Slime Tube Drag Test

Discussion in 'Cycling Equipment' started by [email protected], Dec 13, 2004.

  1. Another current thread on Slime tubes led me to waste an
    hour happily playing with an upside-down bicycle, a
    rear-wheel speedometer, and a stopwatch.

    First, I cranked the tire with a normal inner tube twenty
    times up to 35-40 mph and timed how long it took to spin
    down from around 30 mph to around 10 mph.

    Even with a speedometer reading in tenths of a mile per
    hour, it's hard to start and stop because the speedometer
    samples over a short time as the magnet spins past and then
    shows the latest average.

    Around 30 mph, the figures fall at about 1 mph or a little
    more every time. By the time the speed has dropped to 10
    mph, there are about two readings per mph.

    Waiting for the wheel to spin down any further would
    probably decrease even rough accuracy, since the magnet is
    spinning slower and slower past the sensor.

    Given the lack of precision and the length of time, I
    rounded to the nearest second on the stopwatch.

    After twenty spins, I pulled the normal tube out, stuffed in
    a Slime tube, and did it all again.

    http://home.comcast.net/~carlfogel/download/slime.txt

    http://home.comcast.net/~carlfogel/download/slime.wk1

    As expected, the heavier Slime tube took noticeably longer
    to spin down, the greater mass having greater inertia,
    averaging 1.96 seconds for each mph lost, versus only 1.67
    seconds for the lighter normal tube.

    This supports Jobst Brandt's prediction in the other thread
    that the liquid Slime isn't so much sloshing around and
    adding friction as plastering itself around the outer curve
    of the tube.

    What's curious is that about 70 grams of Slime smoothed
    things out impressively. The seconds/mph-lost varied wildly
    on the normal tube, producing a jagged graph compared to the
    Slime tube's almost level graph.

    I'm curious why a little liquid would smooth things out so
    dramatically. It doesn't seem as if 70 grams would have much
    of flywheel effect on what's probably a 2000 gram or more
    wheel and tire, so maybe some kind of friction is involved?

    Tomorrow, I'll probably weigh things, which might matter.

    The plain text of the results is below.

    Carl Fogel

    plain tube

    max 30.80 10.90 36.00 20.80 1.87
    avg 29.81 10.04 32.95 19.77 1.67
    min 28.70 9.60 29.00 18.60 1.40

    start stop speed sec/
    speed speed time range mph

    #01 28.7 10.1 34 18.6 1.83
    #02 29.4 9.8 36 19.6 1.84
    #03 28.9 10.1 32 18.8 1.70
    #04 29.1 10.3 32 18.8 1.70
    #05 30.1 10.0 31 20.1 1.54
    #06 30.6 9.9 29 20.7 1.40
    #07 29.9 10.0 30 19.9 1.51
    #08 29.2 10.0 30 19.2 1.56
    #09 30.6 9.8 34 20.8 1.63
    #10 28.9 10.0 32 18.9 1.69
    #11 29.7 10.0 33 19.7 1.68
    #12 29.1 9.9 32 19.2 1.67
    #13 30.4 10.0 33 20.4 1.62
    #14 30.6 10.0 35 20.6 1.70
    #15 29.7 9.6 36 20.1 1.79
    #16 30.8 10.9 32 19.9 1.61
    #17 30.8 10.3 33 20.5 1.61
    #18 30.4 10.3 34 20.1 1.69
    #19 30.1 9.9 35 20.2 1.73
    #20 29.1 9.9 36 19.2 1.87


    slime tube

    max 30.80 10.80 40.00 20.80 2.03
    avg 29.78 10.24 38.20 19.54 1.96
    min 28.90 9.80 36.00 18.30 1.83

    start stop speed sec/
    speed speed time range mph

    #01 29.9 10.2 36 19.7 1.83
    #02 30.4 10.0 38 20.4 1.86
    #03 28.9 9.8 38 19.1 1.99
    #04 30.1 10.2 38 19.9 1.91
    #05 29.6 10.0 38 19.6 1.94
    #06 29.4 10.1 38 19.3 1.97
    #07 29.9 10.3 38 19.6 1.94
    #08 29.4 10.3 38 19.1 1.99
    #09 29.6 10.0 38 19.6 1.94
    #10 30.8 10.0 40 20.8 1.92
    #11 29.9 10.3 38 19.6 1.94
    #12 29.1 10.8 36 18.3 1.97
    #13 29.9 10.6 38 19.3 1.97
    #14 30.1 10.6 38 19.5 1.95
    #15 29.9 10.5 38 19.4 1.96
    #16 29.4 10.3 38 19.1 1.99
    #17 29.9 10.1 40 19.8 2.02
    #18 29.7 10.0 40 19.7 2.03
    #19 29.2 10.5 38 18.7 2.03
    #20 30.4 10.2 40 20.2 1.98
     
    Tags:


  2. Leo Lichtman

    Leo Lichtman Guest

    <[email protected]> wrote: (clip) Even with a speedometer reading in
    tenths of a mile per hour, it's hard to start and stop because the
    speedometer samples over a short time as the magnet spins past and then
    shows the latest average.(clip)
    ^^^^^^^^^^^^^
    Carl, if you want to improve on the sampling times/averages, I suggest that
    you add additional magnets to the wheel. If you want the display to read in
    true MPH, you would then have to adjust the input circumference to the
    computer. Or you could just compare the numbers, and ignore the fact that
    they are not true MPH. Just an idea.
     
