The importance of crank length to the cyclist.

[Turner29]

I slight force can be generated by angling the pedal a bit. Here is a good explanation and the concept of effective pedal force:

From Figure 1 it is evident that the pedal forces vary continuously both in magnitude and orientation throughout the pedal stroke. The consequence of the changing orientation is a change in the proportion of the total force that is effective. For example, at the bottom of the stroke the total force is quite large but is applied almost parallel to the crank arm, where as about 90 degrees after TDC the force is applied almost perpendicular to the crank. In these examples even if the total forces were the same, the effective component would be much larger at a crank angle of 90 degrees than at bottom dead center. It may well be said that when the force is not perpendicular to the crank, it is wasted, at least in terms of propulsion.

http://www2.bsn.de/cycling/articles/cycling_kinematics.html

 

[Turner29]

Thus, the ideal pedal stroke would not be "round" but more forceful at 90 degrees, just as Coyle noted...

 

[coapman]

Thus, the ideal pedal stroke would not be "round" but more forceful at 90 degrees, just as Coyle noted...

Which is what I do at 12, 1, 2, and 3 o'c. Do you have an opinion on which is best, short or long cranks ?

 

[Turner29]

Which is what I do at 12, 1, 2, and 3 o'c. Do you have an opinion on which is best, short or long cranks ?

Longest possible crank, smallest possible front chainring.

 

[Turner29]

And going back to the Coyle paper, the very pedaling style promoted by some here (round, with some positive upstroke force) is that of the weakest cyclists in the study.

 

[Boeing]

No science here. no aero advantage. no pi$$ing contest

On my mountain bikes

I ride a 177.5 on the Single Speed

and a 170 on my long travel bikes

the former is a lever for all the out of saddle climbing in socal

the ladder is for clearance cornering and pedal strike technical climbing. when my wheels used to leave the ground i preferred a compact fit to maneuver and find pedal again easier with the shortest. Id go 165 saint

strokes for folks

 

[FrankDay]

I slight force can be generated by angling the pedal a bit. Here is a good explanation and the concept of effective pedal force:

From Figure 1 it is evident that the pedal forces vary continuously both in magnitude and orientation throughout the pedal stroke. The consequence of the changing orientation is a change in the proportion of the total force that is effective. For example, at the bottom of the stroke the total force is quite large but is applied almost parallel to the crank arm, where as about 90 degrees after TDC the force is applied almost perpendicular to the crank. In these examples even if the total forces were the same, the effective component would be much larger at a crank angle of 90 degrees than at bottom dead center. It may well be said that when the force is not perpendicular to the crank, it is wasted, at least in terms of propulsion.

http://www2.bsn.de/cycling/articles/cycling_kinematics.html

Perhaps you missed this from the next paragraph in that paper

The presentation in Figure 1 tells us that propulsion occurs whenever the effective component of the applied force is positive and in the direction of pedaling. In Figure 1 it is clear that the resultant force is effective beyond the 180 degrees after TDC. Indeed, the desired goal in cycling is to make the propulsive phase as long as possible.

By my way of thinking "as long as possible" encompasses the entire circle.

 

[Oldman]

Good Lord...is this dialogue still going on? I got my other TT monster to go down to....172.5 for his best performance ever.

 

[sciguy]

Good Lord...is this dialogue still going on? I got my other TT monster to go down to....172.5 for his best performance ever.

But.....But......But ...just think how fast he'd be with 170s

 

[CoachFergie]

Sci guy you're not imagining hard enough to yourself, how much faster would he be on 145s!!!

 

[coapman]

Perhaps you missed this from the next paragraph in that paper

By my way of thinking "as long as possible" encompasses the entire circle.

I would change that last sentence to read " Indeed, the desired goal in cycling is to make the propulsive phase with maximal torque as long as possible, extending it from 30 deg. to 120 deg of the pedaling circle."

 

[Turner29]

I would change that last sentence to read " Indeed, the desired goal in cycling is to make the propulsive phase with maximal torque as long as possible, extending it from 30 deg. to 120 deg of the pedaling circle."

