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  1. #1
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    How stiffer bike has less energy lost

    I heard abt the stiffer the bike, the lesser the energy will be lost thru your effort in peddling.

    Assuming all things being equal, same rider, same wind direction, same wheel size, same road, etc. Below an example:

    Assuming peddling at 90 rpm at gear 7 on a less stiffer bike, wheel rotates x no. of revolution/min and bike travels a distance of 700m/min. As compare with similar peddling at 90 rpm on a stiffer bike at gear 7, can I assume wheel should also rotates the same x nos. of rev/min that will result in the same distance travel of 700m.

    I like to know how energy lose comes into play.

  2. #2
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    Yes same distance will be covered , but less energy will be put into the stiffer bike to meet that rpm and speed.

    Final power output to the ground is the same, although power output from the rider would vary.

  3. #3
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    Hold on...we need the over 50 dude on an old steel bike to drop in and say stiffness doesnt matter. He should be here shortly, then we can continue this discussion.

  4. #4
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    Yes, but...on long rough rides the stiff bike can beat the snot out of the rider which fatigues him/her. A fatigued rider puts lets power to the pedals. "Special" bikes for Paris Roubaix are made for a reason.

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    Quote Originally Posted by novetan View Post
    I heard abt the stiffer the bike, the lesser the energy will be lost thru your effort in peddling.

    Assuming all things being equal, same rider, same wind direction, same wheel size, same road, etc. Below an example:

    Assuming peddling at 90 rpm at gear 7 on a less stiffer bike, wheel rotates x no. of revolution/min and bike travels a distance of 700m/min. As compare with similar peddling at 90 rpm on a stiffer bike at gear 7, can I assume wheel should also rotates the same x nos. of rev/min that will result in the same distance travel of 700m.

    I like to know how energy lose comes into play.
    In simple physics.... yes. a stiffer bike means less energy is wasted through the frame and more of that energy is applied to the wheels.
    2010 Specialized Secteur Elite upgraded with 32T cassette and does not have Stan's (yet)
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  6. #6
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    Quote Originally Posted by Blue CheeseHead View Post
    Yes, but...on long rough rides the stiff bike can beat the snot out of the rider which fatigues him/her. A fatigued rider puts lets power to the pedals. "Special" bikes for Paris Roubaix are made for a reason.
    Bikes designed for Roubaix are not less stiff, They simply add mechanical/design features that add vertical absorbtion to accomodate the 50 km of cobbles in a 260 km race. They stll make the BB and HT as stiff as their standard race rigs.

  7. #7
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    In actual practice it is not that big of a deal, there are a hundred other fitness
    and mechanical issues that eclipse it.
    All I said was that our son, the apple of our three eyes, Martha being a cyclops, our son is a beanbag, and you get testy!

  8. #8
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    Quote Originally Posted by RkFast View Post
    Hold on...we need the over 50 dude on an old steel bike to drop in and say stiffness doesnt matter. He should be here shortly, then we can continue this discussion.
    Yes, I'm the no helmet wearing 55 yo dude riding a wet noodle of a single speed steel bike with the handlebars flipped upside down, schrader drilled wheels, wearing jean daisy dukes and wife beater dropping all you lyrca wearing mofos on the local MUP.








    Just kidding.

  9. #9
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    Quote Originally Posted by tednugent View Post
    In simple physics.... yes. a stiffer bike means less energy is wasted through the frame and more of that energy is applied to the wheels.
    If it is simple then quantify the amount of energy lost. Give us Watts. Give us a percentage. Is it 1%, 0.1%, 0.01%? What?

    I will wager that energy lost in tire flex is a couple of orders of magnitude greater than what is lost in frame flex.

  10. #10
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    Quote Originally Posted by trailrunner68 View Post
    If it is simple then quantify the amount of energy lost. Give us Watts. Give us a percentage. Is it 1%, 0.1%, 0.01%? What?

    I will wager that energy lost in tire flex is a couple of orders of magnitude greater than what is lost in frame flex.
    If you want in terms of quantifiable percentage, it is no longer simple physics. It becomes quite complex. That is why you have engineers with finite element expertise that the various bike manufacturers figuring this out when they go in and analyze frames
    2010 Specialized Secteur Elite upgraded with 32T cassette and does not have Stan's (yet)
    2009 Specialized Rockhopper Comp 29er upgraded with 36T cassette and Stan's Arch EX rims and tubeless. Considering a 1x10 upgrade
    2013 Cannondale CAADX-6 Tiagra upgraded to 32T cassette and Stan's Alpha 400 rims and tubeless
    2008/2009 Burton T6 156cm with Burton Triad Bindings & DC Judge boots

  11. #11
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    Quote Originally Posted by tednugent View Post
    If you want in terms of quantifiable percentage, it is no longer simple physics. It becomes quite complex. That is why you have engineers with finite element expertise that the various bike manufacturers figuring this out when they go in and analyze frames
    in other words: quite small
    Blows your hair back.

