Stupid fork (zoke Z1) Q....

Discussion in 'Mountain Bikes' started by Slacker, Jun 19, 2003.

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  1. Slacker

    Slacker Guest

    Does the oil level have any effect on the preload? And yes, I know I need springs, but I'm broke
    right now.

    Damn, I lost about 22 lbs and can't get no sag.....me rig feels like a evil hardtail!

    --
    Slacker
     
    Tags:


  2. Technician

    Technician Guest

    Slacker <[email protected]> spoke thusly...
    > Does the oil level have any effect on the preload? And yes, I know I need springs, but I'm broke
    > right now.
    >
    > Damn, I lost about 22 lbs and can't get no sag.....me rig feels like a evil hardtail!
    >
    > --
    > Slacker
    >
    >
    >

    no.

    preload is in the spring. It generally means how much pressure is put on a spring before it is
    loaded (hence preload). it would be like adding or taking away weights from a backpack that you use
    to ride (maybe you could carry a 22 pound weight ;-). the oil just dampens the motion so you don't
    go for a bouncy ride. for example, my grandmothers car had lost all the oil from the front and rear
    shocks. there was no dampening at all except for the friction of a dry shock. hit a good bump and
    that thing would bounce for several blocks. stop quick and ride the wave. it would rock back and
    forth for a few blocks.

    So to make a long story longer, the oil is what regulates the rate the spring is allowed to
    compress, and return.

    As a fairly risky option, you could alter the spring length. it is a bit

    how many pounds needed to compress the spring 1 inch). then you could calculate out a rough figure
    so you could remove so much spring to sag it so many inches. but like i said, i wouldn't recommend
    it as there are many factors that may need accounting for, and it is a shame to ruin a perfectly
    good spring for a few inches of sag.

    look at the bright side, i bet you don't get much pedal bob ;-)
    --
    ~Travis

    http://www.megalink.net/~farmers/
     
  3. Shaun Rimmer

    Shaun Rimmer Guest

    Slacker <[email protected]> wrote in message news:[email protected]...
    > Does the oil level have any effect on the preload? And yes, I know I need
    springs, but I'm broke right now.
    >
    > Damn, I lost about 22 lbs and can't get no sag.....me rig feels like a
    evil hardtail!

    Well, in my experience, putting *more* oil in increases the pre-load, because you are effectively
    reducing the air volume, making it harder to compress (they are obviously partially air sprung in
    this respect). So, I suppose less oil should have the reverse effect, but by how much I don't know.
    Also, I have no idea what problems might be caused if you went below the recommended
    minimum.......?!?!?

    HTH, at least a bit......

    Shaun aRe
     
  4. Shaun Rimmer

    Shaun Rimmer Guest

    Technician <[email protected]> wrote in message
    news:[email protected]...
    > Slacker <[email protected]> spoke thusly...
    > > Does the oil level have any effect on the preload? And yes, I know I
    need springs, but I'm broke right now.
    > >
    > > Damn, I lost about 22 lbs and can't get no sag.....me rig feels like a
    evil hardtail!
    > >
    > > --
    > > Slacker
    > >
    > >
    > >
    >
    > no.

    _YES_

    > preload is in the spring. It generally means how much pressure is put on a spring before it is
    > loaded (hence preload). it would be like adding or taking away weights from a backpack that you
    > use to ride (maybe you could carry a 22 pound weight ;-). the oil just dampens the motion so you
    > don't go for a bouncy ride. for example, my grandmothers car had lost all the oil from the front
    > and rear shocks. there was no dampening at all except for the friction of a dry shock. hit a good
    > bump and that thing would bounce for several blocks. stop quick and ride the wave. it would rock
    > back and forth for a few blocks.
    >
    > So to make a long story longer, the oil is what regulates the rate the spring is allowed to
    > compress, and return.
    >
    > As a fairly risky option, you could alter the spring length. it is a bit

    > how many pounds needed to compress the spring 1 inch). then you could calculate out a rough figure
    > so you could remove so much spring to sag it so many inches. but like i said, i wouldn't recommend
    > it as there are many factors that may need accounting for, and it is a shame to ruin a perfectly
    > good spring for a few inches of sag.
    >
    > look at the bright side, i bet you don't get much pedal bob ;-)

    See my reply.

    Imagine this, you have a PET bottle, cap on. Squeeze the bottle. Easy to do, isn't it? Now, take the
    cap off and add liquid to the half way point then replace cap. Now squeeze it. Harder to compress,
    no? Add more liquid, harder still? Of course it is - this is why the oil level _will_ make 'a'
    difference to the pre-load.

    Shaun aRe
     
  5. Michael Dart

    Michael Dart Guest

  6. Technician

    Technician Guest

    Shaun Rimmer <[email protected]> spoke thusly...
    >
    > Technician <[email protected]> wrote in message
    > news:[email protected]...
    > > Slacker <[email protected]> spoke thusly...
    > > > Does the oil level have any effect on the preload? And yes, I know I
    > need springs, but I'm broke right now.
    > > >
    > > > Damn, I lost about 22 lbs and can't get no sag.....me rig feels like a
    > evil hardtail!
    > > >
    > > > --
    > > > Slacker
    > > >
    > > >
    > > >
    > >
    > > no.
    >
    > _YES_
    >
    > > preload is in the spring. It generally means how much pressure is put on a spring before it is
    > > loaded (hence preload). it would be like adding or taking away weights from a backpack that you
    > > use to ride (maybe you could carry a 22 pound weight ;-). the oil just dampens the motion so you
    > > don't go for a bouncy ride. for example, my grandmothers car had lost all the oil from the front
    > > and rear shocks. there was no dampening at all except for the friction of a dry shock. hit a
    > > good bump and that thing would bounce for several blocks. stop quick and ride the wave. it would
    > > rock back and forth for a few blocks.
    > >
    > > So to make a long story longer, the oil is what regulates the rate the spring is allowed to
    > > compress, and return.
    > >
    > > As a fairly risky option, you could alter the spring length. it is a bit

