Let's discuss crank length, my opinion - shorter is better

[lostintime]

The video has to do with Time trialing. It's also selling Power Cranks . Reach your own conclusions.

Sounds like the latest "next best thing". Yawn ..... how many have there been over the years?


If you really want shorter cranks, save yourself the $1000 entry price of a Power cranks and get some aluminum ones shortened from someone like these guys . http://bikesmithdesign.com/Short_Cranks/index.html
http://bikesmithdesign.com/Short_Cranks/shorten.html

Or get some Bulletproof/Origin8 crank arms for $40 a pair. http://www.origin-8.com/product_det...n-8+Single-Speed+Series&cl1=CRANK+ARMS+&+SETS

 

[FrankDay]

The video has to do with Time trialing. It's also selling Power Cranks . Reach your own conclusions.

Sounds like the latest "next best thing". Yawn ..... how many have there been over the years?


If you really want shorter cranks, save yourself the $1000 entry price of a Power cranks and get some aluminum ones shortened from someone like these guys . http://bikesmithdesign.com/Short_Cranks/index.html
http://bikesmithdesign.com/Short_Cranks/shorten.html

Or get some Bulletproof/Origin8 crank arms for $40 a pair. http://www.origin-8.com/product_det...n-8+Single-Speed+Series&cl1=CRANK+ARMS+&+SETS

Thanks for the links to reasonably priced cranks that will allow those not interested in PowerCranks to try this concept out if they wish.

As I stated earlier, the reason for mentioning PowerCranks in the video was to indicate that we now included this feature in order to make this easy for our customers. I guess it might sway a few potential customers who are on the fence about the product to try it but I find it hard to believe that many would plunk down $1,000 USD just to experiment with crank length with my product if they didn't also believe in the underlying principle of the product.

The purpose of the video was to present a compelling case for shorter cranks to stimulate discussion and, hopefully, get some to experiment and report their results. For the purposes of this discussion it would be more compelling if people made this change without using the PowerCranks because if improvements were seen when both changes were made one wouldn't know how much to attribute to each change. This information has been around for 10 years and no one seems the least bit interested (probably because of Martin's stated conclusions even though he ignored the aerodynamic aspects of such a change) and I don't know anyone who has actually tried very short cranks, except for a few who I have arm twisted. I guess, like PowerCranks, it is just "too weird" or "too different" for people to consider. Maybe that will change now.

 

[mountaindew]

i'm going to try it. I'm 6' and ride 172.5's now. thinking about trying the 165's.

 

[FrankDay]

i'm going to try it. I'm 6' and ride 172.5's now. thinking about trying the 165's.

That is a baby step but better than nothing. Report back on what you find.

 

[FrankDay]

How about a link to the Martin study quoted in the video?

finally found the link to the entire paper.

http://www.recumbents.com/wisil/MartinDocs...ing%20Power.pdf

 

[Boeing]

zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

 

[dsut4392]

Hang on a minute...
1. you're claiming a 1-2% improvement in power, 2. John Cobb says you get an aero advantage of being able to have a lower position. This aero advantage is much greater than the increased maximum power. So far so good.

But to get the lower position, don't you need to have a lower BB, i.e. custom frame?

Running these cranks on a standard frame, won't you need to raise your seat height to still get good leg extension? If so, won't this raised position cause a significant aerodynamic disadvantage, most likely dar greater than the increased power?

I suppose I really should have watched your advertorial, I can only blame my entrenched cynicism that has prevented me from seeing the light...

 

[FrankDay]

Hang on a minute...
1. you're claiming a 1-2% improvement in power, 2. John Cobb says you get an aero advantage of being able to have a lower position. This aero advantage is much greater than the increased maximum power. So far so good.

But to get the lower position, don't you need to have a lower BB, i.e. custom frame?

Running these cranks on a standard frame, won't you need to raise your seat height to still get good leg extension? If so, won't this raised position cause a significant aerodynamic disadvantage, most likely dar greater than the increased power?

I suppose I really should have watched your advertorial, I can only blame my entrenched cynicism that has prevented me from seeing the light...

I am not claiming a 1-2% power advantage, I simply pointed out Martin's data which showed an approximate 1% difference for the lengths important here.

