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  • Do you produce more power on a direct drive trainer than a 'wheel on' one?
  • tpbiker
    Free Member

    Have done a bit of reading up on this as considering a new turbo. Main reason for changing is that I live in a flat and direct drives are meant be quieter.

    However one of the other benefits I’ve read about is that direct drive turbos give a much more realistic feel than those with a roller. This means the power output you produce is apparently closer to what you can produce outside due to less resistance in the pedal stroke.

    As I use the same power meter both indoors and out that seems like a real benefit to me. It’s not a deal breaker either way, but I’d be interested to know other peoples experiences.

    scaredypants
    Full Member

    It’s meaningless in the end – work on your indoor power on the turbo and your outdoor power will increase as well, even if they have different numbers

    No idea about difference between DD and wheel-on, except that some power must be lost through the tyre/roller. A sensible manufacturer might build in a correction for that, I’d think. I suppose tyre pressure etc might make for greater variability too

    I don’t see why the resistance should be different between the 2 types just because of what they are

    tpbiker
    Free Member

    It’s not so much power is lost through the wheel/roller interface as the reading comes from the crank.
    training peaks explain it thus

    On a rear wheel resistance trainer, there is little to no momentum of the rear wheel. If you stop pedaling the rear wheel comes to an almost immediate stop. Because there is resistance around the entire pedal circle, your legs are not used to having to produce power throughout the entire pedal stroke. As a result of this inefficiency, more strain is put on your cardiovascular system. As a result, this reduces your ability to create the same wattages as outdoors.

    To be clear, it isn’t just the momentum (stored kinetic energy) of the rear wheel that keeps us moving out on the road, but rather that of our body plus the bicycle as a whole. An easy way of envisioning this is to imagine trying to stop the rear wheel of your bike wheel when it’s spinning rapidly in the workstand by grabbing the tire with your hand versus trying to stop that wheel while spinning out on the road using the same technique. In general, until you are “trained” to ride on a rear wheel resistance trainer, your watts will be 20 to 30 watts lower on the trainer than outside.

    They claim that the inertia with a direct drive trainer solves this issue.. But would be useful to have real world experience

    As you say its pretty irrelevant, but still worth considering when in market for a turbo if you are not relying on virtual power.

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    scaredypants
    Full Member

    On a rear wheel resistance trainer, there is little to no momentum of the rear wheel. If you stop pedaling the rear wheel comes to an almost immediate stop

    Oh, OK – I had a kurt kinetic that was a fluid trainer with a flywheel. It definitely generated momentum.
    Buy one that does that ?

    stevious
    Full Member

    Not much difference between a wheel on and wheel off for me. I had a tacx satori and now have tacx flux. Measured with a stages.

    simondbarnes
    Full Member

    On a rear wheel resistance trainer, there is little to no momentum of the rear wheel. If you stop pedaling the rear wheel comes to an almost immediate stop.

    Clearly not used a decent modern turbo then.

    It’s meaningless in the end – work on your indoor power on the turbo and your outdoor power will increase as well, even if they have different numbers

    This

    tpbiker
    Free Member

    Clearly not used a decent modern turbo then.

    For clarity that explanation is a copy and paste from the article rather than my own observations.

    You are right though, it is irrelevant to progress. It is however kinda demoralising when you are seeing such low numbers.. And mentally I need all the motivation I can get to sit on a trainer.

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