Let's discuss crank length, my opinion - shorter is better

[FrankDay]

I have been doing a lot of thinking about this over the last few months. I think the evidence is clear, shorter cranks are better/faster, especially if one is talking time-trial efforts. I have put together a video that I think makes the argument pretty well and is a good start for discussion. Since doing the video I have seen some numbers regarding the aerodynamic part of the argument that simply blow me away and strengthen the argument even more.

One thing of particular interest to me is why, when the evidence is so overwhelming (at least to me), aren't more elites aren't riding shorter cranks or, at least, experimented with them. Is it because their sponsors don't make cranks of the needed size? Is it because they are already "good enough" and it would be too much trouble to do all the experimenting necessary to optimize this piece of equipment? Is it simply because this information is not known? Is it because there simply aren't any cyclists willing to "be first" when it comes to something so "radical"? And, last, where do all these formulas that are out there, for determining optimum crank length, come from?

 

[the student]

shouldnt this be posted in the bikes and gear forum??

oh well i dont this shorter is better but my legs are quite long so i dont know, my city bike has pretty short cranks but i seem to rum out of room to complete the most powerfull strokes, my race bike had longer cranks ( not overly long ones just normal ) and my power output does feel a lot smoother... i know my normal bike isnt built for power ... but its the only comparison i have...

one study doesnt prove all the other studies on crank length wrong... Of course those formula's dont work for evryone but there is no garantee shorter cranks will work for evryone racing bikes either...( i dont see any leg lengths taken into account in this studie, which should matter a lot for power output ) I see no information on test groups average lengths of test groups etcetera... so i cant really form an opinion on this.

its obvious to me now... just an add from powercranks to get people experimenting with shorter ones so we would buy 145 mm cranks... oh whatever

 

[antoine]

numbers?

are you talking 175 vs 165mm, or something even smaller? and where's the overwhelming evidence?

 

[GilTeamS&M]

I have been doing a lot of thinking about this over the last few months. I think the evidence is clear, shorter cranks are better/faster, especially if one is talking time-trial efforts.

I have to get to work, so no time to go into this much further, except to say that here again is yet another example that having a doctoral degree is not the same thing as being smart.

This infomercial is pretty much all baloney.

 

[FrankDay]

are you talking 175 vs 165mm, or something even smaller? and where's the overwhelming evidence?

The evidence/argument is in the video. Perhaps the link I put in is not clear. Here it is again.

http://www.youtube.com/watch?v=HFxBg7BnFlQ

 

[mountaindew]

I agree that this is going to be the next innovation in cycling.

 

[fatandfast]

The evidence/argument is in the video. Perhaps the link I put in is not clear. Here it is again.

http://www.youtube.com/watch?v=HFxBg7BnFlQ

My friend and original cycling coach designed a pedal and within 10 months of production we were riding and racing on the design. He had the pedal being used at an elite level after 2 years of production. Why are pro teams not singing the praises of this new philosophy?. I am a midget and would never think of riding 145's I used 165's on my track bike for years..because thats what everybody who was beating me was riding.I don't know if your theory is sound or not and with my BB and seat height pretty constant this year..how much would it cost to do the experiment that you propose? For me looks like about 250-400 US and if you are wrong who is going to buy a used set of 145-160 cranks? Guys with my same body type like Friere or Cuengo are my guide if they use 145's I will also. How many guys at the worlds will be riding 145's ?

 

[mountaindew]

The vid says tt like efforts. So why would those guys ride them in a road race?

 

[Boeing]

The first article of supporting evidence sounds more like a bike fit problem than a crank length issue

In addition, he offers no sample survey.

As they stand I read dogmatic statements.

Perhaps evidence to debunk the leverage argument is a good place for you to start.

Last there is nothing said about cadence.

answer the above and we have a discussion

 

[galaxy1]

I wouldn't rule this out, but I think we need more evidence - if the advantages are so clear, then plenty of riders with short and very short crank lengths will soon be winning time trials near you.

My first impressions are:
* on power, it seems logical that more crank length = more muscle recruited = more potential to generate power, and there is some anecdotal evidence to agree. That doesn't mean it is necessarily true, of course, but I'd like to see it disproved (as it happens I have long legs and prefer fairly long cranks). The "traditional" stated benefits of short cranks are the opportunity to spin a high cadence and use the most powerful muscles (especially if you have short legs).
* I simply don't believe that the effort of getting leg close to chest is a major use of energy, unless you simply aren't flexible enough.
* on aerodynamics, I don't have enough expertise to say one way or the other, but I'm sure someone has some better evidence than these cartoons. I would have thought that if you want to lower your position another 4cm flexibility would be the more obvious answer, rather than a change in pedalling style.