Anyhow, perhaps you should have watched the video. Most of your questions and objections would have been answered there, I think.

 

[labratty]

Well unless you have a very odd riding position your rear end is no where near as high as your shoulders.
If the crank is 1cm shorter, then without seat movment your knee will be 1cm further away (lower) from your torso at top of stroke. Then raise the seat 1cm to get the pedal to seat distance right again and now your knee is 2cm further from your torso.
So now to restore the same hip angle you had before you can lower your bars 2cm, bringing your shoulders down and lowering your frontal area quite a bit. It also gets the whole torso flatter which should have less hunch back and be more aero.

That is the hypothesis anyway. But the fairly tight UCI TT bike fit rules would get you pretty close to the bar extention limits out the front if you lay the torso out too flat.

 

[FrankDay]

Well unless you have a very odd riding position your rear end is no where near as high as your shoulders.
If the crank is 1cm shorter, then without seat movment your knee will be 1cm further away (lower) from your torso at top of stroke. Then raise the seat 1cm to get the pedal to seat distance right again and now your knee is 2cm further from your torso.
So now to restore the same hip angle you had before you can lower your bars 2cm, bringing your shoulders down and lowering your frontal area quite a bit. It also gets the whole torso flatter which should have less hunch back and be more aero.

That is the hypothesis anyway. But the fairly tight UCI TT bike fit rules would get you pretty close to the bar extention limits out the front if you lay the torso out too flat.

The only issue I have with your response is, using your numbers, we should be able to lower the front of the bike more than the 2cm the cranks change to keep the hip angle the same since the torso is a "lever" pivoting at the hip so to lower the middle of the chest 2 cm requires lowering the shoulders more than 2 cm.

 

[Oldman]

Hang on a minute...
1. you're claiming a 1-2% improvement in power, 2. John Cobb says you get an aero advantage of being able to have a lower position. This aero advantage is much greater than the increased maximum power. So far so good.

But to get the lower position, don't you need to have a lower BB, i.e. custom frame?

Running these cranks on a standard frame, won't you need to raise your seat height to still get good leg extension? If so, won't this raised position cause a significant aerodynamic disadvantage, most likely dar greater than the increased power?

I suppose I really should have watched your advertorial, I can only blame my entrenched cynicism that has prevented me from seeing the light...

That's the counter point: position is both ergonomic and aerodynamic in impact. Shortening cranks/increasing rpm doesn't help if the effort is better done at a larger gear/lower rpm and a lower frontal position. Remember the double-jointed cranks Paula Newby Fraser rode on a smaller bike? They seemed to work for her at her size.

 

[JA.Tri]

Hi Frank,

To my mind your approach via Power cranks:
1. has threatened your impartiality
2. increased the likelihood that your opinions will be discounted as self serving.

It is a shame that you did not present thoughts divorced from your apparent interest in Power Cranks, thereby avoiding, at least in part, an apparent conflict of interest.

That gripe aside, I refer to the following:

Quote:
Originally Posted by mountaindew View Post
i'm going to try it. I'm 6' and ride 172.5's now. thinking about trying the 165's.
That is a baby step but better than nothing. Report back on what you find.

Given your view, that shorter cranks are "better", is verified and applies in at least some situations, IMHO going from 172.5 to 165 is a significant difference (not a baby step). At 6' this is equivalent (approximately) to a 5'6" person going to 150 cranks.

When seeking optimal position, saddle height is changed a mm at a time (at least that is what I do). Large changes offer the significant possibility of overshooting the optimal position. Let's postulate that the overshoot is by such an amount, that the new position is worse than the old position. This may (probably) lead the subject to believe that the whole experiment was a waste of time.

 

[FrankDay]

Hi Frank,

To my mind your approach via Power cranks:
1. has threatened your impartiality
2. increased the likelihood that your opinions will be discounted as self serving.

It is a shame that you did not present thoughts divorced from your apparent interest in Power Cranks, thereby avoiding, at least in part, an apparent conflict of interest.

That gripe aside, I refer to the following:

Quote:
Originally Posted by mountaindew View Post
i'm going to try it. I'm 6' and ride 172.5's now. thinking about trying the 165's.
That is a baby step but better than nothing. Report back on what you find.

