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 Post subject: The short crank trend
PostPosted: Sun Nov 22, 2015 5:29 pm 
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Wiggins is shifting for shorter cranks, but a part from him - most pros seems to keep what they've always been using. I've gotten interested in this short crank trend, and what it might do for me.

I'm born with quite short legs, long arms and quite long torso for my 175cm length. Inseam 80cm and my saddle height is 70.5cm. My hip angle is really tight on both road and TT bike unless I go grandma bike fit. This caught my interest for shorter cranks that could potentially open up my hip and give me a less closed hip and perhaps more power loss in that phase.

I got a short clip of me warming up on 172.5mm cranks, what do you guys think?

https://www.youtube.com/watch?v=pC2aCfr5T9g

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PostPosted: Sun Nov 22, 2015 6:41 pm 
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If you were to search the the forum you would find out that crank length has been discussed quite a bit.
I am one who, in the past, argued that it must make a difference. It seems only logical.
But I have actually experimented quite a bit now with cranks that were 170, 175, and 180. In one case I even went directly from 180 to 170 in the same week and did the same 30 min climb, and my times and powers were virtually identical, which surprised the heck out of me. (Keeping saddle to max pedal extension constant)

So, I figured that if it doesn't make a difference on a long steep climb, I might as well go with what is easier to spin. So I have gone back to the 170, and it even makes me think that experimenting shorter might be interesting.

I was having hamstring pain and lower back pain while using the 180s, which has diminished and almost disappeared on the 170s, so that may also be correlated.

Apparently I have long femurs for my height (172.7 cm). Inseam: 83.2 cm; Saddle to BB Center: ~73.0 cm


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PostPosted: Sun Nov 22, 2015 7:17 pm 
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People tend to focus on leg dynamics, but it often just comes down to whether a longer crank pushes your knees up into your diaphragm and reduces your ability to breathe. On average pro riders can manage longer cranks because (1) they are genetically gifted, (2) with their very thin builds, they don't suffer breathing impingement from their thighs when cycling, and (3) because they tend to have extremely long femurs to go with relatively short tibias. The rest of us aren't as lucky.

The published tests tend to look at whether riders can generate better power on longer or shorter cranks, which is in one sense an accurate test but in another very misleading. Riding consists of much more than sheer power output for short periods. There's breathing, which involves diaphragm impingement, and there's also the question of whether various biomechanics, chemical, and nutritional issues predispose a particular rider to a shorter crank arm. The published work doesn't take these other issues into consideration even though they can be quite formidable. Thus the research that some people rely on is basically insufficient/invalid. And some riders don't have secondary limitations, so they can ride well with any crank arm length.

Not an easy problem to solve, but it's best solved with a sample size of one, and with you doing your own testing and observation (possibly with the assistance of a coach) and determining if you have a superior crank arm length and then using it.


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PostPosted: Sun Nov 22, 2015 7:30 pm 
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I'm 6'1" (183cm) and have used 172.5 almost exclusively for the past 10 years, including racing in category 2 while at university. Recently I have experimented with 165 on my stationary trainer, which has power cranks with adjustable length. I have to say I'm quite sold on short lengths now! I haven't tried it on the road yet but in the trainer, I can't point to any negatives, and as someone with an exercise physiology degree, the shorter length just makes sense. Next road going bike I build will decently have 165s on it, perhaps even shorter!

As far as what the pros, who supposedly have the resources to test which length works the best, I think we can mostly chalk it up to tradition versus what actually works the best. As in, Merckx used this length, so I should too. But who determined 170-180 crank length should even be the standard? Pretty sure it's just a remanent of the days of penny farthing rather than some conclusion of a kinesiology study.


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PostPosted: Sun Nov 22, 2015 7:37 pm 
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In thinking about this, I came up with another (completely unsubstantiated) theory:

Maybe crank-arm length really is almost completely irrelevant.
For example: There is probably, in theory, a perfect handlebar diameter for your hands. But as a practical matter, having that perfect diameter might make you feel slightly better, but will never have any detectable influence on your power production or race results.

Crank-length SEEMS like it should be more influential, because legs are the primary power producers, and are directly in the mechanical chain, etc....but in reality there are other factors in the power-production chain that dominate: heart capacity, lung capacity, cellular mitochondrial density, etc...
Things that are not visually obvious or easily measurable, yet are the things that in truth control human power production.

I think some people have been trying to tell us this for quite a while, and I just refused to believe it until performing my own experiments.

There is probably a limit at which too long cranks or too short cranks make crank-length the limiter, but as long as you are in the reasonable ballpark, you are always limited by other things and crank-arm length is actually, as a practical matter, irrelevant.

