For the "pedaling technique doesn't matter crowd"

[JayKosta]

Similar pattern but it would be incorrect to think of the speeds at the peak and trough of the pseudo-sinusoidal pattern as being significantly variable, when even on a trainer with fairly low inertial loads the difference in highest and lowest instantaneous crank rotational speed is only ~ 0.5%, and I suspect even less than that at higher inertial loads.

=======================================

Alex,

I agree that the crank rotation speed variance is small, but once the rotation speed begins to reduce (even a little), the torque reduces by a much greater percentage - that happens because the inertia of the bike&rider keeps the variance of bike speed less than the variance of crank speed.
The cyclic whir-whir on a trainer/rollers is because only wheel inertia is present in that situation and the wheel rotational variance is more similar to the crank variance. Just because the whir-whir is not heard on the road/track does not mean that the crank speed variance that causes the whir is not present, only that inertia of the bike&rider masks wheel speed variance.

Another concern of mine with crank speed variance is that the force needed to accelerate the crank back to its peak speed is basically 'wasted', it would take less overall force (rotational power to the crank) if the crank speed was truely constant.

And YES, I realize there is a big question about whether a cyclist can produce constant crank speed, and also whether that technique would actually produce more useful power over the duration of an event.

Jay Kosta
Endwell NY USA

 

[FrankDay]

but once the rotation speed begins to reduce (even a little), the torque reduces by a much greater percentage - that happens because the inertia of the bike&rider keeps the variance of bike speed less than the variance of crank speed.

You have a big misconception. Bike speed and crank speed are not independent in normal riding. They are never independent on a fixie. As long as the gearing remains the same crank speed is determined by bike speed except when coasting. If the crank speed is ever lower than "required" by bike speed the freewheel will override and the rider will feel that. That simply never happens in normal riding except when the rider intentionally coasts. If one could eliminate all friction the rider should be able to take his feet off the pedals, bringing torque to zero, and the pedals would keep turning in concert with the bicycle and the bike would never slow down (you can't do that while keeping the feet on the pedal because of the energy needed to "pump" the legs up and down, the leg motion is not circular so cannot continue without continued energy input.

Further, torque and crank speed are also not tied together. Take this example when the bike is going zero mph. It doesn't matter what the torque is on the crank be it zero, small, large, or very large the initial bike speed will still be zero. The only effect of the different bike torques is how fast the bike will accelerate but the bike speed and crank speed are still directly related as long as the wheel is not slipping. So, large variations in torque (unless torque falls to less than zero) do not mean large variations in crank speed because crank speed is tied to wheel speed by the chain.

Edit: as I have thought about this and if someone wanted to get really technical (which seems to happen a lot here on the interweb) crank speed and wheel speed are not entirely 100% in lock step. The reason for this is chain sag, which is determined by chain tension, which is determined by crank torque. So, the easiest example would be when the bike is stopped. Going from a large forward torque to a small forward torque one would watch the pedal move back just a smidge. This is because gravity causes a little more chain sag when tension is removed from the chain (isn't this part of the reason the polar power meter worked?). So, I guess pedal speed would vary more than bike speed as pedal torque varied around the pedal circle but the amount of additional variation is so small as to be inconsequential, IMHO, so I stand by what I wrote above for the purpose of simplifying analysis and calculations.

 

[Alex Simmons/RST]

You have a big misconception. Bike speed and crank speed are not independent in normal riding.

Correct.
Hence the measured crank speeds even on a trainer show such little variance.

(isn't this part of the reason the polar power meter worked?).

The Polar (by Alan Cote) worked by measuring the vibrational frequency of the chain (using a device akin to an electric guitar pickup) and the chain speed (sensor on dérailleur).

Vibrational frequency is proportional to the tension on the chain, mass of the chain and the length of chain between ring and cog (think of piano, harp or guitar strings - the string's thickness/mass, length and tension all change its natural vibration frequency).

Hence, if you know the mass and length of the chain (readily determined), then the only variable (outside of external signals/noise) that's left to impact on vibrational frequency is tension.

Chain tension x chain speed = power

 

[JayKosta]

...
If the crank speed is ever lower than "required" by bike speed the freewheel will override and the rider will feel that. That simply never happens in normal
riding except when the rider intentionally coasts.
...