Given your view, that shorter cranks are "better", is verified and applies in at least some situations, IMHO going from 172.5 to 165 is a significant difference (not a baby step). At 6' this is equivalent (approximately) to a 5'6" person going to 150 cranks.

When seeking optimal position, saddle height is changed a mm at a time (at least that is what I do). Large changes offer the significant possibility of overshooting the optimal position. Let's postulate that the overshoot is by such an amount, that the new position is worse than the old position. This may (probably) lead the subject to believe that the whole experiment was a waste of time.

Well, a change from 172.5 to 165 is large enough that I think he will notice substantial improvement if he takes the effort to adjust his position accordingly and give himself a little time to adapt. The reason I stated it was a "baby step" is it appears to me that the big advantages of this change are not from what it might do for power but what it does for aerodynamics. That improvement occurs regardless of the brand of cranks are on the bike or what pedaling technique he uses. Anyhow, according to Martin he could go close to another inch shorter than that 165 first step and still not lose any power but he could expect to see even bigger aerodynamic gains. How anyone could look at that data and decide they need to try to shorten millimeters instead of centimeters or inches is beyond me. I am 6' 2" and am having no trouble with my 145 cranks even though I am still riding around with cadences in the high 60's or low 70's. I am not sure I could go much shorter but I am about to experiment and find out what happens. I will have to put myself on the ergometer and do some testing. Maybe this can be the subject of another video.

Everyone has to start somewhere. I would hope that when he tries his 165 cranks and sees benefit that he would then not be afraid to take the next step and try something even shorter. Maybe 155. And, if that shows further improvement, then take another step. and keep going until the improvements stop then lengthen a bit. It is impossible for anyone person to know what is optimal without experimenting. 165 is a much better first step for this guy than him going to 170 as a first step. But, I think it is a long way from his ideal, at least for time-trial.

 

[mountaindew]

I sent the link to a freind and this is what he replied. You can comment if you'd like.

The problem I have with this argument is that the study he is referring to uses peak power production (note that at 145mm you’re looking at 1200 watts) and not sustained (time trial) power production.

The reason there is a difference is because to achieve 1200 watts requires very high cadence (or VERY high force)

with a 145mm crank set, the foot needs to travel at about 0.9 meters/ second to maintain 120 rpm. The range of contraction decreases as well.

with a 175mm crank set the same rider would need to move his foot 1.1 m/sec to maintain the same 120 rpm. These numbers are getting close to vMax for contraction in humans. This is very difficult to unless you have massive peak force capability (i.e: body builder)

The circle the foot must travel gets larger as the crank length goes up.

Try making 1000 watts with a cadence of 70 rpm and let me know how that works out. Then try with a cadence of 80…90…100…110…120…higher….

Then try taking lactate samples (cheap handheld meters are about $100) while riding sustained at 300 watts but increasing cadence every 3 minutes. Start at 60 and increase 10 rpm at a time until you hit 120rpm

 

[FrankDay]

I sent the link to a freind and this is what he replied. You can comment if you'd like.

The problem I have with this argument is that the study he is referring to uses peak power production (note that at 145mm you’re looking at 1200 watts) and not sustained (time trial) power production.

The reason there is a difference is because to achieve 1200 watts requires very high cadence (or VERY high force)

with a 145mm crank set, the foot needs to travel at about 0.9 meters/ second to maintain 120 rpm. The range of contraction decreases as well.

with a 175mm crank set the same rider would need to move his foot 1.1 m/sec to maintain the same 120 rpm. These numbers are getting close to vMax for contraction in humans. This is very difficult to unless you have massive peak force capability (i.e: body builder)

The circle the foot must travel gets larger as the crank length goes up.

Try making 1000 watts with a cadence of 70 rpm and let me know how that works out. Then try with a cadence of 80…90…100…110…120…higher….

Then try taking lactate samples (cheap handheld meters are about $100) while riding sustained at 300 watts but increasing cadence every 3 minutes. Start at 60 and increase 10 rpm at a time until you hit 120rpm

I understand his "concern" but I don't see it as a problem. All of the issues he brings up are relevant to whatever power we are talking about. For any given power we can assume there will be an optimum pedal speed. The higher the power the higher the pedal speed. But, still, for any given power there will be an optimum pedal speed and an optimum pedal pressure. I think it reasonable to presume these will both vary directly (as opposed to inversely) with the power.

