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Thread: Wheel Hop

  1. #1
    Forum Admin lotek's Avatar
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    Wheel Hop

    Ok all you wheel builders here's the question
    of the day.
    I finished the rear wheel, true tension, true tension, true
    prestress tension and I'm pretty satisfied with the result.
    My front wheel has a smallish (1/4 in?) hop opposite
    the valve hole. What is really baffling is that its
    small, maybe 1 spoke hole arc, it isn't gradual.
    No amount of tensioning or untensioning opposite
    side seems to move it.
    So, Bad rim? or am I just not doing something right?
    What if any method is there for correcting this type
    of wheel hop? Anything I've read online doesn't seem
    to address this.
    The rims are Mavic GP4's, new when I bought them.
    Appreciate the assist,

    Marty
    Sono pił lento di quel che sembra.
    Odio la gente, tutti.

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  2. #2
    xc AND road WoodyUpstate's Avatar
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    Try adding a little tension right under the hop. Use two spokes from opposite sides to try to maintain true the best you can.

  3. #3
    Senior Member mechBgon's Avatar
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    Let's say spoke C is the one closest to the hop, which I assume refers to an outward bulge, not an inward bulge:

    a b c d e (so spokes a, c and e come from one hub flange, and b and d come from the other)

    if you tighten C and countertighten B and D as Woody suggests, the wheel can maintain trueness. I'd like to add that if C is much looser than A and E, then lower tension on A and E and add it to C also. You can determine the relative tension levels by plucking the spokes and comparing tone.

    Overall, however, if it really is 1/4" out-of-round, that's quite a lot. That's ~6mm, and usually one would want to get the roundness down to the inherent limitations of the rim, typically less than 1mm. If the rim is showning a 6mm bulge concentrated into the area of one spoke, I'd certainly be thinking "bad rim" unless this was due to a radical imbalance in spoke tension in that area. Hope it works out for you!

  4. #4
    Forum Admin lotek's Avatar
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    Originally posted by mechBgon
    Let's say spoke C is the one closest to the hop, which I assume refers to an outward bulge, not an inward bulge:

    a b c d e (so spokes a, c and e come from one hub flange, and b and d come from the other)
    Mech,

    Using your example (above) the outward bulge is at C but as
    I said it doesn't seem to gradually bulge (say from B upwards
    and down to D). That's why I'm thinking bad rim.
    I'll try the suggestions from above and let ya'll know what
    the results are.
    Thanks again
    Marty
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    Senior Member bikerider's Avatar
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    At this point, consider taking it to a shop to allow an experienced wheelbuilder check it out. It sounds like it could be a poorly aligned rim seam. If it is a defective rim and you are lucky, the shop you got it from may replace it out of their pocket. Don't hold your breath expecting a warranty replacement from Mavic.

  6. #6
    Forum Admin lotek's Avatar
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    Well, I tried retruing for the wheel hop as
    mentioned above, no dice, still have the hop.
    I'm taking the rim to LBS to see what their
    number one wheelbuilder says.
    I'll let ya'll know.

    Marty
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  7. #7
    Forum Admin lotek's Avatar
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    well that was interesting.
    I went to the LBS, they brought out their premier
    wheelbuilder who is going for the Sheldon truely Brown
    look alike contest.
    Anyhow he takes one look at the wheel and states:
    "wheels no good, spokes are too short" huh?
    He asked the length, then went to the online calculator
    ran the hubs and rims and came up with the same
    302. Told me sometimes its wrong, and said I'll exchange
    em if you remove em.
    He then prep'd the new spokes, gave me 4 extra and
    said when I finished to bring em in he'll eyeball them
    and tweak em for free.
    He also said that no matter how much I tried I would have
    never gotten them right and have well tensioned wheels.
    So, I'm gonna go relace them now.
    I'll keep ya posted.

    Marty
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  8. #8
    Career Cyclist threadend's Avatar
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    You didn't happen to sneak a peek and see where the on-line calculator is located did you?
    2003 Iceman Challenge - 2:34:55 - 897 / 2,000*
    2002 Iceman Challenge - 2:39:23 - 1093 / 2,186
    2000 Iceman Challenge - 2:49:18 - 1516 / 2,153
    *estimated

  9. #9
    Senior Member mechBgon's Avatar
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    Odd. It's the tension of the spokes, not their length, that influences the wheel's trueness and roundness.

    If anyone ever needs a second opinion on spoke length, I can help in the majority of cases, particularly once I get my hands on a Quality Bicycle Products catalog with the ERD data for the newer rims that aren't in my 9th-edition Wheelsmith book.

  10. #10
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    The tension of the spokes will only determine the wheels roundness if they are all the same length.

  11. #11
    Senior Member mechBgon's Avatar
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    I disagree. The spoke could extend a meter past the nipple, but the force exerted on the rim by the nipple would still have the same effect on trueness and roundness. The tension of a spoke is generated by the amount it is stretched along the span between the nipple and the hub.

    Now, if by "tension" you mean how many threads the nipple was screwed onto the spoke, then unequal spoke lengths would produce uneven tensions, but they're not hard to discern by tone, or by using a tensiometer.

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    I'm a wheelbuilder. You mentioned the hop was opposite the valve hole. This is an assembly point for most rim manufacturers. The rim in question has a pinned joint, not welded and machined like currently produced rims. Pinned joints are prone to giving a hop because the aluminum was bent into a circle. The ends don't want to stay exactly where they were bent, so you get a little hop. Often, when building with older Mavic rims, a very calculated smack with a rubber mallet was what it took to take care of this.

    IMO, spoke length in this case is irrelevant.

  13. #13
    Forum Admin lotek's Avatar
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    Ok, to clarify a bit (hey it was late when I posted).
    The thing the wheelbuilder at the LBS noted
    was a number of the spokes had threads showing
    even tho tension was just about correct for the wheel.
    His thought was that the amount of tension I would need
    to add to pull in the hop was enough to produce an
    unsafe wheel.
    I relaced the wheel last night and things seem
    much better using spokes 2mm longer.

    Marty
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  14. #14
    Senior Member mechBgon's Avatar
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    Cool!

  15. #15
    Forum Admin lotek's Avatar
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    It seems there were 2 different types
    of Mavic GP4 rims, older ones with 615.0 Effective Rim
    diameter and newer rims with 612.0 ERD.
    that would explain the inaccuracy of the spoke calculator.
    I believe that the wrong rim was entered and that
    messed things up from the getgo. I've also replaced
    spokes on rear (although I had it trued etc.) and generally
    feel a whole lot better about the entire wheelbuilding
    adventure.
    Threadend,
    Sheldon Brown has links to spoke calculators. I have Damon
    Rinard's excel spreadsheet which is really good.
    Check Here caculator links
    Marty
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