====================
Frank,
(and I am thinking about a bike with freewheel, not a fixie)
My viewi of what happens when 'crank speek is lower than "required" by bike speed' is that

1) the bike will immediately begin to slow (decelerate) due to mechanical resistance/friction and wind drag.

2) If the reduced crank speed is slighlty greater than the new slower speed of the bike, the rider will still be producing torque.

3) If the reduced crank speed does product torque, then
a) either the bike speed will increase (if the torque give increase crank speed),
or
b) the bike speed will continue to decelerate, but at a reduced rate because the torque and crank speed are less that what is needed to overcome the slowing of the bike due to mechanical resistance & wind drag.

When the rider is again able to produce high torque and crank speed, the bike will accelerate to its previous speed.

Jay Kosta
Endwell NY USA

 

[FrankDay]

====================
Frank,
(and I am thinking about a bike with freewheel, not a fixie)
My viewi of what happens when 'crank speek is lower than "required" by bike speed' is that

1) the bike will immediately begin to slow (decelerate) due to mechanical resistance/friction and wind drag.

2) If the reduced crank speed is slighlty greater than the new slower speed of the bike, the rider will still be producing torque.

3) If the reduced crank speed does product torque, then
a) either the bike speed will increase (if the torque give increase crank speed),
or
b) the bike speed will continue to decelerate, but at a reduced rate because the torque and crank speed are less that what is needed to overcome the slowing of the bike due to mechanical resistance & wind drag.

When the rider is again able to produce high torque and crank speed, the bike will accelerate to its previous speed.

Jay Kosta
Endwell NY USA

Jay, that is an interesting way to think about things and I understand what you are saying and I don't want to be nitpicky but that is simply the wrong way of looking at things. Unless you can describe what is going on using math it is impossible to predict what will happen. If you cannot predict you do not understand. The bike speed varies, not because the crank speed slows but because the instantaneous power drops to below that needed to maintain current speed. As long as there is some forward force on the pedal it will be moving in unison with the bike speed because any forward force is always trying to increase the pedal speed (F=ma). The bike speed only drops when the forward force on the pedals is less than the retarding force transmitted to the pedals by the wind and rolling resistance, when adding the two forces together gives a negative number. So, when the forward force is greater than the retarding force coming from the wind and rolling resistance the bike will speed up, when it is less it will slow down. While the variations in speed you describe do occur you have the cause and effect backwards. Everything that happens can be described using calculus derived from the simple formula F=ma and how the parts of the bicycle are mechanically connected and acting as levers. Nothing can be described mathematically using your premise that I know of.

While your understanding of what happens physically is correct you would be better served by describing it in terms that are mathematically correct vs a laymans interpretation as it will give you more credibility if you ever in the future are talking about this with someone knowledgeable in this area.

 

[coapman]

Here is a study out of Norway that sort of kicks that notion into the garbage can, at least if you think improving efficiency is something to aim for. Now if they will just repeat this and see if power correlates as well and this debate should pretty much end.

I don't agree with everything they say in their analsis but their data is their data.

From the abstract (DC is essentially the size of the force at top and bottom dead center): "Results: Mean work rate was 279 W, mean FCC was 93.1 rpm, and mean GE was 21.7%. FE was 0.47 and 0.79 after correction for inertial forces; DC was 27.3% and 25.7%, respectively. DC size correlated better with GE (r = 0.75) than with the FE ratio (r = 0.50). Multiple regressions revealed that DC size was the only significant (P = 0.001) predictor for GE. Interestingly, DC size and FE ratio did not correlate with each other.

Conclusions: DC size is a pedaling technique parameter that is closely related to energy consumption. To generate power evenly around the whole pedal, revolution may be an important energy-saving trait."

Can you give me a layman's interpretation of this research ?

 

[JayKosta]

...
The bike speed varies, not because the crank speed slows but because the instantaneous power drops to below that needed to maintain current speed. .
...

=========================================

Frank,

I think our only point of contention is the item above.

My thinking is that since F=ma
F= m(change in velocity / change in time)
or
F= m(dv/dt)
So that a change in speed (dv) can result in a change in F, as well as a change in F can result from a change in speed (dv).

