shock absorbers - waste energy?

Discussion in 'Cycling Equipment' started by Wle, Feb 4, 2004.

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  1. Wle

    Wle Guest

    whenever i ride a bike with shocks, it always feels mushy to me and out of control, so in general i
    don;t like them.

    but - is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    bike ahead?

    it seems that this must be true..

    wle.
     
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  2. Kinky Cowboy

    Kinky Cowboy Guest

    On 4 Feb 2004 16:06:07 -0800, [email protected] (wle) wrote:

    >whenever i ride a bike with shocks, it always feels mushy to me and out of control, so in general i
    >don;t like them.
    >
    >but - is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    >bike ahead?
    >
    >it seems that this must be true..
    >
    >wle.

    It's true that a damper absorbs energy (actually, it converts kinetic energy into heat), but whether
    that energy would have been availble for forward propulsion is hard to say. If the suspension is
    well designed to suit the terrain, the energy available for forward propulsion is actually increased
    compared with a completely rigid chassis, because less energy is transferred to the earth.
    Basically, on a rigid bike, every time you hit a bump, the bike bounces backwards and the whole
    earth gets a small change of angular velocity, moving away from you. You then have to pedal harder
    to start the globe spinning back towards you!

    Kinky Cowboy*

    *Batteries not included May contain traces of nuts Your milage may vary
     
  3. Werehatrack

    Werehatrack Guest

    On 4 Feb 2004 16:06:07 -0800, [email protected] (wle) may have said:

    >whenever i ride a bike with shocks, it always feels mushy to me and out of control, so in general i
    >don;t like them.

    Ride a bike with better damping in the shocks.

    >but - is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    >bike ahead?
    >
    >it seems that this must be true..

    Only for the ones with no real damping at all, which is most that are sold as original equipment on
    bikes under $800. With effective damping, so that the bob-bob-bob on hard pedaling is not present,
    this would not be true.

    But where shocks are useful, in an off-road environment, the trade-off may be worth it even with the
    bobbing. (I personally find that a crummy suspension fork has little to recommend it over a regular
    one even in an off-road setting, however.)

    --
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  4. Zilla

    Zilla Guest

    Kinky Cowboy wrote:
    > On 4 Feb 2004 16:06:07 -0800, [email protected] (wle) wrote:
    >
    >> whenever i ride a bike with shocks, it always feels mushy to me and out of control, so in general
    >> i don;t like them.
    >>
    >> but - is it true that any shock absorbing mechanism wastes energy that could be used to propel
    >> the bike ahead?
    >>
    >> it seems that this must be true..
    >>
    >> wle.
    >
    >
    > Basically, on a rigid bike, every time you hit a bump, the bike bounces backwards and the whole
    > earth gets a small change of angular velocity, moving away from you. You then have to pedal harder
    > to start the globe spinning back towards you!
    >
    >
    > Kinky Cowboy*
    >
    > *Batteries not included May contain traces of nuts Your milage may vary

    Theoretically yes. Practically, no! This is just like saying pissing in the ocean increases its
    volume. True, but not to no practical effects.

    --
    - Zilla Cary, NC (Remove XSPAM)
     
  5. Mark Hickey

    Mark Hickey Guest

    Werehatrack <[email protected]> wrote:

    >On 4 Feb 2004 16:06:07 -0800, [email protected] (wle) may have said:
    >
    >>but - is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    >>bike ahead?
    >>
    >>it seems that this must be true..
    >
    >Only for the ones with no real damping at all, which is most that are sold as original equipment on
    >bikes under $800. With effective damping, so that the bob-bob-bob on hard pedaling is not present,
    >this would not be true.

    If your suspension has enough damping to prevent bobbing under out of saddle pedaling, it's not
    going to work on bumps either. You may think your MTB doesn't bob much when you're out of the
    saddle, but it does (unless you have a lockout of course). Try riding over a bridge at sunrise or
    sunset and watch your shadow humping up and down on the railing as you pedal. You'll probably be
    surprised. Or put a twist tie around the your fork's slider just above the seal (so it's touching
    it). Gingerly slide it fully down, then stand up while coasting and make sure it hasn't moved. Now
    do some "hard pedaling" and be amazed where it ends up.

