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Crank Length?

Old 10-27-23, 10:27 AM
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Originally Posted by ls01
lower with a shorter crank, or you won't be able to reach the pedalscat the bottom of the stroke.
Saddle needs to be higher for the same leg extension with a shorter crank. But some fitters recommend leaving the saddle height unchanged which reduces both leg extension and hip impingement in equal measure.
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Old 10-28-23, 11:57 AM
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Originally Posted by Carbonfiberboy
5.5 X inseam in inches is the usual formula. I have a 29" inseam, 78 y.o., use 170 on my road bikes, 175 on our tandem. Works fine...
That'd put me with 189 mm cranks!

I'll stick to my 165mm cranks, thankyou! <grin>

I think between the two of us, we are a good example that proportional sizing doesn't apply for everyone.
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Old 10-28-23, 03:51 PM
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Originally Posted by Iride01
That'd put me with 189 mm cranks!

I'll stick to my 165mm cranks, thankyou! <grin>

I think between the two of us, we are a good example that proportional sizing doesn't apply for everyone.
We're all over the place here, aren't we? Your ratio is 4.78. I'm using ratios of 5.86 and 6.03. My wife has 165s on her road bike and 151s on our tandem. Both work just fine for her, so far, up to a double century. The 151 is close to that 5.5 ratio. I've ridden doubles on both bikes and and 18.5 hour 400 on the road bike. Never a leg or joint issue, can't really complain.

Goes to show how adaptable humans (and well, most mammals) are. Good for our species!
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Old 10-28-23, 08:20 PM
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Everyone is different, but if you are lucky enough to be able to use long pedal cranks effectively then you will be rewarded with more power and speed. Every part of a bicycle is "fitted" to riders based on their size and proportions, so of course pedal cranks can be also. With pedal cranks age and physical problems can limit a rider to shorter crank arms as a work-around, just like some older riders, or those with various problems can not put their bars as low as other riders and take full advantage of aerodynamics.

But if you can effectively spin a set of longer cranks at the same rpm as a set of shorter cranks then it will either be easier to use the same gear, or with no more effort you will be in a higher gear and going faster.

Short small riders need short cranks to go fast because their talent is their lighter short legs that they can move more quickly than a big and tall rider, so to get close to the same power as a big rider they can spin at a higher rpm. Power is torque X rpm, so you either have to have the big torque of long cranks, or you have to have more rpms in the same time with the short cranks. On the level the big rider often has a little advantage, on the hills the small light rider often has an advantage, given that we are talking about serious cyclists or professionals.

The big rider with long heavy legs can not move as quickly, but if they are able to use extra long cranks to fit their big size, then even though their rpm is lower, their torque is higher, and they can still make power.

Everyone one is different, even two riders the same height will have different inseams and will have different optimal crank lengths because of that, their age and their physical advantages or problems. Toward the very top of the list of what makes an athlete pro-caliber is genetics, so nobody can say that anything that works for them will work for others because all were born with different abilities and traits.

So try different things to find the most comfort or speed or fun.
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Old 10-29-23, 03:31 AM
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5'6", 30" inseam, 160mm crank length

I'm 5'6", 30" inseam (roughly), 53 years old, and I have ridden 160mm cranks on all my road bikes for the past 3 years. The shorter crank length reduces likelihood of hip impingement issues.
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Old 10-29-23, 07:17 PM
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Originally Posted by 88ss
Everyone is different, but if you are lucky enough to be able to use long pedal cranks effectively then you will be rewarded with more power and speed. Every part of a bicycle is "fitted" to riders based on their size and proportions, so of course pedal cranks can be also. With pedal cranks age and physical problems can limit a rider to shorter crank arms as a work-around, just like some older riders, or those with various problems can not put their bars as low as other riders and take full advantage of aerodynamics.

But if you can effectively spin a set of longer cranks at the same rpm as a set of shorter cranks then it will either be easier to use the same gear, or with no more effort you will be in a higher gear and going faster.

Short small riders need short cranks to go fast because their talent is their lighter short legs that they can move more quickly than a big and tall rider, so to get close to the same power as a big rider they can spin at a higher rpm. Power is torque X rpm, so you either have to have the big torque of long cranks, or you have to have more rpms in the same time with the short cranks. On the level the big rider often has a little advantage, on the hills the small light rider often has an advantage, given that we are talking about serious cyclists or professionals.

The big rider with long heavy legs can not move as quickly, but if they are able to use extra long cranks to fit their big size, then even though their rpm is lower, their torque is higher, and they can still make power.

Everyone one is different, even two riders the same height will have different inseams and will have different optimal crank lengths because of that, their age and their physical advantages or problems. Toward the very top of the list of what makes an athlete pro-caliber is genetics, so nobody can say that anything that works for them will work for others because all were born with different abilities and traits.

So try different things to find the most comfort or speed or fun.
There is a flaw in your logic here. Spinning a long crank at the same rpm as a short crank requires moving your feet faster around the larger circle. So in reality there is no free lunch here and your power output will not change significantly with crank length.
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Old 10-30-23, 12:54 AM
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Originally Posted by PeteHski
There is a flaw in your logic here. Spinning a long crank at the same rpm as a short crank requires moving your feet faster around the larger circle. So in reality there is no free lunch here and your power output will not change significantly with crank length.
No, there is a flaw in your reading ability, as I said "if" you can spin a set of long cranks effectively. So come back after that remedial reading class......
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Old 10-30-23, 02:53 AM
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Results of recent power-meter-based testing of various crank arm lengths have indicated that many if not most cyclists are more efficient on shorter cranks. But as Sheldon Brown pointed out sensibly, years ago:

Different cyclists have different leg lengths. It seems obvious that crank length should be proportional, so long-legged cyclists should have long cranks, short-legged cyclists should have short cranks....and yet, 99.9% of adult bicycles have crank lengths between 165 and 175 mm. Have the bicycle manufacturers joined in a great conspiracy to force everybody to ride the same length cranks, regardless of their needs?This is a common misunderstanding. The "leverage" of a bicycle drive train, also known as "gain ratio," depends on the crank length, wheel diameter and the sizes of both sprockets.

Yes, if you go to longer cranks without changing any of the other variables, you will have more "leverage", which is another way of saying you'll have a lower effective gear...but on a multi-speed bike, you can change gears at will!

Ay, there's the rub! Assuming you adjust your gearing appropriately, crank length has no effect on leverage, it just has to do with the range of motion of the knee and hip joints.

Too long cranks cause excessive knee flex, and can cause pain/injury if it causes your knee to flex more than it is used to.
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Old 10-30-23, 08:04 AM
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Originally Posted by Trakhak
Results of recent power-meter-based testing of various crank arm lengths have indicated that many if not most cyclists are more efficient on shorter cranks. But as Sheldon Brown pointed out sensibly, years ago:

Different cyclists have different leg lengths. It seems obvious that crank length should be proportional, so long-legged cyclists should have long cranks, short-legged cyclists should have short cranks....and yet, 99.9% of adult bicycles have crank lengths between 165 and 175 mm. Have the bicycle manufacturers joined in a great conspiracy to force everybody to ride the same length cranks, regardless of their needs?This is a common misunderstanding. The "leverage" of a bicycle drive train, also known as "gain ratio," depends on the crank length, wheel diameter and the sizes of both sprockets.

Yes, if you go to longer cranks without changing any of the other variables, you will have more "leverage", which is another way of saying you'll have a lower effective gear...but on a multi-speed bike, you can change gears at will!

Ay, there's the rub! Assuming you adjust your gearing appropriately, crank length has no effect on leverage, it just has to do with the range of motion of the knee and hip joints.Too long cranks cause excessive knee flex, and can cause pain/injury if it causes your knee to flex more than it is used to.
Pretty tired of people taking what Sheldon Brown wrote for granted. If you look at what he actually wrote, he says that having more leverage is another way of saying you'll have a lower effective gear, which is misleading because those with multi-speed bikes getting more "leverage" or mechanical advantage from changing to a lower gear, will not be going slower, they will not be able to go as fast in that lower gear. So if as he so "sensibly" states "gain ratio" depends on crank length and a few other things, you can use longer cranks to get the leverage you need to make your current gear feel easier, or to go faster by changing up instead of changing down a gear and going slower with your short cranks. Sheldon Brown's gear changing down is fine for those who do not care about how fast they are going, but if you do care about going faster, and you are a big and tall person who can use longer crank arms more effectively than a short person, then you can see a gain in speed.

There are tests to be found where researchers tried to find what difference longer and shorter crank arms make for cyclists, but these tests are flawed and maybe impossible because unless you can lengthen the test subjects legs at the same time you change to a longer crank arm, then all you are doing is giving the rider one correctly sized crank arm, and a collection of others to test that are the wrong length for them, so the results will not be any good. And if you test cyclists of different leg lengths you can not get good test results because it is impossible to get a collection of cyclists with the exact same genetics and/or athletic ability together on any single day. This is why most testing of crank arms ends up with just saying that crank-length does not make any difference or the best crank length is the one that "feels good to the rider".

If you test different crank lengths yourself you will find one that feels best to you, but it means nothing to anyone else because they will have different goals, different genetics, different proportions, different health problems or genetic advantages etc..

This is why when I say someone can go faster with longer crank arms, I include the word "if", because it is if a tall person has the stability in his knees and legs and the muscle strength, then they may be able to go faster switching to a longer crank length, or at least the tall person will be able to reach their potential and go just as fast as the little guy because they will have proportional bicycle parts.

In the last few months I have ridden the same level 20 kilometer loop with 165mm, 170mm, 175mm and 180mm cranks using five different road bikes, some of the same bikes with the different cranks arm sizes switched in, and in timing the loops ridden over literally a few hundred laps not only in the last few years, but in more than one decade, the fastest laps have always been with the longest crank length, the 180mm. But I am 6'3" tall, have no knee pain and ride thousands of miles each year and have thousands using 180mm cranks with no problem. If I were not a serious cyclist or had knee problems or different proportions giving me shorter legs and a longer torso, then I would have had completely different results, I am just lucky enough to be able to take advantage of them.
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Old 10-30-23, 08:42 AM
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I appreciate the insights from this link: https://bikedynamics.co.uk/FitGuidecranks.htm#1

I'm 5'6" and according to the stand against the wall and hold a book in place, my inseam is 29.5" - I have switched both primary bikes to 165mm cranks.

The first is a Cannondale Quick 1 hybrid and the change from 170mm to 165mm was subtle but noticable. My cadence is slightly higher but is smoother, more consistant, and it is much easier to ride longer distances. (Some might argue that is dumping the FSA for 105 is the difference but that's only a small part of the change). A win in my book.

The change from 175mm to 165mm on my mid 90's Specialized S-Works M2 was nothing short of a miracle. The hip and knee pain I experienced with it are gone and and I gained tverything that is true with the Cannondale. Other than the spendy price of the 165mm 3x crank for a 30 year old bike, I'm thrilled with the end results. I ride the M2 on our local MTB trails and hold my own. Another win I'll take.

I'm planning to use 165mm cranks on other projects I have in the works.

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Old 10-30-23, 11:20 AM
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Originally Posted by 88ss
No, there is a flaw in your reading ability, as I said "if" you can spin a set of long cranks effectively. So come back after that remedial reading class......
Not really, you are just talking bs.
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Old 10-30-23, 11:30 AM
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Originally Posted by 88ss

This is why when I say someone can go faster with longer crank arms, I include the word "if", because it is if a tall person has the stability in his knees and legs and the muscle strength, then they may be able to go faster switching to a longer crank length, or at least the tall person will be able to reach their potential and go just as fast as the little guy because they will have proportional bicycle parts.

In the last few months I have ridden the same level 20 kilometer loop with 165mm, 170mm, 175mm and 180mm cranks using five different road bikes, some of the same bikes with the different cranks arm sizes switched in, and in timing the loops ridden over literally a few hundred laps not only in the last few years, but in more than one decade, the fastest laps have always been with the longest crank length, the 180mm. But I am 6'3" tall, have no knee pain and ride thousands of miles each year and have thousands using 180mm cranks with no problem. If I were not a serious cyclist or had knee problems or different proportions giving me shorter legs and a longer torso, then I would have had completely different results, I am just lucky enough to be able to take advantage of them.
So why did Bradley Wiggins use 170 mm cranks for his world hour record? He's tall (190 cm) and I would imagine he has more muscle strength and flexibility than you. He actually switched from using 177.5 mm cranks in the build up. It's well documented. Similarly the men's track team switched to 165 mm cranks for the 2016 Olympics and did ok.

“The science is clear,” says Burt (Team GB coach), “crank length is not important in sub-maximal power production, within a range of 80mm to 300mm.”
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Old 10-31-23, 08:33 AM
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Originally Posted by PeteHski
So why did Bradley Wiggins use 170 mm cranks for his world hour record? He's tall (190 cm) and I would imagine he has more muscle strength and flexibility than you. He actually switched from using 177.5 mm cranks in the build up. It's well documented. Similarly the men's track team switched to 165 mm cranks for the 2016 Olympics and did ok.“The science is clear,” says Burt (Team GB coach), “crank length is not important in sub-maximal power production, within a range of 80mm to 300mm.”
Doesn't everyone know that track bikes never use anything but 165mm or 170mm cranks for ground clearance ??? You fit your bike with 80mm long pedal cranks and enter some time trials and lets see how you do. And why would you put up information about sub-maximal power ??? Who cares about Aunt Tilda riding on a path next to the beach ??? If you look up how the height of a person affects their ability to use their legs, you will find that it is not a factor at all. This is because two people who are considered tall can have different leg proportions. The length of their upper and lower legs can be completely different, so a tall person with certain proportions may not need cranks any longer than another person six inches shorter than they. The man with the record for lifting the highest multiple of his body weight is simply a man with unusual proportions who's arms are so long he does not have to bend his knees as much as a normally proportioned human !!! So nothing you mentioned means anything at all, sorry.
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Old 10-31-23, 08:58 AM
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It use to be that engines with long crankshaft throws were slower turning but higher torque engines. Engines with shorter crankshaft throws were for higher RPM and only produced their maximum torque in a narrow range of RPM. Race car engines tend to be the higher RPM engines with shorter throws. Everything that makes them powerful is not in the crank itself, but in the other things of the engine that provide it huge amounts of air and fuel.

Maybe we too should be thinking more about getting our lungs trained to breath more air and fuel properly while on the bike.
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Old 10-31-23, 09:31 AM
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Originally Posted by 88ss
Doesn't everyone know that track bikes never use anything but 165mm or 170mm cranks for ground clearance ??? You fit your bike with 80mm long pedal cranks and enter some time trials and lets see how you do. And why would you put up information about sub-maximal power ??? Who cares about Aunt Tilda riding on a path next to the beach ??? If you look up how the height of a person affects their ability to use their legs, you will find that it is not a factor at all. This is because two people who are considered tall can have different leg proportions. The length of their upper and lower legs can be completely different, so a tall person with certain proportions may not need cranks any longer than another person six inches shorter than they. The man with the record for lifting the highest multiple of his body weight is simply a man with unusual proportions who's arms are so long he does not have to bend his knees as much as a normally proportioned human !!! So nothing you mentioned means anything at all, sorry.
The point is that crank length has been shown countless times to be unimportant for power generation. There is no fundamental advantage in using longer cranks like you appear to be asserting. There was no ground clearance issue for Wiggin's hour record attempt. He specifically chose shorter cranks for a positional aero gain and his power was not compromised by using shorter cranks. His sub-maximal power was in the region of 470W.

The only things that matter regarding crank length are personal preference and physical joint limitations.

This article sums it up pretty well.

https://www.cyclist.co.uk/in-depth/best-crank-length-for-cycling#:~:text=probably%20too%20long.-,',or%20as%20long%20as%20320mm.

TLDR: Crank length as a variable doesn’t affect power or efficiency. Shorter cranks can offer a few advantages,

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Old 11-02-23, 04:45 AM
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Originally Posted by PeteHski
The only things that matter regarding crank length are personal preference and physical joint limitations.
Congratulations on finally finding your posterior with both hands. I have hundreds of laps testing my speed on a few 20 kilometer TT circuits over years and I go much faster the longer my cranks are and I have no problem with my joints, this is why it is worth trying for individuals who may have the physique to use them. As I already said, if you don't have the physique or joints then do what is good for you, but you are missing out on extra power and speed if you never try long cranks if you are comfortable with them. Bye bye now...........
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Old 11-02-23, 05:49 AM
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Originally Posted by 88ss
Congratulations on finally finding your posterior with both hands. I have hundreds of laps testing my speed on a few 20 kilometer TT circuits over years and I go much faster the longer my cranks are and I have no problem with my joints, this is why it is worth trying for individuals who may have the physique to use them. As I already said, if you don't have the physique or joints then do what is good for you, but you are missing out on extra power and speed if you never try long cranks if you are comfortable with them. Bye bye now...........
Yeah I guess Wiggins was missing out on extra power and speed by not using longer cranks (which he could do comfortably with his physique and cycling technique).
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Old 11-02-23, 06:25 AM
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Originally Posted by 88ss
Pretty tired of people taking what Sheldon Brown wrote for granted. If you look at what he actually wrote, he says that having more leverage is another way of saying you'll have a lower effective gear, which is misleading because those with multi-speed bikes getting more "leverage" or mechanical advantage from changing to a lower gear, will not be going slower, they will not be able to go as fast in that lower gear. So if as he so "sensibly" states "gain ratio" depends on crank length and a few other things, you can use longer cranks to get the leverage you need to make your current gear feel easier, or to go faster by changing up instead of changing down a gear and going slower with your short cranks. Sheldon Brown's gear changing down is fine for those who do not care about how fast they are going, but if you do care about going faster, and you are a big and tall person who can use longer crank arms more effectively than a short person, then you can see a gain in speed.
The part in bold is the major flaw in your reasoning. Although the longer cranks increase leverage and make the gear feel easier (less pedal load), your feet also have further to travel for each revolution (larger pedalling circle), so the total work involved is exactly the same at a given cadence. In your example, changing into a higher gear doesn't make you go any faster just because you have made the gear feel harder again (back to original pedal load). It also means your foot speed has reduced (higher gear). That's why Sheldon relates crank length to an effective gear.

Now if you really are losing significant power over a 20 km TT when shortening your cranks by only 5-10 mm, you should be wondering why that would be the case? It doesn't really make any sense that you would lose power (assuming your bike has appropriate multiple gears) and none of the pros tested in research lost any significant power with shorter cranks - other than in standing start sprints in a huge gear. The pro trend in recent years is toward shorter cranks for the advantage it gives in an aggressive aero position (less hip impingement etc).

Being tall does allow you to use longer cranks if you prefer, but there is no inherent power advantage in doing so.

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Old 11-02-23, 06:44 AM
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Originally Posted by 88ss

There are tests to be found where researchers tried to find what difference longer and shorter crank arms make for cyclists, but these tests are flawed and maybe impossible because unless you can lengthen the test subjects legs at the same time you change to a longer crank arm, then all you are doing is giving the rider one correctly sized crank arm, and a collection of others to test that are the wrong length for them, so the results will not be any good. And if you test cyclists of different leg lengths you can not get good test results because it is impossible to get a collection of cyclists with the exact same genetics and/or athletic ability together on any single day. This is why most testing of crank arms ends up with just saying that crank-length does not make any difference or the best crank length is the one that "feels good to the rider".
By your reasoning, the test riders should all produce more power at their "correct" crank length and less power with longer or shorter cranks. But that's not what the results show. There is obviously an upper limit for crank length in relation to a rider's leg proportions, but not really a lower limit. Results consistently show that power is not really dependent on crank length within the range that a rider can actually use. So a tall rider may be able to use longer cranks, but they will tend to generate the same power on shorter cranks. Except for you of course LOL
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Old 11-02-23, 11:23 AM
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Originally Posted by PeteHski
By your reasoning, the test riders should all produce more power at their "correct" crank length and less power with longer or shorter cranks. But that's not what the results show. There is obviously an upper limit for crank length in relation to a rider's leg proportions, but not really a lower limit. Results consistently show that power is not really dependent on crank length within the range that a rider can actually use. So a tall rider may be able to use longer cranks, but they will tend to generate the same power on shorter cranks. Except for you of course LOL
I wonder if those results that show consistent power across crank lengths also show consistent time to fatigue. Do you know if they do?

Personally, I'm mostly concerned about sparing my muscles from fatigue on long climbs, and I prefer longer cranks as they seem to make my legs last stay fresher longer.
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Old 11-02-23, 02:48 PM
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Originally Posted by terrymorse
I wonder if those results that show consistent power across crank lengths also show consistent time to fatigue. Do you know if they do?

Personally, I'm mostly concerned about sparing my muscles from fatigue on long climbs, and I prefer longer cranks as they seem to make my legs last stay fresher longer.
I have no idea. What crank lengths have you compared to notice any difference in leg fatigue? Was your gearing the same in both cases? I would find that a very hard call to make any conclusion. I do have adjustable crank length on my Kickr Bike (165-175 mm) so I could try it for myself if I was motivated. But it's hard to judge fatigue even comparing the same climb day to day with the same crank length. There are so many other variables affecting fatigue on any given day.

My current road bike has 172.5 mm cranks and my spare bike and mountain bike are both 175 mm. I honestly can't even tell the difference between them, although it is a relatively small difference. If I was building a bike from scratch I would probably go with 170 or even 165 cranks at this point, even though I can comfortably pedal 175s (I'm 6'1" with relatively long legs). I just don't see the point in longer cranks, especially for endurance riding. But at the same time I don't feel particularly motivated to fit shorter cranks to any of my current bikes.

Bike fitters I respect are all in favour of shorter cranks and I have no reason to disagree with them.
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Old 11-04-23, 06:10 AM
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Originally Posted by PeteHski
. Except for you of course LOL
You don't have any reasoning or independent thought. I already said that none of the research you regurgitate has tested short riders against tall riders, or tall riders against other tall riders with different femur to calf proportions. Of course if you take the same riders and put them on different crank lengths you will not get any legitimate research, and of course people like you that lap it up will not have any legitimate arguments or things to say about the subject.
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Old 11-04-23, 06:18 AM
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Originally Posted by terrymorse
I wonder if those results that show consistent power across crank lengths also show consistent time to fatigue. Do you know if they do?
Personally, I'm mostly concerned about sparing my muscles from fatigue on long climbs, and I prefer longer cranks as they seem to make my legs last stay fresher longer.
When I switch from short to long cranks, it is like suddenly being able to breathe. It feels so good to get that extra range of motion. If you take things to the extreme in a thought experiment you would be testing non-moving dynamic tension, like a person on a weight machine that is locked and immovable, against another weight machine that lets someone do the work using a large range of motion. Everyone knows that moving is good for you, it is what the entire practice of yoga and other similar disciplines are based on. Of course the person pulling the same gearing up a hill will do better with more leverage and more range of motion for their legs to help move the blood in them etc. as long as they are proportioned and have the healthy joints.
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Old 11-04-23, 10:19 AM
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Originally Posted by 88ss
When I switch from short to long cranks, it is like suddenly being able to breathe. It feels so good to get that extra range of motion. If you take things to the extreme in a thought experiment you would be testing non-moving dynamic tension, like a person on a weight machine that is locked and immovable, against another weight machine that lets someone do the work using a large range of motion.
Maybe a more appropriate thought experiment is climbing stairs. Single steps feel too easy, and your legs have to move quickly to make decent progress. Three steps at a time require a big "oomph" to get your very bent leg to lift your body. Two steps feels less tiring than three steps and more productive than single steps.
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Old 11-04-23, 10:31 AM
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Originally Posted by PeteHski
Saddle needs to be higher for the same leg extension with a shorter crank. But some fitters recommend leaving the saddle height unchanged which reduces both leg extension and hip impingement in equal measure.
When I started buying older bikes, they came with 170s, vs the 175s all my bikes have had since 1995. I set the saddle height from the BB. I felt flatfooted on the 170s, and when I switched back to the 175s, I felt like I was having to reach out with my legs/feet. Then I set the saddle height from the pedal surface at maximum extension, and I feel very little difference. MAYBE the 170s are SLIGHTLY easier to spin faster, but it's subtle.
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