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#951
01-23-13, 01:28
 FrankDay Senior Member Join Date: Sep 2010 Location: N. California Posts: 2,738

Quote:
 Originally Posted by JayKosta ==================================== Frank, I don't understand why you think the variations in crank speed through a rotation are unimportant. If the crank speed was constant through the full rotation, then the torque would also be constant. I think that the torque decreases at certain crank positions mainly because the crank speed slows at those locations. Basically the foot/feet doesn't (or can't) maintain enough circular speed to keep a constant torque. Jay Kosta Endwell NY USA
Huh? There is always some positive torque on the two crank arm system on bicycles with a free wheel because, if there weren't, the cranks would come to a quick stop (the cranks would go "forever" but the attached legs are always accelerating or decelerating in a more linear fashion which requires substantial energy). So, variation in crank speed simply is a result of newtons laws. F=ma. When crank forces are small wind and rolling resitance slows the bike and crank speed and when they are large bike and crank speed increases. At cadences of 90 or so these changes are so small (because of the relatively huge mass of the rider) that variations are miniscule. The question is whether these variations can affect power output. I submit they are so small, whether one is using a non-circular ring or anything else that they have no affect on power production.

edit: and a slower pedal speed makes it easier to apply torque to the crank (not harder) because it is not necessary to get the foot up to a higher pedal speed before force is applied.
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Last edited by FrankDay; 01-23-13 at 01:31.
#952
01-23-13, 11:37
 Alex Simmons/RST Senior Member Join Date: Mar 2009 Location: Sydney, Australia Posts: 1,175

Quote:
 Originally Posted by JayKosta If the crank speed was constant through the full rotation, then the torque would also be constant.
Ummm, no.
...
#953
01-24-13, 02:59
 JayKosta Senior Member Join Date: Nov 2010 Posts: 424

Frank and Alex,

I'm still confused about the 'crank speed variation' and 'torque variation' relationship.

I DO agree that for actual 'on road/track' cycling the torque can vary without affecting the bike's speed due to things such as wind, surface inclination, etc.
But what about for a theoretical 'steady-state resistance' situation (or perhaps a stationary trainer) where the resistance is constant?

In the steady-state situation, I think that constant crank speed and constant total crank spindle torque is needed to give constant wheel speed.
Yes, the torque varies between left and right crank arms, but the spindle speed and torque needs to be constant to give constant wheel speed, when the resistance is constant.

In steady-state resistance, how could a change in crank speed NOT result in a change in wheel speed?

Thanks,
Jay Kosta
Endwell NY USA
#954
01-24-13, 03:57
 FrankDay Senior Member Join Date: Sep 2010 Location: N. California Posts: 2,738

Quote:
 Originally Posted by JayKosta Frank and Alex, I'm still confused about the 'crank speed variation' and 'torque variation' relationship. I DO agree that for actual 'on road/track' cycling the torque can vary without affecting the bike's speed due to things such as wind, surface inclination, etc. But what about for a theoretical 'steady-state resistance' situation (or perhaps a stationary trainer) where the resistance is constant? In the steady-state situation, I think that constant crank speed and constant total crank spindle torque is needed to give constant wheel speed. Yes, the torque varies between left and right crank arms, but the spindle speed and torque needs to be constant to give constant wheel speed, when the resistance is constant. In steady-state resistance, how could a change in crank speed NOT result in a change in wheel speed? Thanks, Jay Kosta Endwell NY USA
You are correct. If all the variables are held constant then in a steady state situation a constant pedal torque would result in a constant pedal/wheel speed. This would be the situation if an electric motor were driving the bicycle. But, it simply cannot happen in the real world with humans powering the bicycle.
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#955
01-24-13, 09:45
 Alex Simmons/RST Senior Member Join Date: Mar 2009 Location: Sydney, Australia Posts: 1,175

Quote:
 Originally Posted by JayKosta Frank and Alex, I'm still confused about the 'crank speed variation' and 'torque variation' relationship. I DO agree that for actual 'on road/track' cycling the torque can vary without affecting the bike's speed due to things such as wind, surface inclination, etc. But what about for a theoretical 'steady-state resistance' situation (or perhaps a stationary trainer) where the resistance is constant? In the steady-state situation, I think that constant crank speed and constant total crank spindle torque is needed to give constant wheel speed. Yes, the torque varies between left and right crank arms, but the spindle speed and torque needs to be constant to give constant wheel speed, when the resistance is constant. In steady-state resistance, how could a change in crank speed NOT result in a change in wheel speed? Thanks, Jay Kosta Endwell NY USA
Refer to those charts I put up earlier - they show the measured variation in instantaneous crank speed per revolution on a trainer in a steady state scenario. In the first one, at 250W and 90rpm, the variance from highest to lowest instantaneous crank speed during a crank revolution is about 0.5%.