    When you're pedaling out of the saddle, you're moving the center of gravity back and forth
    significantly - far too much for any working and worthwhile suspension to ignore.

    Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
     
  6. > is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    > bike ahead?

    Yes and no: Yes, it does waste energy. No, it couldn't be used to propel the bike ahead.
     
  7. Werehatrack

    Werehatrack Guest

    On Thu, 05 Feb 2004 00:53:53 GMT, Kinky Cowboy <[email protected]> may
    have said:

    >Basically, on a rigid bike, every time you hit a bump, the bike bounces backwards and the whole
    >earth gets a small change of angular velocity, moving away from you. You then have to pedal harder
    >to start the globe spinning back towards you!

    Where did I put those waders....

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  8. meb

    meb New Member

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    When irregularities in the road/trail impart vertical movement of the bike and the larger, there is a conversion of the kinetic energy in the longitudinal direction to a vertical direction. Unless the surface is smooth enough on the return from irregularity to return that loss back in the line of travel, the vertical kinetic energy is not redirected back into longitudinal kinetic energy and is lost to the rider. Also, there are energy losses associated with the flexing of the tire, particularly the sidewall as the tire load changes.

    A suspension system allows the wheels to travel up and down without having the heavier rider and frame travel in the vertical direction. The initial vertical direction of the rider/frame suspension would initiate a vertical oscillation of the rider/frame up and down.

    The shock absorber damps this oscillation after the deflection-travel by scrubbing off this oscillating energy as heat in a controlled return zero oscillation, analogous to a brake on a wheel.

    On the down side, suspension and shock absorbers also add weight to the bike, so there is more rolling resistance on flat level surfaces and more mass to move up hills, and often some aero drag added is to the vehicle.

    At some point the energy saved with the suspension by minimizing the travel of the frame & rider is exceeded by the losses of the system. That will differ based on the specifics of the suspension, riding surface, and amount of sprung weight. That tradeoff varies greatly with differing roads and surfaces

    There are also instances of the suspension traveling due to pedaling creating a moment about the pivot points, often oscillating and sometimes referred to as pogoing. That also is an oscillation the shock absorber needs dampen.

    In summary, the shock absorber itself dissipates kinetic energy from the bike, the suspension system as a whole reduces losses by vertical deflection and travel of which are often energy losers, but introduces its own unique losses not found on an unsprung bike.
     
  9. wle wrote:

    > whenever i ride a bike with shocks, it always feels mushy to me and out of control, so in general
    > i don;t like them.
    >
    > but - is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    > bike ahead?
    >
    > it seems that this must be true..

    Yes and no. On a flat smooth road in a sprint, suspension is a PITA. For MTBs that spend most of
    their time on the road, it's pointless - unless you like riding down flights of steps.

    Someone - I think it was Keith Bontrager - set out to prove that suspension made a rider more
    efficient on bumpy surfaces. He put a mountain bike and rider on an inclined treadmill with a lump
    of 2 x 4 fixed across the belt. The rider used significantly less oxygen for a given speed on the
    suspended bike than on the rigid bike. The suspended bike absorbs the impact of the 2 x 4 "bump" and
    allows the rider to maintain a better pedalling rhythm.
     
  10. Werehatrack <[email protected]> wrote:
    >On 4 Feb 2004 16:06:07 -0800, [email protected] (wle) may have said:
    >>but - is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    >>bike ahead?
    >Only for the ones with no real damping at all, which is most that are sold as original equipment on
    >bikes under $800.

    Bunk. Damping converts kinetic energy into heat. Where do you suppose that kinetic energy comes
    from? Little green men?
    --
    David Damerell <[email protected]> flcl?
     