  3. god bless slime!

    yeah-wheel weights!

    picture Fogelsville's badly trued wheel wobbling left right left right
    as the rim spins on the axle bashing Carl's bearings ellipsoidal.
    the wobble left from a mean true circumference is countered by the
    slime's weight not completely connected to the tube's inside surface.
    this is good. two for one.

    as for the gram's. i picked up a substantial increase in speed from a 9
    gram tube weight reduction. Dura-ace!! weight is money. weight is
    psychological.
     
  4. conservation of momentum!!
     
  5. Tom Sherman

    Tom Sherman Guest

    [email protected] wrote:

    > conservation of momentum!!


    Monumental conversation!

    --
    Tom Sherman - Rock Island County Illinois
    Tetrahedral carbon lattices are not forever.
     
  6. On Mon, 13 Dec 2004 01:23:18 -0700, [email protected]
    wrote:

    [snip]

    Several people asked for a picture of the graph:

    http://home.comcast.net/~carlfogel/download/slime.jpg

    For the lighter normal inner tube, the seconds/mph-lost is
    the pink line and varies a good deal. For the heavier Slime
    tube, the line is blue and much smoother. (By sheer luck,
    both sets of data started out with the same result for the
    first of twenty samples.)

    I still have no idea why adding such a small liquid mass
    reduced the variation so noticeably.

    With no quick-release skewer or tube, the rear wheel and
    tire weighed 1.840 kg.

    With a 0.095 kg normal tube from Schwinn, the wheel with no
    quick-release skewer weighed 1.935 kg.

    With a 0.175 kg Slime tube, the same rear wheel with no
    quick-release skewer weighed 2.015 kg, about 4% more.

    On average, the wheel took 1.67 seconds to lose 1 mph
    spinning down from around 30 mph to 10 mph with the lighter
    inner tube, while the heavier Slime tube took 1.96 seconds
    to lose 1 mph--about 17% longer, which shows how non-linear
    aerodynamics are, wind drag on the 36 spokes being the only
    significant braking force.

    Again, the results suggest that any movement of the liquid
    slime isn't producing much frictional drag, since increasing
    the mass only 4% out at the rim produced a 17% longer
    spin-down time. I may waste even more time and stuff 80
    grams of inner-tube strip in with the normal tube and see
    how long it takes to spin down compared to the slime
    tube--any difference would be due to frictional losses, but
    I suspect that they'll be too small to measure by this
    method.

    Carl Fogel
     
  7. Ted

    Ted Guest

    Tom Sherman <[email protected]> wrote:

    > [email protected] wrote:
    >
    > > conservation of momentum!!

    >
    > Monumental conversation!


    Okay, Tom, you now owe me a fresh cup of coffee and a new keyboard.

    --
    Ted Bennett
    Portland, OR
     
  8. R15757

    R15757 Guest

    Carl Fogeled in part:

    > I may waste even more time and stuff 80
    >grams of inner-tube strip in with the normal tube and see
    >how long it takes to spin down compared to the slime
    >tube--any difference would be due to frictional losses, but
    >I suspect that they'll be too small to measure by this
    >method.


    Carl, maybe you should try the same
    experiment with two different tires,
    with similar surfaces but with one tire
    about 4% heavier than the other, no slime
    tubes, and see if
    you get similar results.

    Robert
     
  9. Ron Hardin

    Ron Hardin Guest

    The drag will have some peculiar swerves. If the stuff doesn't move,
    or doesn't have time to move far, it won't produce any drag. So
    at high speed, it won't hurt at all.

    At almost zero speed, it's moving slowly, and won't produce much drag
    for that reason (not taking up much energy because nothing much is
    happening).

    Somewhere in the middle is the speed where it does the most energy
    soak-up. Whether that's well below normal bike speeds or not I don't
    know. It seems likely that it is, though.

    The drag comes as an indirect effect of your lifting it off the
    road level and it sliding back down, meaning you spend more time
    lifting it up than it coasting down the other side and pushing you.

    A lot depends on how far it slides back down and thus on how fast you're
    going.
    --
    Ron Hardin
    [email protected]

    On the internet, nobody knows you're a jerk.
     
  10. I still have no idea why adding such a small liquid mass( a trap)
    reduced the variation so noticeably:
    friction damping loss inside the rim is less than gains in less bearing
    bashing
     
  11. On Mon, 13 Dec 2004 01:23:18 -0700, [email protected]
    wrote:

    I've updated the worksheet and chart picture files. They now
    show how long the same wheel and tire took to spin down 20
    times from about 30 mph to about 10 mph in seconds with a
    normal inner tube, an 80-gram heavier Slime tube, and now
    with the normal inner tube plus an 80-gram section of split
    inner tube:

    http://home.comcast.net/~carlfogel/download/slime.wk1

    http://home.comcast.net/~carlfogel/download/slime.jpg

    The figures to look at are the seconds/mph-lost, since the
    starting and stopping speeds vary.

