What is the truth behind bike weight? Does it really help THAT much?



thoughtforfood

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Crankyfeet said:
Another typical demeaning type "I'm superior" post from the cyclingforums science legend. Well put argument... not.

Here's the point. John makes claims of his model producing linear efficiencies as a function of "power". But the amount of deflection in the frame is not proportional to power. It is proportional to the torque which is dependant on resistance to one's pedal thrust.

So if the model theory/results are invalidated, then they aren't worth much in my book.

I might be wrong, but please show me my error in thinking. I'm prepared to accept that I might have made an error. Can't see it myself though. Otherwise I will have to assume there is no answer to my points of contention and they invalidate the model.

Science is cool because it is egoless and searches for the truth as its primary value. Hypothesis, theory, testing, data, and peer review are all part of this process, as you should know alienator, assuming your claims of being a scientist are true (given your other snake oil BS though... I'm not convinced).

So please don't belittle Phill, the qualified mechanical engineer, with personal condescension. Stick to the points in the debate. Which so far I see that your points are baseless, other than some claim that you have done analysis and looked at all the research on this topic, and stand behind John's results blindly it seems because they support your own opinion.
I dont think Mr. Chickenshit will be back any time soon. He is the cowardly type. Demean someone, get your ass handed to you for doing that, and then lay low. I think I called him a "fuckwit." I stand by that observation.
 

Crankyfeet

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thoughtforfood said:
I dont think Mr. Chickenshit will be back any time soon. He is the cowardly type. Demean someone, get your ass handed to you for doing that, and then lay low. I think I called him a "fuckwit." I stand by that observation.
I think I'll need to see your data... :D .

Please explain your model that produced "fuckwit" as a result. I stuck him into my model and it produced "Pretentious Patronizing *****". I think you might have included his self-perceived "power" instead of just looking at all his ******** "torque".... :D
 

thoughtforfood

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Crankyfeet said:
I think I'll need to see your data... :D .

Please explain your model that produced "fuckwit" as a result. I stuck him into my model and it produced "Pretentious Patronizing *****". I think you might have included his self-perceived "power" instead of just looking at all his ******** "torque".... :D
Damn, you are right..also his full of **** coefficient is off the charts...how did I miss that?
 

alienator

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thoughtforfood said:
I dont think Mr. Chickenshit will be back any time soon. He is the cowardly type. Demean someone, get your ass handed to you for doing that, and then lay low. I think I called him a "fuckwit." I stand by that observation.

uh-huh. Yeah. That must be it, because you said so. "ass handed to you..." uh-huh.
 

Crankyfeet

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alienator said:
uh-huh. Yeah. That must be it, because you said so. "ass handed to you..." uh-huh.
Fortunately your opinion of ass-handing is of no consequence. We'll let independent observers be the judge of that, Mr. "Done did all the analysis - but got no data"... :D

post edit - sorry it's "Mrs." My bad... it was a false assumption... :eek:
 

Crankyfeet

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alienator said:
uh-huh. Yeah. That must be it, because you said so. "ass handed to you..." uh-huh.
uh-huh. Yeah. That must be it, because you said so. "Stiffness of the frame is irrelevant..." uh-huh.
 

Crankyfeet

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thoughtforfood said:
You could actually put that quote to music, you are talented!
Look, let's not get too personal thoughtforfood. Alienator does make some useful contributions that members appreciate. We don't want him to sulk off and leave the forum, like he did for a week the last time his ******** was exposed.

He might run away and go to another cycling forum like RBR. Hang on... he can't do that. He was banned from there for being a pretentious patronizing *****.... Maybe somewhere else.
 

thoughtforfood

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Crankyfeet said:
Look, let's not get too personal thoughtforfood. Alienator does make some useful contributions that members appreciate. We don't want him to sulk off and leave the forum, like he did for a week the last time his ******** was exposed.

He might run away and go to another cycling forum like RBR. Hang on... he can't do that. He was banned from there for being a pretentious patronizing *****.... Maybe somewhere else.
I think he needs to go to a rap forum and post because his "uh-huh's" have some style.
 

Crankyfeet

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I think you're right about that meter in his prose. It's got beat....

Getting back on topic. The weight of your bike is a factor... especially if your competing... it just comes down to whether you want to pay for its benefits or not (assuming you are not compromising anything else like strength or (sic) stiffness).

To all those who think its irrelevant, please stick five pounds of weights in your jersey pocket and see if there is any difference on the hills. You might not notice that much... but I bet you do.

If you don't... I can assure you with some physics... that it is having an effect.... just as it does if your bike has five pounds more weight... center of gravity differences notwithstanding.