My contention is that in road pedaling, the change in crank speed in the low torque sectors is the cause of a significant portion of the change in F.

I think that most well-trained competitive cyclist have adequate strength to maintain constant torque thru a complete pedal rotation when a 'sub-maximal' amount of torque is used (i.e at a level of exertion somewhat less than 'all out').

In this case, in the low torque sectors it is a reduction in crank speed that yields the reduced torque. This reduction in crank speed occurs because the cyclist has difficulty with the physical movement of maintaining the crank speed due to the needed change in muscle usage and timing/coordination of the pedal stroke in the low torque sectors. I doubt that the cyclist lacks the raw strength needed to produce the torque, but that he cannot maintain the crank speed to achieve the torque.

Probably some testing combination of power meter, and muscle & nerve activation is needed to give a more complete understanding of what is really happening.

---- this sounds like the end of a journal article that concludes with
"Our results indicates that further research is needed that would provide valuable information".

Jay Kosta
Endwell NY USA

 

[FrankDay]

So that a change in speed (dv) can result in a change in F, as well as a change in F can result from a change in speed (dv).

Well, while I guess one might think that one has to ask what is a change in speed (it is an acceleration) and how did it come about. This is not a chicken or egg thing. In this case the Chicken (Force) definitely came first.

I think that most well-trained competitive cyclist have adequate strength to maintain constant torque thru a complete pedal rotation when a 'sub-maximal' amount of torque is used (i.e at a level of exertion somewhat less than 'all out').

While that might be true in space where there is no gravity it is not true in a strong gravitational field if one is just looking at one leg. When one combines the two legs together the sum can look pretty constant but the pedal forces are coming from the resultant force of many different muscles working together, some big and strong and others somewhat weaker. As I stated before it is possible to get an almost even torque around the circle when both legs are included as I can do it, achieving spinscan numbers 95 and above. But, such accomplishments are rare. It is pretty rare to see any cyclist with spin scan numbers above 80. Take a poll of Computrainer owners and see what you get. You will be surprised how "low" most of their numbers are.

---- this sounds like the end of a journal article that concludes with
"Our results indicates that further research is needed that would provide valuable information".

No further research necessary. In bicycle pedaling the instantaneous pedal forces dictate both bike and crank speed. Crank speed does not dictate pedal force. For crank speed to dictate pedal force the situation would have to be an outside force driving crank speed against a flacid leg. That could only happen when riding a fixed gear bike and slowing down or going downhill. It could never occur on a freewheel bike (unless one leg was driving the other, flacid, leg and then it would only occur on one leg) except in the case when we see negative forces on the upstroke when the cranks act as one, where pedal speed may play a partial role. This is not the part of the stroke where the bike is slowing down.

I guess some who call themselves "scientists" believe that the universe is only 8,000 years old and that further research is necessary before they will believe the 14 billion year hypothesis. More "scientists" are probably in agreement that the age of the universe is a true controversy than will take your side in the above argument.

 

[JayKosta]

Frank,

Perhaps we just 'need to agree to disagree' about this, but one last question.

With cranks similar to 'Power Cranks', what does the rider need to DO to regain producing torque with a crank arm if/when it rotates out of 180 degree alignment with the other crank arm?

My guess is there are 2 most likely answers -
1) apply more force to the trailing crank arm (by doing what).
or
2) increase the speed of the trailing crank arm to catch-up with the leading arm.

Jay Kosta
Endwell NY USA

 

[FrankDay]

Frank,

Perhaps we just 'need to agree to disagree' about this, but one last question.

With cranks similar to 'Power Cranks', what does the rider need to DO to regain producing torque with a crank arm if/when it rotates out of 180 degree alignment with the other crank arm?

My guess is there are 2 most likely answers -
1) apply more force to the trailing crank arm (by doing what).
or
2) increase the speed of the trailing crank arm to catch-up with the leading arm.

A quote you might find useful -
"Some people believe they are thinking when they are just rearranging their prejudices".

