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  1. #1
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    FSA OS-115 Stem - Thoughts?

    I just installed an FSA OS-115 stem on my bike...and now I'm having reservations, per the link below:

    FSA stem warning (OS-115)(RD-120) [Archive] - Bike Forums

    I know a year or so ago there was a rash of broken steer tubes incidents, with a handful of resources pointing the finger at this stem. Some said it was true, some said it was hogwash.

    I've installed the stem w/ carbon paste on the steerer tube, and torqued the bolts to spec (5nm). Also I'm using one of those compression plugs that extends down the entire length of the stem, so I'd like to think I'm safe.

    Any thoughts on this? Sure is a pretty stem...with all the CNC cutouts.

  2. #2
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    You've linked to a thread that's over six years old. Plus, it's one comment. Did you find other people mentioning steerer tube breakage as a result of this stem? The internet has the power to blow one comment out of proportion so that a small issue appears to be a catastrophe worthy of a product recall.

    I'm doubtful FSA would still be selling a defective product (if it was in fact ever defective) six years later.

    IMO, if you're using a current production OS-115, then you're safe. If you're using an OS-115 from six years ago, then I suppose I'd be cautious and buy a new one.

  3. #3
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    most torque specs are maximum, not suggested. For a stem, 4Nm is typically plenty of torque with paste as a general guideline (not that 5 is likely to damage anything and settings should also depend on riding style etc.)

  4. #4
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    Quote Originally Posted by stevesbike View Post
    most torque specs are maximum, not suggested. ...
    Perhaps for bicycles, but for aircraft, motor vehicles, engines, and machinery, tightening to within the torque spec is required. Insufficient torque can lead to damage or create a hazardous condition. If the spec is only listed as a maximum (e.g. 5 Nm max), it would imply that a lesser torque is acceptable. If not identified as max, then it implies to me that it is required.
    ... 'cuz that's how I roll.

  5. #5
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    The problem with this is that the parts on a bike typically mix and match manufacturers, who each design their own part for a certain max torque. This is especially true in the case of a stem and a steerer tube. There are lots of stems whose max torque significantly exceeds that of steerer tubes, so following the settings on a stem is the wrong thing to do since it's the steerer tube that is the part likely to fail. This is exactly what happened in the case of failures with the stem in question (the clamping design put an unevenly distributed stress on steerer tubes - Trek issued a warning about this and now says only to use their stems...).

    Most manufacturers are also quite coy about giving suggested torque settings, since they are worried about liability for parts that are under-torqued, user error, etc. Also, a dry vs. greased bolt will result in different clamping forces at the same torque setting, so this is also an issue. Some stem manufacturers state whether the bolts should be greased (some include bolts that have loctite applied, etc.).

    The stem/steerer doesn't require a lot of clamping force - there's not a lot of opposing forces (e.g., it's not weight bearing like a seatpost) so over-tightening it is just putting force on the weak property of carbon (it's hoop strength).



    Quote Originally Posted by looigi View Post
    Perhaps for bicycles, but for aircraft, motor vehicles, engines, and machinery, tightening to within the torque spec is required. Insufficient torque can lead to damage or create a hazardous condition. If the spec is only listed as a maximum (e.g. 5 Nm max), it would imply that a lesser torque is acceptable. If not identified as max, then it implies to me that it is required.

  6. #6
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    Quote Originally Posted by turbomatic73 View Post
    I just installed an FSA OS-115 stem on my bike...and now I'm having reservations, per the link below:

    FSA stem warning (OS-115)(RD-120) [Archive] - Bike Forums

    I know a year or so ago there was a rash of broken steer tubes incidents, with a handful of resources pointing the finger at this stem. Some said it was true, some said it was hogwash.

    I've installed the stem w/ carbon paste on the steerer tube, and torqued the bolts to spec (5nm). Also I'm using one of those compression plugs that extends down the entire length of the stem, so I'd like to think I'm safe.

    Any thoughts on this? Sure is a pretty stem...with all the CNC cutouts.
    FSA no longer sells that stem due to the reasons listed, it morphed into the SLK stem and two changes were made:

    1. Stack height was increased to 40mm (from the OS115's 35mm).
    2. The bolts are now opposing threads (OS 115 had both bolts threaded the same direction).

  7. #7
    r4t
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    anyone know why the stem's finish could be raising up and starting to chip like the spot shown here? Is that just powdercoat chipping off or something more concerning, safety/structurally wise? It is the spot above the F in "FSA"
    Attached Thumbnails Attached Thumbnails FSA OS-115 Stem - Thoughts?-img_0319%5B1%5D.jpg   FSA OS-115 Stem - Thoughts?-img_0320%5B1%5D.jpg  

  8. #8
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    Also, ask why you are using carbon paste on the steerer? Some fork manufacturers discourage that.

  9. #9
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    Quote Originally Posted by Mr. Scary View Post
    2. The bolts are now opposing threads (OS 115 had both bolts threaded the same direction).
    That's the big one there. . . In Fairwheel Bike's Stem test the FSA SLK proved to be one of the stiffest stems tested.

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