I have presumed, in my analysis, that the relationship for lower powers will be similar to that found my Martin at higher power. Until there is a study to show that the relationship doesn't hold that presumption seems reasonable as I know of no reason to presume the relationship doesn't hold. We can only work with the data we actually have so, sometimes, we have draw inferences and make presumptions.

The other problem I see with your friends analysis is he is only focused on the power aspect of the argument. Even if the power dropped some with shorter cranks, the aerodynamic improvement part of the argument could trump his power concerns. One cannot focus solely on the power side of the analysis and end up with the "truth" as it pertains, especially, to time-trial efforts.

 

[mountaindew]

This is the response from the friend i was talking about.


I think the idea of a light affordable adjustable crank is a good idea; I just find the claim that ‘shorter cranks will give you increased power’ to be a challenging position, specifically when you are talking about sub maximal efforts. As far as I know, you can’t change MLSS by changing crank length, longer or shorter. I’ve seen studies that state this plainly but for the life of me I can’t find them anymore.



Martin (the author cited in the video) determined that there was no power difference between one crank length and another, but he did show that oxygen uptake favored shorter cranks, likely due to the lower foot speeds at any given cadence. (2001) A high degree of freedom exists in crank length selection in a homogenous population before crank length adversely impacts mean power or peak power. (Inbar 1993)

In general, as crank arms shorten, a rider’s self selected cadence will increase as muscle shortening velocity remains constant. Despite this however, peak gross efficiency still occurs at a cadence well below self selected cadence, and gross muscular efficiency decreases with increasing cadence. (Seabury et al, 1977) (Suzuki, 1979) Delta efficiency does improve slightly during sub maximal intensity as cadence increases. (Faria et al, 1982) (Sidossis et al, 1992)



Muscular efficiency, however, does not translate well into cycling performance and claims about increased ‘efficiency’ need to be viewed with a certain degree of skepticism. Economy, on the other hand, might be a better indicator of performance. Economy as it relates to cadence in steady state cycling forms a parabolic relationship, with the riders’ self selected cadence being the nadir point at which O2 consumption, ventilation, RPE, and serum lactate are lowest. At sub-maximal efforts this cadence was still above the speed of muscle shortening which maximized muscular efficiency for a given workload. Higher and lower cadences resulted in an increase of these parameters. (Marsh and Martin, 1993) (Lollgen et al 1980) (Stamford and Noble 1974)( Borg, 1975)( Ekblom and Goldbarg 1971)



So, adjusting the pedal arm length is really all about trading off one thing for another, certainly not getting extra watts from thin air.



Shorter cranks will decrease frontal surface area. This is true. This decrease in frontal area is primarily seen at the bottom of the pedal stroke where air is already turbulent so I’m not sure you can argue that is would be the same as say decreasing area across a rider’s shoulders, for example, where airflow is laminar. Only your local wind tunnel knows for sure. Nevertheless, there is a small decrease in frontal surface area. Every bit counts.

Of course, the other claims of an aerodynamic advantage due to shorter cranks makes the assumption that the rider’s position (specifically torso) isn’t already ‘ideal.’ It follows in the same logic that some bike fitters use when they advertise that their fitting will produce an increase in power of 20%. It is a claim that might be true for some riders who may have an extremely poor fit, but for others the gains may be significantly less or nonexistent.

Interestingly, Cobb actually argues for shorter cranks because it allows a rider to lower their saddle height due to the decrease in the angle of deflection of the legs seen with a shorter crank. As a result the rider can assume a more compact position without compromising the hip angle at TDC. In general this is consistent with wind tunnel data that suggests that lower and narrower is better. As always though, position changes for aero benefit must be weighed against their potential to compromise power output. Occasionally, the gain in aero advantage is more than offset by a loss in the ability to produce power.



So maybe a shorter crank is better for the TT and I’m just being cynical, but watching the video I find it difficult to take it seriously when it tosses phrases out there like, “Assume shorter is better until proven otherwise.” I think “otherwise” is pretty well accepted already as there is no magic crank length that is going to give you free watts, short or long. There IS a cadence that will allow for highest economy but it is variable amongst riders, and my personal hunch is that it is dependent on neurological recruitment patterns and muscle fiber composition.



