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Wheel truing question

BhimaBhima Posts: 2,145
edited January 2010 in Workshop
I have a 32-spoke front wheel, laced radially. 16 spokes per side, spaced identically.

I tuned the spokes to the same pitch so they all were at the same note when pinged yet the wheel was not true after doing this. I've tuned musical instruments for years and physics tells me that the spokes will be at the same tension if they are resonating at the same frequency, provided they are all the same length and width.

It was pretty close, but I had to compensate by tightening a few spokes significantly more. The wheel was then true after about another 5 adjustments.

Does this extra tension requirement mean the rim is bent somewhere?

Posts

  • NervexProfNervexProf Posts: 4,202
    Bhima,
    Did you de-stress the wheel between achieving lateral and concentric truth?

    It is usual for the spoke heads, on lacing up and after adding tension, to still not be seated in the hub? This would account for some of the differential in spoke turns.

    A very good, low cost e-book on wheel building is available here

    http://www.wheelpro.co.uk/wheelbuilding/book.php
    Common sense in an uncommon degree is what the world calls wisdom
  • Bhima wrote:
    Does this extra tension requirement mean the rim is bent somewhere?

    Probably.

    Very little tuning here mostly fine truing.
    http://www.youtube.com/watch?v=55OZO9ZRWP0
  • RedJohnRedJohn Posts: 272
    Other possibilities -

    Some spokes are twisted - if the thread is stiff the spoke may twist instead of the nipple turning.
    Spokes are made with fractionally different thicknesses.
    Nipples are fractionally different lengths.
    Some spokes have stretched, making them thinner.

    Any of these might change the "tune".

    However if there's a big difference in tension - check by squeezing pairs as well as musical tune - then chnaces are the rim's deformed.

    Easy enough to dismantle and start again, then if the rim's bent it'll be obvious as well.
  • balthazarbalthazar Posts: 1,565
    Small irregularities in rim and spoke manufacture are highly amplified in the total tensioned structure; that is why wheel-building machines must have complex feedback algorithms to build true wheels, rather than simply bringing all the spokes to a precise tension and assuming the wheel will be true.

    A bend that affects a small part of the rim (for instance, from hitting a kerb) cannot be accounted for with spoke tension variation. A larger bend might be, though it may be preferable to manually straighten the rim before tensioning.

    For clarity:

    relieving spoke twist is the procedure wherin spoke twist from tensioning is accounted for during the build; this prevents spokes unscrewing themselves in use and leaving the wheel untrue.

    correcting the spoke line is the procedure wherein the tensioned spokes are manipulated near the nipples to make their line dead straight, rather than gently curved.

    stress-relieving is the process whereby spokes are made as durable as possible.
  • rakerake Posts: 3,204
    you will get some slight variances with any wheel. when trueing always do multiple spokes a bit at a time. never just one alone. it spreads the load better.
  • Are you sure the spokes are all exactly the same length and perfectly uniform in width? Also is the rim bed perfectly level.

    If not then you will still have to adjust the spoke tension even if the rim is perfectly round both vertically and laterally.
  • NuggsNuggs Posts: 1,804
    As it's not possible to build a perfectly round, laterally true rim, uniform spoke tension alone won't create a perfectly true wheel.
  • e999same999sam Posts: 426
    My Easton's are supposedly tensioned with the aid of a tuning fork but they still not all the same pitch.
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