioning of the belt. Everything is static. So how is the force dissipated there? Along the additional belts over a much higher surface area and the neck is restrained with a HANS style device.

I know a lot of people tracking the cars with OEM belts do that locking belt trick. In reality it helps a little by keeping you in the seat and not sliding around, but also -In the case of a major frontal crash, organ and bone injury risk is greater because a lot of the energy normally dissipated before the lock takes place will be instead dissipated by the body and the cervical spine.

Do what you choose with that info.

But... Since we're here, we can discuss this for a bit

Seat belts stretch under tension and up to a point after which they break. This is by design so they don't chop you in half and it's not to be confused with de-acceleration of the body. This only happens if there's no slack in the belt.

Seat belts lock as a reaction to acceleration/g forces. The fact that you can pull it out (if you do it slowly enough) is purely for comfort.

They are meant to keep you in place in case of a crash to reduce the probability of body parts (head and torso) coming into contact with other surfaces. They are the primary driver for de-accelerating the body during the crash. Newer generations have a few improvements over basic g-forces locking:
1) Pyro in the belt systems to increase tension further when a crash occurs,
2) Increase tension (via electric motor) if the car senses increased speed and/or bigger g forces <- this is what's I'm trying to get rid of.

Some google quickies:
https://www.seat.com/car-terms/p/pyrotechnic-belt-tensioner
https://en.wikipedia.org/wiki/Seat_belt

Differences between 3-point and 4/5/6 points are in the way they control the body movement and have little to do with surface area.

Locking the seat belt and it being snug is a good thing because locking of the belt is the whole point of the belt

 

[Z4m40i]

Okay jacob

 

[Gabe]

Ok. So I happen to work with the William Leham Injury Center doing research on crash safety equipment with BMW for over 2 decades. It’s a University of Miami /Ryder trauma center partnership and n which we Trauma surgeons participate. Google that.

so yeah. We are talking about different things. When I say stretch I’m not talking about the cover stretching of the belts. Which truly happens, but by the way are NOT supposed to snap. What I’m talking about is the inertial system that locks the belt on a sudden pull during g a crash or when you pull on it.

you are not supposed to pre lock it for two practical reasons. One, restricts motion needed during road driving and second, it works in conjunction with the airbags and the rest of the safety systems in the front seats - where is really researched- . to allow for time of airbag detonation and dissipating energy that in theory would be tissue crushing if the inertial system would not allow for slower body deceleration before the actual lock happens.

I know people google stuff and in the era of the internet a quick google can replace 2 decades of study and practice by an expert on the field that they work on for a living . So again. That’s, in layman terms how things work and you can do whatever you want to do with that info.

and because this is the internet, I know you now will probably entrench in your position and reply, so I promise you that I will allow you to have the last word because at the end of the day this discussion is irrelevant.

 

[razorlab]

Bro is debating with a trauma surgeon. Please... tell us more.

 

[razorlab]

and because this is the internet, I know you now will probably entrench in your position and reply, so I promise you that I will allow you to have the last word because at the end of the day this discussion is irrelevant.

 

[the_dude]

...

so yeah. We are talking about different things. When I say stretch I’m not talking about the cover stretching of the belts. Which truly happens, but by the way are NOT supposed to snap. What I’m talking about is the inertial system that locks the belt on a sudden pull during g a crash or when you pull on it.

...

Sure, I wasn't precise enough. They do snap, it's just the forces where this happens are high.

you are not supposed to pre lock it for two practical reasons. One, restricts motion needed during road driving and second, it works in conjunction with the airbags and the rest of the safety systems in the front seats - where is really researched- . to allow for time of airbag detonation and dissipating energy that in theory would be tissue crushing if the inertial system would not allow for slower body deceleration before the actual lock happens.

I fail to see how this is contradicting what I said.

 

[the_dude]

Bro is debating with a trauma surgeon. Please... tell us more.

because trauma surgeon = safety expert?

 

[razorlab]

because trauma surgeon = safety expert?

Does an internet expert = real expert?

I dunno about you, but if I saw the FO part of FAFO multiple times a day, every day... I think I would start putting things together and seeing trends of what the FA parts are. Much more than the average human sitting on the couch doom scrolling all day long.

 

[tracer bullet]

because trauma surgeon = safety expert?

Nice straw man.

"I happen to work with the William Leham Injury Center doing research on crash safety equipment with BMW for over 2 decades." does however = qualified to discuss seat belts, which is the topic here per the thread title.

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