Advertise on Bikeforums.net



User Tag List

Results 1 to 9 of 9

Thread: Biking Physics

  1. #1
    Newbie
    Join Date
    Apr 2006
    Posts
    1
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Biking Physics

    My friend and I have recently started street biking, and we have a little disagreement - he thinks it is more work to sit down and pedal rather than stand up. I say standing up just uses more muscles of the body rather than isolating quads, but he says that standing up is easier because you're simply using gravity to push the pedals. I don't think that's consistent with physics, but I want to see if anyone has any conclusive explanation to end this disagreement.

  2. #2
    Dances With Cars TRaffic Jammer's Avatar
    Join Date
    Jan 2006
    Location
    Toronto, Canada
    My Bikes
    TBL Onyx Pro(ss converted), Pake SS (starting to look kinda pimped)
    Posts
    10,527
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    If you are sitting more of the energy from your pumping is translated into the bike's drivetrain, and then into speed/climbing. The less the bike is wiggling back and forth the better. Wait til you get into clipless and you use the whole pedal stroke. Still upper body, pedal like hell..... welcome.

  3. #3
    jur
    jur is offline
    Senior Member
    Join Date
    May 2005
    Posts
    6,288
    Mentioned
    6 Post(s)
    Tagged
    0 Thread(s)
    Quoting from http://www.sheldonbrown.com/standing.html:

    "Standing pedaling allows you to apply more force to the pedals than is possible seated, because you can rest your entire weight on the driven pedal, and, even more, by pulling up on the handlebar, you can push the pedal with more than your actual weight...but is this a good thing?

    Pedaling that hard is very stressful to the joints, and to the bicycle, and usually involves a level of effort that cannot be sustained aerobically. Unless you have unusually good form, it also tends to involve a fair amount of thrashing from side to side, which is a waste of energy. The added stress flexes many parts of the bicycle, and the energy required to do this flexing is not usually recovered when the parts straighten back out."

    Additionally, you are quite right that more muscles are used because you are now supporting your body weight instead of the saddle doing this, so the heart rate for the same speed will tend to be a bit higher.
    My folding bike photo essays www.dekter.net/

  4. #4
    Dances a jig. Mchaz's Avatar
    Join Date
    Sep 2005
    Location
    Central, Ok
    My Bikes
    2007 Surly Long Haul Trucker 54cm (Commuting/Wanna' go tour so bad), 1985 Trek 670 21" (Road), 2003 Gary Fisher Tassajara 17" (MTB), Cannondale DeltaV 600 (commuterized MTB), some junker bikes in my garage
    Posts
    403
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Tell him, by his standards every rider in the Tour De France pedals with the wrong method.

  5. #5
    Prefers Cicero cooker's Avatar
    Join Date
    Jul 2005
    Location
    Toronto
    My Bikes
    1984 Trek 520; 1990s Peugeot (Canadian-made) rigid mountain bike; 2007 Bike Friday NWT; misc others
    Posts
    8,518
    Mentioned
    23 Post(s)
    Tagged
    0 Thread(s)
    If your bike is badly set up, for example the seat is way too low, and you are using too high a gear, I suppose it's possible that your efforts would be so inefficient that you would cycle more effectively standing up, but otherwise seated is more efficient.
    The problem with his gravity explanation is that while you use gravity to push down the pedal, at the same time you have to resist the effect of gravity pulling you down too. When you're seated, the bike supports part of your weight, while when you're standing, your leg muscles have to hold you up.

  6. #6
    Prefers Cicero cooker's Avatar
    Join Date
    Jul 2005
    Location
    Toronto
    My Bikes
    1984 Trek 520; 1990s Peugeot (Canadian-made) rigid mountain bike; 2007 Bike Friday NWT; misc others
    Posts
    8,518
    Mentioned
    23 Post(s)
    Tagged
    0 Thread(s)
    Ps. Invite him to go for a long ride with you and leave his seat at home. We'll see who lasts longest.

  7. #7
    Senior Member
    Join Date
    May 2005
    Location
    Ventura, CA
    My Bikes
    Dean, De Rosa, Langster, some old Brit track iron
    Posts
    428
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jur
    Quoting from http://www.sheldonbrown.com/standing.html:

    "The added stress flexes many parts of the bicycle, and the energy required to do this flexing is not usually recovered when the parts straighten back out."
    I sort of passed high school physics, and that doesn't make sense to me: the energy put into the system can't just be "lost", it either is there or is converted to another form. Unless your bike parts are heating up or giving off light, the energy is still there, no?. I think the difference between rigid and flexy parts and frames is the speed and/or "feel" of how the energy is fed back.

  8. #8
    Senior Member DannoXYZ's Avatar
    Join Date
    Jul 2005
    Location
    Saratoga, CA
    Posts
    11,507
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Some of the flex is lost as heat in the parts that are bending. The more bending you do, the more energy is lost through heat. However, this is a very miniiscule amount. A much larger proportion of the inefficient loss of power is in moving the soft fleshy human body around laterally in motions that's useless in moving the pedals down. Also on a single standing stroke you're using more of your body's mass, but before the very second stroke, you have to move that body mass back up in order to drive down the other pedal. You basically have to give back the extra push on the opposite side.

    The real source of the extra power is that you get to use some of your strongest muscles at their most poweful part of their motion, near the limits of extension. So standing up lets you use several of your muscles to full contraction, giving you more power. However, making muscles exert near their maximum force is also inefficient, consuming more oxygen per watt generated than sitting down. You also drive them over their lactate-threshold easier, thus you won't be able to keep it up as long.

  9. #9
    Senior Member BlazingPedals's Avatar
    Join Date
    Dec 2004
    Location
    Middle of da Mitten
    My Bikes
    Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, homebuilt recumbent
    Posts
    7,341
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Sure you get to have gravity assist you when you stand, but it's not free energy. You have to lift your body at the top of each pedal stroke before you can recover the energy via lowering it again. I agree with Danno - as a bent rider I can't stand, and what I notice is that I can't lift my hips away from the pedals, which limits me in how much of the pedal stroke I can have my knees in a less-stressful (straighter) angle.

Posting Permissions

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