Video to come for you later today.
Using seat-belt inertia lock to stay put for performance driving....how can't this be safe?
- Thread starter TiGeo
- Start date
Your method makes great sense. Ignore the naysayers. They aren't thinking this through. The looseness of the seat belt is only for comfort. Automatic Locking / Emergency Locking seatbelt retractors are really a compromise, to get automobile occupants to wear their seatbelts. I suspect that if automotive safety engineers had their way we would all be buckled in with a 5 point harness, every time we get in a car. But very few would do that.
In my career I used to manage the test lab at a seat belt manufacturing facility, so I am very familiar with the different lock functions of seat belt retractors and pretensioners.
A passenger seat belt retractor has three different lock functions. First is the feature you mentioned, that is activated when you pull the seat belt webbing all the way out, and is intended primarily to hold child safety seats in place. The mechanism for this function is not in a driver's seat belt retractor. Second is a device that locks on either tilt or sudden deacceleration. It locks the seat belt in case of a rollover or a sudden braking. Third is a device that locks the seat belt on inertia. This is the one you are engaging. It locks the seat belt when your body hits the webbing quickly. The second and third devices are somewhat redundant methods to assure the occupant safety in an accident.
The pyrotechnic pretensioners are intended to pull the slack out of the seat belt webbing, so that you are properly positioned for the airbag, reducing the risk of injury from the airbag. These pretensioners are designed to limit the amount of load that they apply, to reduce the risk of body damage that you and Dnewton3 mentioned.
FMVSS regulations require a seat belt to lock up within 25 mm (this is memory from a long time ago. It might be 25.4 mm) of belt movement, once a specific acceleration is reached. So the difference in webbing slack, by you pre-engaging the seat belt, and what would happen in an accident, probably isn't all that different. It seems unlikely that you would have the webbing tight enough to result in too serious of injury from the pretensioner.
In my career I used to manage the test lab at a seat belt manufacturing facility, so I am very familiar with the different lock functions of seat belt retractors and pretensioners.
A passenger seat belt retractor has three different lock functions. First is the feature you mentioned, that is activated when you pull the seat belt webbing all the way out, and is intended primarily to hold child safety seats in place. The mechanism for this function is not in a driver's seat belt retractor. Second is a device that locks on either tilt or sudden deacceleration. It locks the seat belt in case of a rollover or a sudden braking. Third is a device that locks the seat belt on inertia. This is the one you are engaging. It locks the seat belt when your body hits the webbing quickly. The second and third devices are somewhat redundant methods to assure the occupant safety in an accident.
The pyrotechnic pretensioners are intended to pull the slack out of the seat belt webbing, so that you are properly positioned for the airbag, reducing the risk of injury from the airbag. These pretensioners are designed to limit the amount of load that they apply, to reduce the risk of body damage that you and Dnewton3 mentioned.
FMVSS regulations require a seat belt to lock up within 25 mm (this is memory from a long time ago. It might be 25.4 mm) of belt movement, once a specific acceleration is reached. So the difference in webbing slack, by you pre-engaging the seat belt, and what would happen in an accident, probably isn't all that different. It seems unlikely that you would have the webbing tight enough to result in too serious of injury from the pretensioner.
In the meantime:
https://en.wikipedia.org/wiki/HANS_device
https://en.wikipedia.org/wiki/HANS_device
Nice modeling 
.
.I live to serve my BITOG overlords.Nice modeling
Last edited:
My crappy seat in base model 2015 Pilot occasionally slides as not locked fully and this happens.
It depends on the track; the slowest ones maybe 135 mph. My car has a ridiculous 155 mph limiter so that is the best I can do on even a fast track.
-- "They" say you shouldn't put in a 4-5 point harness without a roll cage because of the whole "your body needs to fold inward, out of the way, of the roof collapsing" thing. There are "boy racers" who put in the harness (because it impresses girls) and are "going to put the cage in later" who draw ire for doing this.
-- If you pre-set the 3-point seat belt to locked, and god forbid get in a wreck doing something fun/stupid, your insurance (car, health, life) might be more willing to pay if they can't fully reconstruct the accident. In other words, it'll look more like an accident, and less like a boy-racer out racing with racing gear on.