For the average guy who wants to get fit, it doesn't mean anything. If you want to compete and get up the hill faster, it means something.
 

artemidorus

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Crankyfeet said:
Here's the point. John makes claims of his model producing linear efficiencies as a function of "power". But the amount of deflection in the frame is not proportional to power. It is proportional to the torque which is dependant on resistance to one's pedal thrust. You can't load up the frme much if you take the chain off and stomp down on the pedal. But try putting a 300 tooth chainring on the front and then stomp down from a stationary start and see how much force is lost at the tire/road connection.
John did use torque in his model; he derived average torque from power according to an arbitrary cadence (Power=k.torque.cadence) and then multiplied it by an arbitrary 4 to give a peak torque which he believes is likely to be more than the real peak torque.
 

Crankyfeet

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artemidorus said:
John did use torque in his model; he derived average torque from power according to an arbitrary cadence (Power=k.torque.cadence) and then multiplied it by an arbitrary 4 to give a peak torque which he believes is likely to be more than the real peak torque.
John said that efficiency was a linear function of power. Energy loss is a squared function of torque (F=kx, Energy absorption loss = 1/2 kx^2, increase force and deflection is increased proportionately, Energy absorption in the frame is increased exponentially as a square of the deflection).

Power is irrelevant and a derivative function which is the rate of torque - or includes cadence in simpler terms.

Please correct me if I'm wrong.
 

Crankyfeet

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Travis44 said:
Wow, quite the argument going on. What is the thread about again?
It's about science. Some of us are trying to use it. One of us is just spouting it.

But apologies to you Travis44 if it has gone off your original question. If you want more detail as to the effects of weight on speeds/times up hills of varying slopes, and also the often neglected effect on acceleration in races (like coming out of a corner in a crit), I can perhaps help, but it will take some time to do the calculations.
 

artemidorus

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Crankyfeet said:
John said that efficiency was a linear function of power. Energy loss is a squared function of torque (F=kx, Energy absorption loss = 1/2 kx^2, increase force and deflection is increased proportionately, Energy absorption in the frame is increased exponentially as a square of the deflection).

Power is irrelevant and a derivative function which is the rate of torque - or includes cadence in simpler terms.
Power is not irrelevant to the calculation because it is used firstly to calculate average and peak torque (and hence peak deflection of the frame and energy diverted to bending the frame) and secondly as the denominator of the efficiency fraction.

Cadence is critical to the model - lower the cadence for a given power and you increase torque and hence potential energy wastage into the frame. I'm not sure what cadence he chose for his calculation.

As I've posted earlier, I think it is quite possible that altered tracking of the rear wheel might contribute more to inefficiency than frame "spring" loading, at least in a hypothetical super-noodly frame.
 

Crankyfeet

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artemidorus said:
Power is not irrelevant to the calculation because it is used firstly to calculate average and peak torque (and hence peak deflection of the frame and energy diverted to bending the frame) and secondly as the denominator of the efficiency fraction.
There is no need to work backwards from power. At any given power, there are infinite torques, depending on the cadence you choose. It is the torque that deflects the frame. The energy loss is a function of varying torque (actually the torque squared since the energy loss is proportional to the deflection squared and the deflection (x) is proportional to the torque). Power introduces the irrelevant variable of cadence, which doesn't have anything to do with frame deflection IMHO.

The resulting efficiencies would need to be tabulated either as a function of peak torque, or if you want to use power, you are going to need lots of columns for different cadences.

artemidorus said:
Cadence is critical to the model - lower the cadence for a given power and you increase torque and hence potential energy wastage into the frame. I'm not sure what cadence he chose for his calculation.
You have just explained my point that energy loss can vary for the same power, depending on the cadence (which affects the torque). How can you talk about percentage power loss being constant with respect to power, if the energy loss can vary at the same level of power with different cadences?
artemidorus said:
As I've posted earlier, I think it is quite possible that altered tracking of the rear wheel might contribute more to inefficiency than frame "spring" loading, at least in a hypothetical super-noodly frame.
It could well be very important... but it is not included in the model. As are a myriad of other factors not included, like the effect of tilting the frame from side to side on the respective moment arms and the tilting effect on lateral slippage of the tires, and the effect of other areas of elasticity in the system being loaded first before the frame starts to deflect.

It is complicated IHMO. An empirical test would be perhaps the best, if we could just design a repeating robot to replicate a human cyclist mashing a sprint.
 

Jono L

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Apr 28, 2005
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Crankyfeet said:
uh-huh. Yeah. That must be it, because you said so. "Stiffness of the frame is irrelevant..." uh-huh.
Crankyfeet 15, Alienator 0

EDIT-On in depth reading it's more like more like two sets to nil:D
 

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