General Discussion Triathlon Talk » Shorter cranksets? Rss Feed  
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2011-08-16 7:18 AM

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Subject: Shorter cranksets?

Why does there seem to be a move to shorter cranksets? I overheard a coach telling someone that "It will open up your hip angle and allow you to ride a deeper aero position and facilitate a faster run due to the improved bike position. It will also improve cadence which again positively impacts your run. The days of going with longer crank arms has passed"...

Thoughts? Undecided



2011-08-16 9:41 AM
in reply to: #3645251

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Subject: RE: Shorter cranksets?

Interesting, curious to hear what others have to say.  I am a pretty short guy and using the online calculators to determine optimal crank length typically comes back with something between 150-160...?  Nobody makes cranks that short that I am aware of. 

I currently use a 170 only because that's what my bike came with.  Been considering buying a new crankset but not sure if I should stick with 170 or go smaller with 165, which are the shortest I have seen.  My understanding has been that I should go as long as I can on cranks as it will provide better leverage.  However, longer cranks make it difficult for me to keep my knees above my feet which might explain why I often have knee pain on longer hilly rides that put more stress on the front of the peddle stroke.

 

2011-08-16 11:00 AM
in reply to: #3645251

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Fort Walton Beach
Subject: RE: Shorter cranksets?

I moved from 175s to 170s and feel that it is much easier to get lower on the bars.  I really notice it at the top of the pedal stroke. I always felt like my knees just came up too high. I am 5'10" with average proportions for reference.  I ran the change by the ST fitter that worked on me with my tri bike, he was very enthusiatic about it.

2011-08-16 11:20 AM
in reply to: #3645251

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Subject: RE: Shorter cranksets?

Some of what you heard is probably true. Shorter cranks mean more knee clearance and a smaller pedaling circle. For those who are range of motion-limited in some way (super tight hamstrings and lower back inflexibility), this could be a real lifesaver. Also, you gain a few more potential mm of drop in front b/c you can raise your seat a bit with the same knee clearance. But that comes at the cost of closing your hip angle down, which you just went out of your way to open up...so I'm not sure the improvements are quite linear.

However, you lose leverage like the other poster said. You have to pedal faster/with more force (some combo) to generate the same power. If shorter cranks improve your pedaling enough, this isn't a problem and you're likely to be more comfortable and maybe even more powerful. But yes, there is a tradeoff.

I feel like someone had a scientific study on crank length and power output a while ago, and the gist was that arm length didn't appear to affect sustainable power output (and they tried cranks from like 10 cm out to 30+ cm). Maybe I can dig that one up or someone has easy access to it off hand...

Jason

2011-08-16 11:39 AM
in reply to: #3645251

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Master
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Subject: RE: Shorter cranksets?
Oriondriver02 - 2011-08-16 7:18 AM

Why does there seem to be a move to shorter cranksets? I overheard a coach telling someone that "It will open up your hip angle and allow you to ride a deeper aero position and facilitate a faster run due to the improved bike position. It will also improve cadence which again positively impacts your run. The days of going with longer crank arms has passed"...

Thoughts? Undecided

I think he's right.  He said it all.  Did you disagree?

 

2011-08-16 11:53 AM
in reply to: #3645251

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Elite
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Subject: RE: Shorter cranksets?

By extrapolation, this logic would dictate that shorter and shorter crank arms would provide an increased benefit. Of course, that means the best cranks would be zero length- so that logic doesn't work.

Neither does the logic that long cranks are "over". That is verifiably wrong. Incorrect. Not accurate.

It is correct to say that a shorter crank does open the angle between the hip and torso, and that there is some benefit to that in some contexts.

As a generalization- it is not supportable.

What is supportable- by anecdote and historical results- is that there seems to be a link between the morphology of a rider (their body dimensions and build), optimal pedalling frequency and position- and these factors combine into a "soup" that determines optimal individual crank length.

The emminent author and editor, Lennard Zinn, Technical Editor at Velo-News and Inside Triathlon, and a graduate of the Colorado School of Mines in Engineering- and a frame builder- once did a two year project of correlating crank length to body dimensions to performance. Largely, the project ended in frustration. There was little conclusive evidence to point to an optimal methodology for prescribing a crank length based on some set of finite metrics, be they leg length, femur to tibia ratio, pedalling frequency, power output, etc.

In the broad scheme of things we have riders like Jaques Anquetil, the first man to win 5 Tours de France, on custom 188.5 mm cranks. Miguel Indurain on 180's, Bernard Hinault (at 5'7&1/2" tall) on 175's, Eddy Merckx on 172.5 mm cranks (Merckx is taller than me, about 6'0" I think). Then the triathletes like Dave Scott, Scott Tinley and Mark Allen- each trending longish.

