Maintaining speed with a 7 kg carbon bike

Discussion in 'Road Cycling' started by noamporat, Oct 23, 2004.

  1. noamporat

    noamporat New Member

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    Hello all,
    I doing road cycling for almost a year and until lately I rode a 98’ Giant / Ultegra; the bike were not too light and I could maintain nice speeds with it on the plane roads; 10 days ago I got a Cervélo R2.5 w/ full dura ace 7800; the bike weigh 7 kg and no need to tell that one can accelerate and climb pretty good with it; It seems though that once I reach my cruising speed on plane roads it takes more work to maintain the speed; Physically that might be understood – practically, from your experience, should it be like that ? (As I’m still getting used to it, I might just… imagine that ?)
    Thanks,
    Noam
     
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  2. fixit

    fixit New Member

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    how might that be physically understood?
    i think that on plane roads, when using the same wheels (rim profile), tires, tire pressure and most importantly position on the bike, there is no difference.
     
  3. Azrael

    Azrael New Member

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    Remember Newton's third law. Mass in movement tends to stay in movement....
    So more mass (weight) means more tendency to keep moving and vice versa.....
     
  4. fixit

    fixit New Member

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    accepted, but, correct me if i'm wrong, don't you need more energy to keep a greater mass moving at the same speed?
    :confused:
     
  5. noamporat

    noamporat New Member

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    Hi,
    thanks!
    that's what I thought! the former bike were H e a v i e r ..
    Noam



     
  6. noamporat

    noamporat New Member

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    Yap, you should be right on that. trade-offs I guess


     
  7. donhix1

    donhix1 New Member

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    I noticed something similar when I upgraded to a light bike. When I had a herky jerky pedaling style I could feel it as my bike would respond more.
    My solution would be to ride faster then the you are fighting the air resistance more, making the weight of the bike less of a factor ;)
     
  8. keydates

    keydates New Member

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    Off topic, and unimportant, but isn't that Newton's first law?
     
  9. roadmax

    roadmax New Member

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    I think this has to do with flexing of the new lighter frame, it means that a certain amount of pedaling power will be lost due to flexing. It is not hard to build a light frame-bike, it is very hard to build a light and efficient frame-bike.
    Only few companies can do it.
     
  10. racer dave

    racer dave New Member

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    yes, it is newton's first law. And no, it should not be harder to keep a heavier bike moving.

    Compare a 7kg bike to a 10kg bike. Let's say they both have the same speed, same frontal surface area (same amount of aerodynamic drag, or air resistance), and the same rolling resistances.

    Under these conditions, the only thing that the weight of the bike affects is the momentum. A heavier bike will carry a stronger momentum than a lighter bike, travelling at the same speed (part of Newton's first law).

    The lighter bike is more easily affected by forces because its reduced momentum (as a direct result of reduced weight). If, as in this case, the aerodynamics of each bike were equal, then the lighter bike will be more affected by resistance (it has less momentum) and you'll have to pedal harder to compensate for its "vulnerability" to resistance. On the other hand, the heavier bike will carry its momentum more easily and maintain its speed better than the lighter bike.

    This shouldn;t make that much of a difference though, as 3kg will hardly affect momentum, assuming you and your bike together weigh at least 20 times this difference, so it's almost negligible. Chances are it's a little psychological and maybe your position is different than you're used to. Don't convince yourself that this is harming your performance- it doens't affect you enough to make a difference. The only way it will make you slower is if you think it makes you slower.:)
     
  11. noamporat

    noamporat New Member

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    The bike is a Cervélo R2.5 with D/A 7800 and SSC SLs; this bike should be good isn’t it ? (light a n d stiff..)
     
  12. noamporat

    noamporat New Member

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    Thanks racer dave, roadmax, keydates, donhix1,fixit, Azrael !
     
  13. Roadie_scum

    Roadie_scum New Member

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    f=ma

    so: a=f/m

    Momentum doesn't come into it. To maintain velocity (not accelerate) all that is necessary is for the sum of forces on the bike/rider interface to be zero. The primary forces opposing movement on a flat road are:

    -wind resistance (which is affected by position/wheel choice/other aero considerations)
    -friction (bearing/tyre-road/etc)

    The amount of friction should be reduced marginally by having a lighter bike for the same quality bearings, and significantly more by having better components. This doesn't mean much because the friction component of the equation of movement it is so small anyway. Wind resistance will be unaffected by the weight of the bike.

    The mass of the bike doesn't come into play unless gravity comes into it (climbing/descending), or you need to accelerate or decelerate.
     
  14. Roadie_scum

    Roadie_scum New Member

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    No. In the absence of a force acting on the object it will continue to move indefinitely regardless of its mass.

    f=ma
     
  15. Roadie_scum

    Roadie_scum New Member

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    To clarify - it is the rider that provides the opposing force to wind resistance and friction, whereas the earth itself provides the opposing force to gravity on a flat road. Although a high mass bike would be decelerate less for the same wind resistance, at a constant velocity the rider provides an opposing force which is equal in either case and so the energy requirements to keep either bike going on a flat road are basically the same.
     
  16. donhix1

    donhix1 New Member

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    The more mass you have the more friction on the bearings. I doubt that it would be much more. A bigger rider, with more mass probably would have more wind resisitance which would be a bigger resistance than the friction.
    Now if would could come up with some Super conductor bearings then we would have something. But I think to be truly frictionless they have to be close to absolute zero.
     
  17. closesupport

    closesupport Banned

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    i'd be more inclined to suggest that it was down to air resistance of the frame not the weight and the surface area of the rider plus riding style and the only reason for my suggestion is:
    http://www.sciencemuseum.org.uk/collections/exhiblets/lotus/aerodi.asp

    since my alloy traditiional frame is alot more difficult to maintain speeds on flats incomparisan to my martec (Bp Stealth), i wouldn't have thought it was down to the weight difference however i would like to think it was down to the frame design and the lack of drag it encounters. As for bearings you mean bearing of the ceramic type that chris boardman road on his lotus sport at the time :D

    both have been setup the same and i find the martec (bp stealth) to be eaisier to accellerate and maintain its speed.
     
  18. Roadie_scum

    Roadie_scum New Member

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    That's exactly what I said. The primary influence on energy requirements on a flat road is the aerodynamic characteristics of the bike/rider interface, yes.
     
  19. noamporat

    noamporat New Member

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    Hello!
    I am trying to analyze what are the specific (ranked) causes for a ‘bad day’ (heavy legs);

    Night sleep wise, I know that 8 hours are recommended before a (early) morning ride - I have no Idea how that can be done (i.e. if one has to be up at 4:30 am, one should be asleep at 8:30 pm..) I guess sleeping pills are not to be considered as they might give an unnatural ‘sleepy’ feeling in the morning;

    Have a great day!
     
  20. closesupport

    closesupport Banned

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    i'm lucky if i get 3/4 hrs sleep even less now since starting at 4.00am but i usually ride as soon as i awaken in the aftrnoon, as for heavy legs. i usually find that my afternoon sleep and my enormous breakfast helps wonders.

    Since when i awaken at 3.00am i have 3 vitamin B complex, Vitamin C, Glucosamine sulphate and 2 kelp tablets, this helps me use the carbs and stuff up that i have stored from the day previous, Oops! i forgot to add my x2 Vit B6 and the use of Glutamine in fluids during training sessions.

    but i have found that when i go on long rides, if i use an electrolyte replacement drink along with my normal drinks, this removes the heavy feeling of my legs since the fluid balance is restored.
     
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