Advertise on Bikeforums.net



User Tag List

Results 1 to 10 of 10
  1. #1
    Senior Member
    Join Date
    Jul 2010
    Posts
    193
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Knee behind the pedal?

    What's the theory put forth by the couple of manufacturers who make bikes that place the knee well behind the pedal? How does that work, in terms of power and wear and tear on the body?

    Come to think of it, how do the ergonomics of the traditional knee-over-the-pedal compare to a recumbant?

    I can see that the calf, knee, thigh, and hip are involved---also glutes with a recumbant?---and I suppose the knee would be the weak link there?

    Intuitively I think there would be a loss of power and speed with the knee behind the pedal. Please educate me. Thanks!

    (Just curious because I get paranoid if my knee seems to be behind the pedal.)

  2. #2
    "Chooch" ciocc_cat's Avatar
    Join Date
    Jun 2010
    Location
    Prairieville, Louisiana
    My Bikes
    1980s Ciocc San Cristobal, 2000-ish Ciocc Titan
    Posts
    1,655
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    "A bicycle built by a frame builder has the soul of the builder. A mass produced frame does not have soul. It doesn't know anyone." - Giovanni "Ciocc" Pelizzoli.
    “Beer is proof that God loves us and wants us to be happy.” - Benjamin Franklin
    [SIGPIC][/SIGPIC]My Ciocc San Cistobal
    Visit my website at http://ciocc-cat.angelfire.com/

  3. #3
    Senior Member oldbobcat's Avatar
    Join Date
    Jul 2005
    Location
    Boulder County, CO
    My Bikes
    '79 Gios, '80 Masi, '06 Felt, early '60s Frejus
    Posts
    2,455
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    The bikes you are speaking of are probably crank-forward city bikes such as the Electra Townie, Trek Pure, Specialized Carmel, and Fuji Saratoga. They rotate the entire body backward to create a more upright riding position and allow a lower seat position that lets you plant your feet almost flat on the ground without sacrificing leg extension to the pedals. This style of bike is not my cuppa tea, but there's lots to love fore a casual rider. Try one. I assure you, your knees will not explode.

    I like them all except for the Fuji, which looks and rides as if it were designed from a parts bin.

  4. #4
    rebmeM roineS JanMM's Avatar
    Join Date
    Jan 2006
    Location
    Indiana
    My Bikes
    RANS V3, RANS V-Rex, RANS Screamer
    Posts
    11,547
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Knee-over-pedal position doesn't really translate to recumbent positioning. There is no equivalent 'bent seat adjustment comparable to moving the saddle fore and aft.
    RANS V3 (steel), RANS V-Rex, RANS Screamer

  5. #5
    Senior Member
    Join Date
    May 2005
    Posts
    6,901
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    It has become apparent to many that the KOPS "experts" recommend is total BS anyway.

  6. #6
    I need speed AzTallRider's Avatar
    Join Date
    Sep 2009
    Location
    Phoenix, AZ
    My Bikes
    Giant Propel, Cervelo P2
    Posts
    5,482
    Mentioned
    8 Post(s)
    Tagged
    0 Thread(s)
    This is the best article I've found on the whole KOPS thing, and it has a practical (and dynamic) method for determining your balance point, so long as you have a trainer to mount your bike on:

    SEAT SET BACK: for road bikes

    Essentially, you want to be able to balance, in the drop position while pedaling reasonably hard, with your hands behind your back. This gives you a reasonable distribution of weight between your butt and your hands. Too far back limits performance. Too far forward puts undue weight on your hands, and also fatigues your arms and shoulders. I did Steve Hogg's test, and moved my saddle up significantly without causing any issues. That made the reach, balance and handling better, put the clamp in the middle of the seat rails, etc. As Hermes (and I think A'Jet as well) has pointed out, as you get fitter, and pedal harder and faster, you take the weight off your butt and your hands - your legs lift you up. In addition to reducing butt and hand fatigue, this also enables you to adopt a more agressive (forward) saddle position.

    Physical build differences aside, faster riders will be more likely to be in front of KOPS, while us slower riders are more likely to be behind KOPS.
    "If you're riding less than 18 MPH up a 2% grade please tell people Coggan is coaching you."

  7. #7
    Senior Member
    Join Date
    Jul 2008
    Posts
    830
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    It's not a theory. It's well proven in practice how one sets the ridng position relative to the bottom bracket. It's been done for decades.

    If you are into high cadence, especially going full out like in time trials or triathelons, you want to be in a more forward position relative to the BB bracket a lot. Knee over spindel (kos) or further forward depending what works for the individual and the seat tube angle.

    When you watch a time trial, you'll note how they slide forward on their saddles and sit "on the rivet" which really puts the kee far forward of the kos position. Contadore during the last TDF time trial had to keep pulling himself forward to stay on the very tip of the nose as I remember. He had a great ride.

    Further back is not conducive to high cadence, but it off-loads the quads and makes the hamstrings/glutes share more of the work. Pushing the pedal over top-dead center from say 10-oclock to 2 becomes easier/more effective and powerful further back.

