WheelSmith Tensionometer: How to interpolate?

Discussion in 'Cycling Equipment' started by x, Sep 7, 2003.

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  1. x

    x Guest

    Doesn't seem real intuitive.

    Even 10's, no problem: If the two lines line up, that's it.

    But the example in WheelSmith's leaflet says that just a hair over 60 = 65.

    What about a half-hair? What about 2 hairs?....

    Sounds like the nature of the readout is that the maximum accuracy is 5.

    If that's true, then it seems like there's a problem for the truly-obsessive.

    To wit, Mavic's spec for the 517 supposedly is (I got the figures secondhand) 1,000/1,100 N, which,
    I think, translates to 102-112 Kg.

    But "60" on WheelSmith's gauge seems to translate to 107 kg for a 1.8mm spoke while "65" translates
    to 122 kg for that spoke.

    Seems like an awful lot of slop there....

    Also, what constitutes a lineup of the upper/lower lines? Exact alignment? Any part of one line
    overlapping any part of the other line?

    Is this what they call a "vernier" gauge? Seems like Park's readout is a lot easier to deal with -
    but is Park's added precision just an illusion?
    -----------------------
    PeteCresswell
     
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  2. Jobst Brandt

    Jobst Brandt Guest

    Pete Cresswell writes:

    > Doesn't seem real intuitive.

    > Even 10's, no problem: If the two lines line up, that's it.

    > Also, what constitutes a lineup of the upper/lower lines? Exact alignment? Any part of one line
    > overlapping any part of the other line?

    I think this should help:

    http://www.saburchill.com/physics/chapters/0095.html

    > Is this what they call a "vernier" gauge? Seems like Park's readout is a lot easier to deal with -
    > but is Park's added precision just an illusion?

    Their instrument uses too large a test load and is impeded by excess friction. By the way, it's a
    "tensiometer".

    Jobst Brandt [email protected]
     
  3. x

    x Guest

    RE/
    >I think this should help:
    >
    >http://www.saburchill.com/physics/chapters/0095.html
    >
    >> Is this what they call a "vernier" gauge? Seems like Park's readout is a lot easier to deal with
    >> - but is Park's added precision just an illusion?
    >
    >Their instrument uses too large a test load and is impeded by excess friction. By the way, it's a
    >"tensiometer".

    From that, I conclude:

    1) I just pissed away a hundred bucks..

    2) It's not a verier gauge.

    tensiometer tensiometer tensiometer tensiometer tensiometer.... I think I've got it now....-)

    At the beggining of all this, my instinct was to just take my wheels to somebody who does this for a
    living - on the assumption that they can do it cheaper and better than I can.

    But now my rear wheel's been in this guy's shop for going on three weeks... "The new rim hasn't
    arrived yet....".... Oh well.... Thank goodness I have a spare....

    So I figured I might as well bite the bullet and learn something - as well as avoid exposing myself
    to similar situations in the future...

    Recommendation(s)?
    -----------------------
    PeteCresswell
     
  4. x

    x Guest

    RE/
    >Sounds like the nature of the readout is that the maximum accuracy is 5.

    I think I'm getting somewhere here. Seems like a single rotation of the nipple takes me from, say,
    40 on the tensionometer to 50.... about 20 kg diff on 1.8mm spokes.

    But I'm starting to realize how complicated and interdependent the tensions are. You tighten one,
    and the tension changes on others. Ouch.

    I was doing pretty well true/hop-wise just putting the wheel in a stand, making little marks at
    various nipples and doing a quarter turn here, an eighth of a turn there....

    Now I'm trying to get all spokes at the same tension and the thing wobbles like there's no
    tomorrow...

    But, of course, when I go back and measure the other side of the wheel after making all the spokes
    on one side the same tension, the tensions on the other side are all over the place.

    Questions for somebody who knows:

    1) What's the proper technique for getting consistant readings? I find that if I rotate the
    instrument back and forth a few times the reading changes and settles down after 2-3 movements.
    Before using it, I give it a half-dozen squeezes and sometimes different squeezes produce
    different "zero" readings - and I have to fiddle with the spring until I get exact zero - after
    which I'm careful not to touch the spring during use.

    2) I'm getting the feeling that tension is best played with with the wheel laying horizontal across
    my knees instead of in the truing jig. True?

    3) Is there a strategy for evening out the tensions? e.g. Working on opposite spokes same side?
    Spokes from different sides?

    4) For a front disc wheel, should the tension on each side be the same?

    5) Rear disc wheel? (Rohloff hub - no dish)

    6) If, by some miracle of obsessive-compulsive iteration, I manage to get identical tension readings
    from all spokes - should a non-dished wheel then be true and free of hop?
    -----------------------
    PeteCresswell
     
  5. x

    x Guest

    RE/
    >impeded by excess friction.

    I guess that's where the wiggling before reading comes in...
    -----------------------
    PeteCresswell
     
  6. Jobst Brandt

    Jobst Brandt Guest

    Pete Cresswell writes:

    > I think I'm getting somewhere here. Seems like a single rotation of the nipple takes me from, say,
    > 40 on the tensionometer to
    > 50.... about 20 kg diff on 1.8mm spokes.

