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Too short of a crank?
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Shorter cranks are all the rage right now and for good reason, as several other threads have noted. However, is it possible to go too short? I've come across various "studies" that show benefits of extremely short cranks but how do these play out in the real world? For example, how many STers over 5'10 use cranks with a length of less than 160mm and still produce sufficient power/speed compared to when they were on a longer crank? I'm not discounting the benefits, reduced knee problems, etc of shorter cranks, just trying to determine if there is a given range.
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Re: Too short of a crank? [alaska848] [ In reply to ]
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I'm just shy of 6' and my cut off point seems to be 160. I trialled in 5mm lengths from 170 to 150 over periods of time. My last IM I did with 155 and it just felt too short and I had issues maintaining power with fatigue. I went back to 160 which I had been running for over a season and they feel perfect. I had 150 on briefly a few years ago and it felt just too short and my pedal circumference was just too small and I struggled to maintain power at least in the 70.3 I did with them. So I think it may be personal to many including leg length, your normal cadence and power output but I definitely think there is a tipping point. Also I think as long as your jumps aren't too big it won't take much time if any to adapt but if you make a too bigger jump it then you may have issues and may not know if the are the length for you without proper time for the body to adapt.
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Re: Too short of a crank? [alaska848] [ In reply to ]
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i‘m 1,67 m tall, that’s close to 5‘6 and i use cranks with 145 mm length. i went to that length from 170 and they feel much better. i had no power loss and it took only a few days to get used to the different pedalspeed, but that was more the feel of it.
i didn’t try shorter, so i don’t know about a “too short “.
one thing to consider: you probably want to compare inseam and crank length and not height and crank length, but i’m just guessing.

danny

then someone will say, what is lost can never be saved.
despite all my rage, i am still just a rat in a cage.
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Re: Too short of a crank? [alaska848] [ In reply to ]
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5’8” 145mm cranks.
No regrets
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Re: Too short of a crank? [alaska848] [ In reply to ]
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Yes, you can go too short. Or, yes, you can have too little knee flexion at the top of the stroke. You want the right amount. Many riders have too much flexion with standard size cranks.

For me at 5'11.5", but more importantly with a 77.5cm seat height, going from 172.5 down to 165mm was awesome. Going to 160mm was better still. 155mm was perhaps marginal gains, and 150mm I simply did not like. I would trial these on my fit bike, under thresholdish power, in aero position, multiple, multiple times.

Based on about 1500 fits done by guiding riders to the limits of their current crank before trying multiple shorter lengths, I've come up with a rough guide to get you in the ballpark. The vast majority of riders are self selecting something in these ranges:

<60cm seat height :: Crank 145mm or less. Really as short as you can find, maybe go custom. I’ve fit down to 135mm with custom cut BMX cranks.
60-65cm :: Crank length 140-150mm
65-70cm :: 145-155mm
70-75cm :: 150-160mm
75-80cm :: 155-165mm
80-85cm :: 160-170mm
>85cm :: 165-175mm Keep in mind that of the tallest and strongest professional athletes I have fit literally ZERO of them have preferred anything over 165mm. These are 6’3” and taller athletes pushing wattage over 375 watts at threshold and upper 200s to 300 for IM races. "



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Last edited by: FindinFreestyle: Dec 2, 18 6:41
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Re: Too short of a crank? [FindinFreestyle] [ In reply to ]
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Do you have any experience with mtn bike fit/optimal power with regards to crank length? I can’t think of a valid reason why the findings would be different compared to road/TT.

_______________________________________________
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Re: Too short of a crank? [FindinFreestyle] [ In reply to ]
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I bought my first TT bike a couple of months ago, I had a prefit session with our local, well respected bike fit dude and of course I wanted to buy the right crank length when I ordered the bike. The result of the conversation (and Retul fit) was that I'm on 172.5 cm cranks, the same as my road bike. His reason being that there is no measurable performance difference going from 172.5 to 165. My saddle height is 81 btw. Of course it feels natural to me as that's what I'm used to.

So do I listen to the guy I paid money to or put my trust in a bunch of random experts on the internet?

"Aquabike is a swim then sleep session on aerobars ...."
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Re: Too short of a crank? [Fuller] [ In reply to ]
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I would go with the fitter, but curious how you measured the difference. Just testing different length cranks on a power meter or smart trainer, or some other method?

***
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Re: Too short of a crank? [Fuller] [ In reply to ]
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Fuller wrote:
I bought my first TT bike a couple of months ago, I had a prefit session with our local, well respected bike fit dude and of course I wanted to buy the right crank length when I ordered the bike. The result of the conversation (and Retul fit) was that I'm on 172.5 cm cranks, the same as my road bike. His reason being that there is no measurable performance difference going from 172.5 to 165. My saddle height is 81 btw. Of course it feels natural to me as that's what I'm used to.

So do I listen to the guy I paid money to or put my trust in a bunch of random experts on the internet?

I would say that your perception during an intuitive and collaborative process in which you are taken to the limit of your existing crank before making changes would trump the statement "there is no measurable performance difference..." In fact, I would stake my reputation on it.


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: Too short of a crank? [Bonesbrigade] [ In reply to ]
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Bonesbrigade wrote:
Do you have any experience with mtn bike fit/optimal power with regards to crank length? I can’t think of a valid reason why the findings would be different compared to road/TT.


Knee flexion is likely the primary driver, but not the only driver. Thigh torso plays into it as well, and is not generally an issue on a mountain bike. Also, some riders have expressed to me that stance (length, not width) plays a role in their perception of stability while descending. I would generally put a mountain rider on the same length as they would ride a road bike, which is generally 5 - 15mm longer than their TT bike (And still a touch shorter than stock road lengths in most cases). Out of 3000+ fits, I've done about 20 mountain bike fits, so not my specialty.


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 2, 18 7:39
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Re: Too short of a crank? [Fuller] [ In reply to ]
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my general rule of thumb is 10mm less on TT bike vs. road bike, but like Retul prescriptions, that's just a rule of thumb, and not a proper fit outcome when you go through an iterative process to arrive at the right crank length from a comfort, power, and aerodynamic perspective.

For what purpose are you riding your TT bike?


Fuller wrote:
I bought my first TT bike a couple of months ago, I had a prefit session with our local, well respected bike fit dude and of course I wanted to buy the right crank length when I ordered the bike. The result of the conversation (and Retul fit) was that I'm on 172.5 cm cranks, the same as my road bike. His reason being that there is no measurable performance difference going from 172.5 to 165. My saddle height is 81 btw. Of course it feels natural to me as that's what I'm used to.

So do I listen to the guy I paid money to or put my trust in a bunch of random experts on the internet?

Eric Reid
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Re: Too short of a crank? [ericMPro] [ In reply to ]
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Quote:
For what purpose are you riding your TT bike?

I just want to do well in my Aquabike 65-69 AG. I've been a regular club rider for the last 3 years or so and got into the multisport aspect last summer. Club rides are fun and I've moved up in the pecking order but I also enjoy solo training. I need some structured training and a good bike fit to get on the podium.

"Aquabike is a swim then sleep session on aerobars ...."
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Re: Too short of a crank? [alaska848] [ In reply to ]
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I am 6'2" and on 155s on my TT bike....165 and 170 (Campy) on my road bikes. No issues and can't tell the difference.
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Re: Too short of a crank? [M----n] [ In reply to ]
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M----n wrote:
I would go with the fitter, but curious how you measured the difference. Just testing different length cranks on a power meter or smart trainer, or some other method?

It was more like a bit of fiddling with the fit bike and some computer readouts. No direct empirical measurements. Obviously "my guy" is relying on his past experience to move the process along.

At the time I hadn't plumbed the depths of the ST pages to get a feel for what I should be asking. Now that I'm better informed I know to further explore the issue. I have a follow up session coming to me but it will be delayed due to ski season. The snowy peaks of northern Montana are calling me and I need to start some ski specific training in lieu of beating my brains out on the TT bike.

Not enough time to get good at all the things that I love doing...

"Aquabike is a swim then sleep session on aerobars ...."
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Re: Too short of a crank? [Fuller] [ In reply to ]
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But to get back to the question, it appears that if you were to actually measure the difference you would need to look at both power output in a variety of different scenarios as well as aerodynamic benefits. Is there a published study that supports the prevailing opinion on ST?

I do notice that online communities can quickly rally behind a particular concept or piece of equipment and sometimes it seems that everyone is just jumping on the bandwagon. It happens a lot on the ski forums...

"Aquabike is a swim then sleep session on aerobars ...."
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Re: Too short of a crank? [Fuller] [ In reply to ]
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Fuller wrote:
But to get back to the question, it appears that if you were to actually measure the difference you would need to look at both power output in a variety of different scenarios as well as aerodynamic benefits. Is there a published study that supports the prevailing opinion on ST?

I do notice that online communities can quickly rally behind a particular concept or piece of equipment and sometimes it seems that everyone is just jumping on the bandwagon. It happens a lot on the ski forums...

