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Shear stress ...

Started by Nick Kew · · Last activity · 10 posts · 406 views

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Original section
UK and Europe
Published
19 September 2004
Last activity
20 September 2004
Original author
Nick Kew
Posts
10
Discussion status
Public discussion
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406
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  1. Well, I went for a quick spin on the moors this afternoon.

    Just past the top of the route, something strange happened, and I felt
    myself going over the bars. A strange and interesting experience, as
    I fell I could see in slow motion exactly what was happening, and I
    was able to control my fall rather well, avoiding any injury beyond
    a bump and a couple of light grazes. I strongly suspect that I wouldn't
    have had that level of control if my head had been constrained in an
    eggshell.

    Getting up, I discovered the reason for my fall. My left handlebar was
    hanging loose, having snapped through sheering, presumably at the moment
    of maximum stress as the front wheel (intentionally) hit the slab of rock
    that was the far side of a dip I was traversing. The bars had bent
    round, and the brakes were rubbing due to that. I unhitched the brakes
    and started out to walk the seven or eight rocky - but mostly downhill -
    miles home.

    Anyway, I'm well, and not sure how much I'm going to have to replace
    this time. But I'm wondering how often this kind of thing happens and,
    given that there were no visible signs of deterioration in the handlebars,
    how I should avoid this kind if thing happening in future, perhaps with
    much nastier consequences. Perhaps one should stick to nice heavy steel
    bars? And for similar reasons, forks. And ....

    (oh, and, er, the subject line is intentional :-)

    --
    Nick Kew

  2. Nick Kew said:

    Getting up, I discovered the reason for my fall. My left handlebar was
    hanging loose, having snapped through sheering,

    Someone on rec.bikes.tech recommended that bikes used off-road should have
    their bars replaced every year without fail.
    Alan.

    --
    To reply by e-mail, change the ' + ' to 'plus'.
    http://www.dvatc.co.uk - Off-road cycling in the North Midlands.

  3. Nick Kew said:

    But I'm wondering how often this kind of thing happens and,
    given that there were no visible signs of deterioration in the handlebars,
    how I should avoid this kind if thing happening in future, perhaps with
    much nastier consequences.

    Many years ago (about 16) in a land far south from here (Maidenhead) I was
    riding up to a roundabout on the Asomethingorother (308?) and my left hand
    handlebar[1] came off in my hands. (an SR something or other)

    being in my pre-clipless days I had tightly done up toestraps and cleated
    shoes. And a handlebar in each hand. And a major roundabout coming up.
    Fortunately a piece of road furniture came to my aid as I was able to stop
    and make a lunge for the railing.

    It does happen. It is worth checking your kit frequently, especially if you
    put the bars under any level of stress. And it is a lot easier to do now
    with multi bolt front loading stems. If you are really paranoid you could do
    a dye penetrant test.

    I'll be checking mine when I dismantle the road bike for respraying and
    upgrading. The MTB is steel so should give a bit more warning of imminent
    failure.

    ...d

    [1] until that point it was my left and right handlebar

  4. in message <[email hidden]>, Nick Kew

    (') said:

    Well, I went for a quick spin on the moors this afternoon.

    Just past the top of the route, something strange happened, and I felt
    myself going over the bars. A strange and interesting experience, as
    I fell I could see in slow motion exactly what was happening, and I
    was able to control my fall rather well, avoiding any injury beyond
    a bump and a couple of light grazes. I strongly suspect that I
    wouldn't have had that level of control if my head had been
    constrained in an eggshell.

    Ouch! Glad it's no worse!

    Quoted message said:

    Getting up, I discovered the reason for my fall. My left handlebar
    was hanging loose, having snapped through sheering, presumably at the
    moment of maximum stress as the front wheel (intentionally) hit the
    slab of rock
    that was the far side of a dip I was traversing.

    More detail, please: aluminium or carbon bars? How old? Rigid or
    suspension forks? With bar-ends or without (and if 'with' were you
    using them?). Seeing it's you I'm guessing 'aluminium', 'quite',
    'rigid', 'without' and 'no'...

    Quoted message said:

    Anyway, I'm well, and not sure how much I'm going to have to replace
    this time. But I'm wondering how often this kind of thing happens
    and, given that there were no visible signs of deterioration in the
    handlebars, how I should avoid this kind if thing happening in future,
    perhaps with
    much nastier consequences. Perhaps one should stick to nice heavy
    steel bars? And for similar reasons, forks. And ....

    Well, of course, one can break things. Particularly if one rides bikes
    with silly-light components. But I never have and I'm a big guy and
    ride a lot of fairly silly stuff. If you'd been putting bar ends on
    silly-light carbon bars I'd call that asking for it, but otherwise I'd
    say it's a pretty unusual accident - no less serious for that, of
    course.