    > > how many pounds needed to compress the spring 1 inch). then you could calculate out a rough
    > > figure so you could remove so much spring to sag it so many inches. but like i said, i wouldn't
    > > recommend it as there are many factors that may need accounting for, and it is a shame to ruin a
    > > perfectly good spring for a few inches of sag.
    > >
    > > look at the bright side, i bet you don't get much pedal bob ;-)
    >
    > See my reply.
    >
    > Imagine this, you have a PET bottle, cap on. Squeeze the bottle. Easy to do, isn't it? Now, take
    > the cap off and add liquid to the half way point then replace cap. Now squeeze it. Harder to
    > compress, no? Add more liquid, harder still? Of course it is - this is why the oil level _will_
    > make 'a' difference to the pre-load.
    >
    > Shaun aRe
    >
    >
    >

    you clearly do not value your oil seals, or at the other end of the stick, the dampening value
    of the oil.
    --
    ~Travis

    http://www.megalink.net/~farmers/
     
  7. Shaun Rimmer

    Shaun Rimmer Guest

    Technician <[email protected]> wrote in message
    news:[email protected]...
    > Shaun Rimmer <[email protected]> spoke thusly...
    > >
    > > Technician <[email protected]> wrote in message
    > > news:[email protected]...
    > > > Slacker <[email protected]> spoke thusly...
    > > > > Does the oil level have any effect on the preload? And yes, I know
    I
    > > need springs, but I'm broke right now.
    > > > >
    > > > > Damn, I lost about 22 lbs and can't get no sag.....me rig feels like
    a
    > > evil hardtail!
    > > > >
    > > > > --
    > > > > Slacker
    > > > >
    > > > >
    > > > >
    > > >
    > > > no.
    > >
    > > _YES_
    > >
    > > > preload is in the spring. It generally means how much pressure is put
    on
    > > > a spring before it is loaded (hence preload). it would be like adding
    or
    > > > taking away weights from a backpack that you use to ride (maybe you could carry a 22 pound
    > > > weight ;-). the oil just dampens the motion so you don't go for a bouncy ride. for example, my
    > > > grandmothers car had lost all the oil from the front and rear shocks. there was no
    dampening
    > > > at all except for the friction of a dry shock. hit a good bump and
    that
    > > > thing would bounce for several blocks. stop quick and ride the wave.
    it
    > > > would rock back and forth for a few blocks.
    > > >
    > > > So to make a long story longer, the oil is what regulates the rate the spring is allowed to
    > > > compress, and return.
    > > >
    > > > As a fairly risky option, you could alter the spring length. it is a
    bit

    IOW,
    > > > how many pounds needed to compress the spring 1 inch). then you could calculate out a rough
    > > > figure so you could remove so much spring to sag it so many inches. but like i said, i
    > > > wouldn't recommend it as there
    are
    > > > many factors that may need accounting for, and it is a shame to ruin a perfectly good spring
    > > > for a few inches of sag.
    > > >
    > > > look at the bright side, i bet you don't get much pedal bob ;-)
    > >
    > > See my reply.
    > >
    > > Imagine this, you have a PET bottle, cap on. Squeeze the bottle. Easy to
    do,
    > > isn't it? Now, take the cap off and add liquid to the half way point
    then
    > > replace cap. Now squeeze it. Harder to compress, no? Add more liquid,
    harder
    > > still? Of course it is - this is why the oil level _will_ make 'a' difference to the pre-load.
    > >
    > > Shaun aRe
    > >
    > >
    > >
    >
    > you clearly do not value your oil seals, or at the other end of the stick, the dampening value of
    > the oil.

    Addressed somewhat in my original reply to Slacker. I never suggested going outside of the
    manufacturers min. or max levels, and Slacker is smart enough to know that.

    Shaun aRe
     
  8. > > Slacker wrote:
    > > > Does the oil level have any effect on the preload?

    Shaun Rimmer wrote:
    > Technician wrote:
    > >
    > > no.
    >
    > _YES_

    No, not normally.

    Technician wrote:
    > > preload is in the spring. It generally means how much pressure is put on a spring before it is
    > > loaded (hence preload).

    Yes. But this is the last statement Trav makes that has any apparent connection to reality.

    > > it would be like adding or taking away weights from a backpack that you use to ride

    No. Preload is not the same thing as being heavier.

    > > the oil just dampens the motion so you don't go for a bouncy ride.

    No. Slacker was asking about the oil _height_. Pray tell, how does the oil height affect the
    damping? The oil _weight_ affects the damping.

    > > As a fairly risky option, you could alter the spring length. it is a bit

    > > how many pounds needed to compress the spring 1 inch). then you could calculate out a rough
    > > figure so you could remove so much spring to sag it so many inches. but like i said, i wouldn't
    > > recommend it as there are many factors that may need accounting for, and it is a shame to ruin a
    > > perfectly good spring for a few inches of sag.

    Trav, does it ever occur to you that it is preferable to shut the hell up when you don't know what
    you're talking about, instead of standing up and babbling incoherently in public?