We already know that the instantaneous torque being applied will be in a roughly sinusoidal pattern from near zero newtons-metres to a peak twice per revolution. At 250W and 90rpm, that peak will be approx 50Nm.

The reason the crank doesn't vary speed much during the two torque minimums each pedal stroke is the stored kinetic energy in the system is sufficient to prevent the speed dropping much during those fractions of a second even though there is a variety of resistance forces still acting against the wheel.

On the road and track, the stored KE of the bike/rider is pretty high.

Simple example to demonstrate - when riding along the flat on good road and you completely stop pedalling, you don't suddenly stop moving forward. You slow down quite gradually. Same on an indoor trainer - the wheel doesn't stop the instant you stop pedalling - it continues to roll, slowing down, usually faster than it would on the road because the stored KE is less but it's still enough that the variation in crank speed during a pedal stroke is pretty small.
#956
01-24-13, 14:27
 coapman Senior Member Join Date: Mar 2009 Posts: 695

Quote:
 Originally Posted by FrankDay Remember, there are 360º to the pedaling circle and the pedal is rising during 180º of that circle. Once the pedal is beyond BDC it is rising until it gets to TDC so anyone trying to "scrape the mud off the shoes" is applying positive force when the pedal is rising even if they are not thinking about "pulling up". Or those like you, because you are starting your "max power" application before TDC are also applying positive force when the pedal is rising even though you are not "pulling up". I believe that best technique involves "scraping the mud off" well across the bottom and starting the "push over the top" well before the top, and complete unweighting in between, in addition to pushing down with substantial force. Focusing on only a small portion of the circle wastes a lot of potential IMHO.

In the natural 180 deg. or less pedalling power stroke the brain is working to a set pattern, as it applies that maximal down force it is also preparing the muscles of the other leg to get most out of that down stroke. Scraping the mud from your shoe etc upsets this pattern and concentration. Pedalling is a simple operation, why complicate it with extra activity that results in an overall loss of chain drive power. The only way to increase that chain drive power per pedal stroke without upsetting the natural pedalling pattern is to extend that power stroke to the full 180 deg. and increase the torque return from the maximal force you are applying. If you are not capable of applying maximal torque over the top, you are better off forgetting about that sector as a source of extra power.
#957
01-24-13, 17:05
 JayKosta Senior Member Join Date: Nov 2010 Posts: 424

Frank and Alex,

Continuing on the 'crank speed' and 'torque' issue, I think there are 2 primary ways that cyclists perform their 'pedaling technique', but it is certainly not all 1 way or the other - probably a mix of both in some ratio that is biased either way. The differences are probably due to aspects of the individual's mental and physiological makeup.

CRANK SPEED group - is more concerned with moving the cranks to achieve the desired rotational speed. And perhaps is also concerned with having a constant crank speed.

TORQUE group - is more concerned with applying power/force to the pedals to achieve the desired amount of work. And, again, perhaps is also concerned with having torque throughout the crank rotation.

I think EITHER method can produce good power output, and good results.

But it would be interesting (and beneficial?) to know what method is used by various top-performing cyclist.

I think my primary style is about 70% TORQUE, and 30% CRANK SPEED. When I put more emphasis on CRANK SPEED it takes a lot of mental concentration and I need to think more about my muscle use.

FRANK, do you have any input from your PC users about whether they view the PC training as improving speed or torque?