-- Car seat mode is achieved by pulling the 3 point all the way out, so it engages a ratchet mechanism on the return to the spool. Return it all the way, and the ratchet is released. There's a fat person on my commuter van who frequently does this accidentally and has to reset it. I highly doubt the driver's position would have this mode.
-- Seat belts are sacrificially stretchy. This helps them be "soft" in a wreck and less damaging to your organs. Pretensioners take away some of this "give" so you don't wind up too far out of place in very serious accidents, while letting the give work during slower speed ones. This is why your owners manual reads to inspect/ replace belts after even minor wrecks.
-- If you pre-set the 3-point seat belt to locked, and god forbid get in a wreck doing something fun/stupid, your insurance (car, health, life) might be more willing to pay if they can't fully reconstruct the accident. In other words, it'll look more like an accident, and less like a boy-racer out racing with racing gear on.
-- Car seat mode is achieved by pulling the 3 point all the way out, so it engages a ratchet mechanism on the return to the spool. Return it all the way, and the ratchet is released. There's a fat person on my commuter van who frequently does this accidentally and has to reset it. I highly doubt the driver's position would have this mode.
-- Seat belts are sacrificially stretchy. This helps them be "soft" in a wreck and less damaging to your organs. Pretensioners take away some of this "give" so you don't wind up too far out of place in very serious accidents, while letting the give work during slower speed ones. This is why your owners manual reads to inspect/ replace belts after even minor wrecks.
That was you, TiGeo, in the video? Thanks for the demo.
Yes.
While seat belt webbing does stretch, much more important in protecting the occupant from being injured by the seat belt, is a torsion bar that allows the webbing spool to continue to turn at a specific force.
One exception are the Schroth ASM (anti-submarine) 4 pts. They have a piece of the tail strap that opens to allow it to lengthen slightly on one side and act like a 3 pt in a crash.
Is the term for the stretch called "ride down"? Thats the term used by the Ford reps when they came to oversee how the Crown Vics performed at our driver training facility and mentioned it. They would also show what the webbing would look like after a collision and require replacement if we ever noticed them have that wavy, loose appearance on inspection. Some of our accident re-constructionists used that term when testifying in severe collision cases too. Just curious.
Are you auto cross or showing up and driving on an actual racetrack? Alot of tracks require racing harnesses, helmets etc. I have an rx-7 racecar and yes If you're track racing you should be wearing a HANS Device. It's well known that had Dale Earnhardt had been wearing a hans device he would have survived his accident. From stories after his accident he didn't always pass tech but they locked the other way as he sold lots of tickets.
Videos posted in this thread..scroll through. HPDE on a track. No requirement in HPDE that ive ever seen for a street car for the full cage/seat/harness in a street car. The HANS is shown I use is shown in the thread as well.
I'm not familiar with the term "ride down". We called a seat belt retractor with this feature a 'load limiter" retractor.
If a pretensioner fires after your already have it tight, it’s not like it’s going to crush you against the seat. It’s going to draw a straight line between the points, both hips and above the shoulder, which aren’t so much behind you but next to you. It takes a lot of tension to provide perpendicular bracing at the middle of the belt. I would like for the airbag to catch my face, not punch me back into the seat like a 99mph baseball changing direction when it hits the bat.
Hips and shoulders gonna be sore anyway if you take a hit.
As far as collapse, if the roof collapses at those speeds, one won’t be “getting out of the way,” thats going to be fast and out of the persons control. And, the B-pillars will be collapsing with the roof in that case anyway … everything is going to be loosening up.
I learned with a few MTB accidents that once the accident hits, there’s no thinking, controlling, evading or avoidance - it all happens and then is done and you may not have a clue what was happening during - at that point Sir Isaac Newton is driving.
Hips and shoulders gonna be sore anyway if you take a hit.
As far as collapse, if the roof collapses at those speeds, one won’t be “getting out of the way,” thats going to be fast and out of the persons control. And, the B-pillars will be collapsing with the roof in that case anyway … everything is going to be loosening up.
I learned with a few MTB accidents that once the accident hits, there’s no thinking, controlling, evading or avoidance - it all happens and then is done and you may not have a clue what was happening during - at that point Sir Isaac Newton is driving.
Similar threads