Again: just a theory. :D


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PostPosted: Sun Nov 22, 2015 7:43 pm 
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Form on the video:
It looks very good to me. (I am no authority).
I notice that you pedal "toes down" all the way around. My foot is in a more "neutral" or flatter position at the bottom of the stroke. So I have to wonder if your saddle is a little too high or cranks a little too long, making you want to "reach" for the bottom of the stroke by going toes down.
On the other hand, some people do just pedal toes down more naturally.

Just an impression.


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PostPosted: Sun Nov 22, 2015 10:09 pm 
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If you can perform the same way with shorter and longer cranks without changing your position (except longer crank minus shorter crank saddle height difference), that it seems to me that shorter cranks are obviously better because then you can have the same hip angle with lower body position (usually more aero), and the risk of pedal strike is lower (more confidence - enhanced ability to put power down in the corners). I'm 84cm inseam and ride 172,5mm on my regular bike and 175mm on my training bike and to be honest, i don't feel any difference at all between those two - maybe i will experiment with 170mm or even shorter 165mm cranks. Oh, and of course shorter cranks ale lighter too :D


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PostPosted: Sun Nov 22, 2015 10:27 pm 
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To the OP, i'm a similar height but with longer legs- seat height is approx. 730mm.

I dropped down to 165mm on my TT bike midway through this season from 172.
Power delivery or output was no different, but started spinning gears a bit better (even with a 54 osym on).
My performance did improve but there were a few other factors there too.

What is most noticeable at first is the feel at 3 and 9 o'clock positions; it feels slightly truncated, but this is one of the areas I think that shorter cranks are said to improve. Basically the pedal "orbit" is shorter , and its velocity doesn't alter so much. Think peanut shaped...

Regarding saddle height, its a win win situation compared to longer ones. Saddle up by 5mm to account for 5mm shorter cranks translates to 10mm at the 12 o'clock position. Means you can drop the front end a bit more without chest strike.

My fixed winter bike came with 170's on it, but I've dropped them down to 165 as well.
If I can find another set of rotor 3D's at the right price, I might even take the road bike down that road :)

Edit: as Rick says, saddle could be a little high, or are you very tight in the hamstrings etc? Shorter cranks reduce range of motion, but if theres an underlying reason to think about them, id attend to that first.

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PostPosted: Mon Nov 23, 2015 6:54 am 
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jekyll man wrote:
To the OP, i'm a similar height but with longer legs- seat height is approx. 730mm.

I dropped down to 165mm on my TT bike midway through this season from 172.
Power delivery or output was no different, but started spinning gears a bit better (even with a 54 osym on).
My performance did improve but there were a few other factors there too.

What is most noticeable at first is the feel at 3 and 9 o'clock positions; it feels slightly truncated, but this is one of the areas I think that shorter cranks are said to improve. Basically the pedal "orbit" is shorter , and its velocity doesn't alter so much. Think peanut shaped...

Regarding saddle height, its a win win situation compared to longer ones. Saddle up by 5mm to account for 5mm shorter cranks translates to 10mm at the 12 o'clock position. Means you can drop the front end a bit more without chest strike.

My fixed winter bike came with 170's on it, but I've dropped them down to 165 as well.
If I can find another set of rotor 3D's at the right price, I might even take the road bike down that road :)

Edit: as Rick says, saddle could be a little high, or are you very tight in the hamstrings etc? Shorter cranks reduce range of motion, but if theres an underlying reason to think about them, id attend to that first.


Thanks for so quick and great answers. I've promised to hear a friend's thoughts on crank length next week. After that I'm getting myself a 165mm crankset I think! My only fears has been the possibility of losing too much strength in road races, but I figure after your feedback - if you don't lose power in TT's, why should you in RR?

It's definitely going to be interesting to see how well the shorter cranks live up to the praise.

Those of you who tried shorter cranks - have you felt any setbacks in longer stages and road races?

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PostPosted: Mon Nov 23, 2015 6:34 pm 
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I haven't entered a sanctioned race for two years now, but I have been monitoring power and time over some of my favorite intervals ranging from very short to ~30 minutes. And for the past couple years have been targeting centuries, that usually are ridden "competitively".
So, for what my experience is worth: No, there has been no negative effect noticed, and in fact, my performances have been disgustingly consistently mediocre, with no degradation, but also no improvement. If anything, my spin feels a little fresher at the end of a long ride with the shorter cranks. I'm 64 years old, so maybe my training is just offsetting the natural aging decay. :)


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PostPosted: Tue Nov 24, 2015 3:40 am 
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A while back I researched this quite a bit. Studies show very little difference in oxygen consumption between 140 to 180mm cranks. They show a marginal improvement with even shorter cranks. The difference between off the shelf sized cranks is probably not measurable.

A shorter crank though can be more comfortable with the wider hip angle and it allows one to go lower and be more aerodynamic.

Doing my own experiment I switched to 170s after riding 175s for decades. 170s felt good, especially during longer intervals on the flats. I felt like I could turn the pedals over faster and stay on top of the gear better. They promoted a higher cadence. I climbed just fine with them though I felt like I needed bigger cogs and a higher cadence. And just a 5mm change did feel more comfortable. I raised my saddle 5mm and kept my stem where it was.

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PostPosted: Tue Nov 24, 2015 5:43 am 
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aerodynamiq wrote:
Wiggins is shifting for shorter cranks, but a part from him - most pros seems to keep what they've always been using. I've gotten interested in this short crank trend, and what it might do for me.


I say give them a try too. I am more comfortable with a more open hip angle and have used from 165-180. I don't have power data to compare, but kept up with all of the same riding buddies with all sizes. I think the bigger factor is comfort and proper fit, and shorter cranks, by reducing the range of motion of the legs, can make it easier to strike upon a fit that works for you in more situations as lower body alignment becomes less of a moving target and you are not as close to the limits of your physical range. More fluidity over the top of the pedal stroke, and/or less reaching at the bottom.

One question though...How short is Wiggins going? I hadn't seen a reference to his change elsewhere yet. While I'm at it, anyone know is he still back on round rings?


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PostPosted: Tue Nov 24, 2015 8:55 am 
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AJS914 wrote:
A while back I researched this quite a bit. Studies show very little difference in oxygen consumption between 140 to 180mm cranks. They show a marginal improvement with even shorter cranks. The difference between off the shelf sized cranks is probably not measurable.

A shorter crank though can be more comfortable with the wider hip angle and it allows one to go lower and be more aerodynamic.

Doing my own experiment I switched to 170s after riding 175s for decades. 170s felt good, especially during longer intervals on the flats. I felt like I could turn the pedals over faster and stay on top of the gear better. They promoted a higher cadence. I climbed just fine with them though I felt like I needed bigger cogs and a higher cadence. And just a 5mm change did feel more comfortable. I raised my saddle 5mm and kept my stem where it was.


I've seen a number of studies addressing this question and they all seem to have material shortcomings. For example,

1. Increasing the saddle height by the length of crank arm reduction. That increases diaphragm impingement slightly and could offset the improvements one might otherwise see in that respect.
2. Generally riders get to self-determine position after changing crank arm lengths. If a rider is riding upright, shorter cranks won't give the same improvements in hip angle and power output that might come about from being in a more aggressive position. In my experience fitting and coaching a lot of track riders, shorter cranks don't do much if the rider likes to sit upright, but the riders who pursue lower positions can achieve faster pursuit times. In short, this isn't a passive analysis with different crank arm lengths thrown in.
3. Rider fitness, experience, speed, and other parameters all affect the results. Riders who are reporting inconclusive results after riding 20-22 mph pacelines aren't necessarily a test of shorter cranks. The riders who are doing 35-38 mph in very fast massed start track events are testing the benefits of shorter cranks a lot more.
4. Hip angle may not be a measured outcome of shorter crank arm usage but rather a qualifier for it, with only riders with certain prior and post hip angles comprising the data set that correctly test whether shorter crank arms matter.
5. Even when studies are done on quote-unquote athletes, very few are being done on qualified racing samples. The Australian and British track cycling teams have done extensive studies on their own riders and most riders have moved to shorter cranks based on performance data. I was told Wiggins is now on 165 mm cranks at his last major track appearance after years of riding 170 mm minimum. He also tested 165's extensively for his hour attempt; I've heard varying reports about whether he rode them or not (the press coverage was based mostly on test bikes and those varied between different crank lengths and other parameters so the reports may not have been accurate).


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PostPosted: Tue Nov 24, 2015 8:57 am 
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TheKaiser wrote:
aerodynamiq wrote:
Wiggins is shifting for shorter cranks, but a part from him - most pros seems to keep what they've always been using. I've gotten interested in this short crank trend, and what it might do for me.


I say give them a try too. I am more comfortable with a more open hip angle and have used from 165-180. I don't have power data to compare, but kept up with all of the same riding buddies with all sizes. I think the bigger factor is comfort and proper fit, and shorter cranks, by reducing the range of motion of the legs, can make it easier to strike upon a fit that works for you in more situations as lower body alignment becomes less of a moving target and you are not as close to the limits of your physical range. More fluidity over the top of the pedal stroke, and/or less reaching at the bottom.

One question though...How short is Wiggins going? I hadn't seen a reference to his change elsewhere yet. While I'm at it, anyone know is he still back on round rings?


Thanks for the reply. More and more pointers towards the short cranks. Love you guys!

Wiggins is back on round SRAM Red rings and 170mm cranks. I do recall him changing back to round rings after the 2012 TDF, and since then I've not seen his osymetric anywhere.

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PostPosted: Wed Feb 17, 2016 11:32 pm 
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6'1, 172.5 cranks. I tried going short but found the increased ability to "spin" didn't compensate for "stomping" power losses. No issues with hitting the torso at the top of the stroke.


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