Jay Kosta
Endwell NY USA

What does a person need to do when on PowerCranks to start applying torque when they fall out of synch (because they stopped applying torque). That is easy, all they need do is start moving the foot as fast as the other pedal. As soon as the foot is moving as fast as the other pedal which is applying torque it will lock up and the two cranks will remain in the same relative position to each other regardless of how much more torque is applied.

Then, the question you might ask is, if the cranks will remain in the same relative position when I am pushing forward on them how do they ever get to be 180º again? The answer to that is "Easy." All one does is keep the pressure off the one of the cranks allowing the cranks to fall further apart until they line up again and then start applying positive pressure and, voila, they are again locked up at 180º. The clutch will lock up whether one applies a lot or a little positive pressure. Sounds hard to get it just right but it is easy. Most people do this by coasting with one leg at the bottom while pedaling with the other let and then starting pedaling with the coasting leg as the power leg comes over the top. (Edit: It doesn't matter how much positive force is on the right and left pedals or how much difference there is between the right and left pedals, as long as both pedals have a positive force on them the pedals will be moving at the same speed and the cranks will stay in synch.)

This is all pretty simple physics/mechanics stuff. This is basically a conservation of momentum thing. If momentum changes in a system energy must either come into or leave a system. Looking at the bicycle I think it is a convention that we call positive forces as those that tend to speed the bike up and negative forces those that cause the bike to lose speed. Wind resistance and rolling resistance are always negative. Forces due to gravity can be either negative or positive (depending upon whether one is going up or down a hill). On a perfect bicycle with a perfect (no friction) free wheel forces from the pedal that drive the bike can only be positive and the conservation of momentum says the pedals will not slow down unless there is a negative force applied to them. The pedals will not slow simply because the positive pressure is reduced, they can only slow if there is another force larger than the positive pedal force slowing them. So, the bike doesn't slow because the pedals slow but the bike slows because the forces slowing the bike (wind, rolling, gravity) are larger than the forces trying to increase bike speed (pedals, gravity). When the bike slows the pedals slow and when the bike speeds up the pedals speed up because they are all tied together via the chain. It is that simple.

 

[JayKosta]

What does a person need to do when on PowerCranks to start applying torque when they fall out of synch (because they stopped applying torque). That is easy, all they need do is start moving the foot as fast as the other pedal. As soon as the foot is moving as fast as the other pedal which is applying torque it will lock up and the two cranks will remain in the same relative position to each other regardless of how much more torque is applied.
...

====================================================
Yes, I agree with this

"... all they need do is start moving the foot as fast as the other pedal. As soon as the foot is moving as fast as the other pedal which is applying torque it will lock up ..."

I had a misunderstanding about how the PC operated - I thought that torque could only be applied to both crank arms simultaneously when the arms were at 180 degrees. From your explanation, simultaneous torque can be applied at any crank arm angle as long the the crank arms are rotating at the same speed. Is there a way for the rider to know when the arms are at 180 degrees?
Thanks for the clarification about how PC operate.

Jay Kosta
Endwell NY USA

 

[FrankDay]

====================================================
Yes, I agree with this

"... all they need do is start moving the foot as fast as the other pedal. As soon as the foot is moving as fast as the other pedal which is applying torque it will lock up ..."

I had a misunderstanding about how the PC operated - I thought that torque could only be applied to both crank arms simultaneously when the arms were at 180 degrees. From your explanation, simultaneous torque can be applied at any crank arm angle as long the the crank arms are rotating at the same speed. Is there a way for the rider to know when the arms are at 180 degrees?
Thanks for the clarification about how PC operate.

Jay Kosta
Endwell NY USA

Yes. the rider knows when the cranks are at 180º when the timing of the knees coming up is 50-50. If off just a little bit the timing turns into a "gallop". Even the smallest "failure" is quickly noticed as the cranks fall apart. If not very close to 50-50 people don't like the feel and fix it quickly. (Edit: the only time you can have "failures" and not notice it is when the failures are repetitive and bilateral. that is say each leg falls 5º behind on each upstroke. Because each leg is doing the same thing it won't be felt because the timing will still feel 50-50. This is very unlikely as it is extremely unusual for riders to have perfectly balanced legs.)

You aren't the first person to not understand how the cranks work.

 

[coapman]

Conclusions: DC size is a pedaling technique parameter that is closely related to energy consumption. To generate power evenly around the whole pedal, revolution may be an important energy-saving trait."