    > But I'm starting to realize how complicated and interdependent the tensions are. You tighten one,
    > and the tension changes on others. Ouch.

    Don't use a tensiometer to tighten spokes, one by one, to the desired tension. Tighten the spokes
    and true the wheel. Then measure how tight the wheel is by sampling a few spokes. Tension ought
    to be fairly uniform before you make measurements if you have checked the tome of spokes around
    the wheel.

    > I was doing pretty well true/hop-wise just putting the wheel in a stand, making little marks at
    > various nipples and doing a quarter turn here, an eighth of a turn there....

    > Now I'm trying to get all spokes at the same tension and the thing wobbles like there's no
    > tomorrow...

    You are probably changing too much at once. Once you have some tension, even up the spokes before
    adding more tension.

    > But, of course, when I go back and measure the other side of the wheel after making all the spokes
    > on one side the same tension, the tensions on the other side are all over the place.

    I doubt that your rim is that out of whack. Whose instructions are you following?

    > Questions for somebody who knows:

    > 1) What's the proper technique for getting consistent readings? I find that if I rotate the
    > instrument back and forth a few times the reading changes and settles down after 2-3 movements.
    > Before using it, I give it a half-dozen squeezes and sometimes different squeezes produce
    > different "zero" readings - and I have to fiddle with the spring until I get exact zero - after
    > which I'm careful not to touch the spring during use.

    The change in reading when you wiggle the gauge back and forth is because you are relaxing friction
    between and supports and anvil. The unit pictured in "the Bicycle Wheel" uses ball bearings as end
    supports to avoid this. It also measures from the support side so the wire thickness does not enter
    into the measurement.

    > 2) I'm getting the feeling that tension is best played with with the wheel laying horizontal
    > across my knees instead of in the truing jig. True?

    The wheel can be lying horizontal but that doesn't change the readings if you use the instrument
    correctly. What does your lap do?

    > 3) Is there a strategy for evening out the tensions? e.g. Working on opposite spokes same side?
    > Spokes from different sides?

    Make the wheel true first, then check for tensions above and below average and balance them out
    while checking trueness. This is where radial trueness should be as close as possible to true.

    > 4) For a front disc wheel, should the tension on each side be the same?

    That depends on the "dish". Is the rim off of the hub center?

    > 5) Rear disc wheel? (Rohloff hub - no dish)

    How can they have different tensions if the rim is centered?

    > 6) If, by some miracle of obsessive-compulsive iteration, I manage to get identical tension
    > readings from all spokes - should a non-dished wheel then be true and free of hop?

    Well it won't be dished if all spokes are the same tension.

    Jobst Brandt [email protected]
     
  7. [email protected] wrote in message news:<[email protected]>...
    > Pete Cresswell writes: I doubt that your rim is that out of whack. Whose instructions are you
    > following?

    Instructions? You mean there are instructions? ....-) It's starting to dawn on me that maybe I ought
    to break down and buy this guy Brandt's book.... got any in stock? (email is my first name at the
    "FatBelly" commercial domain

    > The change in reading when you wiggle the gauge back and forth is because you are relaxing
    > friction between and supports and anvil. The unit pictured in "the Bicycle Wheel" uses ball
    > bearings as end supports to avoid this. It also measures from the support side so the wire
    > thickness does not enter into the measurement.

    - So, does that mean that I should wiggle it? I think so....
    - Is the "Bicycle Wheel" instrument the one called "DT"?

    > What does your lap do?
    Ideosyncratic comfort issue. Easier to repeatedly apply the instrument and read it...

    > Make the wheel true first, then check for tensions above and below average and balance them out
    > while checking trueness. This is where radial trueness should be as close as possible to true.

    Bottom line to me: the instrument is to make sure I don't exceed the mfr's specs on individual
    spokes. Everything else is "just get it true..."

    > > 4) For a front disc wheel, should the tension on each side be the same?
    > Well it won't be dished if all spokes are the same tension.

    Sounds like relative tension between the two sides is a product of dish.
     
  8. In article <[email protected]>, [email protected] says...

    >1) What's the proper technique for getting consistant readings? I find that
    if
    >I rotate the instrument back and forth a few times the reading changes and settles down after 2-3
    >movements. Before using it, I give it a half-dozen squeezes and sometimes different squeezes
    >produce different "zero" readings - and I have to fiddle with the spring until I get exact zero -
    >after which I'm careful not to touch the spring during use.

    Make sure your spokes are clean. I've had my WS tensiometer for 10 years or so and it gives me the
    same repeatable reading without having to play with it.

    >2) I'm getting the feeling that tension is best played with with the wheel laying horizontal across
    > my knees instead of in the truing jig. True?

    No on the truing stand should work fine. Having to pull the wheel to check tension will add a lot of
    time to your wheel building.

    >3) Is there a strategy for evening out the tensions? e.g. Working on opposite spokes same side?
    > Spokes from different sides?