The recent trend in shorter cranks is a well-conceived Empfield-ian (Dan Empfield, the lad who invented the tri bike and triathlon bike fitting) approach to the continued quest to open hip angle. It is a good quest, but it isn't a panacea. It isn't all things to all people.

At some point shorter cranks- while absolutely opening hip angle- do begin to slow you down. You lose leverage, you can't physiologically maintain pedalling frequency without a higher metabolic cost.

You slow down.

Throughout the envelope of common performance pedalling cadences- on the low end 70 RPM's grinding up a nasty hill, to the very high end almost spun out at 110 RPM's, it is tough to nail the one optimal crank. Ideally, a crank would change its length, adapting to cadence. There have been experiments with this too. In this year's Tour de France Fabian Cancellara experimented with a variable geometry seatpost to vary his saddle height with cadence- as his cadence went up, so did his saddle.

Ultimately striking a reasonable balance between fit, leverage and cadence in crank length has been the most effective approach, and the one commonly held among elite cyclists and most elite triathletes- although it should be said that even among six-figure pro triathletes there is a tremendous lack of cycling sopistication and general tech savvy.

I've tried 167.5, 170, 172.5, 175, 177 and (briefly) 180. I've permanently settled on 175mm after years of triathlons and road races/time trials. I'm 5'9" and have short-ish legs and a long torso. Across the specturm of fits and positions I trend long for cranks, using 175mm's over Time RXS pedals at a saddle height of almost exactly 72cm. I did briefly go back to 172.5's after a knee surgery from an unrelated trauma (ski accident). At about the same heart rate range, I was a little slower and had a tough time turning the big gears. I could increase my cadence but there was a metabolic cost to that. When my knee healed I went back to 175mm's.

The long and short of it is: There are no crank length generalizations that hold water.



Edited by Tom Demerly. 2011-08-16 11:58 AM


2011-08-16 12:22 PM
in reply to: #3645817

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Master
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Subject: RE: Shorter cranksets?

Tom has just demonstrated that he's not an engineer.

The 2 relavent points here are:

1) Recent studies have found no increase or decrease in cycling performance as measured with a power meter between a very wide range of crank lengths...ranging from silly short like 130mm to 190mm

2) 'leverage' on the rear wheel is an interplay between crank length, chain ring size, rear gear, wheel size.  They are ALL part of the one equation defining torque.  So shorter crank arms do NOT mean you need to pedal differently...you just shift gears.  they do not mean you need to turn higher RPMs or lower. 

 

Take aways:

- use whatever crank you want and it won't hurt your performance

- if your aggressive TT position that is most aero decreases your power output because of the thighs/knees interfering with your waist/stomach/diaphragm...then you have a huge benefit by using shorter crank arms.

 

2011-08-16 1:30 PM
in reply to: #3645790

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Subject: RE: Shorter cranksets?
JeffY - 2011-08-16 11:39 AM
Oriondriver02 - 2011-08-16 7:18 AM

Why does there seem to be a move to shorter cranksets? I overheard a coach telling someone that "It will open up your hip angle and allow you to ride a deeper aero position and facilitate a faster run due to the improved bike position. It will also improve cadence which again positively impacts your run. The days of going with longer crank arms has passed"...

Thoughts? Undecided

I think he's right.  He said it all.  Did you disagree?

 

It is a single data point... I am not a single data point kind of person... was not a matter of agreement and thus the question... was looking for more of an explanatory response other than... "he's right"...

2011-08-16 2:41 PM
in reply to: #3646028

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Master
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Subject: RE: Shorter cranksets?
Oriondriver02 - 2011-08-16 1:30 PM
JeffY - 2011-08-16 11:39 AM
Oriondriver02 - 2011-08-16 7:18 AM

Why does there seem to be a move to shorter cranksets? I overheard a coach telling someone that "It will open up your hip angle and allow you to ride a deeper aero position and facilitate a faster run due to the improved bike position. It will also improve cadence which again positively impacts your run. The days of going with longer crank arms has passed"...

Thoughts? Undecided

I think he's right.  He said it all.  Did you disagree?

 

It is a single data point... I am not a single data point kind of person... was not a matter of agreement and thus the question... was looking for more of an explanatory response other than... "he's right"...

Well, I understand wanting explanation for sure...but your quote of what he said was a pretty good explanation itself.  Can I offer elaboration on a specific point he made?

