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  1. #1
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    A T-Day puzzler to ponder....

    Let's suppose I have a bike with a flip-flop rear wheel--fixed on one side, free on the other--with a single chainring up front. The fixed sprocket and freewheel are both identically sized; that is, they have the same number of teeth (and neither one is missing teeth ).

    On a windless day, I climb a hill, from base to summit, with the bike in freewheel mode. After walking the bike back down to the base of the hill--and taking enough time to recover completely--I flip the wheel over. I then climb the same hill, from base to summit, in fixed-gear mode. A glance at the bike computer shows both rides are done with the same average speed.

    My question, then, is as follows....

    Assuming my strength remains constant, which ride--if any--requires less energy to reach the summit?

    ECB

  2. #2
    Blaster of Reality Scrodzilla's Avatar
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    If you're pedaling constantly in freewheel mode - as you would be when running the fixed side - I would think there is no difference.

    But...when riding fixed, the up pressure on your trailing foot caused by pushing down with your leading foot (on every revolution of the crank) might mean you're using less energy than with a freewheel because the momentum is kinda helping you on the upstroke.

    Thanks. Now I'm all confused and stuff.
    Last edited by Scrodzilla; 11-26-09 at 12:49 PM.

  3. #3
    Oddjob Cassanova gutbucket's Avatar
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    Simply put, it would take you the same amount of energy in either freewheel or fixed mode in the situation you described. in climbing (moving mass up an incline) you have to apply effort continuously, even if you come to a standstill.
    I will add though, that under normal type biking in the real word, I found myself working a lot harder (expending a lot more energy doing rides of the same distance AND duration) riding a freewheel equipped bike (even multi-speed) than on a fixed gear.
    "I n'er go up just for the money,
    I n'er go halfway..."

  4. #4
    The bus, Gus mrvile's Avatar
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    I think that if rear-wheel momentum affected the pedal turn in any way that would benefit fixed gear riding (which would be marginal anyway) it would have to be on flat ground.

  5. #5
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    A fixed drive is just a little more efficient than an ss although lifting a mass to a certain height will always require a set amount of energy...time is not actually factor in this base calculation although it is a factor when you are riding and need to balance speed with short term energy use / conservation.

    After climbing the hill once on the ss, being able to climb the hill at the same speed on the FG is an indication that the FG is just a little more efficient and compensates for the energy loss / muscle fatigue you experienced on the first climb... the advantage stems from how a FG conserves momentum and turns the rear wheel into a flywheel.

    You would have to try the experiment reversed with the FG first and after a good rest period... even then... the performance of a human being will not be 100% consistent from day to day so errors would creep in.

  6. #6
    Senior Member
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    i'll bite.

    to get the bike + rider up the hill requires the same absolute amount of energy regardless of fixed or freewheel.

    however, the efficiency of the drivetrain may not be equal for fixed or freewheel. the fixed gear should be slightly more efficient due to the conservation of momentum in the pedal stroke, but i can't back that up with any numbers.
    i won't deny it i'm a straight ridah

  7. #7
    Blaster of Reality Scrodzilla's Avatar
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    Quote Originally Posted by mrvile View Post
    I think that if rear-wheel momentum affected the pedal turn in any way that would benefit fixed gear riding (which would be marginal anyway) it would have to be on flat ground.
    You're right. I was actually thinking about this during Thanksgiving dinner. haha

  8. #8
    Senior Member REMspeedwagon's Avatar
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    Quote Originally Posted by gutbucket View Post
    I will add though, that under normal type biking in the real word, I found myself working a lot harder (expending a lot more energy doing rides of the same distance AND duration) riding a freewheel equipped bike (even multi-speed) than on a fixed gear.
    i feel the same.
    null

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