  12. #12
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    Quote Originally Posted by den bakker View Post
    in other words: quite small
    that's what she said...in bed...

  13. #13
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    I can tell you this. When I got my new bike (Tarmac S-Works SL3) I took my old bike (original Tarmac S-Works SL) and took both out for back to back sprints. I ride with a PowerTap, and used the same wheels for the comparison. I was consistently putting it 5-8% higher wattage at the rear wheel on the new bike. The difference...the new bike is more stuff laterally, and I was not spending as much energy wagging the BB side to side.

    Make sense?

  14. #14
    irony intended
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    ^^^^

    I wish I could say it does. But when I get a shiny new toy, objectivity goes out the window....who's to say you weren't just trying harder, unconsciously?

    Having said all that, I'm a believer that stiffer is better but mostly about sprinting/accelerating...

  15. #15
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    Quote Originally Posted by Cyclin Dan View Post
    I can tell you this. When I got my new bike (Tarmac S-Works SL3) I took my old bike (original Tarmac S-Works SL) and took both out for back to back sprints. I ride with a PowerTap, and used the same wheels for the comparison. I was consistently putting it 5-8% higher wattage at the rear wheel on the new bike. The difference...the new bike is more stuff laterally, and I was not spending as much energy wagging the BB side to side.

    Make sense?
    for sprints? assuming just 1000w sprints that would be 50-80watt of loss. now how did materialize: in a warm bottom bracket or in rather strong vibrations in the frame, quite possibly including a lot of noise? the energy has to go somewhere.
    Blows your hair back.

  16. #16
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    Quote Originally Posted by den bakker View Post
    in other words: quite small
    What do you base that off of? If you're drawing that conclusion because of the words 'finite element', then you're mistaken. FEA is routinely used to analyze very large stresses and displacements, as well as the very small. It's a method to break up a complex mechanical system into a finite number of smaller elements whose interactions can be calculated individually; it has nothing to do with the amount of internal stresses dealt with.

  17. #17
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    Quote Originally Posted by Cyclin Dan View Post
    I can tell you this. When I got my new bike (Tarmac S-Works SL3) I took my old bike (original Tarmac S-Works SL) and took both out for back to back sprints. I ride with a PowerTap, and used the same wheels for the comparison. I was consistently putting it 5-8% higher wattage at the rear wheel on the new bike. The difference...the new bike is more stuff laterally, and I was not spending as much energy wagging the BB side to side.

    Make sense?
    Yes, yes it does. And contrary to my perceived effort ratings over a long period of time (which as always dismissed by several here that think they know what's going on in my head and with my body), you were actually able to quantify it with a power meter. One of these days I'll get a power meter and be able to do the same.

    I am not surprised by your result.

  18. #18
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    Even if a flexible frame absorbs energy when you push down on the pedals, that doesn't mean the energy is lost, because at least some of it will be returned when the frame flexes back to its original shape, like a spring.

  19. #19
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    Quote Originally Posted by Mr Evil View Post
    Even if a flexible frame absorbs energy when you push down on the pedals, that doesn't mean the energy is lost, because at least some of it will be returned when the frame flexes back to its original shape, like a spring.
    And how is that side to side flex being converted into forward momentum?

  20. #20
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    Quote Originally Posted by ratherBclimbing View Post
    What do you base that off of? If you're drawing that conclusion because of the words 'finite element', then you're mistaken. FEA is routinely used to analyze very large stresses and displacements, as well as the very small. It's a method to break up a complex mechanical system into a finite number of smaller elements whose interactions can be calculated individually; it has nothing to do with the amount of internal stresses dealt with.
    if you cannot even give an order of magnitude estimate it has to be small. a 1%change would roughly be a water bottle on a climb whereas 10% would be a 15pound backpack. clearly, for any reasonable choice of frame, we are not talking about the equivalent to a 15lb backpack or people would go from struggling at the back to motoring at the front.
    it would mean, for pros, a new frame would destroy the competition completely, even at the few percent level.
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  21. #21
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    The only place this energy (work is actually a more useful term) would - could - possibly go is into the form of heat, from the molecular friction of the bending frame members.

    Of the force (note: force, not energy) used to flex a fractionally less stiff frame, the vast majority is simply returned, unwasted, to the system.

    So how hot does your frame get? Not very, I'd wager.

    If the bending were actually plastic deformation - it bent and stayed that way rather than bending back - there'd be significant loss. The bike also wouldn't last to the end of the block.