    If I need to move the rim to one side and the closet spoke is already at my target tension I check
    the first spokes to the left and right of the high spot to see if they have room for an adjustment
    and still stay in the range I need. That almost always works.

    >4) For a front disc wheel, should the tension on each side be the same?

    I think not because the hub flanges are not symetrical. Just like on a rear wheel.

    >5) Rear disc wheel? (Rohloff hub - no dish)

    NO idea.

    >6) If, by some miracle of obsessive-compulsive iteration, I manage to get identical tension
    > readings from all spokes - should a non-dished wheel then be true and free of hop?

    Not always.
    -----------------
    Alex __O _-\<,_ (_)/ (_)
     
  9. David Kunz

    David Kunz Guest

    (Pete Cresswell) wrote:
    > RE/
    >
    >>Sounds like the nature of the readout is that the maximum accuracy is 5.
    >
    >
    > I think I'm getting somewhere here. Seems like a single rotation of the nipple takes me from, say,
    > 40 on the tensionometer to 50.... about 20 kg diff on 1.8mm spokes.
    >
    > But I'm starting to realize how complicated and interdependent the tensions are. You tighten one,
    > and the tension changes on others. Ouch.
    >
    > I was doing pretty well true/hop-wise just putting the wheel in a stand, making little marks at
    > various nipples and doing a quarter turn here, an eighth of a turn there....
    >
    > Now I'm trying to get all spokes at the same tension and the thing wobbles like there's no
    > tomorrow...
    >
    > But, of course, when I go back and measure the other side of the wheel after making all the spokes
    > on one side the same tension, the tensions on the other side are all over the place.
    >
    >
    > Questions for somebody who knows:
    >
    > 1) What's the proper technique for getting consistant readings? I find that if I rotate the
    > instrument back and forth a few times the reading changes and settles down after 2-3 movements.
    > Before using it, I give it a half-dozen squeezes and sometimes different squeezes produce
    > different "zero" readings - and I have to fiddle with the spring until I get exact zero - after
    > which I'm careful not to touch the spring during use.

    Mine gives that same reading unless I put it too close to the rim. It's very repeatable.

    > 2) I'm getting the feeling that tension is best played with with the wheel laying horizontal
    > across my knees instead of in the truing jig. True?

    Why? You check tension evenness by plucking the spokes and listening to the tone.

    > 3) Is there a strategy for evening out the tensions? e.g. Working on opposite spokes same side?
    > Spokes from different sides?

    There's an art to it. To start, you have to realize that a spoke as many as 3 or 4 away can impact
    the truness of a position on the wheel. So, you pluck both sides of the wheel for several spokes on
    each side of the out of true spot and listen to the sound on each side. Find the spoke that's the
    most out of balance with the rest (different pitch when plucked) and add or remove 1/4-1/2 turn from
    that spoke (depending on which way you want to move the out of true place and how different the
    pitch is) and move on (or 1/4-1/2 turn on both sides to bring-in a high spot). Note that the drive
    and non-drive sides will have different "pitches" because you want more tension on the drive side to
    get the dish right (centering of the rim). When you have the wheel true and all of the spokes pluck
    about the same on each side, then you check torque on a couple and see where you are (always low --
    the question is how much). If it's truly balanced at that point, you can add 1/4-1/2 turns all of
    the way around to bring the wheel up to full tension (note that a
    1/4 turn on the drive side will pull more than a 1/4 turn on the non-drive side, so watch dish).

    > 4) For a front disc wheel, should the tension on each side be the same?

    No, the disc side will be tighter because it is inset.

    > 5) Rear disc wheel? (Rohloff hub - no dish)

    Mine is still not the same (Chris King Iso Disc).

    Don't worry about matching the tension on both sides. Get the drive side tension right and when the
    dish is right, the non-drive side tension will be also :). Just make sure it's at least 60-70 kg.

    > 6) If, by some miracle of obsessive-compulsive iteration, I manage to get identical tension
    > readings from all spokes - should a non-dished wheel then be true and free of hop?

    No. You may have the same tension, but if you haven't balanced the adding of tension across multiple
    spokes, the wheel won't be true (the spoke lengths will be wrong).

    David
     
  10. x

    x Guest

    RE/
    >Make sure your spokes are clean. I've had my WS tensiometer for 10 years or so and it gives me the
    >same repeatable reading without having to play with it.
    >

    This isn't a wiseguy question, but how do you know
    -----------------------
    PeteCresswell
     
  11. x

    x Guest

    RE/
    >This isn't a wiseguy question, but how do you know

    Oops, that one slipped out before it was done.

    ...how do you know the reading is the same without wiggling the device every so often to see if
    it changes?
    -----------------------
    PeteCresswell
     
  12. Sorni

    Sorni Guest

    "(Pete Cresswell)" <[email protected]> wrote in message news:m[email protected]...

    > Oops, that one slipped out before it was done.
    >
    > ...how do you know the reading is the same without wiggling the device
    every so
    > often to see if it changes?

    Hey! This is a family newsgroup...

    Bill "slow evening" S.
     
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