  11. Carl Fogel

    Carl Fogel Guest

    Werehatrack <[email protected]> wrote in message news:<[email protected]>...
    > On 4 Feb 2004 16:06:07 -0800, [email protected] (wle) may have said:
    >
    > >whenever i ride a bike with shocks, it always feels mushy to me and out of control, so in general
    > >i don;t like them.
    >
    > Ride a bike with better damping in the shocks.
    >
    > >but - is it true that any shock absorbing mechanism wastes energy that could be used to propel
    > >the bike ahead?
    > >
    > >it seems that this must be true..
    >
    > Only for the ones with no real damping at all, which is most that are sold as original equipment
    > on bikes under $800. With effective damping, so that the bob-bob-bob on hard pedaling is not
    > present, this would not be true.
    >
    > But where shocks are useful, in an off-road environment, the trade-off may be worth it even with
    > the bobbing. (I personally find that a crummy suspension fork has little to recommend it over a
    > regular one even in an off-road setting, however.)

    Dear Werehatrack,

    As others have pointed out, working the suspension takes energy, but is worthwhile if it makes the
    ride possible, saves the frame, or doesn't rob too much energy.

    Interestingly, many downhill racers insist on hard-tail frames when they coast down dry ski-resort
    runs at frightening speeds.

    I think that the racers have found that they roll down the slope faster with as little suspension as
    possible. Maybe someone familiar with this odd sport will explain what's really happening.

    Carl Fogel
     
  12. Kinky Cowboy

    Kinky Cowboy Guest

    On Wed, 4 Feb 2004 21:10:50 -0500, "Zilla"
    <[email protected]> wrote:

    >Kinky Cowboy wrote:
    >> On 4 Feb 2004 16:06:07 -0800, [email protected] (wle) wrote:
    >>
    >>> whenever i ride a bike with shocks, it always feels mushy to me and out of control, so in
    >>> general i don;t like them.
    >>>
    >>> but - is it true that any shock absorbing mechanism wastes energy that could be used to propel
    >>> the bike ahead?
    >>>
    >>> it seems that this must be true..
    >>>
    >>> wle.
    >>
    >>
    >> Basically, on a rigid bike, every time you hit a bump, the bike bounces backwards and the whole
    >> earth gets a small change of angular velocity, moving away from you. You then have to pedal
    >> harder to start the globe spinning back towards you!
    >>
    >>
    >> Kinky Cowboy*
    >>
    >> *Batteries not included May contain traces of nuts Your milage may vary
    >
    >Theoretically yes. Practically, no! This is just like saying pissing in the ocean increases its
    >volume. True, but not to no practical effects.

    To take up your analogy, yes it makes little difference to the ocean, but it makes a big difference
    to your bladder. Same on the bike; the energy imparted to the earth is a microscopic fraction of the
    earths total kinetic energy, but it's a worthwhile proportion of yours and once it's gone you have
    to get it back by spending chemical energy in your muscles.

    Kinky Cowboy*

    *Batteries not included May contain traces of nuts Your milage may vary
     
  13. Rick Onanian

    Rick Onanian Guest

    On Wed, 4 Feb 2004 21:10:50 -0500, "Zilla"
    <[email protected]> wrote:
    >> on a rigid bike, every time you hit a bump, the bike bounces backwards and the whole earth gets a
    >> small change of angular velocity, moving away from you. You then have to pedal harder to start
    >> the globe spinning back towards you!
    >>
    >> Kinky Cowboy*
    >
    >Theoretically yes. Practically, no! This is just like saying pissing in the ocean increases its
    >volume. True, but not to no practical effects.

    Practical effect of hitting a bump: The _bump_ probably moves a little, or flexes, or takes some
    fatigue. You and the bike slow down and must pedal harder to resume previous speed. Suspension can
    help reduce the amount of forward speed lost.

    Practical effect of pissing in the ocean: You get rid of your piss, which you needed to get rid of.
    The water becomes less comfortable for any life in the immediate vicinity until it disperses enough.

    So, maybe no practical effect on the whole earth or the whole ocean, but practical effects on small
    local spots, and much more importantly, practical effects on you!
    --
    Rick Onanian
     
  14. Wle

    Wle Guest

    David Damerell <[email protected]> wrote in message
    >
    > Bunk. Damping converts kinetic energy into heat. Where do you suppose that kinetic energy comes
    > from? Little green men?

    ah. good point. i agree.

    wle.
     