    Shaun wrote:
    > Imagine this, you have a PET bottle, cap on. Squeeze the bottle. Easy to do, isn't it? Now, take
    > the cap off and add liquid to the half way point then replace cap. Now squeeze it. Harder to
    > compress, no? Add more liquid, harder still?

    Agreed.

    But then Shaun continued:
    > Of course it is - this is why the oil level _will_ make 'a' difference to the pre-load.

    Agh! No! It might change the sag a little, but that's not the same as preload.

    Time for a short rant on the physics of springs, methinks. A coil spring, sitting all by its
    lonesome, has a linear force law. This means that the amount of force required to compress the
    spring a given amount (call it "x") is proportional to the amount the spring is compressed:

    F = k x

    Here k is some number that will depend on which spring you use -- for a heavier spring, the force
    required to compress the spring some amount x will be larger, meaning k will be larger.

    * First point: changing the spring weight changes the force constant
    k.

    "Sag" is just the amount the spring displaces under the force of your weight. If we call your weight
    W, the sag is just

    x = W / k

    Now suppose you want to reduce the amount of sag on a spring without getting a heavier spring (i.e.,
    without changing k?). You preload it. That is, you pre-compress the spring a small amount (we'll
    call it "x0"). Now the force required to compress the preloaded spring by a distance x is

    F = k (x + x0)

    It takes more force to compress a preloaded spring, because it already has a force on it,

    F0 = k x0

    So now we can write the sag as:

    x = (W - F0) / k

    If your weight W is less than the preload force F0, there is no sag at all! You have to place a
    minimum force on the spring to get it to start moving. Note that this is _not_ the same thing as
    changing the spring weight, i.e. changing the force constant k. A very heavy spring with no preload
    will always sag a little bit under even a small weight. A preloaded spring will not sag at all until
    the preload force is overcome.

    * Second point: changing the preload changes the force F0.

    Now what about oil height? Oil in the fork does two things: first, as Trav rather incoherently
    pointed out, oil is used for damping. We are not going to discuss damping. But fork oil does
    something else that is not so obvious: it puts a second spring in your fork. Rather, it is the air
    on top of the oil that acts like a spring. Compress the air in the fork, and it pushes back. This is
    what Shaun was talking about.

    So, really, a coil/oil fork has two springs in it -- the coil spring, and the air in the fork. If
    you have two springs (call the weights k1 and k2) acting together (in "parallel"), they are
    equivalent to a single, heavier spring. In terms of the spring constants k1 and k2, the effective
    spring constant k is just the sum of the individual spring constants:

    k = k1 + k2

    and

    F = k x = (k1 + k2) x

    So Shaun is right that changing the oil height will have some effect on the sag, but he is wrong in
    saying that it is preload. It is actually more like changing the weight of the spring. You're
    messing with k, not with the preload force F0.

    But there's a catch: the air in the fork is not like the coil spring. It does _not_ have a linear
    force law F = k2 x. The air in the fork has a nonlinear force law, something like F = k2 x^2.
    (Here x^2 denotes x squared.) Relative to a linear spring, it is easier to compress the air a
    little bit, but much harder to compress it a lot. So the force law for a coil + air spring is
    something more like:

    F = k1 x + k2 x^2

    This deviation from a linear force law is called "progressiveness". For small amounts of compression
    (small bumps), the response of the spring is nice and linear. But when you compress it a lot (big
    bumps), the force required goes up much faster than linear. This is good, because you can tune the
    progressiveness so that the fork is responsive on small bumps (tuning the spring weight k1), but
    won't top out on big bumps (tuning the "air spring" weight k2 by changing the oil height).

    * Third point: changing the oil height changes the progressiveness, or nonlinear spring constant k2.

    To sum up, spring weight, preload, and oil height are independent adjustments of a fork. Each does
    something different:

    * Changing the spring weight changes the linear force constant k.
    * Changing the preload adds a static force F0. You use this to reduce sag without getting a
    heavier spring.
    * Changing the oil height changes the nonlinear spring constant k2 (the "progressiveness"). This
    allows you to be supple on small bumps but avoid a harsh top-out on big bumps.

    Can you tell it's raining here?

    CC
     
  9. Shaun Rimmer

    Shaun Rimmer Guest

    Corvus Corvax <[email protected]> wrote in message
    news:[email protected]...
    > > > Slacker wrote:
    > > > > Does the oil level have any effect on the preload?
    >
    >
    > Shaun Rimmer wrote:
    > > Technician wrote:
    > > >
    > > > no.
    > >
    > > _YES_
    >
    > No, not normally.

    OK - I'll address this further down.

    > Technician wrote:
    > > > preload is in the spring. It generally means how much pressure is put
    on
    > > > a spring before it is loaded (hence preload).
    >
    > Yes. But this is the last statement Trav makes that has any apparent connection to reality.

    I think it was an accident...........

    > Shaun wrote:
    > > Imagine this, you have a PET bottle, cap on. Squeeze the bottle. Easy to
    do,
    > > isn't it? Now, take the cap off and add liquid to the half way point
    then
    > > replace cap. Now squeeze it. Harder to compress, no? Add more liquid,
    harder
    > > still?
    >
    > Agreed.
    >
    > But then Shaun continued:
    > > Of course it is - this is why the oil level _will_ make 'a' difference to the pre-load.
    >
    > Agh! No! It might change the sag a little, but that's not the same as preload.

