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14079Re: [rootsradicals] Re: rear wheel?

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  • Devian Gilbert
    Mar 18, 2012
    • 0 Attachment
      the basic deal with standard bicycle wheel:

      the hub hangs by spokes from the rim.
      from the factory the rim is true and round (hopefully)
      1 spoke can handle about 125,000 psi of pulling force before it breaks, when it breaks it pulls apart like taffy.

      why do wheels fail?

      most of the strength is in the rim.
      rims can and often do flex, it doesn't take much flex to change spoke tension.

      if you have a spoke, that is not in the wheel, and hold it in your hand, you can push on it, it will flex, and in fact you can bend it and fold it.
      like a piece of string, you can pull on it and its very strong.  I think its about 125,000 psi that a spoke can hold when pulled.

      when a spoke fails, typically its because its been flexed over and over and over and over and over and over and over and over... and some more.. over and over.

      when it goes thru those cycles it will fail.  typically at the J-bend (at the hub)

      if a spoke fails at the top of the spoke nipple...
      there is a good chance that the spoke(s) are not long enough.
      a spoke is supposed to be long enough where it protrudes about 1mm past the base of the spoke nipple.
      when tension is built up, the nipple/spoke/rim interface starts to deform, applying more tension to the spoke.
      if the spoke is too short, that spoke nipple/spoke interface pressure is not uniform along the length of the threaded section of spoke.
      which creates more stress at the margin (the shelf between the spoke nipple and spoke).

      finally, sometimes spokes are contaminated during the manufacturing process.  I have no idea what this is, I suppose its some kind of contamination.
      typically what you find is a nice stainless steel spoke will start to "pit", just like a cavity on a tooth, where a pit develops (corrosion/oxidation).
      then the spokes breaks.

      basically this is what happens with a wheel.
      we build them, they are measured in a static manner.
      however, wheels are not used sitting still, they are dynamic things.

      wheel goes down the road, spins...
      a load is applied, the rim resists bending.
      even tension and proper build help pull the wheel together adding strength.

      wheel, hits bump.
      rim has to resist bending or even flexing
      the hub is hanging in the rim by the spokes.
      if there is not enough tension to keep the hub in place, there is flex.
      if there is not enough tension to keep the spokes in place, something will flex or move, it will be a small amount, typically the wheel makes a "ping" sound.
      as if maybe a spoke nipple as re-seated, meaning it moved!

      with enough cycles, something will fail.

      spokes sometimes pull out of rim eyelets.
      typically the cause of this is too much of a load on the rim.
      i.e. one of my buddies is about 250lbs, and super strong (think NFL type of guy), he pulled out spokes from a rear DT SWISS RR 1.1 rim.  the eyelets simply failed, the rim cracked at the margin... no bueno.

      or more accurately:
      the rim was strong enough to withstand his weight and banging road imperfections, to the extent that the rim basically kept true.
      however, the hub, being that it hangs from the rim by spokes, pulled at the rim (due to his weight) with enough force to start cracking the rim at the stainless steel spoke eyelet/rim interface.
      once the rims structure became compromised, spokes started to loose tension, small space opened up between the spokes and eyelets, until the rim started to tear apart, eventually collapsing the wheel.  in this instance, none of the spokes broke.  The rim failed.

      brief overview off:
      devian 



      On Mar 18, 2012, at 8:46 PM, Dave Lloyd wrote:

       

      No problem! The best advice I think anyone could give, though, is to get a wheel built by your local bike shop or to build one yourself (It's not that hard, just a takes a Saturday evening and a few beers, and it's very liberating). Machine made wheels are notorious for uneven tension and for not stress relieving spokes as they're tensioned which leads to the conditions you're describing.

      --dlloyd



      On Sun, Mar 18, 2012 at 22:35, poppamando <b4kids@...> wrote:
      It's a 26". Thanks, Dave.

      --- In rootsradicals@yahoogroups.com, Dave Lloyd <dave@...> wrote:
      >
      > if it's a 26, I've had pretty good luck with a wheel I built up with 36
      > straight gauge spokes, a Sun Rhyno Lite rim and a Deore hub. The only
      > problem I've had is water infiltration into the Deore hub. I did have an
      > XT, but that developed a nasty habit of the freehub body fixing bolt
      > working its way loose. That also happened to a friend of mine, so I can't
      > recommend them. The Deore or SLX hubs are probably the best bang fore the
      > buck.
      >
      > --dlloyd
      >
      >
      >
      > On Sun, Mar 18, 2012 at 21:07, poppamando <b4kids@...> wrote:
      >
      > > Folks, I have a several year old Trek 4300 as the base for my X. Over the
      > > last year or so, I've popped at least 3 spokes on the rear wheel. My LBS
      > > owner (who sold me the Trek and assembled the X) tells me it's because the
      > > stock spokes are inferior and he recommends I get a new rear wheel with
      > > stronger rim and spokes. As I'm fairly ignorant about buying wheels, I
      > > could use recommendations for a strong wheel that won't break my bank
      > > account. I only rarely carry more than 100 lbs on it (child plus
      > > groceries), but commute about 5 miles round trip through all kinds of
      > > weather and over rural RR track crossings (3 tracks with a good deal of
      > > "bump" to each track).
      > >
      > > Thanks in advance,
      > > Phil
      > >
      > >
      >




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