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  1. #1
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    Do disc brakes slow you down when coasting?

    My girlfriend and I both have hardtails. I have 2000 GT Aggressor with rim brakes and she has a 2008 Cannondale F5 with Shimano M415 disc brakes. If we are riding at the same speed next to each other and start to go downhill (paved path) with no pedaling or braking by either of us, I quickly pull ahead and end up going much faster than her. I always ask her if she's feathering the brakes, but she says she isn't (and sometimes I watch to make sure she's not touching the brakes). I could understand if we were going the same speed and coasting, that I might keep speed up for longer than her since I am ~60-70 lbs heavier, but the weight difference should not have an effect on acceleration from gravity down a hill. Is this common with disc brakes? If not, what other components could be slowing her down so much?

  2. #2
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    Quote Originally Posted by intoflatlines
    My girlfriend and I both have hardtails. I have 2000 GT Aggressor with rim brakes and she has a 2008 Cannondale F5 with Shimano M415 disc brakes. If we are riding at the same speed next to each other and start to go downhill (paved path) with no pedaling or braking by either of us, I quickly pull ahead and end up going much faster than her. I always ask her if she's feathering the brakes, but she says she isn't (and sometimes I watch to make sure she's not touching the brakes). I could understand if we were going the same speed and coasting, that I might keep speed up for longer than her since I am ~60-70 lbs heavier, but the weight difference should not have an effect on acceleration from gravity down a hill. Is this common with disc brakes? If not, what other components could be slowing her down so much?

    No it is not the brakes (well unless they are dragging).

    Yes the weight difference matters quite a bit....

    Althought the acceleration due to gravity is the same for each, the heavier person gains more kinetic energy per foot of fall.

    The drag effects air and rolling resistance are not linear to weight, so the heavier guy will go faster.

  3. #3
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    Do the brakes drag on the rotor when you spin the wheels? If so then you need to re-center the caliper. If they aren't dragging, I would think it's probably the wheel bearings or tires.

  4. #4
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    Quote Originally Posted by jeffscott
    No it is not the brakes (well unless they are dragging).

    Yes the weight difference matters quite a bit....

    Althought the acceleration due to gravity is the same for each, the heavier person gains more kinetic energy per foot of fall.

    The drag effects air and rolling resistance are not linear to weight, so the heavier guy will go faster.
    Ah, I forgot to factor in air resistance and such. I guess I'll test it out next time by switching bikes and see if I still go faster.

  5. #5
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    Quote Originally Posted by oldskoolbiker
    Do the brakes drag on the rotor when you spin the wheels? If so then you need to re-center the caliper. If they aren't dragging, I would think it's probably the wheel bearings or tires.
    There isn't any noticeable noise or drag on the wheel when spinning, but it does seem like occasionally there will be intermittent quiet squeaking when walking the bike. It seems like it happens more when the wheels is turned. I heard that the pads need some use to break in, which I don't think they have enough use yet?

  6. #6
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    Yes, disc brakes do slow you down due to drag.

  7. #7
    human dehumidifier
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    Could be hub bearing drag on the slower bike too
    When you get older, much of your hate comes from knowledge and experience, which is why really old people hate everyone

  8. #8
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    Quote Originally Posted by glitz
    Yes, disc brakes do slow you down due to drag.
    What drag? If they are set up properly then there is no drag.
    Friends don't let friends cheer for the TML

  9. #9
    Meh.
    Reputation: XSL_WiLL's Avatar
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    Exactly, properly set up disc brakes will not drag. There are a number of other factors including drag in the hub from misadjusted bearings, drags from seals, drag from engagement points, rolling resistance from tires, difference in air pressure, difference in weight of wheels and tires, difference in height of tires, difference in size of contact patch, etc.

  10. #10
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    Quote Originally Posted by Dgage
    What drag? If they are set up properly then there is no drag.

    Mine drag plenty, that's how I stop

  11. #11
    ~Disc~Golf~
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    Quote Originally Posted by Dgage
    What drag? If they are set up properly then there is no drag.
    ignore him - glitz is a troll
    Honestly... ahh I give up

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