Weight Less important than thought?

Discussion in 'Cycling Equipment' started by Strumpetto, Jul 30, 2007.

  1. Strumpetto

    Strumpetto New Member

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    "What does it matter how much a bike weighs? As a general rule, the overall weight has little to do with how fast it will go or how easy it is to pedal. These things are a direct relationship with rotating mass- the wheels.

    Keep in mind that as wheels turn they create substantial inertial forces that actually force the bike backwards... the bottom of the wheel may be going forwards but the top of the wheel is going opposite. The farther out on the wheel, the more weight becomes a concern.

    Just as a simple computation, saving 10 grams off each wheel (easily done by going with lighter tires and tubes) affords the same performance as saving 280 grams off anything else."


    Any comments?
     
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  2. mikesbytes

    mikesbytes New Member

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    You picked a hot topic

    The nut behind the handlebars is the most important thing. Look at aerodynamics on the nuts body.
     
  3. alienator

    alienator Well-Known Member

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    Actually, this isn't correct. The moment of inertia for a bicycle wheel is pretty small. In fact, the benefit of using wheels with smaller MOI is minimal at best. It's been discussed and demonstrated here several times.
     
  4. bobbyOCR

    bobbyOCR New Member

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    Primarily, the weight of a bike is for personal gratification and the ability to say 'my bike weighs xg less than yours' at a race, just for a motivation boost and morale drop for your competitor.
     
  5. Dietmar

    Dietmar New Member

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    This is wrong. Inertial forces are only created during acceleration of the wheel. So, yes, a heavier wheel (more precisely one with a higher inertial moment) will take more power to accelerate. However, once you are going at constant speed, the weight has no effect, unless you are going uphill, of course.
     
  6. Oigi

    Oigi New Member

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    Weight is important. Your bikes and yours.

    Sure, that importance is a matter of objectives ... if you simply want to ride and enjoy the view and have no intention of going fast and making good times weight isn't that of a matter .. but I don't really buy into the "I don't need go fast" line from most cause those who really don't, don't even bother reading these tech forums :D

    I'm primarilly a xcm mtb rider and only recently started using road bikes for training ... I've found that the more weight I drop on the bikes (and on myself), the faster a can acellerate uphills ... and I don't mean mountain only, cause even on mostly flat circuits there are lots of small inclines and acelleration ability is key for good averages ... grams matter, even if your only competition is the clock and the ability to evolve.

    If you can't afford it .. drop the weight.
     
  7. Strumpetto

    Strumpetto New Member

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    I found that written somewhere on the net, and at first it seemed counterintuitive and incorrect, which it is, as you have all confirmed. However, I don't see the point in being a weight weenie if you've got weight to lose yourself. I suppose if you can't lose the weight, make your bike lose weight. Makes sense.

    However, as an XC MTB'er, riding ability is of supreme importance. If you can't ride well, it doesn't matter how light your bike is, especially on techinal ascents and descents, where getting your center of gravity correct is everything. And with a lighter bike, if you don't have the skills, your front tire is lifting off on the steepest of climbs. It's a different story for roadies. But as far as MTBing, I don't quite buy weight as much.
     
  8. kdelong

    kdelong Well-Known Member

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    I like to ride fast, just like most of the readers of this forum. I feel good when I've knocked a minute ot two off of one of my routes. But I don't race, so my speed is not as important to me as my enjoyment of the sport. Weight is not a big factor in my choice of components, but I also will not add 1 or 2 kg to my bike because the extra effort to pedal would make riding too much like work.
     
  9. mikesbytes

    mikesbytes New Member

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  10. Dietmar

    Dietmar New Member

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    The second equation given by this author is subject to misinterpretation. As I pointed out above, "inertial forces" only come up during acceleration, so the term "Inertial" in the second equation is only nonzero during acceleration, a fact that is not made mention of in the explanation of the terms appearing below the equation. It is, however, correctly explained in the author's Appendix A, and further down in the article.

    Very nice piece, by the way, that gives a lot of useful insight into what is important. My take on this is that the 20 bucks spent on a pair of premium low-rolling-resistance tires may be your best investment, given that rolling resistance can indeed vary by tens of percent between different tires.
     
  11. 531Aussie

    531Aussie Well-Known Member

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    There's no doubt that bike weight is WAY, WAY overstated, including (perhaps especially) wheel weight.

    I'd rather have a 9kg stiff bike with stiff and strong wheels than some 7kg floppy jalopy
     
  12. david462

    david462 New Member

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    an aerodynamic and stiff bike is more important in terms of speed than weight. the total weight is the bike plus rider. use a bike that weighs 3 pounds more than another, but is much stiffer and more aerodynamic, and lose the measly 3 pounds off yourself.
     
  13. Bob Ross

    Bob Ross New Member

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    Um, yes, weight is less important than thought. I'd say there's nothing more important than thought; more cyclists should try it.


    It does however have a lot to do with how hard it is to lift yer freakin' bike up! Which those of us who live in apartment buildings or ride to a workplace in a multifloor office building or store our bikes on ceiling-mounted hangers have to do every freakin' ride!
     
  14. alienator

    alienator Well-Known Member

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    While "stiffness" may feel good to certain riders, there is no evidence, anywhere, that correlates stiffness with improved performance.
     
  15. Dietmar

    Dietmar New Member

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    Very good point. There is this notion floating around that a "flexy" frame will cost you power. However, since the frame deformations that cause the feeling of flexibility are elastic, they do not rob you of any power at all. This is not to say that there are not good reasons to prefer a stiff (as in laterally stiff, mind you) frame over a less stiff one, but performance, in the strict sense of the word, is not one of them.
     
  16. ScienceIsCool

    ScienceIsCool New Member

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    Agreed with Dietmar and Alienator with one pedantic nit to pick. The power lost into frame deflection does not get returned back into forward momentum. It gets sucked up by your body, frame hysteresis, etc. So in that way the power is indeed lost. It's just a very small amount.

    The small amount assertion is based on taking published numbers for frame deflection and calculating the energy of a simple spring model, assuming certain things about power and cadence. I'm pretty sure I've written about it in another thread.

    John Swanson
    www.bikephysics.com
     
  17. kdelong

    kdelong Well-Known Member

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    I'm sure that you have too, John, because I had to go look up the word "hysteresis".
     
  18. mikesbytes

    mikesbytes New Member

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    It struck me after reading that articile, that getting a fitout is probably the best single improvement I can make.

    Weight wise, it seem to me that you needed to drop 4kg to get any noticable improvement due to weight reduction. mmm... what's for dinner ?
     
  19. sogood

    sogood New Member

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    As CSC riding aero Cervelo frames doesn't clean up the tour or others on the racing calendar, I question just how much benefit an aero frame really provides.
     
  20. david462

    david462 New Member

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    so after reading all the replies it just seems like weight, stiffness, and aero is not a big factor at all. then why do we spend thousands on our bikes? c'mon, there has to be a difference between the $600 bike and the $6000
     
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