I don't look at power output. I use electronic resistance and perform trials at the same power. So output is necessarily the same, and the rider's perception of effort is what matters most. No, I don't look at HR either. Cadence generally goes up with shorter cranks, sometimes dramatically, but that is not a driver either. No concern with aerodynamics either.

It's rider feel > my eyeballs > knee flexion angle > thigh/torso angle > falling within a range that generally works. Maybe in the future there will be some published studies explaining the why behind what I know works, but I'm not really concerned.


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: Too short of a crank? [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
Bonesbrigade wrote:
Do you have any experience with mtn bike fit/optimal power with regards to crank length? I can’t think of a valid reason why the findings would be different compared to road/TT.


Knee flexion is likely the primary driver, but not the only driver. Thigh torso plays into it as well, and is not generally an issue on a mountain bike. Also, some riders have expressed to me that stance (length, not width) plays a role in their perception of stability while descending. I would generally put a mountain rider on the same length as they would ride a road bike, which is generally 5 - 15mm longer than their TT bike (And still a touch shorter than stock road lengths in most cases). Out of 3000+ fits, I've done about 20 mountain bike fits, so not my specialty.

Interesting comment about stance when cranksrms are horizontal - I hadn’t considered that. That could alter your stability I suppose. Not sure it would make too much difference though.

I’m coming at this more from a practicable position - based on all the crank length studies I’ve read, power remains the same within quite a wide range. I’d like shorter cranks to reduce the occurance of pedal strikes, and actually allow me get extra pedal strokes in when riding through technical areas in race situations. Not to mention, this could also allow me get a little more saddle to bar drop. These 29ers have high front ends!

_______________________________________________
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Re: Too short of a crank? [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
Fuller wrote:
But to get back to the question, it appears that if you were to actually measure the difference you would need to look at both power output in a variety of different scenarios as well as aerodynamic benefits. Is there a published study that supports the prevailing opinion on ST?

I do notice that online communities can quickly rally behind a particular concept or piece of equipment and sometimes it seems that everyone is just jumping on the bandwagon. It happens a lot on the ski forums...


I don't look at power output. I use electronic resistance and perform trials at the same power. So output is necessarily the same, and the rider's perception of effort is what matters most. No, I don't look at HR either. Cadence generally goes up with shorter cranks, sometimes dramatically, but that is not a driver either. No concern with aerodynamics either.

It's rider feel > my eyeballs > knee flexion angle > thigh/torso angle > falling within a range that generally works. Maybe in the future there will be some published studies explaining the why behind what I know works, but I'm not really concerned.

Honestly the "feels" part of this sets me back a bit. It's not that I don't believe it to be true, it's just that perceptions can be guided by suggestion in very powerful ways. Take homeopathy for instance, I used to get into knock down drag out fights with my wife because she would spend significant bucks on what I considered a major scam. The pro homeopathy folks can only tell you that it works no matter how outlandish the premise is. Over time I think she adopted some of my skepticism and I certainly learned that I didn't have to win every issue in our marriage so we resolved our problem.

The OP mentioned some "studies". In the sports world that could amount to anything on the internet that supports the conclusion. Maybe we could start by listing the perceived benefits; from memory these are the things I've seen on ST.

Better knee angle
Better torso / hip angle
Better endurance
Aero benefits (due to being able to hold position)
More watts
It just feels better.

Anything else to consider? Any links to "studies"?

"Aquabike is a swim then sleep session on aerobars ...."
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Re: Too short of a crank? [Fuller] [ In reply to ]
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In less time than it takes to find studies, discuss, debate, ponder, and decide you could find a competent fitter with proper equipment and feel for yourself. I do understand the sentiment, but the entire F.I.S.T. process is driven by rider feel. Riders feel their way into orthodox, aerodynamic, world class positions everyday.


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: Too short of a crank? [Bonesbrigade] [ In reply to ]
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Bonesbrigade wrote:
FindinFreestyle wrote:
Bonesbrigade wrote:
Do you have any experience with mtn bike fit/optimal power with regards to crank length? I can’t think of a valid reason why the findings would be different compared to road/TT.


Knee flexion is likely the primary driver, but not the only driver. Thigh torso plays into it as well, and is not generally an issue on a mountain bike. Also, some riders have expressed to me that stance (length, not width) plays a role in their perception of stability while descending. I would generally put a mountain rider on the same length as they would ride a road bike, which is generally 5 - 15mm longer than their TT bike (And still a touch shorter than stock road lengths in most cases). Out of 3000+ fits, I've done about 20 mountain bike fits, so not my specialty.