Why is DC size closely related to energy consumption and what's the point in making that statement about generating power evenly when everyone knows it cannot be done.

 

[FrankDay]

Why is DC size closely related to energy consumption and what's the point in making that statement about generating power evenly when everyone knows it cannot be done.

Actually, quite a bit of power is generated on the backstroke but it is hidden and difficult to measure. Huh? you say. The fact is that a lot of potential energy is put into the leg when lifting the foot on the upstroke. Much of that energy is returned as power on the down stroke when that potential energy is converted back to kinetic energy. Power is generated much more evenly around the pedal stroke than most people think.

Further, it was simply the finding of the study that those who generated more power/torque at TDC/BDC were more efficient on average. It is up to others to prove/explain why although anyone can hypothesize, as they did, even though they might have better said "more evenly" than "evenly".

 

[coapman]

Actually, quite a bit of power is generated on the backstroke but it is hidden and difficult to measure. Huh? you say. The fact is that a lot of potential energy is put into the leg when lifting the foot on the upstroke. Much of that energy is returned as power on the down stroke when that potential energy is converted back to kinetic energy. Power is generated much more evenly around the pedal stroke than most people think.

Further, it was simply the finding of the study that those who generated more power/torque at TDC/BDC were more efficient on average. It is up to others to prove/explain why although anyone can hypothesize, as they did, even though they might have better said "more evenly" than "evenly".

That was DC research, nothing to do with the upstroke. How could it be said that power is generated more evenly around the pedal stroke when minimal if any torque is applied between 6 and 12 o'c. In that research DC force was 27.3% and 25.7%, can you explain what that is referring to and how many degrees of the pedalling circle are included in TDC.

 

[FrankDay]

How could it be said that power is generated more evenly around the pedal stroke when minimal if any torque is applied between 6 and 12 o'c. In that research DC force was 27.3% and 25.7%, can you explain what that is referring to and how many degrees of the pedalling circle are included in TDC.

There can not be more than 100% power generated around the circle. If we assume that the bulk of the power is generated on the downstroke then anytime we increase the DC percentage then the downstroke/upstroke percentage must decrease the same amount which is pretty much the definition of "more even" when the DC component and the "power" components come closer together.

I suggest you read the full paper if you want to know how they defined DC size. My guess is they took the average of the top and bottom quadrants and added them together for DC power.

 

[coapman]

There can not be more than 100% power generated around the circle. If we assume that the bulk of the power is generated on the downstroke then anytime we increase the DC percentage then the downstroke/upstroke percentage must decrease the same amount which is pretty much the definition of "more even" when the DC component and the "power" components come closer together.
.

If I use the mashing style I will apply 100 % of my leg's total torque in my downstroke. ----------------------------------------------------------------------------------------------------------------------------------
If I use the circular style and apply some torque at TDC and BDC, I will apply about 95 % of mashing's total torque in my pedal stroke. ---------------------------------------------------------------------------------If I change to the semi circular style and apply maximal torque at TDC while ignoring BDC, I can apply 150 % of mashing's total torque in my pedal stroke without changing peak torque around 3 o'c.

 

[CoachFergie]

As has been kindly offered by Dr Jim Martin on Slowtwitch, please avail yourself of the research facilities in the UK to test this theory.

 

[FrankDay]

If I use the mashing style I will apply 100 % of my leg's total torque in my downstroke. ----------------------------------------------------------------------------------------------------------------------------------
If I use the circular style and apply some torque at TDC and BDC, I will apply about 95 % of mashing's total torque in my pedal stroke. ---------------------------------------------------------------------------------If I change to the semi circular style and apply maximal torque at TDC while ignoring BDC, I can apply 150 % of mashing's total torque in my pedal stroke without changing peak torque around 3 o'c.

No, If we divide the stroke in half most mashers apply more than 100% of their total torque on the downstroke because they have to make up for the negative torques they apply on the backstroke. What is the advantage of applying 150% of the total torque on the downstroke when that means that 50% of that effort is totally wasted?

Further, everyone applies some force total at TDC and BDC because if they didn't the pedals would stop. The difference between mashers and spinners is one of degree, not absolutes.