P

 

[FrankDay]

This is the response from the friend i was talking about.


I think the idea of a light affordable adjustable crank is a good idea; I just find the claim that ‘shorter cranks will give you increased power’ to be a challenging position, specifically when you are talking about sub maximal efforts. As far as I know, you can’t change MLSS by changing crank length, longer or shorter. I’ve seen studies that state this plainly but for the life of me I can’t find them anymore.



Martin (the author cited in the video) determined that there was no power difference between one crank length and another, but he did show that oxygen uptake favored shorter cranks, likely due to the lower foot speeds at any given cadence. (2001) A high degree of freedom exists in crank length selection in a homogenous population before crank length adversely impacts mean power or peak power. (Inbar 1993)

Your friend is wrong here. Martin found no SUBSTANTIAL difference in power between crank lengths ranging from 145 to 195. Because the differences were small he concluded there was no penalty to riding 170 mm cranks, at least as it applied to power.

In general, as crank arms shorten, a rider’s self selected cadence will increase as muscle shortening velocity remains constant. Despite this however, peak gross efficiency still occurs at a cadence well below self selected cadence, and gross muscular efficiency decreases with increasing cadence. (Seabury et al, 1977) (Suzuki, 1979) Delta efficiency does improve slightly during sub maximal intensity as cadence increases. (Faria et al, 1982) (Sidossis et al, 1992)


Muscular efficiency, however, does not translate well into cycling performance and claims about increased ‘efficiency’ need to be viewed with a certain degree of skepticism. Economy, on the other hand, might be a better indicator of performance. Economy as it relates to cadence in steady state cycling forms a parabolic relationship, with the riders’ self selected cadence being the nadir point at which O2 consumption, ventilation, RPE, and serum lactate are lowest. At sub-maximal efforts this cadence was still above the speed of muscle shortening which maximized muscular efficiency for a given workload. Higher and lower cadences resulted in an increase of these parameters. (Marsh and Martin, 1993) (Lollgen et al 1980) (Stamford and Noble 1974)( Borg, 1975)( Ekblom and Goldbarg 1971)

My problem with the above is most of these studies looking at "self selected cadence" do not take into account training effect. Asking someone who has spent years training at a cadence of 90 to test what happens at a cadence of 60 may not give the same result compared to taking that person and training them to ride at a cadence of 60 for a period of time and then retesting them. Riding at low cadences takes some getting used to just as riding at very high cadences takes some getting used to. I have always wondered what would happen if one tested a person and found out what their most efficient cadence was and what their most efficient crank length was and then had them train at that cadence and crank length and see what happens (compared to someone who didn't change). That study has yet to be done.

So, adjusting the pedal arm length is really all about trading off one thing for another, certainly not getting extra watts from thin air.

Your friend, again, seems fixated on the power side of the going fast equation and ignoring what the shorter cranks do for the aerodynamics. It is actually possible to go faster with less power if the aerodynamics improve enough to overcome the power drop.

Shorter cranks will decrease frontal surface area. This is true. This decrease in frontal area is primarily seen at the bottom of the pedal stroke where air is already turbulent so I’m not sure you can argue that is would be the same as say decreasing area across a rider’s shoulders, for example, where airflow is laminar. Only your local wind tunnel knows for sure. Nevertheless, there is a small decrease in frontal surface area. Every bit counts.

Actually, he is wrong here. He needs to go back and look at the video again. It is true, the bottom foot does move up to reduce frontal area there but the top foot moves down the equivalent amount so this is a wash. The turbulence of the air has no influence as this is the case regardless of how long the cranks are. The reductions in frontal area are occurring at the torso, where more of the body is put in the shadow of the shoulders/head/arms.

Of course, the other claims of an aerodynamic advantage due to shorter cranks makes the assumption that the rider’s position (specifically torso) isn’t already ‘ideal.’ It follows in the same logic that some bike fitters use when they advertise that their fitting will produce an increase in power of 20%. It is a claim that might be true for some riders who may have an extremely poor fit, but for others the gains may be significantly less or nonexistent.