 

2011-08-16 4:47 PM
in reply to: #3645251

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Subject: RE: Shorter cranksets?
Jeff... Based on your responses thus far I am not sure I am interested in listening to what you might have to offer... I was looking for more than simply an individual opinion as everyone is physically different...  it is my feeling that his blanket statement was a hasty generalization that did not properly take into account all of the individual factors that go into fitting someone to a bike... as Tom D pointed out... there are a lot of variables that would dictate what size cranks would be appropriate for two equally proportioned riders given different physical characteristics (flexibility, range of motion, aggressiveness of positioning on bike, etc)... what may be great for one rider may be a bad setup for another... at the elite level he may have been spot on but for the average person the deeper aero position may prove detrimental... 
2011-08-16 4:55 PM
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Subject: ...
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2011-08-16 9:04 PM
in reply to: #3645251


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Subject: RE: Shorter cranksets?
I switched from 175's to 165's and experienced all the things you mention.  After a few adjustments on the trainer my first ride was 108 miles and I had one of my best ever t-runs after.  I got them on Bonktown for $99, so they were a cheap experiment that ended well (for me).
2011-08-16 9:27 PM
in reply to: #3645817

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Subject: RE: Shorter cranksets?

I think Tom pretty much nailed that one. For all our "analyzing", we are not immune to fads.

And Jeff, while the interplay of all the various parts of the bike might very well define torque, you are forgetting the engine. By continually shortening the cranks, you lose range in motion, and therefore muscle groups recruited to pedal. To take a page from Tom's post, if shorter is better, than we would all be super aero and pedaling with just our ankles. Crank length is dependant on many variables, with flexibility and already developed muscle groups being 2 making the list.

All that aside, if it was truly better, than all the top pros would be on 165's, yet none that I know of are.

Bottom line is that some will love the shorter cranks, and for others, it'll be a disaster.

2011-08-16 9:33 PM
in reply to: #3645857

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Subject: RE: Shorter cranksets?
JeffY - 2011-08-16 12:22 PM

Tom has just demonstrated that he's not an engineer.

The 2 relavent points here are:

1) Recent studies have found no increase or decrease in cycling performance as measured with a power meter between a very wide range of crank lengths...ranging from silly short like 130mm to 190mm 

Just curious...can you cite this study?  I would very much enjoy reading it.

Thanks!

2011-08-16 9:55 PM
in reply to: #3645251

Master
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Westlake Village , Ca.
Subject: RE: Shorter cranksets?

I've always ridden 175's.....my new Shiv came with 172.5's

I can't notice the difference....LOL......

2011-08-16 10:18 PM
in reply to: #3646696

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Subject: RE: Shorter cranksets?
Fastyellow - 2011-08-16 9:55 PM

I've always ridden 175's.....my new Shiv came with 172.5's

I can't notice the difference....LOL......

 

ooooooooooohhhhhhhhhhhh, Shiv. Nice rig!



2011-08-17 11:10 AM
in reply to: #3646678

Master
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Columbia, TN
Subject: RE: Shorter cranksets?
NiceTriCoaching - 2011-08-16 9:33 PM
JeffY - 2011-08-16 12:22 PM

Tom has just demonstrated that he's not an engineer.

The 2 relavent points here are:

1) Recent studies have found no increase or decrease in cycling performance as measured with a power meter between a very wide range of crank lengths...ranging from silly short like 130mm to 190mm 

Just curious...can you cite this study?  I would very much enjoy reading it.

Thanks!

This should get you started.  Google pulls up a lot of stuff, but the difficulty is that most of the studies are flawed, or at least not applicable to cycling performance because of the test parameters.

http://pezcyclingnews.com/?pg=fullstory&id=8845

 

2011-08-17 11:17 AM
in reply to: #3645251

Elite
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Subject: RE: Shorter cranksets?
I went from  172.5 to 165...solely just to see if it reduced wear and tear on the knees.  I'm 5'5" and realized most folks that rode 172.5s were a lot taller than me, hence part of my logic.

I haven't noticed any difference at all.
2011-08-17 12:12 PM
in reply to: #3645251

Expert
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Prattville, AL
Subject: RE: Shorter cranksets?

In my quest to better understand the original statement.... I found this interesting...

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1724616/pdf/v037p00154.pdf

"Compared with an isolated run, completion of a cycling
event impairs the performance of a subsequent run
independently of the pedalling cadence. However,
running strategy, stride rate, and metabolic contribution
seem to be improved by the use of a low pedalling
cadence (60 rpm). The choice of cycling cadence may
have an effect on the running adaptation during a sprint or
short distance triathlon."

Jury still out on this one...

2011-08-17 12:37 PM
in reply to: #3647440

Master
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Columbia, TN
Subject: RE: Shorter cranksets?

There is a consistent chorus of people suggesting that slower than typical cycling cadences are best for Ironman events.  Somewhere around 80 perhaps?  Since the typical is in the 90s. But 60 doesn't sound like a good idea, at least not for a competitive athlete.  Folks just in it to finish might benefit though.

That quote seems a little weird.  "completion of a cycling event impairs the performance of a subsequent run independently of the pedaling cadence."

Then: "The choice of cycling cadence may have an effect on the running adaptation during a sprint or short distance triathlon"

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