The importance of crank length to the cyclist.

[CoachFergie]

You and Fergie (and a few others) seem to be missing the entire point of my first post. Short cranks, from my theorizing and our experimenting seem allow the rider to achieve a much lower and more aerodynamic position without losing much, if any, power.

Experimenting? Then you will have data to prove your position.

So, we would expect the change to be faster. Of course, if one isn't willing to experiment one will never know will one?

Good thing we have a tool that we can actually measure changes in performance so we don't have to rely on subjective experience or outcome measures.

 

[180mmCrank]

Wow! You guys when you get your teeth into something you really don't let go! It's quite humbling. I guess there are things I care this much about but it probably isn't crank length.

Can we quit with the name calling and innuendo it doesn't really add anything to the debate.

Thanks

Terry
Admin

 

[180mmCrank]

Oh and by the way the real limiting factor in geometry isn't crank length it's wheel diameter. But hey that's a whole new topic to get our teeth in to. Maybe I will start a thread.... Or maybe not.

 

[FrankDay]

he is saying that both that being low is not always more aero and he is ALSO saying that being low is not always faster.

I, obviously, interpret what he wrote differently than you. Here is what he wrote: "going lower is not always more aero (or faster) anyway ". I take that to read that he isn't actually measuring aeroness but is suggesting that the fact that one isn't faster suggests they are less aero. I am simply saying that it could just as well mean that they could be more aero but have lost so much power getting into the position that they are actually slower. How fast one is depends upon both how much power they have and how aero they are.

Unless one has bothered to measure both drag and power with the position change one cannot know whether it is power or drag that is causing the rider to go slower, if the rider is going slower.

I find it quite interesting that those here who are so focused on power as a training tool seem completely uninterested in how power is affected by rider position, which would include crank length.

 

[FrankDay]

Wow! You guys when you get your teeth into something you really don't let go! It's quite humbling. I guess there are things I care this much about but it probably isn't crank length.

Perhaps that is because you haven't thought much about it or played around with it much.

 

[Oldman]

read it again:



he is saying that both that being low is not always more aero and he is ALSO saying that being low is not always faster.

Don't need to read it again. I agree with him.

 

[FrankDay]

Don't need to read it again. I agree with him.

I can agree with that statement. Now the next question you both should be asking is "Why?"

 

[blutto]

I find it quite interesting that those here who are so focused on power as a training tool seem completely uninterested in how power is affected by rider position, which would include crank length.

...so to repeat a question I asked later...how does changing the TDC of a pedal circle affect power output ( we already assume that the BDC position is somewhat important )...and why would it?...

Cheers

blutto

 

[FrankDay]

...so to repeat a question I asked later...how does changing the TDC of a pedal circle affect power output ( we already assume that the BDC position is somewhat important )...and why would it?...

Cheers

blutto

I thought you asked that of others earlier. I do have my thoughts as to why this is important (I can think of at least three important aspects). If you want me to answer your question say so and I will now.

 

[180mmCrank]

Perhaps that is because you haven't thought much about it or played around with it much.

Yeah right! That's why I have over a dozen different cranks of multiple sizes and configurations in my closet. Right now I ride a 180mm aluminum campag record with a TA triple converter middle ring... Don't worry I have played around with cranks

As I said above for me it's the wheel size that limits geometry especially for smaller riders.

T

 

[Tapeworm]

As I said above for me it's the wheel size that limits geometry especially for smaller riders.

Not to mention the UCI's restrictions on rider position and equipment geometries.

 

[FrankDay]

Not to mention the UCI's restrictions on rider position and equipment geometries.

Does the UCI restrict crank length?

 

[blutto]

I thought you asked that of others earlier. I do have my thoughts as to why this is important (I can think of at least three important aspects). If you want me to answer your question say so and I will now.

...please do...

Cheers

blutto

 

[180mmCrank]

Does the UCI restrict crank length?

Well you have to have one!

T

 

[Martin318is]

Frank,
that post is so full of dodgy conclusions I have decided to address them individually.

I, obviously, interpret what he wrote differently than you.... I take that to read that he isn't actually measuring aeroness but is suggesting that the fact that one isn't faster suggests they are less aero.

don't address this with me, address it with the person that wrote it. All you are doing here is reworking his words to suit yourself - especially since he has REPEATEDLY stated that measuring aero and power are BOTH essential before adopting any change on the bike (as opposed to just assuming that getting lower on the bike automatically makes you more aero OR faster)

I am simply saying that it could just as well mean that they could be more aero but have lost so much power getting into the position that they are actually slower. How fast one is depends upon both how much power they have and how aero they are.

great, then you agree completely with Alex (its all through his posts) - so what is the problem?

I find it quite interesting that those here who are so focused on power as a training tool seem completely uninterested in how power is affected by rider position, which would include crank length.