    OK - I should have clarified for other's benefits, rather than just answering Slacker, and the way
    he _appeared_ to be mis-using the term 'pre-load' - it will change the overall spring strength of
    the fork, and therefore alter the amount of sag (as Slacker seemed to desire).

    > Time for a short rant on the physics of springs, methinks. A coil spring, sitting all by its
    > lonesome, has a linear force law. This means that the amount of force required to compress the
    > spring a given amount (call it "x") is proportional to the amount the spring is compressed:
    >
    > F = k x
    >
    > Here k is some number that will depend on which spring you use -- for a heavier spring, the force
    > required to compress the spring some amount x will be larger, meaning k will be larger.
    >
    > * First point: changing the spring weight changes the force constant
    > k.
    >
    > "Sag" is just the amount the spring displaces under the force of your weight. If we call your
    > weight W, the sag is just
    >
    > x = W / k
    >
    > Now suppose you want to reduce the amount of sag on a spring without getting a heavier spring
    > (i.e., without changing k?). You preload it. That is, you pre-compress the spring a small amount
    > (we'll call it "x0"). Now the force required to compress the preloaded spring by a distance x is
    >
    > F = k (x + x0)
    >
    > It takes more force to compress a preloaded spring, because it already has a force on it,
    >
    > F0 = k x0
    >
    > So now we can write the sag as:
    >
    > x = (W - F0) / k
    >
    > If your weight W is less than the preload force F0, there is no sag at all! You have to place a
    > minimum force on the spring to get it to start moving. Note that this is _not_ the same thing as
    > changing the spring weight, i.e. changing the force constant k. A very heavy spring with no
    > preload will always sag a little bit under even a small weight. A preloaded spring will not sag at
    > all until the preload force is overcome.
    >
    > * Second point: changing the preload changes the force F0.
    >
    > Now what about oil height? Oil in the fork does two things: first, as Trav rather incoherently
    > pointed out, oil is used for damping. We are not going to discuss damping. But fork oil does
    > something else that is not so obvious: it puts a second spring in your fork. Rather, it is the air
    > on top of the oil that acts like a spring. Compress the air in the fork, and it pushes back. This
    > is what Shaun was talking about.
    >
    > So, really, a coil/oil fork has two springs in it -- the coil spring, and the air in the fork. If
    > you have two springs (call the weights k1 and k2) acting together (in "parallel"), they are
    > equivalent to a single, heavier spring. In terms of the spring constants k1 and k2, the effective
    > spring constant k is just the sum of the individual spring constants:
    >
    > k = k1 + k2
    >
    > and
    >
    > F = k x = (k1 + k2) x
    >
    > So Shaun is right that changing the oil height will have some effect on the sag, but he is wrong
    > in saying that it is preload.

    Addressed above - thanks for pulling me up on my laxness.

    > It is actually more like changing the weight of the spring. You're messing with k, not with the
    > preload force F0.
    >
    > But there's a catch: the air in the fork is not like the coil spring. It does _not_ have a linear
    > force law F = k2 x. The air in the fork has a nonlinear force law, something like F = k2 x^2.
    > (Here x^2 denotes x squared.) Relative to a linear spring, it is easier to compress the air a
    > little bit, but much harder to compress it a lot. So the force law for a coil + air spring is
    > something more like:
    >
    > F = k1 x + k2 x^2
    >
    > This deviation from a linear force law is called "progressiveness". For small amounts of
    > compression (small bumps), the response of the spring is nice and linear. But when you compress it
    > a lot (big bumps), the force required goes up much faster than linear. This is good, because you
    > can tune the progressiveness so that the fork is responsive on small bumps (tuning the spring
    > weight k1), but won't top out on big bumps (tuning the "air spring" weight k2 by changing the oil
    > height).

    Aware of this too (gee, aren't I a smarty pants, heheheh.....).

    > * Third point: changing the oil height changes the progressiveness, or nonlinear spring
    > constant k2.
    >
    > To sum up, spring weight, preload, and oil height are independent adjustments of a fork. Each does
    > something different:
    >
    > * Changing the spring weight changes the linear force constant k.
    > * Changing the preload adds a static force F0. You use this to reduce sag without getting a
    > heavier spring.
    > * Changing the oil height changes the nonlinear spring constant k2 (the "progressiveness"). This
    > allows you to be supple on small bumps but avoid a harsh top-out on big bumps.
    >
    >
    > Can you tell it's raining here?
    >
    > CC

    Well CC, you're preaching to the converted with me mate ',;~}~

    I just tend to forget when I'm addressing an individual's question(s) that their are others likely
    reading also, so tend to (occasionally....hopefully not too often....) use them in the context they
    were used in the original question (very lazy of me, but it does ease communication).

    Shaun aRe - not _too_ shabby with layman's physics.
     
