The Case of the Ever Shrinking Elastomer

Discussion in 'Road Cycling' started by Stephen Harding, Jan 24, 2003.

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  1. My mountain bike is equiped with a Girvin "flex stem". There is a small elastomer at the top of the
    stem that allows the handlebar to pivot somewhat. There are three colored elastomers with differing
    flex qualities, so one can have stiff, moderate or soft "suspension". A poor man's front shock
    absorber. Works great!

    However this week, I noticed when taking the bike out of the barn, at ambient outside temperature,
    the handlebar sort of wiggled. It was clearly loose. I thought the elastomer attachment bolt had
    come loose and grabbed a hex key to tighten it up. It was quite secure!

    Hmmm. Never noticed that before. But then, this is the first time I've ridden the bike in sub 20
    degree temperature. In fact, about degree temperatures! The elastomer seemed to have shrunk!

    So I rode my bike to work, annoyed by the flopping handlebar every time I stood up to accelerate up
    a rise, or off from a stoplight, and thinking it is time to replace the elastomer with a new one
    come the weekend.

    As 5:30/6 pm rolled around, I began dressing up for the 0 degree, -20 degree (F) wind chill ride
    home, and low and behold, my "flop stem" had been magically replace by the "flex stem"!

    Temperature was indeed the culprit! During the hour it took to ride home, the flex stem slowly
    transformed itself back to a flop stem. Probably took about 30 minutes. The final stage of my ride
    had my headlight beams flopping around the skies of Northampton MA like an airport search light!

    The elastomer appears to shrink down to non-service in temperatures below 20 degrees F. Can't say
    exactly, except I've ridden the bike before at those tempertures and never noticed any reduced flex
    or extra play in the handlebars. Only during this past week with temps at 0 and below 0 has the
    problem shown itself.

    I know some types of MTB front shocks used to have elastomers in them along with springs. Don't know
    if this is done any more, but I would presume they would display the same type of behavior in cold
    weather. Does anyone ride a front shock equiped MTB, or flex stem equiped bike in very cold weather
    and note reduced performance?

    Kind of annoying actually.

    SMH
     
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  2. Edward Dike

    Edward Dike Guest

    "Stephen Harding" <[email protected]> wrote in message
    news:[email protected]...
    | My mountain bike is equiped with a Girvin "flex stem". There is a small elastomer at the top of
    | the stem that allows the handlebar to pivot somewhat. There are three colored elastomers with
    | differing flex qualities, so one can have stiff, moderate or soft "suspension". A poor man's front
    | shock absorber. Works great!
    |
    | However this week, I noticed when taking the bike out of the barn, at ambient outside temperature,
    | the handlebar sort of wiggled. It was clearly loose. I thought the elastomer attachment bolt had
    | come loose and grabbed a hex key to tighten it up. It was quite secure!
    |
    | Hmmm. Never noticed that before. But then, this is the first time I've ridden the bike in sub 20
    | degree temperature. In fact, about degree temperatures! The elastomer seemed to have shrunk!
    |
    | So I rode my bike to work, annoyed by the flopping handlebar every time I stood up to accelerate
    | up a rise, or off from a stoplight, and thinking it is time to replace the elastomer with a new
    | one come the weekend.
    |
    | As 5:30/6 pm rolled around, I began dressing up for the 0 degree, -20 degree (F) wind chill ride
    | home, and low and behold, my "flop stem" had been magically replace by the "flex stem"!
    |
    | Temperature was indeed the culprit! During the hour it took to ride home, the flex stem slowly
    | transformed itself back to a flop stem. Probably took about 30 minutes. The final stage of my ride
    | had my headlight beams flopping around the skies of Northampton MA like an airport search light!
    |
    | The elastomer appears to shrink down to non-service in temperatures below 20 degrees F. Can't say
    | exactly, except I've ridden the bike before at those tempertures and never noticed any reduced
    | flex or extra play in the handlebars. Only during this past week with temps at 0 and below 0 has
    | the problem shown itself.
    |
    | I know some types of MTB front shocks used to have elastomers in them along with springs. Don't
    | know if this is done any more, but I would presume they would display the same type of behavior in
    | cold weather. Does anyone ride a front shock equiped MTB, or flex stem equiped bike in very cold
    | weather and note reduced performance?
    |
    | Kind of annoying actually.
    |
    |
    | SMH