    The light normal tube spun down quickest and varied
    considerably: 1.67 seconds/mph-lost.

    The Slime tube with the added liquid took noticeably longer
    (80 grams more mass) and varied much less in how long it
    took to spin down: 1.96 seconds/mph-lost.

    The normal tube plus an 80-gram section from another inner
    tube took even longer to spin down: 2.03 seconds/mph-lost.

    This suggests that there is a slight frictional drag from
    the liquid--when the extra 80 grams of mass is liquid, the
    wheel slows down more quickly.

    Of course, it's worth pointing out that the forces and drag
    involved are absurdly small--the wheel cranks up by hand to
    35-40 mph easily, it takes 33-42 seconds of wind drag to
    spin down from around 30 mph to around 10 mph, and you can
    stop it instantly with your bare hand. Without a stopwatch
    and all this fuss, the difference would not be noticeable
    (try to hit a covered stopwatch at 30 versus 40 seconds
    without consciously counting).

    This suggests that riders are not likely to notice such
    small differences in wheel weights in blind testing, since
    the hard-to-distinguish behavior of the kg of the wheel
    would be swamped by the 70 kg or so of bike and rider, plus
    the vagaries of the road and breeze.

    The text of the 3-tube chart is below.

    Carl Fogel

    plain tube

    max 30.80 10.90 36.00 20.80 1.87
    avg 29.81 10.04 32.95 19.77 1.67
    min 28.70 9.60 29.00 18.60 1.40

    start stop speed sec/
    speed speed time range mph

    #01 28.7 10.1 34 18.6 1.83
    #02 29.4 9.8 36 19.6 1.84
    #03 28.9 10.1 32 18.8 1.70
    #04 29.1 10.3 32 18.8 1.70
    #05 30.1 10.0 31 20.1 1.54
    #06 30.6 9.9 29 20.7 1.40
    #07 29.9 10.0 30 19.9 1.51
    #08 29.2 10.0 30 19.2 1.56
    #09 30.6 9.8 34 20.8 1.63
    #10 28.9 10.0 32 18.9 1.69
    #11 29.7 10.0 33 19.7 1.68
    #12 29.1 9.9 32 19.2 1.67
    #13 30.4 10.0 33 20.4 1.62
    #14 30.6 10.0 35 20.6 1.70
    #15 29.7 9.6 36 20.1 1.79
    #16 30.8 10.9 32 19.9 1.61
    #17 30.8 10.3 33 20.5 1.61
    #18 30.4 10.3 34 20.1 1.69
    #19 30.1 9.9 35 20.2 1.73
    #20 29.1 9.9 36 19.2 1.87
    0

    slime tube

    max 30.80 10.80 40.00 20.80 2.03
    avg 29.78 10.24 38.20 19.54 1.96
    min 28.90 9.80 36.00 18.30 1.83

    start stop speed sec/
    speed speed time range mph

    #01 29.9 10.2 36 19.7 1.83
    #02 30.4 10.0 38 20.4 1.86
    #03 28.9 9.8 38 19.1 1.99
    #04 30.1 10.2 38 19.9 1.91
    #05 29.6 10.0 38 19.6 1.94
    #06 29.4 10.1 38 19.3 1.97
    #07 29.9 10.3 38 19.6 1.94
    #08 29.4 10.3 38 19.1 1.99
    #09 29.6 10.0 38 19.6 1.94
    #10 30.8 10.0 40 20.8 1.92
    #11 29.9 10.3 38 19.6 1.94
    #12 29.1 10.8 36 18.3 1.97
    #13 29.9 10.6 38 19.3 1.97
    #14 30.1 10.6 38 19.5 1.95
    #15 29.9 10.5 38 19.4 1.96
    #16 29.4 10.3 38 19.1 1.99
    #17 29.9 10.1 40 19.8 2.02
    #18 29.7 10.0 40 19.7 2.03
    #19 29.2 10.5 38 18.7 2.03
    #20 30.4 10.2 40 20.2 1.98
    0

    plain tube + 80 gram inner tube strip

    max 30.60 10.80 42.00 20.30 2.14
    avg 29.96 10.41 39.75 19.55 2.03
    min 29.10 10.00 36.00 18.60 1.92

    start stop speed sec/
    speed speed time range mph

    #01 29.1 10.5 36 18.6 1.94
    #02 29.5 10.8 36 18.7 1.93
    #03 30.4 10.6 38 19.8 1.92
    #04 29.1 10.4 38 18.7 2.03
    #05 30.1 10.1 39 20.0 1.95
    #06 30.1 10.3 40 19.8 2.02
    #07 29.6 10.7 38 18.9 2.01
    #08 29.9 10.2 40 19.7 2.03
    #09 29.7 10.4 40 19.3 2.07
    #10 30.1 10.0 41 20.1 2.04
    #11 29.9 10.4 40 19.5 2.05
    #12 29.7 10.5 41 19.2 2.14
    #13 30.6 10.7 40 19.9 2.01
    #14 30.1 10.0 42 20.1 2.09
    #15 29.9 10.6 40 19.3 2.07
    #16 30.4 10.5 40 19.9 2.01
    #17 30.1 10.7 40 19.4 2.06
    #18 30.1 10.2 42 19.9 2.11
    #19 30.1 10.2 42 19.9 2.11
    #20 30.6 10.3 42 20.3 2.07
    0
     