    It is not non-zero, but it's not significant, either. No one has ever been able to quantify the amount of energy the frame dissipates, that I've seen. Even if it were quantified, it's not at all universally agreed that this is entirely a negative. Indeed, there are many that do accept the notion that the added comfort of a slightly more flexible bike will produce less fatigue, and so enable greater overall output over time.

    Much* of what is perceived as 'loss' in the sense of frame flex is due to ineffiecient biodynamics, i.e. pressing through the bottom of the pedal stroke. But that can never be put onto the road anyway: it either goes into the frame, or is equally (and harmfully) wasted as an isometric shock to the body.

    Some motion analyses have concluded just the opposite, in fact: That by allowing this BDC effort to move the BB laterally, some amount of it is recovered in the initiation of the subsequent pedal stroke, where a completely stiff bike would put it all back into the skeletal system. I'm not completely convinced, and it's trivial anyway, but just to say there is another way to look at the situation.

    Obviously, track sprinters would feel differently - they aren't on the bike long enough for that shock-induced fatigue factor to kick in, and their riding surface is glass-smooth. And for other riders, the psychological perception of 'fastness' that comes from a stiff-feeling frame may help them 'feel' better and so perform better. The same thing can be shown with tires - it's easily provable that tires at appropriate pressures reduce total rolling resistance over skinny tires inflated to the max (on real roads). But people continue to do max them out because they "know" that it "feels" faster.

    And of course there is the simple matter of confirmation bias - if you believe the bike is stiffer and will make you perform better, any gains will be attributed there, rather than wind, hydration, diet, or other factors.

    About the 'Roubaix' discussion previous: partially true in the modern sense, but it's not categorically true that the tubing/layups aren't changed, or that when changed, they don't contribute to comfort. As hinted at above, one of the great contributors to long-ride discomfort is the shock and buzz transmitted to the rider as they continue to push the pedal downward through the bottom of the pedal stroke. Because their leg is extended and carrying a significant percentage of body weight, shock is transmitted very effectively through the leg to the pelvis and spine. Having some lateral give (rotation, primarily) in the BB can provide a useful level of 'suspension' at that point, reducing rider fatigue.

    This also points out the myth of the 'laterally stiff, vertically compliant' marketing bloviate. Unless there are specific suspension components involved, nearly anything one tries to do to make a bike vertically compliant will make it laterally mushy far more quickly. The overall design of a bike is a very effective truss structure. But there's simply no room to truss effectively against lateral movement. Sure, you can get creative with where you put the materal and where you take it away, but you can't improve one without impacting the other. And since there's a big leverage multiplier on the vertical changes, there's effectively no way to significantly manage vertical feel without giving up perceived stiffness even faster.

    Bottom line: If you like the feel of stiff bikes, ride those. If you like the feel of a more lively machine, choose that. Suiting your personal beliefs, preferences, and riding situation will impact the outcome far more than the absolute physics will.




    *The place where 'real' losses would be available is if during the effective portion of the pedal stroke, chain tension allowed the BB to rotate relative to the seattube, going out of parallel with the rear axle when viewed from above. But chainstay design gets around that issue pretty easily. Perceived stiffess (or flexibility) comes mostly from the lateral plane, and that is almost entirely 'free' with respect to the change in work that can find it's way to the road.
    A good habit is as hard to break as a bad one..

  22. #22
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    Best explanation I've read yet.
    I may be short but I sure am skinny.

  23. #23
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    On a similar subject, you could also question why cycling shoes need to be stiff. When pedalling, the energy transfer seems to be in a direct line from the ball of the foot straight to the cleat. What difference does it make if the sole is still from the ball of the foot to the heel?
    Insert something clever here:

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  24. #24
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    As long as the frame is not physically distorted by the rider's input force the frame's stiffness is (obviously) irrelevent.

    For the frame itself to have an energy loss function, it would have to absorb force as heat and then loose it to the environment, as someone else said. This does happen, but the effect is very small, perhaps a handfull of watts in a worst case violent sprint.

    Where flexible frames do loose rider energy is when the bottom bracket area is displaced laterally from the direction of travel, as when sprinting or climbing out of the saddle. In this case, the rear wheel is twisted off the line of travel, which significantly increases friction.

    A property designed CF frame has a significant advantage in this regard, as the BB area can be over-built in relation to the reast of the frame. When riders say that they stomp on the pedals and the frame just seems to surge forward with no lag or power loss, that's where the feel is coming from. That's easily seen in most CF Giants, Dales, and Treks for instance.

  25. #25
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    All I know is that when I went from a noodly old steel bike to a Cannondale Caad10, my racing results and sprint performances improved and stayed at the higher level.
    * posted by Creakybot 2013 all rights reserved.
    * not actually waterproof.

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