  10. J'M Sm'Th

    J'M Sm'Th Guest

    Corvus Corvax wrote:
    >
    > > > Slacker wrote:
    > > > > Does the oil level have any effect on the preload?
    >
    > Shaun Rimmer wrote:
    > > Technician wrote:
    > > >
    > > > no.
    > >
    > > _YES_
    >
    > No, not normally.
    >
    > Technician wrote:
    > > > preload is in the spring. It generally means how much pressure is put on a spring before it is
    > > > loaded (hence preload).
    >
    > Yes. But this is the last statement Trav makes that has any apparent connection to reality.
    >
    > > > it would be like adding or taking away weights from a backpack that you use to ride
    >
    > No. Preload is not the same thing as being heavier.
    >
    > > > the oil just dampens the motion so you don't go for a bouncy ride.
    >
    > No. Slacker was asking about the oil _height_. Pray tell, how does the oil height affect the
    > damping? The oil _weight_ affects the damping.
    >
    > > > As a fairly risky option, you could alter the spring length. it is a bit

    > > > how many pounds needed to compress the spring 1 inch). then you could calculate out a rough
    > > > figure so you could remove so much spring to sag it so many inches. but like i said, i
    > > > wouldn't recommend it as there are many factors that may need accounting for, and it is a
    > > > shame to ruin a perfectly good spring for a few inches of sag.
    >
    > Trav, does it ever occur to you that it is preferable to shut the hell up when you don't know what
    > you're talking about, instead of standing up and babbling incoherently in public?
    >
    > Shaun wrote:
    > > Imagine this, you have a PET bottle, cap on. Squeeze the bottle. Easy to do, isn't it? Now, take
    > > the cap off and add liquid to the half way point then replace cap. Now squeeze it. Harder to
    > > compress, no? Add more liquid, harder still?
    >
    > Agreed.
    >
    > But then Shaun continued:
    > > Of course it is - this is why the oil level _will_ make 'a' difference to the pre-load.
    >
    > Agh! No! It might change the sag a little, but that's not the same as preload.
    >
    > Time for a short rant on the physics of springs, methinks. A coil spring, sitting all by its
    > lonesome, has a linear force law. This means that the amount of force required to compress the
    > spring a given amount (call it "x") is proportional to the amount the spring is compressed:
    >
    > F = k x
    >
    > Here k is some number that will depend on which spring you use -- for a heavier spring, the force
    > required to compress the spring some amount x will be larger, meaning k will be larger.
    >
    > * First point: changing the spring weight changes the force constant
    > k.
    >
    > "Sag" is just the amount the spring displaces under the force of your weight. If we call your
    > weight W, the sag is just
    >
    > x = W / k
    >
    > Now suppose you want to reduce the amount of sag on a spring without getting a heavier spring
    > (i.e., without changing k?). You preload it. That is, you pre-compress the spring a small amount
    > (we'll call it "x0"). Now the force required to compress the preloaded spring by a distance x is
    >
    > F = k (x + x0)
    >
    > It takes more force to compress a preloaded spring, because it already has a force on it,
    >
    > F0 = k x0
    >
    > So now we can write the sag as:
    >
    > x = (W - F0) / k
    >
    > If your weight W is less than the preload force F0, there is no sag at all! You have to place a
    > minimum force on the spring to get it to start moving. Note that this is _not_ the same thing as
    > changing the spring weight, i.e. changing the force constant k. A very heavy spring with no
    > preload will always sag a little bit under even a small weight. A preloaded spring will not sag at
    > all until the preload force is overcome.
    >
    > * Second point: changing the preload changes the force F0.
    >
    > Now what about oil height? Oil in the fork does two things: first, as Trav rather incoherently
    > pointed out, oil is used for damping. We are not going to discuss damping. But fork oil does
    > something else that is not so obvious: it puts a second spring in your fork. Rather, it is the air
    > on top of the oil that acts like a spring. Compress the air in the fork, and it pushes back. This
    > is what Shaun was talking about.
    >
    > So, really, a coil/oil fork has two springs in it -- the coil spring, and the air in the fork. If
    > you have two springs (call the weights k1 and k2) acting together (in "parallel"), they are
    > equivalent to a single, heavier spring. In terms of the spring constants k1 and k2, the effective
    > spring constant k is just the sum of the individual spring constants:
    >
    > k = k1 + k2
    >
    > and
    >
    > F = k x = (k1 + k2) x
    >
    > So Shaun is right that changing the oil height will have some effect on the sag, but he is wrong
    > in saying that it is preload. It is actually more like changing the weight of the spring. You're
    > messing with k, not with the preload force F0.
    >
    > But there's a catch: the air in the fork is not like the coil spring. It does _not_ have a linear
    > force law F = k2 x. The air in the fork has a nonlinear force law, something like F = k2 x^2.
    > (Here x^2 denotes x squared.) Relative to a linear spring, it is easier to compress the air a
    > little bit, but much harder to compress it a lot. So the force law for a coil + air spring is
    > something more like:
    >
    > F = k1 x + k2 x^2
    >
    > This deviation from a linear force law is called "progressiveness". For small amounts of
    > compression (small bumps), the response of the spring is nice and linear. But when you compress it
    > a lot (big bumps), the force required goes up much faster than linear. This is good, because you
    > can tune the progressiveness so that the fork is responsive on small bumps (tuning the spring
    > weight k1), but won't top out on big bumps (tuning the "air spring" weight k2 by changing the oil
    > height).
    >
    > * Third point: changing the oil height changes the progressiveness, or nonlinear spring
    > constant k2.
    >
    > To sum up, spring weight, preload, and oil height are independent adjustments of a fork. Each does
    > something different:
    >
    > * Changing the spring weight changes the linear force constant k.
    > * Changing the preload adds a static force F0. You use this to reduce sag without getting a
    > heavier spring.
    > * Changing the oil height changes the nonlinear spring constant k2 (the "progressiveness"). This
    > allows you to be supple on small bumps but avoid a harsh top-out on big bumps.
    >
    > Can you tell it's raining here?
    >
    > CC

    Cool. Hey Dr. Science, now can you tell us why the Grid Leak Drip Pan in the final amplifier in
    Tavis' brain is corroded?