  15. meb

    meb New Member

    Joined:
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    If the downhill were smooth enough that you didn’t need the softride for handling and control and was prevailent enough you could count on the bounced consistently landing on a slope, you might prefer to let the slope redirect that vertical kinetic energy from the bounce back into kinetic energy down the slope rather than thermally damp the energy from the bump with the shocks.

    The smooth ski slopes of Colorado that Carl appears to allude might fit such a description.

    A compromise option might be undamped springs hoping the later slope perturbations would balance out any oscillations started from earlier bumps. Would vary greatly from course to course and rider to rider.
     
  16. Werehatrack

    Werehatrack Guest

    On Wed, 04 Feb 2004 23:00:30 -0800, LioNiNoiL at NetScApE_DoT_NeT
    <[email protected]> may have said:

    >> is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    >> bike ahead?
    >
    >Yes and no: Yes, it does waste energy. No, it couldn't be used to propel the bike ahead.

    If it wasn't wasted to begin with, it could have been used to propel the bike.

    --
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  17. Werehatrack

    Werehatrack Guest

    On 05 Feb 2004 14:46:25 +0000 (GMT), David Damerell
    <[email protected]> may have said:

    >Werehatrack <[email protected]> wrote:
    >>On 4 Feb 2004 16:06:07 -0800, [email protected] (wle) may have said:
    >>>but - is it true that any shock absorbing mechanism wastes energy that could be used to propel
    >>>the bike ahead?
    >>Only for the ones with no real damping at all, which is most that are sold as original equipment
    >>on bikes under $800.
    >
    >Bunk. Damping converts kinetic energy into heat. Where do you suppose that kinetic energy comes
    >from? Little green men?

    If the damping was sufficiently effective (which it seldom is), there would be little suspension
    motion from pedalling. The more motion, the more loss. Damping reduces motion, and loss; below a
    certain point, it could be ignored. I doubt that any OE shock on an under-$800 bike has damping
    that even reduces the motion to any appreciable extent. (None that I've tried would qualify, in
    any event.)

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  18. Werehatrack

    Werehatrack Guest

    On 5 Feb 2004 10:49:13 -0800, [email protected] (Carl Fogel) may
    have said:

    >Interestingly, many downhill racers insist on hard-tail frames when they coast down dry ski-resort
    >runs at frightening speeds.
    >
    >I think that the racers have found that they roll down the slope faster with as little suspension
    >as possible. Maybe someone familiar with this odd sport will explain what's really happening.

    I don't know if this is the answer for everyone, but I've heard a comment that the last thing you
    want when going downhill fast is substantial suspension rebound in the rear of the bike, since that
    pitches you forward. A hardtail also will ride lower in back; I personally suspect that's the real
    reason it's preferred. I haven't got the nerve to try what those guys do, so it's not like I really
    need to know.

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  19. Werehatrack

    Werehatrack Guest

    On Thu, 05 Feb 2004 20:49:48 GMT, meb <[email protected]>
    may have said:

    >In summary, the shock absorber itself dissipates kinetic energy from the bike, the suspension
    >system as a whole reduces losses by vertical deflection and travel of which are often energy
    >losers, but introduces its own unique losses not found on an unsprung bike.

    Well said.

    --
    My email address is antispammed; pull WEEDS if replying via e-mail.
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  20. x

    x Guest

    RE/
    >whenever i ride a bike with shocks, it always feels mushy to me and out of control, so in general i
    >don;t like them.
    >
    >but - is it true that any shock absorbing mechanism wastes energy that could be used to propel the
    >bike ahead?

    What kind of shocks? I've got a set of Manitou Black 3" travel that, when the oil gets in the wrong
    place and they lose their damping, feel awful to ride.

    OTOH, my 'zocci's feel good enough that there might be a semantic issue around "waste". If a shock
    absorbes a little energy but saves me from a lot of pounding, maybe that absorbed energy was
    "invested" instead of "wasted"...

    --
    PeteCresswell
     
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