  12. <[email protected]> wrote in message
    news:[email protected]
    > On Mon, 13 Dec 2004 01:23:18 -0700, [email protected]
    > wrote:
    >
    > I've updated the worksheet and chart picture files. They now
    > show how long the same wheel and tire took to spin down 20
    > times from about 30 mph to about 10 mph in seconds with a
    > normal inner tube, an 80-gram heavier Slime tube, and now
    > with the normal inner tube plus an 80-gram section of split
    > inner tube:
    >
    > http://home.comcast.net/~carlfogel/download/slime.wk1
    >
    > http://home.comcast.net/~carlfogel/download/slime.jpg
    >
    > The figures to look at are the seconds/mph-lost, since the
    > starting and stopping speeds vary.
    >
    > The light normal tube spun down quickest and varied
    > considerably: 1.67 seconds/mph-lost.
    >
    > The Slime tube with the added liquid took noticeably longer
    > (80 grams more mass) and varied much less in how long it
    > took to spin down: 1.96 seconds/mph-lost.
    >
    > The normal tube plus an 80-gram section from another inner
    > tube took even longer to spin down: 2.03 seconds/mph-lost.
    >
    > This suggests that there is a slight frictional drag from
    > the liquid--when the extra 80 grams of mass is liquid, the
    > wheel slows down more quickly.
    >
    > Of course, it's worth pointing out that the forces and drag
    > involved are absurdly small--the wheel cranks up by hand to
    > 35-40 mph easily, it takes 33-42 seconds of wind drag to
    > spin down from around 30 mph to around 10 mph, and you can
    > stop it instantly with your bare hand. Without a stopwatch
    > and all this fuss, the difference would not be noticeable
    > (try to hit a covered stopwatch at 30 versus 40 seconds
    > without consciously counting).
    >
    > This suggests that riders are not likely to notice such
    > small differences in wheel weights in blind testing, since
    > the hard-to-distinguish behavior of the kg of the wheel
    > would be swamped by the 70 kg or so of bike and rider, plus
    > the vagaries of the road and breeze.
    >
    > The text of the 3-tube chart is below.
    >
    > Carl Fogel
    >
    > plain tube
    >
    > max 30.80 10.90 36.00 20.80 1.87
    > avg 29.81 10.04 32.95 19.77 1.67
    > min 28.70 9.60 29.00 18.60 1.40
    >
    > start stop speed sec/
    > speed speed time range mph
    >
    > #01 28.7 10.1 34 18.6 1.83
    > #02 29.4 9.8 36 19.6 1.84
    > #03 28.9 10.1 32 18.8 1.70
    > #04 29.1 10.3 32 18.8 1.70
    > #05 30.1 10.0 31 20.1 1.54
    > #06 30.6 9.9 29 20.7 1.40
    > #07 29.9 10.0 30 19.9 1.51
    > #08 29.2 10.0 30 19.2 1.56
    > #09 30.6 9.8 34 20.8 1.63
    > #10 28.9 10.0 32 18.9 1.69
    > #11 29.7 10.0 33 19.7 1.68
    > #12 29.1 9.9 32 19.2 1.67
    > #13 30.4 10.0 33 20.4 1.62
    > #14 30.6 10.0 35 20.6 1.70
    > #15 29.7 9.6 36 20.1 1.79
    > #16 30.8 10.9 32 19.9 1.61
    > #17 30.8 10.3 33 20.5 1.61
    > #18 30.4 10.3 34 20.1 1.69
    > #19 30.1 9.9 35 20.2 1.73
    > #20 29.1 9.9 36 19.2 1.87
    > 0
    >
    > slime tube
    >
    > max 30.80 10.80 40.00 20.80 2.03
    > avg 29.78 10.24 38.20 19.54 1.96
    > min 28.90 9.80 36.00 18.30 1.83
    >
    > start stop speed sec/
    > speed speed time range mph
    >
    > #01 29.9 10.2 36 19.7 1.83
    > #02 30.4 10.0 38 20.4 1.86
    > #03 28.9 9.8 38 19.1 1.99
    > #04 30.1 10.2 38 19.9 1.91
    > #05 29.6 10.0 38 19.6 1.94
    > #06 29.4 10.1 38 19.3 1.97
    > #07 29.9 10.3 38 19.6 1.94
    > #08 29.4 10.3 38 19.1 1.99
    > #09 29.6 10.0 38 19.6 1.94
    > #10 30.8 10.0 40 20.8 1.92
    > #11 29.9 10.3 38 19.6 1.94
    > #12 29.1 10.8 36 18.3 1.97
    > #13 29.9 10.6 38 19.3 1.97
    > #14 30.1 10.6 38 19.5 1.95
    > #15 29.9 10.5 38 19.4 1.96
    > #16 29.4 10.3 38 19.1 1.99
    > #17 29.9 10.1 40 19.8 2.02
    > #18 29.7 10.0 40 19.7 2.03
    > #19 29.2 10.5 38 18.7 2.03
    > #20 30.4 10.2 40 20.2 1.98
    > 0
    >
    > plain tube + 80 gram inner tube strip
    >
    > max 30.60 10.80 42.00 20.30 2.14
    > avg 29.96 10.41 39.75 19.55 2.03
    > min 29.10 10.00 36.00 18.60 1.92
    >
    > start stop speed sec/
    > speed speed time range mph
    >
    > #01 29.1 10.5 36 18.6 1.94
    > #02 29.5 10.8 36 18.7 1.93
    > #03 30.4 10.6 38 19.8 1.92
    > #04 29.1 10.4 38 18.7 2.03
    > #05 30.1 10.1 39 20.0 1.95
    > #06 30.1 10.3 40 19.8 2.02
    > #07 29.6 10.7 38 18.9 2.01
    > #08 29.9 10.2 40 19.7 2.03
    > #09 29.7 10.4 40 19.3 2.07
    > #10 30.1 10.0 41 20.1 2.04
    > #11 29.9 10.4 40 19.5 2.05
    > #12 29.7 10.5 41 19.2 2.14
    > #13 30.6 10.7 40 19.9 2.01
    > #14 30.1 10.0 42 20.1 2.09
    > #15 29.9 10.6 40 19.3 2.07
    > #16 30.4 10.5 40 19.9 2.01
    > #17 30.1 10.7 40 19.4 2.06
    > #18 30.1 10.2 42 19.9 2.11
    > #19 30.1 10.2 42 19.9 2.11
    > #20 30.6 10.3 42 20.3 2.07
    > 0
    >


    A Slime Tube Drag Test?
    What for?
    -tom
     
  13. On Fri, 17 Dec 2004 08:08:17 -0800, "Tom Nakashima"
    <[email protected]> wrote:

    [snip]

    >A Slime Tube Drag Test?
    >What for?
    >-tom


    Dear Tom,

    In a related recent thread, the claim was made that the
    addition of a few ounces of slime turned a "nice, light,
    lively bike" into "a pig"--the poster was convinced that
    there was a marked difference in acceleration due to the
    extra rotating mass.

    I was dubious, since the amount worked out to about a 5%
    increase in mass on 3kg of wheels, which in turn were about
    4% of the total 75 kg of bike and rider. It seemed more
    likely to be a psychological effect--the poster rode his
    wife's fairly similar bike, thought that it felt different
    than his bike, learned that Slime had been added, installed
    non-Slime tires, and naturally felt a tremendous difference,
    just as a clean, well-oiled chain makes a large difference
    in almost everything except tests for power transmission.

    I was curious what kind of difference adding a few ounces of
    Slime actually makes, so I hand-cranked an upside-down spare
    bike's rear wheel twenty times after fitting a speedometer
    and timed how long it took to spin down from around 30 mph
    to about 10 mph.

    Then I installed a heavier Slime tube and did the same
    thing. Reassuringly, the heavier tube listened to Newton and
    took longer to spin down, suggesting that more mass at the
    same speed has more momentum. But the increase from around
    33 to only about 38 seconds on such a delicate test (air
    drag on the spokes was practically the only braking force)
    suggests that the small increase in rotating mass would not
    be noticeable to a rider--touch the spinning tire gently
    once with your finger, and the results would change
    dramatically.

    Oddly, the Slime tube's twenty times were much more regular
    than the times for the normal tube--the graph for the spin
    down time rates (seconds/mph-lost) is much more level for
    the slightly heavier tube.

    It could be that the extra mass simply smoothed things out,
    a flywheel effect, but the amount seemed awfully small for
    such a noticeable improvement in regularity. I wondered why
    adding under a hundred grams of Slime would make a tire spin
    down so much more evenly.

    Slime is lurid green liquid, so a question also arose about
    how much frictional drag might be involved as the liquid
    slithered endlessly inside the tube due to gravity. Jobst
    Brandt predicted that the liquid would be plastered to the
    tube at normal speeds and doing nothing, so I had to find
    out.

    I did twenty more tests with the original normal inner tube
    wrapped inside an 80-gram sleeve made from another tube--the
    same rotating mass as the Slime tube in the same place. Any
    difference in times would be due to the lack of liquid
    frictional drag.

    I predicted that there might be a difference, but that it
    would be too small to measure reliably with such crude
    equipment. Like many of my predictions, this one was wrong.

    The rear wheel with a dry normal tube spun down quickest,
    taking about 33 seconds to drop from 30 mph to 10 mph, at an
    average rate of 1.67 seconds for every mph lost. Lighter
    objects have less momentum.

    The 80-gram heavier Slime tube took longer to spin down,
    about 38 seconds per run, at an average rate of 1.96
    seconds/mph-lost.

    A dry tube with a rubber sleeve added to match the weight of
    the Slime took even longer to spin down--about 40 seconds
    per run, an average rate of 2.03 seconds/mph-lost.

    So hidden inside the tube, the Slime endlessly flowing or
    dripping adds a small but detectable drag--the Slime wheel
    slows down from 30 to 10 mph about two seconds faster than a
    wheel with a dry inner tube of the same mass.

