Why is it harder..?

Discussion in 'Power Training' started by cjjeeper, Dec 20, 2011.

  1. cjjeeper

    cjjeeper New Member

    Joined:
    Dec 20, 2011
    Messages:
    2
    Likes Received:
    0
    I have a resistance trainer that I do intervals against in a Power v. Time mode. Why does it seem like 450 Watts at 108 rpms in a very low gear (21kph) is harder than 450 Watts in a higher gear (44kph) @ same rpms (108)?

    Seems like power is power and the time (interval is the same)...power = work/time.

    I blow up at the low gear but I can blow through the interval in the high gear.

    Thanks for the input.
     
    Tags:


  2. daveryanwyoming

    daveryanwyoming Well-Known Member

    Joined:
    Oct 3, 2006
    Messages:
    3,857
    Likes Received:
    97
    At higher wheel speeds you come closer to simulating the momentum of a bike rolling down the road. Unless you have a very big flywheel on your trainer you won't get as much momentum as you would have while actually riding but the extra wheel speed definitely helps. So for the same power at the same cadence but at higher wheel speed the dead spots of the pedal stroke aren't so hard to spin through and the power and peak pedal force requirements are the same at the same cadence.

    It's also possible that your particular trainer in ergo mode doesn't hold the power as constant as the marketing materials might indicate across a wide range of wheel speeds. Have you had a chance to verify that the power is actually the same using a bike power meter like a PowerTap, SRM or Quarg?

    -Dave
     
  3. cjjeeper

    cjjeeper New Member

    Joined:
    Dec 20, 2011
    Messages:
    2
    Likes Received:
    0
    Thanks Dave, I was missing the fly wheel. That makes sense...inertia.

    I have not had a chance to check the indicated vs. actual power with a power meter. I would also be inclined to think that inconsistencies in the device itself would factor into it but I am comfortable that it is typically within 2-5% (based on feedback from other users).
     
Loading...
Loading...