    I recently noticed the same phenomenon with my ThudBuster suspension seatpost. Not sure what the
    temperature was on my unheated front porch where the bike is stored, but probably close to the OAT
    of +5F. BTW the bike is equipped with an older Manitou front susp. I have noticed it to be harder in
    sub freezing temps. Were it loose like the seat post, I don't think I'd ride. ED3
     
  3. Matt O'Toole

    Matt O'Toole Guest

    "Stephen Harding" <[email protected]> wrote in message
    news:[email protected]...

    > My mountain bike is equiped with a Girvin "flex stem". There is a small elastomer at the top of
    > the stem that allows the handlebar to pivot somewhat. There are three colored elastomers with
    > differing flex qualities, so one can have stiff, moderate or soft "suspension". A poor man's front
    > shock absorber. Works great!
    >
    > However this week, I noticed when taking the bike out of the barn, at ambient outside temperature,
    > the handlebar sort of wiggled. It was clearly loose. I thought the elastomer attachment bolt had
    > come loose and grabbed a hex key to tighten it up. It was quite secure!
    >
    > Hmmm. Never noticed that before. But then, this is the first time I've ridden the bike in sub 20
    > degree temperature. In fact, about degree temperatures! The elastomer seemed to have shrunk!
    >
    > So I rode my bike to work, annoyed by the flopping handlebar every time I stood up to accelerate
    > up a rise, or off from a stoplight, and thinking it is time to replace the elastomer with a new
    > one come the weekend.
    >
    > As 5:30/6 pm rolled around, I began dressing up for the 0 degree, -20 degree (F) wind chill ride
    > home, and low and behold, my "flop stem" had been magically replace by the "flex stem"!
    >
    > Temperature was indeed the culprit! During the hour it took to ride home, the flex stem slowly
    > transformed itself back to a flop stem. Probably took about 30 minutes. The final stage of my ride
    > had my headlight beams flopping around the skies of Northampton MA like an airport search light!
    >
    > The elastomer appears to shrink down to non-service in temperatures below 20 degrees F. Can't say
    > exactly, except I've ridden the bike before at those tempertures and never noticed any reduced
    > flex or extra play in the handlebars. Only during this past week with temps at 0 and below 0 has
    > the problem shown itself.
    >
    > I know some types of MTB front shocks used to have elastomers in them along with springs. Don't
    > know if this is done any more, but I would presume they would display the same type of behavior in
    > cold weather. Does anyone ride a front shock equiped MTB, or flex stem equiped bike in very cold
    > weather and note reduced performance?

    Yup, they definately do stiffen up in the cold. Even at 40F the difference could be enough to
    matter, so at 0F I wouldn't be surprised if the thing felt completely solid -- especially with a
    small hunk like the one in your stem.

    Matt O.
     
  4. Tim Cain

    Tim Cain Guest

    > Yup, they definately do stiffen up in the cold. Even at 40F the
    difference
    > could be enough to matter, so at 0F I wouldn't be surprised if the thing felt completely solid --
    > especially with a small hunk like the one in your stem.
    >

    After the "Challenger" disaster, you would have thunk that any self-respecting mechanical designer
    would be painfully aware of the pitfalls of using elastomers in (potentially) cold environments.

    BTW, this effect ought to be even more pronounced in elastomeric suspension seatposts a la
    Cane Creek.
    - Anybody using one of these in cold climes care to comment?

    Cheers,

    Tim.
     
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