Not sure how to treat this because personally all I see here is trolling. Here's why - NOBODY has said that - ever in this thread. In fact, your "opposition" has made this statement more times than you have. Being dismissive of shorter cranks does not logically extend to what you are claiming here. All you are trying to do is fire up the likes of CoachFergie, etc with this statement.

 

[FrankDay]

...so to repeat a question I asked later...how does changing the TDC of a pedal circle affect power output ( we already assume that the BDC position is somewhat important )...and why would it?...

Cheers

blutto

OK. I see each of the following related to crank length possibly modifying power and aero positioning potential.
1. Depending upon rider flexibility, how high the knee is forced up by the crank arm will determine how low the rider can physically go, affecting frontal area and aerodynamic potential.
2. If the rider cannot actively raise the foot as far as the crank length requires then energy must be diverted from the wheel to get the foot over the top. The greater the discrepancy the more the energy cost, affecting efficiency and lowering power.
3. The higher the foot at TDC the more the knee is bent, causing the knee joint to lose efficiency, making the quads to contract harder for any given pedal force, affecting efficiency and, potentially, lowering power.
4. The higher the foot at TDC, the more the hip angle, causing the hip to lose pushing efficiency, making the glutes to contract harder for any given pedal force, affecting efficiency and, potentially, lowering power.
5. The greater the pedaling circle the higher the pedal speed at any given cadence. Higher pedal speeds make it more difficult to apply force to the pedal. Pedal speed and tangential force are the components that actually determine power. For any given power, there will be an optimum pedal speed for optimum power production, both too high and too low are less efficient.
6. If one's pedal is moving at the optimum pedal speed the crank length will affect cadence. I believe as cadence increases above 90 or so efficiency will drop because of the fixed time it takes for a muscle to relax, affecting blood flow potential during recovery (this explains why we can't just keep going shorter and shorter).
7. The higher the pedal speed the more difficult it is to get the foot out of the way on the recovery portion (increasing back pressure on the upstroke and increasing efficiency)
8. At the extreme levels at TDC, the hip flexors may be outside of their most efficient contraction range, further reducing efficiency.

Now, before anyone comments that I don't have proof of any of this, I admit I don't have proof of any of this (even though much of this is nothing more than well known physiological principles). These are all theoretical considerations that I believe can help explain the improvements being reported by those trying these extremely short and unconventional crank lengths.

Comments are welcome. This should get this thread to over a thousand replies soon.

 

[Alex Simmons/RST]

I, obviously, interpret what he wrote differently than you. Here is what he wrote: "going lower is not always more aero (or faster) anyway ". I take that to read that he isn't actually measuring aeroness but is suggesting that the fact that one isn't faster suggests they are less aero. I am simply saying that it could just as well mean that they could be more aero but have lost so much power getting into the position that they are actually slower. How fast one is depends upon both how much power they have and how aero they are.

Unless one has bothered to measure both drag and power with the position change one cannot know whether it is power or drag that is causing the rider to go slower, if the rider is going slower.

I find it quite interesting that those here who are so focused on power as a training tool seem completely uninterested in how power is affected by rider position, which would include crank length.

Strawman once again Frank. will it ever cease?

I never said I am only looking at one and ignoring the other.

I am well aware of the both the numerator and denominator when testing a rider's power to drag ratio.

I actually measure both. You measure neither.

 

[FrankDay]

don't address this with me, address it with the person that wrote it. All you are doing here is reworking his words to suit yourself - especially since he has REPEATEDLY stated that measuring aero and power are BOTH essential before adopting any change on the bike (as opposed to just assuming that getting lower on the bike automatically makes you more aero OR faster)

Do you really see any problem with restating something to clarify the meaning. If the author thinks I misinterpreted his remarks then he can clarify them. He has never clarified that he has actually measured the power drop in his rider as he put him in that scrunched up position. All he has said is that dropping the front end can slow a rider down, which he presumes comes from increasing the drag. He has never given any data to support his statement.

great, then you agree completely with Alex (its all through his posts) - so what is the problem?

The problem is he has never acknowledged that the position a rider is in can adversely affect power. All he has said is going lower can slow you down. I agree with this. What we disagree on is why this might be the case and whether anything can be done about it.

Not sure how to treat this because personally all I see here is trolling. Here's why - NOBODY has said that - ever in this thread. In fact, your "opposition" has made this statement more times than you have. Being dismissive of shorter cranks does not logically extend to what you are claiming here. All you are trying to do is fire up the likes of CoachFergie, etc with this statement.

You are right. Nobody, except for me, has acknowledged in this thread that rider position can affect power output. If rider position can affect power output one needs to ask why does this happen? If one asks why one is directed back to what is happening at TDC and how crank length affects that. This question, which you consider trolling, goes directly to the reason this thread was started. Start answering some of these questions and the point I am trying to make might start making some sense to you.