I guess if you believe your bike fit is ideal already, and no improvement is possible, then I would say it is ok to ignore this. However, if one isn't so sure this is the case it seems it would be worth some experimenting. To assume everything is now ideal, without experimenting to prove the case, seems to me to be the height of hubris.

Interestingly, Cobb actually argues for shorter cranks because it allows a rider to lower their saddle height due to the decrease in the angle of deflection of the legs seen with a shorter crank. As a result the rider can assume a more compact position without compromising the hip angle at TDC. In general this is consistent with wind tunnel data that suggests that lower and narrower is better. As always though, position changes for aero benefit must be weighed against their potential to compromise power output. Occasionally, the gain in aero advantage is more than offset by a loss in the ability to produce power.

I believe the comment about the lower saddle is a mistake of the author/editor. It makes no sense. It is obvious the article was poorly edited in view of the spelling error.

So maybe a shorter crank is better for the TT and I’m just being cynical, but watching the video I find it difficult to take it seriously when it tosses phrases out there like, “Assume shorter is better until proven otherwise.” I think “otherwise” is pretty well accepted already as there is no magic crank length that is going to give you free watts, short or long. There IS a cadence that will allow for highest economy but it is variable amongst riders, and my personal hunch is that it is dependent on neurological recruitment patterns and muscle fiber composition.



P

Again, the article went to the combination of power and aerodynamics. This last paragraph of your friend again ignores the importance of the aerodynamics part of the equation, focusing on power alone. The power effects of such a change are tiny. But, the aerodynamics effects are potentially huge. It is this kind of thinking, looking at parts of the problem without looking at the whole, that slows progress, IMHO. The best cyclists in the world thought aerodynamics wasn't worth worrying about until LeMond won the tour because he did and his opponents didn't.

If everyone is doing everything the same it doesn't make any difference. That is until someone discovers that it does and figures out how to implement it and then kicks everyone else's ****. Then, the world will change.

 

[labratty]

The only issue I have with your response is, using your numbers, we should be able to lower the front of the bike more than the 2cm the cranks change to keep the hip angle the same since the torso is a "lever" pivoting at the hip so to lower the middle of the chest 2 cm requires lowering the shoulders more than 2 cm.

Yes, you probably could, I was just taking very round numbers to try to explain the concept clearly. Strictly on the numbers that is certain you would go lower to reproduce the hip angle, although that might take a while to get used to, dropping down that much lower than what you are used to must feel very odd for a while. Ultimately you might get down 3+cm I guess, and that is going to require a lot less power.

ratty

 

[mountaindew]

Wouldn't that put a lot of weight/pressure on your hands?

 

[Night Rider]

Wouldn't that put a lot of weight/pressure on your hands?

Yes it would and that idea a few pages back of raising the seat because of shorter cranks, but lowering the bars is just simpy wrong.

Yes, you do have to raise the seat for shorter cranks. You also raise the stem height the same distance when you make any change. If seat goes up, stem height goes up. Seat goes down, stem goes down.

*of course naturally taking into account you are starting from an optimal position with your original cranks.

 

[FrankDay]

Yes it would and that idea a few pages back of raising the seat because of shorter cranks, but lowering the bars is just simpy wrong.

Yes, you do have to raise the seat for shorter cranks. You also raise the stem height the same distance when you make any change. If seat goes up, stem height goes up. Seat goes down, stem goes down.

*of course naturally taking into account you are starting from an optimal position with your original cranks.

I really don't understand either of these posts. To me, moving the rider forward is what increases pressure on the handlebars, not moving the bars down. Moving the bars down would, if anything, reduce pressure on the bars, as I see it.

And, what determines "optimum" position? Why on earth would you say that optimum position is independent of crank length? You believe if the seat moves up the stem must also moves up even though knee is further from the chest. Makes no sense to me (I explain my thoughts in the video - did you watch it?). Perhaps you could explain your thoughts here more clearly as to why you say this.

 

[M Sport]

I really don't understand either of these posts. To me, moving the rider forward is what increases pressure on the handlebars, not moving the bars down. Moving the bars down would, if anything, reduce pressure on the bars, as I see it.