    It seems likely that this friction, tiny though it is,
    accounts for the oddly improved regularity of the Slime
    tube's spin-down time. The times for both dry tubes varied
    much more. (My notes for the Slime tests include the comment
    "this is getting silly" after six 38-second results in a
    row, referring only, of course, to the regularity, not the
    testing itself.)

    Thus "Principia Slimata" demonstrates (to the ineffable
    advancement of human knowledge) that adding Slime to inner
    tubes does indeed reduce acceleration, but not enough for a
    rider to notice, even though the extra mass not only suffers
    the disadvantage of being rotating mass, but also the
    horrors of being liquid and producing a measurable
    frictional drag.

    In other words, riders who think that they can detect the
    extra few ounces of rotating mass holding them back are
    probably mistaken (try to detect the difference in spin-down
    times without a stop-watch), Jobst was faintly mistaken in
    predicting that the Slime would plaster itself against the
    tube and not produce frictional drag (38 seconds versus 40
    seconds in a ridiculously delicate test), and I proved
    myself dead wrong in predicting that the high-precision test
    equipment at Fogel Labs would be unable to measure the drag
    of Slime sloshing around in an inner tube.

    I expect that Michelson and Morley felt much the same sense
    of triumph after they finished playing with flashlights on
    that stone slab floating in the pool of mercury.

    Carl Fogel
     
  14. Bill Sornson

    Bill Sornson Guest

    [email protected] wrote:
    > On Fri, 17 Dec 2004 08:08:17 -0800, "Tom Nakashima"
    > <[email protected]> wrote:
    >
    > [snip]
    >
    >> A Slime Tube Drag Test?
    >> What for?
    >> -tom

    >
    > Dear Tom,
    >
    > In a related recent thread, the claim was made that the
    > addition of a few ounces of slime turned a "nice, light,
    > lively bike" into "a pig"--the poster was convinced that
    > there was a marked difference in acceleration due to the
    > extra rotating mass.
    >
    > I was dubious, since the amount worked out to about a 5%
    > increase in mass on 3kg of wheels, which in turn were about
    > 4% of the total 75 kg of bike and rider. It seemed more
    > likely to be a psychological effect--the poster rode his
    > wife's fairly similar bike, thought that it felt different
    > than his bike, learned that Slime had been added, installed
    > non-Slime tires, and naturally felt a tremendous difference,
    > just as a clean, well-oiled chain makes a large difference
    > in almost everything except tests for power transmission.
    >
    > I was curious what kind of difference adding a few ounces of
    > Slime actually makes, so I hand-cranked an upside-down spare
    > bike's rear wheel twenty times after fitting a speedometer
    > and timed how long it took to spin down from around 30 mph
    > to about 10 mph.
    >
    > Then I installed a heavier Slime tube and did the same
    > thing. Reassuringly, the heavier tube listened to Newton and
    > took longer to spin down, suggesting that more mass at the
    > same speed has more momentum. But the increase from around
    > 33 to only about 38 seconds on such a delicate test (air
    > drag on the spokes was practically the only braking force)
    > suggests that the small increase in rotating mass would not
    > be noticeable to a rider--touch the spinning tire gently
    > once with your finger, and the results would change
    > dramatically.
    >
    > Oddly, the Slime tube's twenty times were much more regular
    > than the times for the normal tube--the graph for the spin
    > down time rates (seconds/mph-lost) is much more level for
    > the slightly heavier tube.
    >
    > It could be that the extra mass simply smoothed things out,
    > a flywheel effect, but the amount seemed awfully small for
    > such a noticeable improvement in regularity. I wondered why
    > adding under a hundred grams of Slime would make a tire spin
    > down so much more evenly.
    >
    > Slime is lurid green liquid, so a question also arose about
    > how much frictional drag might be involved as the liquid
    > slithered endlessly inside the tube due to gravity. Jobst
    > Brandt predicted that the liquid would be plastered to the
    > tube at normal speeds and doing nothing, so I had to find
    > out.
    >
    > I did twenty more tests with the original normal inner tube
    > wrapped inside an 80-gram sleeve made from another tube--the
    > same rotating mass as the Slime tube in the same place. Any
    > difference in times would be due to the lack of liquid
    > frictional drag.
    >
    > I predicted that there might be a difference, but that it
    > would be too small to measure reliably with such crude
    > equipment. Like many of my predictions, this one was wrong.
    >
    > The rear wheel with a dry normal tube spun down quickest,
    > taking about 33 seconds to drop from 30 mph to 10 mph, at an
    > average rate of 1.67 seconds for every mph lost. Lighter
    > objects have less momentum.
    >
    > The 80-gram heavier Slime tube took longer to spin down,
    > about 38 seconds per run, at an average rate of 1.96
    > seconds/mph-lost.
    >
    > A dry tube with a rubber sleeve added to match the weight of
    > the Slime took even longer to spin down--about 40 seconds
    > per run, an average rate of 2.03 seconds/mph-lost.
    >
    > So hidden inside the tube, the Slime endlessly flowing or
    > dripping adds a small but detectable drag--the Slime wheel
    > slows down from 30 to 10 mph about two seconds faster than a
    > wheel with a dry inner tube of the same mass.
    >
    > It seems likely that this friction, tiny though it is,
    > accounts for the oddly improved regularity of the Slime
    > tube's spin-down time. The times for both dry tubes varied
    > much more. (My notes for the Slime tests include the comment
    > "this is getting silly" after six 38-second results in a
    > row, referring only, of course, to the regularity, not the
    > testing itself.)
    >
    > Thus "Principia Slimata" demonstrates (to the ineffable
    > advancement of human knowledge) that adding Slime to inner
    > tubes does indeed reduce acceleration, but not enough for a
    > rider to notice, even though the extra mass not only suffers
    > the disadvantage of being rotating mass, but also the
    > horrors of being liquid and producing a measurable
    > frictional drag.
    >
    > In other words, riders who think that they can detect the
    > extra few ounces of rotating mass holding them back are
    > probably mistaken (try to detect the difference in spin-down
    > times without a stop-watch), Jobst was faintly mistaken in
    > predicting that the Slime would plaster itself against the
    > tube and not produce frictional drag (38 seconds versus 40
    > seconds in a ridiculously delicate test), and I proved
    > myself dead wrong in predicting that the high-precision test
    > equipment at Fogel Labs would be unable to measure the drag
    > of Slime sloshing around in an inner tube.
    >
    > I expect that Michelson and Morley felt much the same sense
    > of triumph after they finished playing with flashlights on
    > that stone slab floating in the pool of mercury.