Jay Kosta
Endwell NY USA

Last edited by JayKosta; 01-24-13 at 17:07.
#958
01-24-13, 19:12
 FrankDay Senior Member Join Date: Sep 2010 Location: N. California Posts: 2,738

Quote:
 Originally Posted by JayKosta Frank and Alex, thanks for your info. Continuing on the 'crank speed' and 'torque' issue, I think there are 2 primary ways that cyclists perform their 'pedaling technique', but it is certainly not all 1 way or the other - probably a mix of both in some ratio that is biased either way. The differences are probably due to aspects of the individual's mental and physiological makeup. CRANK SPEED group - is more concerned with moving the cranks to achieve the desired rotational speed. And perhaps is also concerned with having a constant crank speed. TORQUE group - is more concerned with applying power/force to the pedals to achieve the desired amount of work. And, again, perhaps is also concerned with having torque throughout the crank rotation. I think EITHER method can produce good power output, and good results.
Of course either method can produce good power output no one would deny that both Armstrong and Ulrich were able to produce "good" power despite having completely different approaches regarding speed and torque. The question then becomes what is optimal and a further question is "can more be done"?
Quote:
 But it would be interesting (and beneficial?) to know what method is used by various top-performing cyclist.
And, it is not particularly good evidence that the best riders are using one method or another as to what is best because we don't know what else they are doing to become "best" since both Ulrich and Armstrong (and probably almost everyone else in that era) were doping.
Quote:
 I think my primary style is about 70% TORQUE, and 30% CRANK SPEED. When I put more emphasis on CRANK SPEED it takes a lot of mental concentration and I need to think more about my muscle use.
Any technique that requires the rider to think about when riding is likely to be less than optimal, at least for any event lasting more than a few seconds.
Quote:
 FRANK, do you have any input from your PC users about whether they view the PC training as improving speed or torque?
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Life is short, both reading my posts and training with PowerCranks will make it seem longer

Last edited by FrankDay; 01-24-13 at 19:25.
#959
01-24-13, 21:24
 FrankDay Senior Member Join Date: Sep 2010 Location: N. California Posts: 2,738

Quote:
 Originally Posted by coapman In the natural 180 deg. or less pedalling power stroke the brain is working to a set pattern, as it applies that maximal down force it is also preparing the muscles of the other leg to get most out of that down stroke. Scraping the mud from your shoe etc upsets this pattern and concentration. Pedalling is a simple operation, why complicate it with extra activity that results in an overall loss of chain drive power. The only way to increase that chain drive power per pedal stroke without upsetting the natural pedalling pattern is to extend that power stroke to the full 180 deg. and increase the torque return from the maximal force you are applying. If you are not capable of applying maximal torque over the top, you are better off forgetting about that sector as a source of extra power.
If you want to restrict yourself to what you believe is natural why don't we talk about what is really natural to humans, running. In running all of the forces that provide power are backwards (the downward forces only support the body). To say we should be restricting our power production to the pushing phase because it is "natural" when the reason this is "natural" is we all learned the coordination on platform pedals, where if we pulled back, lifted on the backstroke, or pushed forward over the top with any force meant our foot would come off of the pedal, is just silly to me. Yet that is the philosophy of many more than just you (to include the entirety of the "just push harder" crowd).
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Life is short, both reading my posts and training with PowerCranks will make it seem longer
#960
01-24-13, 22:07
 CoachFergie Senior Member Join Date: Apr 2009 Location: Christchurch, New Zealand Posts: 2,302

Quote:
 Originally Posted by FrankDay If you want to restrict yourself to what you believe is natural why don't we talk about what is really natural to humans, running. In running all of the forces that provide power are backwards (the downward forces only support the body). To say we should be restricting our power production to the pushing phase because it is "natural" when the reason this is "natural" is we all learned the coordination on platform pedals, where if we pulled back, lifted on the backstroke, or pushed forward over the top with any force meant our foot would come off of the pedal, is just silly to me. Yet that is the philosophy of many more than just you (to include the entirety of the "just push harder" crowd).
Nice that what you think happens is at odds with the well performed research that compares pedalling with and without cleats (no difference), pedalling effectiveness (less effective = more power), being instructed to change the application of power around the pedal stroke (no improvement in power), changing crank length (no improvement in power or efficiency), using a crank that forces you to change the application of power around the stroke (no improvement in power and only 1 study saying an improvement in efficiency and every subsequent study saying there isn't), using elliptical rings (no improvement in power expect for a very short term test).

Maybe what you think is just thrown out there to sell Gimmickcranks.
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http://coachfergblog.blogspot.co.nz/

Power Meters like Powercranks don't improve performance one bit. But at least with a Power Meter you can see yourself not improving because of it

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