It would seem more weight would be faster for downhill...

machinebike
machinebike Posts: 39
edited November 2016 in MTB general
It would seem.
A 25-30 lb bike
vs
A 40-45 lb bike....

Who would reach the bottom of the hill sooner?

Comments

  • Briggo
    Briggo Posts: 3,537
    Few other variables to add into the equation.

    Add them in and we may be able to comment.
  • fat daddy
    fat daddy Posts: 2,605
    Depends on the hill ... one with lots of changes in direction and I would take the lighter bike as it will change direction easier and require less bleeding of speed before the bends

    Long downhill, straight with flat sections and poor surface, I'll go heavy to maintain speed.

    Also how big is the rider ... a lightweight won't be able to manhandle a heavy bike down a course as quickly as he would a light bike

    Why is the Heavy bike heavy ?? ... frame, fatter tyres, more suspension ?
  • cooldad
    cooldad Posts: 32,599
    The one with the best rider.
    I don't do smileys.

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  • cooldad
    cooldad Posts: 32,599
    In reality, as the combined weight including rider would be relatively smaller, the lighter bike any time, all other things being equal.
    Unless you consider riding over a cliff DH, although once terminal velocity is reached, all bets are off.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

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  • Giraffoto
    Giraffoto Posts: 2,078
    All other things being equal - and they never are, but what the hey - the lighter bike will be more manouevrable and the lower unsprung weight that it represents will make for better grip and traction. So the lighter bike it is. Downhill bikes are heavy because they're strong - if weight was desirable, DH competitors would ballast them, and I'm pretty sure none of them do that.
    Weight doesn't make you go downhill faster. A 20Kg bike has twice the gravitational force pulling it down that a 10Kg bike has, but it has to accelerate twice the mass. Acceleration = Force applied/Mass, so both will experience the same acceleration due to gravity.
    Specialized Roubaix Elite 2015
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  • The Rookie
    The Rookie Posts: 27,812
    Giraffoto wrote:
    Acceleration = Force applied/Mass, so both will experience the same acceleration due to gravity.
    As the weight doesn't change the aero, then the heavier bike will have a higher terminal velocity as the force increases but the aero drag hasn't.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    It depends on the rider and the track.
    Strong rider on a short, steep track then heavy would probably not be slower but add in rider fatigue on longer tracks due to cornering and getting back up to speed then weight makes a difference. Also consider that most tracks have flat sections where light weight helps. A light bike is easier to Corner quickly and get airborne over rough ground.
    It does get to a point where a really light bike feels less stable over rough ground.
    If I was riding Redbull Hardline or Rampage I'd take a 45lb Brooklyn Racelink. At Fort William I'd go for a 32lb Mondraker Summum carbon.
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