 

[coapman]

No, If we divide the stroke in half most mashers apply more than 100% of their total torque on the downstroke because they have to make up for the negative torques they apply on the backstroke. What is the advantage of applying 150% of the total torque on the downstroke when that means that 50% of that effort is totally wasted?

Further, everyone applies some force total at TDC and BDC because if they didn't the pedals would stop. The difference between mashers and spinners is one of degree, not absolutes.

Another way of explaining my last post would be as follows. For torque generating purposes per pedal stroke, circular pedalling is about 5% less effective than mashing and semi circular is about 50% more effective than mashing. As for smoothing the power application, the chain ring is last in the line of transfer of chain drive power from muscles to the chain and the chain ring is where the smoothing of power application should be concentrated with each leg responsible for 180 degrees of its circle.

 

[FrankDay]

Another way of explaining my last post would be as follows. For torque generating purposes per pedal stroke, circular pedalling is about 5% less effective than mashing and semi circular is about 50% more effective than mashing. As for smoothing the power application, the chain ring is last in the line of transfer of chain drive power from muscles to the chain and the chain ring is where the smoothing of power application should be concentrated with each leg responsible for 180 degrees of its circle.

a better way of explaining what you are saying would be to give us the actual data from which you derive those numbers. To most of us it is simply a bunch of guessing and wishful thinking.

 

[coapman]

a better way of explaining what you are saying would be to give us the actual data from which you derive those numbers. To most of us it is simply a bunch of guessing and wishful thinking.

Commonsense is all that's required. Without any extra training your muscles are already strong enough to apply continuous maximal torque through 12, 1, 2 and 3 o'c, but you don't know how to use them. They can give that extra 50% extra torque, and about 20% of that extra torque could be considered free torque because it is the wasted non tangential pedal force in the upper half of a natural pedaller's downstroke that has been converted into crank torque. PC's have been around for many years and an explanation has never been given as to where any of that 40% power increase occurs. That latest PC research is another waste of time because all that is being tested is the unweighting technique.

 

[JayKosta]

Commonsense is all that's required. Without any extra training your muscles are already strong enough to apply continuous maximal torque through 12, 1, 2 and 3 o'c, but you don't know how to use them.

===================================

coapman,

I trust that you believe what you write, but I just don't understand it!

You keep mentioning 'continuous maximal torque' but what is that for you?
Is it

'the max torque that YOU produce in the best 30 degree section of pedaling'?

or is it something like

'the max torque that YOU produce for EACH 30 degree section of pedaling'? So that YOUR 'max torque' number differs depending on what section is considered.

It would help me to understand what torque you think you are producing if you gave a 'torque estimate' for each 30 degree section of a full rotation of either your left or right foot (I assume they are similar).

Jay Kosta
Endwell NY USA

 

[coapman]

===================================

coapman,

I trust that you believe what you write, but I just don't understand it!

You keep mentioning 'continuous maximal torque' but what is that for you?
Is it

'the max torque that YOU produce in the best 30 degree section of pedaling'?

or is it something like

'the max torque that YOU produce for EACH 30 degree section of pedaling'? So that YOUR 'max torque' number differs depending on what section is considered.

It would help me to understand what torque you think you are producing if you gave a 'torque estimate' for each 30 degree section of a full rotation of either your left or right foot (I assume they are similar).

Jay Kosta
Endwell NY USA

Between 11-12 o'c, the same torque as you apply between 2-3 o'c. From 12 -1, 1-2 and 2-3 o'c, in all three of these sectors the same torque as you would apply around 3 o'c. From 3- 5 o'c, normal reducing torque is applied there. From 5 to 11 o'c, unweighting takes place.

 

[JayKosta]

Between 11-12 o'c, the same torque as you apply between 2-3 o'c. From 12 -1, 1-2 and 2-3 o'c, in all three of these sectors the same torque as you would apply around 3 o'c. From 3- 5 o'c, normal reducing torque is applied there. From 5 to 11 o'c, unweighting takes place.

================
coapman,

Thanks for the info.
It will be interesting if/when someone who is adept at that pedaling technique is tested on a power meter that shows power in each sector.

Jay Kosta
Endwell NY USA