Interesting comment about stance when cranksrms are horizontal - I hadn’t considered that. That could alter your stability I suppose. Not sure it would make too much difference though.

I’m coming at this more from a practicable position - based on all the crank length studies I’ve read, power remains the same within quite a wide range. I’d like shorter cranks to reduce the occurance of pedal strikes, and actually allow me get extra pedal strokes in when riding through technical areas in race situations. Not to mention, this could also allow me get a little more saddle to bar drop. These 29ers have high front ends!
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Re: Too short of a crank? [Bonesbrigade] [ In reply to ]
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Bonesbrigade wrote:
FindinFreestyle wrote:
Bonesbrigade wrote:
Do you have any experience with mtn bike fit/optimal power with regards to crank length? I can’t think of a valid reason why the findings would be different compared to road/TT.


Knee flexion is likely the primary driver, but not the only driver. Thigh torso plays into it as well, and is not generally an issue on a mountain bike. Also, some riders have expressed to me that stance (length, not width) plays a role in their perception of stability while descending. I would generally put a mountain rider on the same length as they would ride a road bike, which is generally 5 - 15mm longer than their TT bike (And still a touch shorter than stock road lengths in most cases). Out of 3000+ fits, I've done about 20 mountain bike fits, so not my specialty.

Interesting comment about stance when cranksrms are horizontal - I hadn’t considered that. That could alter your stability I suppose. Not sure it would make too much difference though.

I’m coming at this more from a practicable position - based on all the crank length studies I’ve read, power remains the same within quite a wide range. I’d like shorter cranks to reduce the occurance of pedal strikes, and actually allow me get extra pedal strokes in when riding through technical areas in race situations. Not to mention, this could also allow me get a little more saddle to bar drop. These 29ers have high front ends!

This is interesting, I ride a lot of mtb in the shoulder seasons but have never been invested enough to consider CL.

Basically I see the advantages of tight clearance, the only drawback *might* be that instantaneous max torque you need for 1-4 pedal strokes to over come some obstacles etc.

Really funny how basically every single mtb in the industry comes with 175 cranks, or at least used to several years.

Still ride 175’s because I consider mtb to be “fresh air” and “holistic” so don’t want to stress out about the performances details as I don’t race.

Maurice
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Re: Too short of a crank? [alaska848] [ In reply to ]
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My n=1 is that 165s (at 5'10.5") caused knee problems but my left leg is 2 LOOK cleats shorter then the right. Confirmed when I switched out twice but then went out on my wife's bike (no road bike at the time) and had forgotten about it (2 years) and right at 20 miles knee pain started and by 25 it was almost unbearable. I had never had knee pain in my life (hips are the first to go (mildly). Just something to think about with shorter cranks.

http://adambeston.blogspot.com
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Re: Too short of a crank? [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
In less time than it takes to find studies, discuss, debate, ponder, and decide you could find a competent fitter with proper equipment and feel for yourself. I do understand the sentiment, but the entire F.I.S.T. process is driven by rider feel. Riders feel their way into orthodox, aerodynamic, world class positions everyday.

I DO have a competent fitter with proper equipment. It seems his professional opinion differs from many here on ST, hence the pfaffing and pondering. I honestly don't have a dog in this hunt either way, I'm just looking for the easiest path to getting where I need to be.

"Aquabike is a swim then sleep session on aerobars ...."
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Re: Too short of a crank? [mauricemaher] [ In reply to ]
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Yeah I have been riding and racing mtn bikes for 20 years and hadn’t put much thought into it either until I got a new bike this year. I have been slowly getting shorter cranks on all my other bikes - road, gravel, TT. What really got me thinking was the amount of pedal strikes I’ve been getting with my new Ibis ripley. The newer 29ers have been running more BB drop for better stability and cornering, but as a consequence less pedal clearance. The high front end also adds another problem with me getting my bars low enough in relation to my saddle. Shorter cranks can help in both of these areas. Not huge, but for sure a meaningful amount - particularily pedal clearance.

Edit: I did think about the torque issue for those critical one or two pedal stroke moments to clear an obstacle, but I doubt that would make a difference - not sure on this though.

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Last edited by: Bonesbrigade: Dec 2, 18 15:17
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Re: Too short of a crank? [Bonesbrigade] [ In reply to ]
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It’s an interesting discussion, more on the technical end. For reference I’ve been riding for about 25 years, first in Whistler now out my front door in Kamloops BC.

Still riding a 26 rocky vertex 10 y/o with a dropper seat post.

It does what I need it to do but as you say for the short burst technical elements there might be a slight retraining affect to shorter, but likely we could clean them after a few passes.

Maurice
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