Sometimes to get to where you want to go all you need do is ask the right questions. Why does power generally drop as riders get into the aero position?

edit: Then, ask the question as to why the Martin study data, even though not statistically significant, has a clear tendency to higher power as crank length gets shorter down to 145 mm? How can that be explained? Start with those questions and the answers pretty much inevitably lead to the post that started this thread. But, I am open to alternative explanations if you got them.

 

[FrankDay]

I never said I am only looking at one and ignoring the other.

I am well aware of the both the numerator and denominator when testing a rider's power to drag ratio.

I actually measure both. You measure neither.

Then, give us the data for your rider in the picture. How much does his power drop for the same effort when in that position from his usual riding position? How much does it drop further if you try to lower him further.

 

[Martin318is]

You are right. Nobody, except for me, has acknowledged in this thread that rider position can affect power output. If rider position can affect power output one needs to ask why does this happen?

Frank, that is once again a BLATANT troll. You put words in my mouth that contradict what I actually said - again.

Not only have people 'acknowledge' that position affects power output, it has repeatedly been put forward as a reason to include power testing when determining whether a change in postion (eg crank length) is a good or bad idea. You only need to go a few posts back to see a number of people listing out numerous other reasons why position can affect output.

 

[FrankDay]

Frank, that is once again a BLATANT troll. You put words in my mouth that contradict what I actually said - again.

Not only have people 'acknowledge' that position affects power output, it has repeatedly been put forward as a reason to include power testing when determining whether a change in postion (eg crank length) is a good or bad idea. You only need to go a few posts back to see a number of people listing out numerous other reasons why position can affect output.

Really? Can you give me a post number where someone other than me (and on the other side) acknowledges that rider position affects power? And, if they did, did they address why this might be the case? If so, I humbly apologize. I look forward to being corrected.

 

[Tapeworm]

Really? Can you give me a post number where someone other than me (and on the other side) acknowledges that rider position affects power? And, if they did, did they address why this might be the case? If so, I humbly apologize. I look forward to being corrected.

Post #576
Going lower doesn't always improve aero. And it can end up reducing the power to drag ratio. That's why we measure these things, so we can be sure and not make WAGs and/or rely on folklore.

Thank you Alex.

Unless, Frank, you have a new interpretation of what power to drag ratio is?

 

[Alex Simmons/RST]

Then, give us the data for your rider in the picture.

No. That would be unprofessional.

My comments are not specific to one rider.

The picture was to simply illustrate that sometimes riders are already low. The picture was already in the public domain.

I will say that his highest 20 minute power is attained in that position and that includes all road and TT racing and training.

 

[oldborn]

OK. I see each of the following related to crank length possibly modifying power and aero positioning potential.
1. Depending upon rider flexibility, how high the knee is forced up by the crank arm will determine how low the rider can physically go, affecting frontal area and aerodynamic potential.
2. If the rider cannot actively raise the foot as far as the crank length requires then energy must be diverted from the wheel to get the foot over the top. The greater the discrepancy the more the energy cost, affecting efficiency and lowering power.
3. The higher the foot at TDC the more the knee is bent, causing the knee joint to lose efficiency, making the quads to contract harder for any given pedal force, affecting efficiency and, potentially, lowering power.
4. The higher at the foot TDC, the more the hip angle, causing the hip to lose pushing efficiency, making the glutes to contract harder for any given pedal force, affecting efficiency and, potentially, lowering power.5. The greater the pedaling circle the higher the pedal speed at any given cadence. Higher pedal speeds make it more difficult to apply force to the pedal. Pedal speed and tangential force are the components that actually determine power. For any given power, there will be an optimum pedal speed for optimum power production, both too high and too low are less efficient.
6. If one's pedal is moving at the optimum pedal speed the crank length will affect cadence. I believe as cadence increases above 90 or so efficiency will drop because of the fixed time it takes for a muscle to relax, affecting blood flow potential during recovery (this explains why we can't just keep going shorter and shorter).
7. The higher the pedal speed the more difficult it is to get the foot out of the way on the recovery portion (increasing back pressure on the upstroke and increasing efficiency)
8. At the extreme levels at TDC, the hip flexors may be outside of their most efficient contraction range, further reducing efficiency.

Now, before anyone comments that I don't have proof of any of this, I admit I don't have proof of any of this (even though much of this is nothing more than well known physiological principles). These are all theoretical considerations that I believe can help explain the improvements being reported by those trying these extremely short and unconventional crank lengths.

Comments are welcome. This should get this thread to over a thousand replies soon.

Well I am switching from 175 road bike to 172 new TTbike, and must said that I hope to see some sort of relief. I will post my experience for sure.

How should I knew that potential improvement may come from shorter crancks?

For average Joe with some experience that should be easy, with pretty much same traning stress and well known course I should be at least faster, and more confortable on run leg when doing tri. Off course those kind of thing can happens from better adaptations to brick set training, but I can live with that

 

[Alex Simmons/RST]

Comments are welcome. This should get this thread to over a thousand replies soon.

Quality over quantity:
http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf