Problem truing Shimano WH-7850 C24 CL front wheel

Discussion in 'Cycling Equipment' started by bikerx68, Mar 8, 2011.

  1. bikerx68

    bikerx68 New Member

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    I have a new set of Shimano WH-7850 C24 CL wheels and am having a problem truing up the front wheel. the wheel has 16 bladed spokes and is radially laced. What is happening is that when in the truing stand, I get the wheel trued almost perfect. But when spinning the wheel in the stand, the indicator rubs right where the spoke enters the rim. This happens on each side at every other spoke (due to the spokes going to alternating sides of the hub). I hope I explained that right. I also had the same problem with Shimano WH-RS80 (same rim and spoke count as the dura ace) front wheel. Anyone else have this problem? Any tips or tricks?

    Thanks
     
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  2. tafi

    tafi Member

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    Not sure how you can say you have it "almost perfect" yet it will still rub in the truing stand. Perhaps you need to explain it again.

    In general the spokes should be loosened to move the rim further away from the side which the spokes pulls to and they should be tightened to move the rim closer to that side. I'm sure you already knew that. There must be something else happening. Does the clamp of the stand hold the hub tightly enough?
     
  3. bikerx68

    bikerx68 New Member

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    the wheel is in the stand tight, using QR skewer.

    Let me elaborate on the issue: the wheels would be considered trued within spec by any shop that looked at them. I just have never seen this type of issue before on a wheel. It seems to me like the spoke tension is pulling the rim laterally out ever so slightly in the direction that the spoke is pulling. So as the wheel spins, there is s slight rub with the indicator right at where the spoke enters the rim. The rub alternates from side to side depending on which side the spoke goes into the hub. in other words the "high spot" on the rim is on the same side that the spoke goes into the hub. I don't have a tensionometer so I can't give a number on amount of tension, but using the "pluck the spoke" method, the spokes are all very close in tone, if not exact. I have never seen this type of issue on all the wheels I have ever owned or worked on. i was thinking of relieving the tension on the whel and bringing it up again, but was hesitant to do so because I don't have a tensionometer or a "pro" truing stand. I am using a performance spin doctor truing stand.
     
  4. BHOFM

    BHOFM Active Member

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    I have no idea how to help, but as I read your post, the wheel. looking at it head on
    would be like a continuous series of S's? I would think, maybe all the spokes are
    too tight? I have no idea what I am talking about!
     
  5. bikerx68

    bikerx68 New Member

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    that is what I was thinking, too. they may have come from the factory a bit high in tension and need to be backed off a bit. I think I will back each nipple out a 1/2 turn or so and re-true them and see. thanks
     
  6. tafi

    tafi Member

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    Okay now I get it...

    Any wheel with a low spoke count is likely to suffer from this. In fact every wheel suffers from this to a certain extent (its just often not possible to see). The reasons it is more obvious on this wheel are:
    1) The wheel has few spokes so each spoke has no real opposite near neighbour to counteract its tension.
    2) The lack of spokes also requires spoke tension to be higher than with more spokes in order to have a stable wheel.

    The results of this can be seen in 32 or 36 spoke wheels once the brake surface has seen a little use. Usually it is evidenced by a uneven and periodic shading of the brake track in the immediate vicinity of each nipple. It doesn't seem to cause brake pulsing.

    If all you have done is nip up a slight warp, I would leave it as it is. Lowering the tension will not make for as strong a wheel. If however, in the process of truing, you have hugely ramped up the tension in ALL spokes (and you can only do this if you have actually tightened all the spokes), then you might think about backing off a little.
     
  7. bikerx68

    bikerx68 New Member

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    Thanks for the great info. I am buying a Park tension meter so I know that I am within spec for the tension before I hit the road to test.
     
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