    --
    J'm

    To Reply Direct, Remove Clothes. ...-.-
     
  11. J'm Sm'th <[email protected]> wrote
    >
    > Cool. Hey Dr. Science, now can you tell us why the Grid Leak Drip Pan in the final amplifier in
    > Tavis' brain is corroded?

    Cheap oil filter.

    CC
     
  12. Jon Bond

    Jon Bond Guest

    "Michael Dart" <[email protected]> wrote in message news:[email protected]...
    >
    > "Corvus Corvax" <[email protected]> wrote in message
    > news:[email protected]... <snip excellent, albiet lengthly
    > disertation on mechanical physics>
    > >
    > > Can you tell it's raining here?
    > >
    >
    > Yes but what's less apparent is that I took the time to read that whole thing because it's raining
    > here too.
    >
    > Mike

    ditto.

    Jon Bond although the sun just came out - looks like the Allez Pro is going out for a spin
     
  13. Slacker

    Slacker Guest

    "Corvus Corvax" <[email protected]> wrote in message
    news:[email protected]...
    > > > Slacker wrote:
    > > > > Does the oil level have any effect on the preload?
    >
    >
    > Shaun Rimmer wrote:
    > > Technician wrote:
    > > >
    > > > no.
    > >
    > > _YES_
    >
    > No, not normally.
    >
    >
    > Technician wrote:
    > > > preload is in the spring. It generally means how much pressure is put on a spring before it is
    > > > loaded (hence preload).
    >
    > Yes. But this is the last statement Trav makes that has any apparent connection to reality.
    >
    > > > it would be like adding or taking away weights from a backpack that you use to ride
    >
    > No. Preload is not the same thing as being heavier.
    >
    > > > the oil just dampens the motion so you don't go for a bouncy ride.
    >
    > No. Slacker was asking about the oil _height_. Pray tell, how does the oil height affect the
    > damping? The oil _weight_ affects the damping.
    >
    > > > As a fairly risky option, you could alter the spring length. it is a bit

    > > > how many pounds needed to compress the spring 1 inch). then you could calculate out a rough
    > > > figure so you could remove so much spring to sag it so many inches. but like i said, i
    > > > wouldn't recommend it as there are many factors that may need accounting for, and it is a
    > > > shame to ruin a perfectly good spring for a few inches of sag.
    >
    > Trav, does it ever occur to you that it is preferable to shut the hell up when you don't know what
    > you're talking about, instead of standing up and babbling incoherently in public?
    >
    > Shaun wrote:
    > > Imagine this, you have a PET bottle, cap on. Squeeze the bottle. Easy to do, isn't it? Now, take
    > > the cap off and add liquid to the half way point then replace cap. Now squeeze it. Harder to
    > > compress, no? Add more liquid, harder still?
    >
    > Agreed.
    >
    > But then Shaun continued:
    > > Of course it is - this is why the oil level _will_ make 'a' difference to the pre-load.
    >
    > Agh! No! It might change the sag a little, but that's not the same as preload.
    >
    > Time for a short rant on the physics of springs, methinks. A coil spring, sitting all by its
    > lonesome, has a linear force law. This means that the amount of force required to compress the
    > spring a given amount (call it "x") is proportional to the amount the spring is compressed:
    >
    > F = k x
    >
    > Here k is some number that will depend on which spring you use -- for a heavier spring, the force
    > required to compress the spring some amount x will be larger, meaning k will be larger.
    >
    > * First point: changing the spring weight changes the force constant
    > k.
    >
    > "Sag" is just the amount the spring displaces under the force of your weight. If we call your
    > weight W, the sag is just
    >
    > x = W / k
    >
    > Now suppose you want to reduce the amount of sag on a spring without getting a heavier spring
    > (i.e., without changing k?). You preload it. That is, you pre-compress the spring a small amount
    > (we'll call it "x0"). Now the force required to compress the preloaded spring by a distance x is
    >
    > F = k (x + x0)
    >
    > It takes more force to compress a preloaded spring, because it already has a force on it,
    >
    > F0 = k x0
    >
    > So now we can write the sag as:
    >
    > x = (W - F0) / k
    >
    > If your weight W is less than the preload force F0, there is no sag at all! You have to place a
    > minimum force on the spring to get it to start moving. Note that this is _not_ the same thing as
    > changing the spring weight, i.e. changing the force constant k. A very heavy spring with no
    > preload will always sag a little bit under even a small weight. A preloaded spring will not sag at
    > all until the preload force is overcome.
    >
    > * Second point: changing the preload changes the force F0.
    >
    > Now what about oil height? Oil in the fork does two things: first, as Trav rather incoherently
    > pointed out, oil is used for damping. We are not going to discuss damping. But fork oil does
    > something else that is not so obvious: it puts a second spring in your fork. Rather, it is the air
    > on top of the oil that acts like a spring. Compress the air in the fork, and it pushes back. This
    > is what Shaun was talking about.
    >
    > So, really, a coil/oil fork has two springs in it -- the coil spring, and the air in the fork. If
    > you have two springs (call the weights k1 and k2) acting together (in "parallel"), they are
    > equivalent to a single, heavier spring. In terms of the spring constants k1 and k2, the effective
    > spring constant k is just the sum of the individual spring constants:
    >
    > k = k1 + k2
    >
    > and
    >
    > F = k x = (k1 + k2) x
    >
    > So Shaun is right that changing the oil height will have some effect on the sag, but he is wrong
    > in saying that it is preload. It is actually more like changing the weight of the spring. You're
    > messing with k, not with the preload force F0.
    >
    > But there's a catch: the air in the fork is not like the coil spring. It does _not_ have a linear
    > force law F = k2 x. The air in the fork has a nonlinear force law, something like F = k2 x^2.
    > (Here x^2 denotes x squared.) Relative to a linear spring, it is easier to compress the air a
    > little bit, but much harder to compress it a lot. So the force law for a coil + air spring is
    > something more like:
    >
    > F = k1 x + k2 x^2
    >
    > This deviation from a linear force law is called "progressiveness". For small amounts of
    > compression (small bumps), the response of the spring is nice and linear. But when you compress it
    > a lot (big bumps), the force required goes up much faster than linear. This is good, because you
    > can tune the progressiveness so that the fork is responsive on small bumps (tuning the spring
    > weight k1), but won't top out on big bumps (tuning the "air spring" weight k2 by changing the oil
    > height).
    >
    > * Third point: changing the oil height changes the progressiveness, or nonlinear spring
    > constant k2.
    >
    > To sum up, spring weight, preload, and oil height are independent adjustments of a fork. Each does
    > something different:
    >
    > * Changing the spring weight changes the linear force constant k.
    > * Changing the preload adds a static force F0. You use this to reduce sag without getting a
    > heavier spring.
    > * Changing the oil height changes the nonlinear spring constant k2 (the "progressiveness"). This
    > allows you to be supple on small bumps but avoid a harsh top-out on big bumps.
    >
    >
    > Can you tell it's raining here?
    >
    > CC

