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Seat belt tightens and then doesn't release?

Discussion in 'Model S: Driving Dynamics' started by gp100dl, Jul 8, 2017.

  1. gp100dl

    gp100dl Member

    Aug 31, 2016
    Trying to work out if this is a problem or normal behaviour: on hard acceleration in my Model S the driver's seat belt tightens (makes sense) but then stays tight for a long while afterwards. I can usually get it to slacken if I really push back in my seat to loosen it, but it's annoying. Passenger seat belt doesn't behave in the same way.

    Do others have the same issue or is there a problem with the inertia reel on the belt?
  2. scottm

    scottm Version 9 software sufferer

    Jun 13, 2014
    You have to give it quite a bit of slack to get it out of the auto-tightening lock it has on you after hard braking.

    I know, it can be hard to do when the belt has its auto-ratcheting boa-constrictor-like lock going.. you may have to unlatch the belt buckle to do it, then put on your seatbelt again.
  3. Pezpunk

    Pezpunk Member

    Aug 12, 2016
    Bristow, VA
    yes, this is normal standard behavior for a seat belt on ALL cars of any make or model. passenger seatbelts work the same way. it's mechanical -- there's no electronic control of the belt. i don't think the release is time based -- only letting in a certain amount of slack will allow it to loosen. this may require unbuckling and rebuckling.

    most of the time, it's experienced because of slamming on the brakes -- most cars don't accelerate fast enough to trigger it. ;)

    most likely, there is nothing wrong with your seat belts.
  4. dhrivnak

    dhrivnak Active Member

    Jan 8, 2011
    NE Tennessee
    Not sure I agree as the Model S belt is locking far more than my other cars. I our case it is the Passinger belt.
  5. David29

    David29 Supporting Member

    Aug 1, 2015
    Here is what the Model S owner's manual says on this topic.

    "Both the driver and passenger seats are
    equipped with three-point inertia reel seat
    belts. Inertia reel belts are automatically
    tensioned to allow occupants to move
    comfortably during normal driving conditions.
    To securely hold child safety seats, all
    passenger [emphasis mine] seating positions are equipped with
    an automatic locking retractor (ALR) that, by
    pulling the seat belt beyond the length
    needed for a typical adult occupant, locks the
    belt into place until the seat belt is unbuckled....

    "The seat belt reel automatically locks to
    prevent movement of occupants if Model S
    experiences a force associated with hard
    acceleration, braking, cornering, or an impact
    in a collision."

    So it seems as if gp100dl is experiencing the second behavior mentioned in the manual, under "hard acceleration." i suspect that people driving Teslas may experience this more often than ICE drivers, because of the high torque of EVs and the high performance of some Tesla models -- and of how much fun it is to utilize that performance!

    By coincidence there has been a discussion in the Facebook Tesla Owners Worldwide Group about this in the past day or two. Some people were complaining about the same behavior and suggesting that Tesla uses "cheap seat belts." I hope that is not a factor. I think this is intended behavior and probably required by regulations.

    The behavior of the passenger seat belts locking up was also mentioned in the Facebook posts. I have experienced that in several cars, especially taxis for some reason. It can be very uncomfortable if the belt locks up and you can't relax it. At least a passenger can briefly unbuckle and re-buckle. it is more difficult for a driver to do that.
    • Informative x 1
    • Like x 1
  6. Ulmo

    Ulmo Active Member

    Jan 19, 2016
    Vienna Woods, Aptos, California
    #6 Ulmo, Jul 8, 2017
    Last edited: Jul 8, 2017
    I think I experience this on Highway 17 multiple times in my Tesla Model S.

    But I also had a similarly fast Mercedes on that same road and never had trouble with its belt.

    I think my 300hp E500 was as capable as my 75D at the 40mph-70mph speed range encountered in the mountain twistes during commute stresses. I think Mercedes has a better belt. I think the belt Tesla used might have been tuned for less capable cars, inappropriate for vehicles with Tesla caliber. Give us a slower car, and its belt is tuned to its slower G forces. Give us a faster car, and its belt is tuned to its G forces. Give us a new manufacturer, and they make novice mistakes by using off the shelf hardware not properly specified, but selected due to lying salesmanship of suppliers.

    As I proofread this message, I remember the MB belt being more rich (wide, thick, soft, sturdy, refined, smoother rolling action) than the Tesla belt (many things match that comparison between the two brands), and I recall that occasionally it did lock up, but (here's the key) it had a tiny amount of breathing slack (perhaps with its own breathing lock range??) which allowed me to breath while in tight corners. (I recall it was enough slack that I'd put two fingers to hold my body against my fingers against the belt around the curve so my lounges had room to breath around my fingers; the Tesla doesn't have that two fingers room ... it's odd the things you forget then remember later --- your excerpt probably spurred my understanding and memory). It was just consistent with this great feeling and experience that I always had that the Mercedes car did everything right. Probably it came from a century of being best and first, a horribly hard thing for a newbie to beat. It's just that once identified, these problems ought to be solved by the newbie, not flunked.

    Heck, for all I know, that MB belt is suboptimal; but, the dangerous asphyxiation and required dangerous acrobatics encountered regularly with the Tesla in California mountain driving sure seems inferior.

    You can't use regulations as an excuse when other traditional manufacturers get it right (if indeed they did).

    I agree. It's a dangerous acrobatic driving maneuver, but often there's not a choice in the types of roads that apparently trigger this. I wait for a curve which leans my body in the correct direction to not throw me free when I unbuckle.
    • Informative x 1
  7. Ulmo

    Ulmo Active Member

    Jan 19, 2016
    Vienna Woods, Aptos, California
    After writing that above, I was driving home and realized my newest coping mechanism with the Tesla Model S, since I did it unconsciously and noted what I was doing. The following quote helps explain part of it (my bolded part related):

    That's what I do another way (my unconscious figured it out):

    When the seat belt locks up, I rock my torso back in the seat, pushing the upper portion of the seat backward, releasing pressure on the belt, which causes it to come free, pretty usually. But this is because of another problem because of the Tesla: the headrest juts forward, pushing my head too far forward, rather than being straight up, so I put a cushion back there between my back and the Tesla seat. That also helps reduce the pinching on the sides of my back from the seat. This cushion itself has some squeeze that when I push my back into it gives me some room to release that seat belt. I figure now that it also is going to wear the seat out quicker. But, apparently, my unconscious found a way to unlock the seat belt, at least in some situations.

    Other people should try that, but it might not be as easy without the extra cushion I have there. Basically, push back the seat with your back. Also, moving the seat back with the controls might also work.

    As we get more and more used to our cars, we get more comfortable with them, because we find all the little tricks.
  8. SMAlset

    SMAlset Active Member

    Mar 4, 2017
    SF Bay Area
    So far I've only experienced the boa constrictor grip when I pulled the seat belt out too far on a few occasion when belting up and it really can feel tight and prevent you from moving forward as intended. What I don't get is if the inertia reel seat belts are designed to work on hard acceleration, braking, cornering, or an impact in a collision like you guys have experienced, what happened during the IIHS testing (twice now)?

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