    --
    [email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
    Das Internet is nicht fuer gefingerclicken und giffengrabben... Ist
    nicht fuer gewerken bei das dumpkopfen. Das mausklicken sichtseeren
    keepen das bandwit-spewin hans in das pockets muss; relaxen und
    watchen das cursorblinken. -- quoted from the jargon file

  5. In article <[email hidden]>,

    Simon Brooke said:
    Quoted message said:

    Getting up, I discovered the reason for my fall. My left handlebar
    was hanging loose, having snapped through sheering, presumably at the
    moment of maximum stress as the front wheel (intentionally) hit the
    slab of rock
    that was the far side of a dip I was traversing.

    More detail, please: aluminium or carbon bars? How old? Rigid or
    suspension forks? With bar-ends or without (and if 'with' were you
    using them?). Seeing it's you I'm guessing 'aluminium', 'quite',
    'rigid', 'without' and 'no'...

    Hehe, right on every count (I'm impressed; we've only met twice and
    never in a cycling context).

    The bars say aluminium alloy. The idea of Al actually bothers me a
    bit precisely because I know it's weak against sheering, but I kind-of
    assumed bike manufacturers would know about that, and the kind of alloy
    used in bars would be different. The frame is a cr-mo, fwiw.

    --
    Nick Kew

  6. in message <[email hidden]>, Nick Kew

    (') said:

    In article <[email hidden]>,

    Simon Brooke said:
    Quoted message said:

    Getting up, I discovered the reason for my fall. My left handlebar
    was hanging loose, having snapped through sheering, presumably at
    the moment of maximum stress as the front wheel (intentionally) hit
    the slab of rock
    that was the far side of a dip I was traversing.

    More detail, please: aluminium or carbon bars? How old? Rigid or
    suspension forks? With bar-ends or without (and if 'with' were you
    using them?). Seeing it's you I'm guessing 'aluminium', 'quite',
    'rigid', 'without' and 'no'...

    Hehe, right on every count (I'm impressed; we've only met twice and
    never in a cycling context).

    The bars say aluminium alloy. The idea of Al actually bothers me a
    bit precisely because I know it's weak against sheering, but I kind-of
    assumed bike manufacturers would know about that, and the kind of
    alloy
    used in bars would be different. The frame is a cr-mo, fwiw.

    Well, I bet at least 70% of the bars out there are aluminium alloys of
    one sort or another, and failures are pretty rare. Nasty when it
    happens of course. Carbon composite is possibly a better material for
    bars but most CC bars are silly-light so also fragile, and, of course,
    carbon composite suffers from the problem that weakening due to damage
    is not always evident. Steel bars are still available, if rare.

    You might consider a set of 'downhill' bars, on the basis that the
    downhill boys value strength over weight.

    --
    [email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

    ;; Madness takes its toll. Please have exact change.

  7. A.Lee said:

    Someone on rec.bikes.tech recommended that bikes used off-road should
    have their bars replaced every year without fail.

    Manufacturers of road bars recommend replacing the bars regularly as well.
    I've never bothered to do that myself but should rethink about it now,
    especially as mine have (light) score marks either side of the stem!

    ~PB

  8. Pete Biggs said:

    Manufacturers of road bars recommend replacing the bars regularly as
    well.

    Mine failed after about 18 years IIRC.

    Guy
    --
    May contain traces of irony. Contents liable to settle after posting.
    http://www.chapmancentral.co.uk

    88% of helmet statistics are made up, 65% of them at Washington
    University

  9. In article <[email hidden]>,

    Just zis Guy said:
    Quoted message said:

    Manufacturers of road bars recommend replacing the bars regularly as
    well.

    Mine failed after about 18 years IIRC.

    Mine lasted a little less than half that, in mixed on/off road use.

    --
    Nick Kew

  10. snip

    Quoted message said:

    Just past the top of the route, something strange happened, and I felt
    myself going over the bars. A strange and interesting experience, as
    I fell I could see in slow motion exactly what was happening, and I
    was able to control my fall rather well, avoiding any injury beyond
    a bump and a couple of light grazes. I strongly suspect that I wouldn't
    have had that level of control if my head had been constrained in an
    eggshell.

    Sounds like you've never fallen before, lucky sod.
    Around 55 years ago we had a schoolfriend who was a goalie and
    used to practise taking dives on the schoolfield.
    We thought this would be great practise for falling off our bikes
    and devised ways of rolling over the bars onto the grass and stepping
    off a sliding bike. We didnt have spd's in those days.
    Over the years I've put my shoulders out in falls but never, thankfully,
    put my arm out to break the fall. Thats a learned skill.
    And we didnt have 'eggshells' !

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