    Dang, you just brought me back 18 years to my HS math class. Thanks for the lesson!
    --
    Slacker
     
  14. Dave Stocker

    Dave Stocker Guest

    "Corvus Corvax" <[email protected]> schrieb im Newsbeitrag
    news:[email protected]...

    > > > Slacker wrote:
    > > > > Does the oil level have any effect on the preload?
    >
    >
    > Shaun Rimmer wrote:
    > > Technician wrote:
    > > >
    > > > no.
    > >
    > > _YES_
    >
    > No, not normally.
    >

    I would go with no on this one.

    <Snipped for brevety/>

    >
    > Time for a short rant on the physics of springs, methinks. A coil spring, sitting all by its
    > lonesome, has a linear force law. This means that the amount of force required to compress the
    > spring a given amount (call it "x") is proportional to the amount the spring is compressed:
    >
    > F = k x

    And the horse is a shpere, but basically yes. Springs are really only linear in a small region about
    a point (I will call it X1 since you already grabbed X0). We can still reasonably approximate it to
    being linear.

    >
    > Here k is some number that will depend on which spring you use -- for a heavier spring, the force
    > required to compress the spring some amount x will be larger, meaning k will be larger.
    >
    > * First point: changing the spring weight changes the force constant
    > k.
    >
    > "Sag" is just the amount the spring displaces under the force of your weight. If we call your
    > weight W, the sag is just
    >
    > x = W / k

    Agreed.

    >
    > Now suppose you want to reduce the amount of sag on a spring without getting a heavier spring
    > (i.e., without changing k?). You preload it. That is, you pre-compress the spring a small amount
    > (we'll call it "x0"). Now the force required to compress the preloaded spring by a distance x is
    >
    > F = k (x + x0)
    >
    > It takes more force to compress a preloaded spring, because it already has a force on it,
    >
    > F0 = k x0
    >
    > So now we can write the sag as:
    >
    > x = (W - F0) / k
    >
    > If your weight W is less than the preload force F0, there is no sag at all! You have to place a
    > minimum force on the spring to get it to start moving. Note that this is _not_ the same thing as
    > changing the spring weight, i.e. changing the force constant k. A very heavy spring with no
    > preload will always sag a little bit under even a small weight. A preloaded spring will not sag at
    > all until the preload force is overcome.
    >

    I think we need to use this post the next time someone asks: "What does this preload knob do?".

    > * Second point: changing the preload changes the force F0.

    And hence X0.

    >
    > Now what about oil height? Oil in the fork does two things: first, as Trav rather incoherently
    > pointed out, oil is used for damping. We are not going to discuss damping. But fork oil does
    > something else that is not so obvious: it puts a second spring in your fork. Rather, it is the air
    > on top of the oil that acts like a spring. Compress the air in the fork, and it pushes back. This
    > is what Shaun was talking about.
    >
    > So, really, a coil/oil fork has two springs in it -- the coil spring, and the air in the fork. If
    > you have two springs (call the weights k1 and k2) acting together (in "parallel"), they are
    > equivalent to a single, heavier spring. In terms of the spring constants k1 and k2, the effective
    > spring constant k is just the sum of the individual spring constants:
    >
    > k = k1 + k2
    >
    > and
    >
    > F = k x = (k1 + k2) x
    >

    Uh huh.

    > So Shaun is right that changing the oil height will have some effect on the sag, but he is wrong
    > in saying that it is preload. It is actually more like changing the weight of the spring. You're
    > messing with k, not with the preload force F0.
    >
    > But there's a catch: the air in the fork is not like the coil spring. It does _not_ have a linear
    > force law F = k2 x. The air in the fork has a nonlinear force law, something like F = k2 x^2.
    > (Here x^2 denotes x squared.) Relative to a linear spring, it is easier to compress the air a
    > little bit, but much harder to compress it a lot. So the force law for a coil + air spring is
    > something more like:
    >
    > F = k1 x + k2 x^2
    >

    Ohhh baby, a quadratic equation. BTW- I am 100% agreement with your analysis.