    Oh.

    I though a "Slime Tube Drag Test" was a competition among Arizona mountain
    bikers wearing dresses.

    Bill "always looking for simple explanations" S.
     
  15. B.B.

    B.B. Guest

    In article <[email protected]>,
    [email protected] wrote:

    >I still have no idea why adding such a small liquid mass
    >reduced the variation so noticeably.


    Probably due to two different effects taking place together. One is
    a harmonic dampener-like effect that will smooth out rotational velocity
    variations you could get from imperfect bearings or windage losses and
    the other is a self-balancing act you get from a viscous fluid inside a
    pneumatic tire.
    Some 4x4 rock crawlers use this trick to keep their knobbies balanced
    reasonably well at speed while looking for rocks to crawl around on.
    But they tend to add a pound or so of BBs or lead shot to the mix
    instead of just lots of tire slime.
    The mass won't distribute evenly. Rather, it tends to lump in parts
    of the tire that are closer to the center of rotation.
    An out-of-balance wheel will want to rotate around it's center of
    balance--that center just isn't where the bearings are located. You
    wind up with a small orbit of the hub unless the hub's mount is
    infinitely rigid. The tire wall flexes a bit, too. All RPMs being
    equal, being farther from the center of the hub's orbit means more
    linear velocity and more centrifugal force, (I know, not a real force,
    but simplifies things greatly) so the liquid in the out-of-orbit chunk
    of the wheel is effectively heavier than liquid ion the other parts. As
    far as it's concerned, the slower-moving chunk of wheel is lighter. The
    liquid in the "heavier" parts of the wheel flows downhill to the
    "lighter" parts of the wheel, and forces everything into rough balance
    around where the rigid bearings want it. This attenuates the shaking
    already there, but will never eliminate it since the out-of balance
    condition is what's needed to keep the liquid in the right place. Being
    in good balance from the beginning before adding the liquid will help a
    lot.
    You could probably smooth out the non-slime tire by going through
    heroic efforts to balance it before the test. Or try collecting data as
    speed drops to zero and you'll probably see the slimed tire get
    noticeably worse that the non-slimed at some point. That's where
    there's no longer enough speed to keep the liquid in place, so it begins
    sloshing.
    Try adding a bunch more pickup magnets to your wheel and dividing the
    computer's results to improve your average accuracy when going slow.
    Though I don't know if this will really help or just drive your computer
    batshit crazy.
    You might also want to repeat your spin down test with a roller.
    When the wheel is actually rolling along the ground that liquid
    distribution gets disturbed and has to resituate itself--taking energy.
    I believe that's what causes some people to dislike slime.

    --
    B.B. --I am not a goat! thegoat4 at airmail dot net
    http://web2.airmail.net/thegoat4/
     
  16. On Fri, 17 Dec 2004 14:18:05 -0600, "B.B."
    <[email protected]> wrote:

    >In article <[email protected]>,
    > [email protected] wrote:
    >
    >>I still have no idea why adding such a small liquid mass
    >>reduced the variation so noticeably.