    One of the reasons that mountain bike saddles are so long is that it allows varying the riders position a lot relative to the bottom bracket (it's all about the bottom bracket). That seems to be happening in road as well with those Fizik (sp?) saddles. My wife's new Fizik is like 12.5 inches long; longer than my 11" mtn bike saddle.

    I like my knee about an inch back for mountain and about 1/2 inch back for road. Some mountain bike racers are more than 2" back (like 3" as i remember) like Ned Overend.

    Last monday I was doing a tough 16 mile trail ride with a lot of tough climbing. My hamstrings were some what fatigued at the beginingg of the ride as I've been doing a lot tree sawing (bucking), toting/dragging and stacking firewood and brush on sloping ground.

    About half way through the ride I had to stay forward and load the quads more just to climb. The effect is very noticeable when you're tired.

    Time-trial/tri bikes use a very steep seat tube angle to move you forward to begin with. So how much one sets his knee forward or aft of the kos depends on the bike geometery and one's preference/requirements.

    Al
    Last edited by alcanoe; 05-26-11 at 11:19 AM.

  8. #8
    I need speed AzTallRider's Avatar
    Join Date
    Sep 2009
    Location
    Phoenix, AZ
    My Bikes
    Giant Propel, Cervelo P2
    Posts
    5,482
    Mentioned
    8 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by alcanoe View Post
    It's not a theory. It's well proven in practice how one sets the ridng position relative to the bottom bracket. It's been done for decades.
    It's kind of like the Max Heart Rate formula. Average a big population, and it works, but that doesn't mean it works, for any specific individual, to be at KOPS. When you say relative to KOPS, then of course that makes sense, as that could describe a wide range of saddle positions

    Contadore during the last TDF time trial had to keep pulling himself forward to stay on the very tip of the nose as I remember. He had a great ride.
    Actually, he was pushing himself back, then sliding forward until he was about to fall off, then pushing himself back. He was asked about it, and attributed it to a minor fit issue that was later corrected.

    Time-trial/tri bikes use a very steep seat tube angle to move you forward to begin with. So how much one sets his knee forward or aft of the kos depends on the bike geometery and one's preference/requirements.
    TT geometry doesn't just slide the rider forward, it rotates the entire body, both bringing it forward and tilting it into an agressive aero position. How far forward is limited by UCI rules, at least for those racing in UCI events, and there are saddles (e.g., ISM) designed to get the rider as far forward as possible without violating UCI rules.
    "If you're riding less than 18 MPH up a 2% grade please tell people Coggan is coaching you."

  9. #9
    Senior Member
    Join Date
    Jul 2008
    Posts
    830
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by AzTallRider View Post
    It's kind of like the Max Heart Rate formula. Average a big population, and it works, but that doesn't mean it works, for any specific individual, to be at KOPS. When you say relative to KOPS, then of course that makes sense, as that could describe a wide range of saddle positions



    Actually, he was pushing himself back, then sliding forward until he was about to fall off, then pushing himself back. He was asked about it, and attributed it to a minor fit issue that was later corrected.


    TT geometry doesn't just slide the rider forward, it rotates the entire body, both bringing it forward and tilting it into an agressive aero position. How far forward is limited by UCI rules, at least for those racing in UCI events, and there are saddles (e.g., ISM) designed to get the rider as far forward as possible without violating UCI rules.
    I couldn't remember if it was forwards or back.

    I don't see the relationship to a HR formula. People have been adjusting the sitting position relative to the spindle and not necessarily over the spindle to achieve different ends forever. It's well recognized that exactly where you adjust your knee relative to the spindle is just a guess until you get some experience. The HR formula never changes no matter the experience factor. The age variation is bogus as well.

    When you rotate the seat tube forward, you do rotate the entire body forward, just like when you adjust the knee forward by moving the seat forward. The rider goes forward relative to the bb/spindel and his knees move forward of his original kos relative position in both cases. The only difference I can see is that while in both instances the seat height changes, the change is in opposite directions.

    You can (could?) get seat posts wth set-forward instead of set-back to accomplish the same thing as rotating the seat tube forward.

    A steeper seat tube angle also moves the handlebars further away from the rider IF he keeps his original position relative to the bb/pedal spindle. Most folks ignore that when fitting a bike.

    It's all related and it's all just adjusting the default or starting sitting position relative to the BB to emphasize different factors.

    Al
    Last edited by alcanoe; 05-26-11 at 01:07 PM.

  10. #10
    coprolite fietsbob's Avatar
    Join Date
    Jun 2010
    Location
    NW,Oregon Coast
    My Bikes
    7
    Posts
    40,071
    Mentioned
    27 Post(s)
    Tagged
    0 Thread(s)
    crank forward is not a performance bike design, its for people who want to stop
    and have their feet not tippy-toed.
    it is for the racer style rider, to really dial it in the seat tube angle is on the table.
    frame not made yet, custom design.
    thigh length on the riders body, is what is to be accommodated.
    and setback of the seat the seatpost.. are all part of the adaptation.

    coping with an off the shelf,say 73 degree seat tube frame,
    just leaves changing saddle setback and crank length.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •