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Crank arm length from fit perspective
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So up front I was not going to mine thru all 29 pgs of the odyssey started by H20man on crank length and performance. So if what I'm about to ask explained somewhere in it I am sorry and please point me to it.

Anyways, small rider here 5'5" 135 lbs (61cm saddle height) and am currently riding on a tri bike with 165mm cranks. In the process of building a new bike (N+1 is real) and I am looking at possibly going even shorter on crank length since well; I am tiny compared to most.

Reading articles such as those from cycling weekly and Cobbs site, while performance gains are very debatable, the real gain from going to a shorter crank has to do with fit.

Since it seems like everything to do with fit has a method to it, does anyone know if there is a way to measure this, say since my "x" is this, a good guess at a optimal crank length would be "y".

Lastly, resides Cobbs carbon one crank set, are there another other options for short (<165mm) carbon crank sets on the market.

Thanks,
Zinny
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Re: Crank arm length from fit perspective [zinny] [ In reply to ]
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This is everything I have learned about fitting crank length after over 1000 attempts.

1. The only way to intuitively understand the benefits of shorter cranks is to have a competent fitter utilizing proper equipment take you to the limit of your current crank length before making a change. In other words, if your fit is not at least in the ballpark of optimized, you probably won't notice much, or even worse, you might have a different experience than if you were close to optimal.

2. When done as described above, about 80-90% of riders are going to prefer a crank length from .5 to 1.5 cm shorter than what would typically come on a stock bike in their size.

3. Many of the things previously mentioned are important, especially riding a lower / more aero position, but the first thing the fitter and rider need to determine is "Do you prefer this?". It is the same question asked when seat height, setback or drop is changed.... How does this effect your intuitive sense of pedaling? After which, we can look at the power, how much drop you can ride, etc. First is always rider feedback.

4. There is no perfect crank length, or if there is I don't know how to find it. I do know how to find an acceptable range for a given rider. Acceptable here is synonymous with appropriate, and NOT the same thing as aggressive. The #1 thing I look at is how close to the FIST described 100 degrees of hip angle can we achieve with this rider? Is their lack of mobility or excess belly fat getting in the way of this angle? If we have a lean and reasonable limber rider who just can't seem to pedal effectively when we dip below 105 degrees of hip angle, crank length absolutely becomes the prime suspect.

5. Crank length is often the most important metric I change for riders under 5'6" or so. The majority of these riders are what I term "massively over-cranked". These riders typically reduce crank length from 1-2cm, with the shortest commonly available length of 145mm (Cobb) being frequently used for riders under 5'3".

6. Generally, not one watt is gained or lost from a crank length change. Now if the crank was so long that it was basically contributing to a lousy fit, sure, we will probably find some power, but that is more a function of fixing the overall fit. This leads me into one of the final points...

7. Crank length is not fundamental to your bike fit. Seat height, setback, reach to bars, drop to bars ARE your bike fit. Nail those four and you've got a fit. Saddle selection, aerobar shape/tilt/width, crank length, cleat position etc are all secondary factors. Crank length is probably the most important secondary factor for the majority of riders, right up there with saddle selection. What this means is that if we determine 160mm is in your ideal range, your bike fit still exists on 175mm cranks. Saddle height will change, drop will change, set back will change and even reach may change with the less optimal length, but the fit isn't ruined by the wrong cranks. If cost is an issue, we adjust the saddle, ride a bit less drop and advise to change the cranks when you can.

8. Adaptation time for changes in crank length is about 3-5 minutes. Seriously, it just disappears. Which somewhat addresses the question, “Do I need the same length crank on my road bike.” Generally, no. For ‘cross training’ triathletes, road bikes tend to be more of a laid back affair. Specifically, we are not trying to ride in our most bent over, reduced thigh to torso positions, as we do on the tri bikes. So it is not usually as big of an issue.

Crank lengths on road bikes have been around for over a century, and generally work well. The problem with crank length arose when we transferred those historical lengths to commensurately sized aerobar bikes, without realizing the inherent difference in those styles of bikes. For those riding a road bike set up low, in a racing position, an exploration of crank length could be useful. Keep in mind the one tangible drawback that I have found with shorter cranks is a reduced ability to perform out of the saddle climbing. This seems to be a situation where one lever (crank length) comes to the forefront, and diminishes our sense of the system of six levers* used in propelling the bike.


*Foot, crank, lower leg, upper leg, gears, spokes.


3 Months of Paradigm Shifting Swim Instruction for Cheap ---- Your Professional & Private “Critique my Fit”
The Swim Help Compilation Thread

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Re: Crank arm length from fit perspective [FindinFreestyle] [ In reply to ]
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Nice!
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Re: Crank arm length from fit perspective [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
This is everything I have learned about fitting crank length after over 1000 attempts.

1. The only way to intuitively understand the benefits of shorter cranks is to have a competent fitter utilizing proper equipment take you to the limit of your current crank length before making a change. In other words, if your fit is not at least in the ballpark of optimized, you probably won't notice much, or even worse, you might have a different experience than if you were close to optimal.

2. When done as described above, about 80-90% of riders are going to prefer a crank length from .5 to 1.5 cm shorter than what would typically come on a stock bike in their size.

3. Many of the things previously mentioned are important, especially riding a lower / more aero position, but the first thing the fitter and rider need to determine is "Do you prefer this?". It is the same question asked when seat height, setback or drop is changed.... How does this effect your intuitive sense of pedaling? After which, we can look at the power, how much drop you can ride, etc. First is always rider feedback.

4. There is no perfect crank length, or if there is I don't know how to find it. I do know how to find an acceptable range for a given rider. Acceptable here is synonymous with appropriate, and NOT the same thing as aggressive. The #1 thing I look at is how close to the FIST described 100 degrees of hip angle can we achieve with this rider? Is their lack of mobility or excess belly fat getting in the way of this angle? If we have a lean and reasonable limber rider who just can't seem to pedal effectively when we dip below 105 degrees of hip angle, crank length absolutely becomes the prime suspect.

5. Crank length is often the most important metric I change for riders under 5'6" or so. The majority of these riders are what I term "massively over-cranked". These riders typically reduce crank length from 1-2cm, with the shortest commonly available length of 145mm (Cobb) being frequently used for riders under 5'3".

6. Generally, not one watt is gained or lost from a crank length change. Now if the crank was so long that it was basically contributing to a lousy fit, sure, we will probably find some power, but that is more a function of fixing the overall fit. This leads me into one of the final points...

7. Crank length is not fundamental to your bike fit. Seat height, setback, reach to bars, drop to bars ARE your bike fit. Nail those four and you've got a fit. Saddle selection, aerobar shape/tilt/width, crank length, cleat position etc are all secondary factors. Crank length is probably the most important secondary factor for the majority of riders, right up there with saddle selection. What this means is that if we determine 160mm is in your ideal range, your bike fit still exists on 175mm cranks. Saddle height will change, drop will change, set back will change and even reach may change with the less optimal length, but the fit isn't ruined by the wrong cranks. If cost is an issue, we adjust the saddle, ride a bit less drop and advise to change the cranks when you can.

8. Adaptation time for changes in crank length is about 3-5 minutes. Seriously, it just disappears. Which somewhat addresses the question, “Do I need the same length crank on my road bike.” Generally, no. For ‘cross training’ triathletes, road bikes tend to be more of a laid back affair. Specifically, we are not trying to ride in our most bent over, reduced thigh to torso positions, as we do on the tri bikes. So it is not usually as big of an issue.

Crank lengths on road bikes have been around for over a century, and generally work well. The problem with crank length arose when we transferred those historical lengths to commensurately sized aerobar bikes, without realizing the inherent difference in those styles of bikes. For those riding a road bike set up low, in a racing position, an exploration of crank length could be useful. Keep in mind the one tangible drawback that I have found with shorter cranks is a reduced ability to perform out of the saddle climbing. This seems to be a situation where one lever (crank length) comes to the forefront, and diminishes our sense of the system of six levers* used in propelling the bike.


*Foot, crank, lower leg, upper leg, gears, spokes.

Posts like this are why we need sitcky’s in this forum.

get comfortable being uncomfortable
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Re: Crank arm length from fit perspective [stevej] [ In reply to ]
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stevej wrote:

Posts like this are why we need sitcky’s in this forum.

There is a "Hot Forum Topics" pull down on the right side of the forum (at least on the desktop version of the forum). That would be a great place to collect these "pearls of wisdom" pages.

DeSoto Sports
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Re: Crank arm length from fit perspective [zinny] [ In reply to ]
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The way to figure out whether cranks are too long is to use Motion capture and look for whether the closed knee angle is less than ~68deg. And closed hip angle less than ~45deg.
I agree with Daves (findinfreestyle) points about changing cranks. Having Mocap does mean you can identify the possibility of needing to change cranks earlier in the process.

However, at your height it's a fairly safe bet to go straight to 145mm. Stronglight Junior if you want square taper BSA BB, Cobb Alloy for more frame fit options, Cobb carbon if you must have carbon. Or bikesmith will shorten all manner of alloy cranks.


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Re: Crank arm length from fit perspective [FindinFreestyle] [ In reply to ]
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Do you have this in a Word Doc ready to post?
Last edited by: LAI: Dec 5, 17 12:51
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Re: Crank arm length from fit perspective [LAI] [ In reply to ]
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LAI wrote:
Do you have this in a Word Doc ready to post?


Absolutely. I posted it on waterboy's thread a couple weeks ago. It didn't help.


3 Months of Paradigm Shifting Swim Instruction for Cheap ---- Your Professional & Private “Critique my Fit”
The Swim Help Compilation Thread

Last edited by: FindinFreestyle: Dec 5, 17 12:57
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Re: Crank arm length from fit perspective [FindinFreestyle] [ In reply to ]
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Yeah...you guys that take on trying to help him amaze me. Anyhow, thanks for sharing your insight on crank length. I wish I would have had it back in 2012 when I went "short".
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Re: Crank arm length from fit perspective [zinny] [ In reply to ]
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The mob answer is it makes zero difference, and just pay to get a bike fit on whatever you are already riding.

Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep
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Re: Crank arm length from fit perspective [cyclenutnz] [ In reply to ]
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cyclenutnz wrote:
The way to figure out whether cranks are too long is to use Motion capture and look for whether the closed knee angle is less than ~68deg.

That is the exact number I've found as well. Thanks for mentioning it; it's too often overlooked.

Jim Manton / ERO Sports

Aero Tidbits posted on Instagram & Facebook
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Re: Crank arm length from fit perspective [FindinFreestyle] [ In reply to ]
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Thanks for the thorough answer findinfreestyle. From LAI's response, I figure he had a negative or at least not beneficial experience from going "short". Which I haven't really considered.

So with that thought, while the majority of the examples seem to be people "over cranking". Are there any of people "under cranking" and its affects? Could that negatively affect fit?
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Re: Crank arm length from fit perspective [zinny] [ In reply to ]
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zinny wrote:
Thanks for the thorough answer findinfreestyle. From LAI's response, I figure he had a negative or at least not beneficial experience from going "short". Which I haven't really considered.

So with that thought, while the majority of the examples seem to be people "over cranking". Are there any of people "under cranking" and its affects? Could that negatively affect fit?

Interesting, I asked this question for a new thread, and guess what, ... :

Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep
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Re: Crank arm length from fit perspective [h2ofun] [ In reply to ]
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Sorry I generally don't enjoy the threads with the back forth so I probably missed it. Not to start a storm I'll file that question under for another day.
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Re: Crank arm length from fit perspective [zinny] [ In reply to ]
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zinny wrote:
Sorry I generally don't enjoy the threads with the back forth so I probably missed it. Not to start a storm I'll file that question under for another day.

Just FYI

http://forum.slowtwitch.com/...tring=short#p6490300

Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep
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Re: Crank arm length from fit perspective [zinny] [ In reply to ]
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zinny wrote:
Thanks for the thorough answer findinfreestyle. From LAI's response, I figure he had a negative or at least not beneficial experience from going "short". Which I haven't really considered.

So with that thought, while the majority of the examples seem to be people "over cranking". Are there any of people "under cranking" and its affects? Could that negatively affect fit?

Yes there can be a negative effect with going too short. You could go too short where replicating your same fit is impossible, extremely difficult, or just unsafe (stability). There is also gearing to take into consideration. You will spin out your gearing quicker on downhills.

Edit: Another negative could be aerodynamics. You have to keep on raising your saddle as you go shorter on crank length. There will be a point in which your cda will increase when you go shorter cranks and raise the saddle. This is probably the extreme though and would take a huge step to change this. (Eg 200 to 130)

get comfortable being uncomfortable
Last edited by: stevej: Dec 5, 17 15:08
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Re: Crank arm length from fit perspective [h2ofun] [ In reply to ]
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h2ofun wrote:
The mob answer is it makes zero difference, and just pay to get a bike fit on whatever you are already riding.

You are being intentionally obtuse.
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Re: Crank arm length from fit perspective [stevej] [ In reply to ]
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stevej wrote:
zinny wrote:
Thanks for the thorough answer findinfreestyle. From LAI's response, I figure he had a negative or at least not beneficial experience from going "short". Which I haven't really considered.

So with that thought, while the majority of the examples seem to be people "over cranking". Are there any of people "under cranking" and its affects? Could that negatively affect fit?


Yes there can be a negative effect with going too short. You could go too short where replicating your same fit is impossible, extremely difficult, or just unsafe (stability). There is also gearing to take into consideration. You will spin out your gearing quicker on downhills.

I thought the same thing until I actually TESTed this assumption on my super steep martis/brockway downhills. On either a 150 or 175 crank, 50/11, in both cases, I got up to 45 mph before I "spun" out. Since I in real life stop gaining speed at 30 mph, who cares about downhills. The real question is uphills. And yes, I am finding I can use gearing to adjust for going from my 200's to 150's on those steep hills and do just fine. (I was not expecting this)

Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep
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Re: Crank arm length from fit perspective [h2ofun] [ In reply to ]
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Please, do us all a favour and stay off this thread. Things tend to become "less than civil" whenever you are involved, and since you have the thread to end all threads describing your experiences, how about a thread devoted to the methodologies that actual fitters use?

____________________________________
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Re: Crank arm length from fit perspective [stevej] [ In reply to ]
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stevej wrote:
Yes there can be a negative effect with going too short. You could go too short where replicating your same fit is impossible, extremely difficult, or just unsafe (stability). There is also gearing to take into consideration. You will spin out your gearing quicker on downhills.

Gearing is unrelated to crank length.
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Re: Crank arm length from fit perspective [nightfend] [ In reply to ]
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nightfend wrote:
stevej wrote:
Yes there can be a negative effect with going too short. You could go too short where replicating your same fit is impossible, extremely difficult, or just unsafe (stability). There is also gearing to take into consideration. You will spin out your gearing quicker on downhills.

Gearing is unrelated to crank length.

Sheldon Brown would disagree with you.

https://www.sheldonbrown.com/gain.html

get comfortable being uncomfortable
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Re: Crank arm length from fit perspective [JasoninHalifax] [ In reply to ]
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JasoninHalifax wrote:
Please, do us all a favour and stay off this thread. Things tend to become "less than civil" whenever you are involved, and since you have the thread to end all threads describing your experiences, how about a thread devoted to the methodologies that actual fitters use?

I just bought a Quarq and went with 165mm instead of my previous normal 170mm. My methodology was "that's the shortest it comes in and doesn't seem like it should be too short and then I can get lower". How's that for methodology?

No, seriously.

---
The point is, ladies and gentleman, that speed, for lack of a better word, is good. Speed is right, Speed works. Speed clarifies, cuts through, and captures the essence of the evolutionary spirit.
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Re: Crank arm length from fit perspective [Toby] [ In reply to ]
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That's pretty much mine. I have a 165mm dura ace track crankset w 48t ring. It's the shortest i have and happens to be the shortest p2max crank length. So that's gonna be it once I get a pm.

____________________________________
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Re: Crank arm length from fit perspective [zinny] [ In reply to ]
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zinny wrote:
Thanks for the thorough answer findinfreestyle. From LAI's response, I figure he had a negative or at least not beneficial experience from going "short". Which I haven't really considered.

So with that thought, while the majority of the examples seem to be people "over cranking". Are there any of people "under cranking" and its affects? Could that negatively affect fit?

I think you can go too short, and I think you can largely "feel" your way to that as well. For starters, many (most?) riders can get to such a low position with reasonably short cranks, that going lower via shorter cranks would be of questionable benefit to aerodynamics anyway.

For me, having the luxury of an adjustable crank fit bike at my disposal for many years, I hovered between 160 and 155 as my lower limit. At a long legged 6 feet tall with a 78cm seat height at my old 172.5s, going down through 170, 165, 160 all felt great. All shorter lengths felt better than the longer. Swapping back and forth between 160 and 155 (many, many times) has been interesting. The shorter the crank, the higher the natural RPMs, and I have tentatively reached the conclusion that 160s is ideal for me. I can comfortably ride 17cm of drop at that length with zero power loss from a well developed road position.

On my recently ordered PC fit bike, I am going to utilize both the standard 155-185mm cranks as well as the shorter 140-170mm set. Shorter riders are certainly not under cranked at 155mm, and those shorter adjustable cranks are probably the one piece of hardware I have wished for over the last few years. I am a little curious how the 140 - 150 length treats me, but I am fairly confident that the 155s are getting a bit under my range. It's subtle, but once noticed, it's consistent with every trial.

For the record, I also think all the 'testing' Dave C. is doing with HR and power and speed over courses is NOT a path to finding a proper range of crank lengths. I think it is a bottomless rabbit hole, and I hope he can keep it off this thread.


3 Months of Paradigm Shifting Swim Instruction for Cheap ---- Your Professional & Private “Critique my Fit”
The Swim Help Compilation Thread

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Re: Crank arm length from fit perspective [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
zinny wrote:
Thanks for the thorough answer findinfreestyle. From LAI's response, I figure he had a negative or at least not beneficial experience from going "short". Which I haven't really considered.

So with that thought, while the majority of the examples seem to be people "over cranking". Are there any of people "under cranking" and its affects? Could that negatively affect fit?


I think you can go too short, and I think you can largely "feel" your way to that as well. For starters, many (most?) riders can get to such a low position with reasonably short cranks, that going lower via shorter cranks would be of questionable benefit to aerodynamics anyway.

For me, having the luxury of an adjustable crank fit bike at my disposal for many years, I hovered between 160 and 155 as my lower limit. At a long legged 6 feet tall with a 78cm seat height at my old 172.5s, going down through 170, 165, 160 all felt great. All shorter lengths felt better than the longer. Swapping back and forth between 160 and 155 (many, many times) has been interesting. The shorter the crank, the higher the natural RPMs, and I have tentatively reached the conclusion that 160s is ideal for me. I can comfortably ride 17cm of drop at that length with zero power loss from a well developed road position.

On my recently ordered PC fit bike, I am going to utilize both the standard 155-185mm cranks as well as the shorter 140-170mm set. Shorter riders are certainly not under cranked at 155mm, and those shorter adjustable cranks are probably the one piece of hardware I have wished for over the last few years. I am a little curious how the 140 - 150 length treats me, but I am fairly confident that the 155s are getting a bit under my range. It's subtle, but once noticed, it's consistent with every trial.

For the record, I also think all the 'testing' Dave C. is doing with HR and power and speed over courses is NOT a path to finding a proper range of crank lengths. I think it is a bottomless rabbit hole, and I hope he can keep it off this thread.

So, what type of adjustable cranks are you buying? Those sound like ones from highsierra?

Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep
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