    >
    > Probably due to two different effects taking place together. One is
    >a harmonic dampener-like effect that will smooth out rotational velocity
    >variations you could get from imperfect bearings or windage losses and
    >the other is a self-balancing act you get from a viscous fluid inside a
    >pneumatic tire.
    > Some 4x4 rock crawlers use this trick to keep their knobbies balanced
    >reasonably well at speed while looking for rocks to crawl around on.
    >But they tend to add a pound or so of BBs or lead shot to the mix
    >instead of just lots of tire slime.
    > The mass won't distribute evenly. Rather, it tends to lump in parts
    >of the tire that are closer to the center of rotation.
    > An out-of-balance wheel will want to rotate around it's center of
    >balance--that center just isn't where the bearings are located. You
    >wind up with a small orbit of the hub unless the hub's mount is
    >infinitely rigid. The tire wall flexes a bit, too. All RPMs being
    >equal, being farther from the center of the hub's orbit means more
    >linear velocity and more centrifugal force, (I know, not a real force,
    >but simplifies things greatly) so the liquid in the out-of-orbit chunk
    >of the wheel is effectively heavier than liquid ion the other parts. As
    >far as it's concerned, the slower-moving chunk of wheel is lighter. The
    >liquid in the "heavier" parts of the wheel flows downhill to the
    >"lighter" parts of the wheel, and forces everything into rough balance
    >around where the rigid bearings want it. This attenuates the shaking
    >already there, but will never eliminate it since the out-of balance
    >condition is what's needed to keep the liquid in the right place. Being
    >in good balance from the beginning before adding the liquid will help a
    >lot.
    > You could probably smooth out the non-slime tire by going through
    >heroic efforts to balance it before the test. Or try collecting data as
    >speed drops to zero and you'll probably see the slimed tire get
    >noticeably worse that the non-slimed at some point. That's where
    >there's no longer enough speed to keep the liquid in place, so it begins
    >sloshing.
    > Try adding a bunch more pickup magnets to your wheel and dividing the
    >computer's results to improve your average accuracy when going slow.
    >Though I don't know if this will really help or just drive your computer
    >batshit crazy.
    > You might also want to repeat your spin down test with a roller.
    >When the wheel is actually rolling along the ground that liquid
    >distribution gets disturbed and has to resituate itself--taking energy.
    >I believe that's what causes some people to dislike slime.


    Dear B.B.,

    The 4x4 trick is interesting--thanks for mentioning it.
    Curiously, the dry normal tube spun quite smoothly, but
    there was some wheel hop at 35-40 mph with the slime tube
    and the normal tube with the sleeve added.

    Apart from convenience in measurement, measuring losses
    below 10 mph seemed less than practical, since bicyclists
    going less than 10 mph are not usually interested in whether
    their bicycles seem "light" and "lively"--and Lord knows
    this sort of experimentation is ruthlessly concerned with
    practicality! Plus, it would take forever to let the wheel
    spin all the way down--20 seconds from 30 mph down to 20
    mph, 40 seconds down to 10 mph, 70 seconds down to 5 mph,
    and 90 seconds to stop (0.0 mph indicated for the last ten
    seconds or so). For sixty test spins, even testing down to 5
    mph would have required an extra half hour.

    Adding the magnets might improve the resolution. As the
    readings dropped from 35-40 mph, I had to make a quick
    choice when I saw a 30.x or a 29.x because the wheel is
    slowing down so rapidly at that speed with the high wind
    drag on the spokes. About 12 seconds later, the speedometer
    would be showing 20 mph. Then it would drop more and more
    slowly, until there were usually two readings in the 10.x
    mph range--I'd try to hit the lower one, but sometimes the
    next figure was a 9.x.

    A potential problem with extra magnets has been mentioned in
    other threads--too many magnets at 30 mph can give the
    switch fits and lead to no readings at all if the magnets
    are going past too frequently.

    You're the first person to raise the interesting point about
    the normal bulge in a loaded tire possibly making the Slime
    drag worse. Unfortunately, I suspect that testing this is
    impractical--the Slime effect, though measurable, is so tiny
    that it barely shows up on a free-spinning tire slowed only
    by the air drag on the spokes. It probably wouldn't show up
    at the levels of force needed to turn a loaded rubber tire,
    which won't spin for 38 or 40 seconds. The effect of the
    Slime flowing around the slight bulge in a normally loaded
    tire would have to be enormous compared to what I measured,
    if anyone was going to notice it.

    At this point, I'd be astonished if a rider could actually
    tell any difference in blind testing between a dry tube and
    one with 80 grams of Slime added in terms of acceleration. I
    never noticed any difference while cranking the wheel up to
    35-40 mph sixty times with a few arm-turns. Again, adding
    about 150 grams of Slime to a 3kg pair of wheels is an
    increase of about 5% on what in turn is only about 4% of the
    total mass of a 75 kg bicycle and rider--or around 0.2%.

    Still, I'd be delighted if someone took the trouble to have
    a friend randomly switch Slime and dry tubes on his bike
    over a few weeks (covering the valves to hide the
    difference), recorded what changes he noticed, and posted
    the results against what his friend secretly did. If someone
    really can tell the difference reliably, then your point
    about the Slime constantly hitting the bulge of normally
    loaded tire would be thing to consider.

    Carl Fogel
     
  17. Well Carl, I think this is really neat. My hat is off to you in thanks.
    This is just the type of information cyclists need. I would love to set
    up a lab to test all sorts of things such as the stiffness (or
    resistance to load) of handlebars & stems to destruction. Bicycling
    Mag. was doing this sort of thing years ago, (before it became so
    absurdly vapid) but much have lost too many paying advertisers to
    continue.
    Anyway, Thanks again, John
     
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