    > This deviation from a linear force law is called "progressiveness". For small amounts of
    > compression (small bumps), the response of the spring is nice and linear. But when you compress it
    > a lot (big bumps), the force required goes up much faster than linear. This is good, because you
    > can tune the progressiveness so that the fork is responsive on small bumps (tuning the spring
    > weight k1), but won't top out on big bumps (tuning the "air spring" weight k2 by changing the oil
    > height).
    >
    > * Third point: changing the oil height changes the progressiveness, or nonlinear spring
    > constant k2.
    >
    > To sum up, spring weight, preload, and oil height are independent adjustments of a fork. Each does
    > something different:
    >
    > * Changing the spring weight changes the linear force constant k.
    > * Changing the preload adds a static force F0. You use this to reduce sag without getting a
    > heavier spring.
    > * Changing the oil height changes the nonlinear spring constant k2 (the "progressiveness"). This
    > allows you to be supple on small bumps but avoid a harsh top-out on big bumps.
    >
    >
    > Can you tell it's raining here?
    >
    > CC

    Next time kids, we will approximate hitting a rock F(t) as a delta function and solve the
    rebound problem.

    -Dave
     
  15. Dave Stocker

    Dave Stocker Guest

    "Michael Dart" <[email protected]> schrieb im Newsbeitrag news:[email protected]...
    >
    > "Corvus Corvax" <[email protected]> wrote in message
    > news:[email protected]... <snip excellent, albiet lengthly
    > disertation on mechanical physics>
    > >
    > > Can you tell it's raining here?
    > >
    >
    > Yes but what's less apparent is that I took the time to read that whole thing because it's raining
    > here too.
    >

    It is a beautiful cool sunny morning here, but no way in hell am I riding before I have finished
    my coffee!

    -Dave
     
  16. Westie

    Westie Guest

    "Shaun Rimmer" <[email protected]> wrote in message
    news:[email protected]...
    >
    > Corvus Corvax <[email protected]> wrote in message
    > news:[email protected]...
    > > > > Slacker wrote:
    > > > > > Does the oil level have any effect on the preload?
    > >
    > >
    > > Shaun Rimmer wrote:
    > > > Technician wrote:
    > > > >
    > > > > no.
    > > >
    > > > _YES_
    > >
    > > No, not normally.
    >
    > OK - I'll address this further down.
    >
    > > Technician wrote:
    > > > > preload is in the spring. It generally means how much pressure is
    put
    > on
    > > > > a spring before it is loaded (hence preload).
    > >
    > > Yes. But this is the last statement Trav makes that has any apparent connection to reality.
    <snip the whole kit and kaboodle>

    Umm, OK. I think that I followed that. The first practical thing that occurred to me as I read
    Trav's stuff was that a snipped spring simply won't work when you put it back into the forks.
    Doesn't fit properly. Too short, isn't it? Therefore, there's no k to begin with.... Other than
    that, I really enjoyed all that science and fizics stuff.
    --
    Westie
     
  17. Westie

    Westie Guest

    "Dave Stocker" <[email protected]> wrote in message news:[email protected]...
    > "Corvus Corvax" <[email protected]> schrieb im Newsbeitrag
    > news:[email protected]...
    <snip>

    > Next time kids, we will approximate hitting a rock F(t) as a delta
    function
    > and solve the rebound problem.
    >
    Sounds like fun. Who are we hitting it with? If it's MV, you know that you'll never be able to prove
    a delta function is involved? Westie
     
  18. "Westie" <[email protected]> wrote
    >
    > The first practical thing that occurred to me as I read Trav's stuff was that a snipped spring
    > simply won't work when you put it back into the forks. Doesn't fit properly.

    Exercise for the student: suppose you took an 80mm fork spring and cut it in half. You'd end up with
    a fork with 40mm travel -- but what would the stiffness (spring constant k) of the 40mm pieces be
    relative to the original 80mm spring?

    If Baker and Hickey can't answer this one off the tops of their heads I will be very
    disappointed. ;-)

    CC
     
  19. Dave Stocker

    Dave Stocker Guest

    "Corvus Corvax" <[email protected]> schrieb im Newsbeitrag
    news:[email protected]...
    > "Westie" <[email protected]> wrote
    > >
    > > The first practical thing that occurred to me as I read Trav's stuff was that a snipped spring
    > > simply won't work when you put it back into the
    forks.
    > > Doesn't fit properly.
    >
    > Exercise for the student: suppose you took an 80mm fork spring and cut it in half. You'd end up
    > with a fork with 40mm travel -- but what would the stiffness (spring constant k) of the 40mm
    > pieces be relative to the original 80mm spring?
    >
    > If Baker and Hickey can't answer this one off the tops of their heads I will be very
    > disappointed. ;-)
    >

    OK, here is my guess: Since a given mm of travel would deform this spring twice as much the 80mm
    version (relative to its original length that is), I would venture to guess that k is doubled.

    -Dave
     
  20. Shaun Rimmer

    Shaun Rimmer Guest

    Corvus Corvax <[email protected]> wrote in message
    news:[email protected]...
    > J'm Sm'th <[email protected]> wrote
    > >
    > > Cool. Hey Dr. Science, now can you tell us why the Grid Leak Drip Pan
    in the
    > > final amplifier in Tavis' brain is corroded?
    >
    > Cheap oil filter.
    >
    > CC

    I am going to laugh out loud now - 'LOL' Heheheheh..............ahem.

    Shaun aRe
     
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