You're are seeing it wrong I can assure you that if you start in any given position and lower the bars in relation to the seat then you are transfering more weight there. Simple physics my friend. How long have you been bike fitting for?

And, what determines "optimum" position? Why on earth would you say that optimum position is independent of crank length? You believe if the seat moves up the stem must also moves up even though knee is further from the chest. Makes no sense to me (I explain my thoughts in the video - did you watch it?). Perhaps you could explain your thoughts here more clearly as to why you say this.

I don't quite think you're getting the point here. The optimum leg angle at full extension is 30 degrees +/- a few degrees, this ensures maximum power without hyper extending the knee and causing injury and staying in effective range of motion.

So lets say you're set up for correctly for 172.5mm cranks, optimum leg angles, correct torso angles so as not to cause back injury, or maximise aero position, or both, etc, etc. If you go to shorter cranks you have to move the seat up, you also need to move it back to keep the same knee position relative to the end of the crank. To keep your original torso angle you have to also raise the bars and in theory you should move the bars back but as stem lengths only vary by 10mm you might skip this step.

What you don't do if you already have a perfect bike fit but want to experiment with different cranks is go different directions in your seat bar height.

It's just basic bike fitting practiced by the pro fitters like Pruitt, Hog, etc.

 

[FrankDay]

You're are seeing it wrong I can assure you that if you start in any given position and lower the bars in relation to the seat then you are transfering more weight there. Simple physics my friend. How long have you been bike fitting for?

Such a statement makes no sense to me. As an extreme example let's put the bars as low as the person can bend over. If I were to lower the bars any more, the person could not reach the bars so the pressure on the bars would have to be reduced, not increased, because the weight on the bars would be zero. It is the increased resistance to bending the body more that reduces the weight on the bars as they are lowered, not "simple physics" increasing it, as I see it.

I don't quite think you're getting the point here. The optimum leg angle at full extension is 30 degrees +/- a few degrees, this ensures maximum power without hyper extending the knee and causing injury and staying in effective range of motion.

So lets say you're set up for correctly for 172.5mm cranks, optimum leg angles, correct torso angles so as not to cause back injury, or maximise aero position, or both, etc, etc. If you go to shorter cranks you have to move the seat up, you also need to move it back to keep the same knee position relative to the end of the crank. To keep your original torso angle you have to also raise the bars and in theory you should move the bars back but as stem lengths only vary by 10mm you might skip this step.

What you don't do if you already have a perfect bike fit but want to experiment with different cranks is go different directions in your seat bar height.

It's just basic bike fitting practiced by the pro fitters like Pruitt, Hog, etc.

Well, if you move the bars with the seat as you change the crank length all of the theoretical advantages of shorter cranks disappear. If you do that, I would agree, why bother. Apparently you haven't watched the video.

 

[Boeing]

I havent given much thought to crank length on my roadie in some time so perhaps it is a good idea to re think

However I am in a constant debate personally and among peers with regards to Mountain biking and SS mtn biking.....

Does any of your evidence point to mountain biking or cyclocross where momentum is at a premium.


what are your thoughts on 26 vs 29er pedaling

what about singlespeed mountain bikes

 

[FrankDay]

I havent given much thought to crank length on my roadie in some time so perhaps it is a good idea to re think

However I am in a constant debate personally and among peers with regards to Mountain biking and SS mtn biking.....

Does any of your evidence point to mountain biking or cyclocross where momentum is at a premium.


what are your thoughts on 26 vs 29er pedaling

what about singlespeed mountain bikes

As near as I can tell, the biggest advantage of shorter cranks has to do with aerodynamics. From Martin's study one can infer there might be a small advantage to shorter cranks for power but it would be small. Another advantage to shorter cranks, at least for mountainbiking, that I can see might be better ground clearance. I see no reason any rider might not want to consider shorter cranks although the advantages for other disciplines, if any, are probably going to be much smaller than those seen by the TT specialist.

The issue of wheel size probably has little to do with power because, just as the change in leverage from a different crank size can be adjusted by gearing so can the change in leverage from a different wheel size. Wheel size, from a mountainbike and cyclocross perspective, probably has it's main effect in how a bike handles and rides over obstacles and little to do with how much power the rider can apply.