That would be a good clarification that is also consistent with Coyle's findings. Nevertheless, the most of the additional force generated by the most powerful riders in his study comes from greater peak forces near 90 degrees (from 60 degrees to 120 degrees), and not from more force elsewhere.

 

[coapman]

That would be a good clarification that is also consistent with Coyle's findings. Nevertheless, the most of the additional force generated by the most powerful riders in his study comes from greater peak forces near 90 degrees (from 60 degrees to 120 degrees), and not from more force elsewhere.

That's the natural way of doing it. I was not satisfied with that, I knew there had to be a better way and was right. That sector can be extended to cover from 330 deg. to 120 deg or 11 to 4 o'c. You concentrate on generating greatest possible torque with each leg over 180 deg., (11-5 o'c) and not around the entire circle. In that way you can give total concentration to each leg in turn.

 

[Turner29]

That's the natural way of doing it. I was not satisfied with that, I knew there had to be a better way and was right. That sector can be extended to cover from 330 deg. to 120 deg or 11 to 4 o'c. You concentrate on generating greatest possible torque with each leg over 180 deg., (11-5 o'c) and not around the entire circle. In that way you can give total concentration to each leg in turn.

From a one leg perspective, there should be no force applied on the upstroke (180-270-0) and I think you mean 2 to 4 o'c or even 1 to 5 o'c.

Take a look at this:

http://www.sportsphysionorthsydney.com.au/cycling_kinematics.php

 

[FrankDay]

From a one leg perspective, there should be no force applied on the upstroke (180-270-0) and I think you mean 2 to 4 o'c or even 1 to 5 o'c.

Take a look at this:

http://www.sportsphysionorthsydney.com.au/cycling_kinematics.php

from this paper:

Fig 2: pedal effective force: the light shaded area represents ‘unused force' whereas the dark shaded area represents negative effective forces. The objective of the rider is to reduce the size of the unused force and eliminate the negative effective forces without decreasing the size of the propulsive impulse

From a physics perspective this is true. He is stating that it would be most efficient to eliminate any radial force (that has no propulsive component) and only have tangential forces. Unfortunately, in the real world, that is probably not the case because a lot of the force is simply due to gravity so the direction of that force component is fixed in both magnitude (weight of leg) and direction (down). In order to eliminate this with the sole intent to "reduce the size of the unused force" would require muscle action in the opposite direction that would serve no propulsive purpose.

Anyhow, as long as there are no negative forces anywhere around the circle
(whether using Coapman's technique or a more standard technique) this qualifies as "pedaling in circles" in my book.

Unfortunately, this is somewhat off topic for this thread (there are threads devoted to pedaling technique here) unless we were to discuss how crank length affects pedaling technique. I personally believe crank length does affect pedaling technique in that two things happen that affect how the rider pedals. First, the range of motion is changed with shorter cranks making it easier to unweight on the upstroke because of the smaller range of motion. Second, pedal speed is reduced for the same cadence. Slower pedal speed makes it easier for the rider to both apply more force on the down stroke (or top and bottom also) and unweight better on the upstroke. Hopefully, I got us back on topic.

 

[FrankDay]

Perhaps you missed this from the next paragraph in that paper

The presentation in Figure 1 tells us that propulsion occurs whenever the effective component of the applied force is positive and in the direction of pedaling. In Figure 1 it is clear that the resultant force is effective beyond the 180 degrees after TDC. Indeed, the desired goal in cycling is to make the propulsive phase as long as possible.

By my way of thinking "as long as possible" encompasses the entire circle.

I was thinking today on my ride about this and I think how to ride powerfully can all be summed up in an old Bing Crosby/Johnny Mercer song: Ac-Cent-Tchu-Ate The Positive.

You've got to accentuate the positive
Eliminate the negative
Latch on to the affirmative
Don't mess with Mister In-Between

 

[CoachFergie]

Always the show man. Got any data to support that argument

 

[coapman]

Perhaps you missed this from the next paragraph in that paper

By my way of thinking "as long as possible" encompasses the entire circle.

Does this mean you still believe there is something to be gained by pulling up?

 

[FrankDay]

Does this mean you still believe there is something to be gained by pulling up?

Yes, at least up to the point of "pulling up" enough to completely unweight the pedal on the "recovery" (e.i., completely eliminating any anti-propulsive negative forces). Whether there is any further advantage to "pulling up" any more (to actually provide substantial propulsion on the upstroke) is open to question.

 

[coapman]

Yes, at least up to the point of "pulling up" enough to completely unweight the pedal on the "recovery" (e.i., completely eliminating any anti-propulsive negative forces). Whether there is any further advantage to "pulling up" any more (to actually provide substantial propulsion on the upstroke) is open to question.

Unweighting does not have to involve pulling up, pulling up can never provide substantial propulsion. What was the result of the testing you did on short and long cranks?

 

[FrankDay]

Unweighting does not have to involve pulling up, pulling up can never provide substantial propulsion. What was the result of the testing you did on short and long cranks?

Sure unweighting involves pulling up. It involves pulling the weight of the leg up against gravity. It involves putting potential energy into the leg which means doing work. That work has to be done by either the muscles in the recovery leg pulling it up, the muscles of the pushing leg being diverted to push it up, or some combination (the usual case). Just because there are not forces seen on the pedal with complete unweighting does not mean the cyclist is not "pulling up" against gravity and doing a lot of work (which actually gets recovered on the downstroke - not all of those pedal forces on the downstroke are due to muscles pushing, some are from the weight of the leg on the pedal). Even mashers "pull up" a little because even they partially unweight. All "pedaling in circles" involves is pulling up a little more so complete unweighting occurs.

To which testing are you referring? Not sure I have done anything that I haven't already posted the results.

 

[FrankDay]

Another anecdotal report:

"I thought I would update you on this year's racing. My tri bike has 150mm crank arms. While I have had some good results, age group win at Kansas 70.3, this past weekend I won my age group at the Vegas 70.3 world championships. And it was my bike split that did it for me. I rode the first 15 mile or so and an Ironman pace, getting the legs moving, ingesting fluids and getting a sense for how hot it would be. 105 by race end! By the first turn at mile 25 I was pushing nearly as hard as an olympic distance race. My split for the last 30 miles was equal to or faster than most everyone over 40! Not bad for 58! While not extreme, my position is lower than ever and comfortable thanks to the 150s. Loss of power? Not by looking at my split times."

 

[FrankDay]

Another anecdotal report:

"I thought I would update you on this year's racing. My tri bike has 150mm crank arms. While I have had some good results, age group win at Kansas 70.3, this past weekend I won my age group at the Vegas 70.3 world championships. And it was my bike split that did it for me. I rode the first 15 mile or so and an Ironman pace, getting the legs moving, ingesting fluids and getting a sense for how hot it would be. 105 by race end! By the first turn at mile 25 I was pushing nearly as hard as an olympic distance race. My split for the last 30 miles was equal to or faster than most everyone over 40! Not bad for 58! While not extreme, my position is lower than ever and comfortable thanks to the 150s. Loss of power? Not by looking at my split times."

I found out something new about the above athlete, Greg Taylor, today. "There are 23 70.3 age group world champions. And there are 23 Ironman age group world champions. But there is only one person who is both 70.3 and Ironman age group world champion. And that person is me."

We are going to try to set him up with some of our lightest weight racing cranks as he tries to defend his title in less than a month. He has asked for 150 mm on the left and 145 mm on the right. If he wins again what crank length should we claim he used?

 

[CoachFergie]

Hey Frank, I'm not convinced. Do you have any more meaningless anecdotes to share?

Just out of curiosity what testing has Greg performed to show that his crank length selection hasn't held back his performance?

 

[FrankDay]

Just out of curiosity what testing has Greg performed to show that his crank length selection hasn't held back his performance?

My guess is he has simply tried different crank lengths and determined, through trial and error and, possibly, some testing, what works best for him. It is certainly more than most of the people reading this thread who are probably simply riding the crank length that came with their bike. That is part of the reason for this thread and the posting of the anecdotes - to get people to, at least, try shorter cranks. Each person is forced to do their own experimenting to see what is best for them. I am simply trying to get them to consider doing so. While I guess it is possible to argue that Greg could do even better on a different crank length I don't think it is possible to argue that he could have had any better race results.