 

[Vegan Dave]

This is a favored topic of mine. =)

It's a bit unfortunate that the video ends as a commercial for a product, but overall with it and i'd agree that shorter cranks are generally better and offer more advantages.

I'd flip the discussion on leverage this way: prove that the longer crank is actually *helpful*. Just as using a level to lift objects begins to lose usefulness and efficiency at longer lengths, it can happen on a bike as well. I don't know if we have a baseline to say 170mm is 'the' number, but it can be figured out just as we can for other levers. It's just math.

Perhaps at lower cadences (climbing) it may become a factor, but there's a trade-off: you're using more energy moving your legs in bigger circles. If 10% of your ride involves steep climbing, is it worth it to move your feed in a wider arc the other 90% of the time? Probably not. (Whenver i get on a bike with 175m cranks now, i feel like my legs are practically flailing around!)

I don't know if the metabolic cost of moving your legs in a bigger circle is really worth the 'increased leverage' for what's generally a small proportion of your ride time - assuming that the leverage issue is actually even a concern.

The next benefit is an increase in cadence - people tend to pedal faster on shorter cranks...and this is useful given that it pushes the energy use into an aerobic rather than muscular dependency..keeps your legs a bit fresher.

As for the myth of 'loss of power' from shorter cranks, the people who can pump out the most wattage, track sprinters, are well known to use shorter cranks. (It's no coincidence that the higher wattage ranges mostly come at higher cadences...further, these riders don't seem to suffer from the 'loss of leverage' in standing start events like the Kilo.)

The faster cadence is also hugely beneficial in events like Crits, where maintaining a higher cadence allows faster response times to accelerations, etc.. Plus, with a shorter crank you're less likely to clip in corners. I don't think i clipped a pedal once this year, and generally can pedal through corners.

The aerodymics make sense, both from a better body position, and the legs spinning around in the air less.

I guess a little weight is shaved off as well.

Admittedly they do take a little getting used to...i come from a track background but rode 170's on the road. I switched to 165's, and climbing out of the saddle felt a bit weird at first, but for the rest of my riding, it really felt 'right'. My stroke and spin felt significantly smoother and i was riding more comfortably in the cadence range i'm accustomed to (typically 105-112rpm). And now, i don't notice anything out of the saddle.

The main downfall is that access to shorter cranks is nuts. I run Campy, but can't get anything under 170mm...so am running SRAM Red cranks on my road/CX machines.

I have been very keen to try out the Quarq power meter, but finding a compatable crank in 165mm (in Canada at least) has been near-impossible without doing a rather expensive special order. (So sticking to PowerTap for now.)

Okay, that's my $0.10 on the matter.

 

[FrankDay]

The vid says tt like efforts. So why would those guys ride them in a road race?

I can think of a couple of reason's.

It is true that the power increase on might surmise is very small moving from 170 to 145 cranks at the usual race power, say 1-2 watts and there is hardly any aerodynamic benefit when riding in a pack of 100 riders but:

1. Why would anyone pass up any power improvement, even a small one, when it comes so easily? and,

2. While the aerodynamic benefits are negligible while in the pack they certainly would offer an advantage if in a small group or solo breakaway or while trying to bridge a gap.

 

[Master50]

How about a link to the Martin study quoted in the video?

 

[FrankDay]

How about a link to the Martin study quoted in the video?

http://www.ncbi.nlm.nih.gov/pubmed/11417428

I have found the entire article on-line but I can't find the link to it right now.

 

[titleshot]

I didnt watch the video, so i dont know what that is about, but I like this topic.
Im 5'10" with 31 inch inseem. I rode on 172.5mm cranks for 2 years, I was a super fast climber, but seemed to lack acceleration on the flats in criteriums, and I wasnt that great at Time trials. I was getting decent at sprinting but I always felt I couldnt spin up to a high enough cadence.

Last year I switched to 170mm cranks, and had an instant improvement in cadence, I can accelerate and sprint very well. My time trialing is improving as well because I can keep my legs going faster and I feel lower on my bike.
My climbing ability has suffered a little, but only on really long 5 plus minute climbs because I can feel like I have lost the leverage/torque on the uphills, but I seem to be able to accelerate uphills much faster on short climbs.

Other than that I feel like shorter cranks are really worth a try. I still wish I had gone to shorter cranks sooner, I would have won more bunch sprints.


Another example I have seen in the pro peloton is mark cavendish, he runs 170mm cranks and has amazing acceleration, compared to the other sprinters like farrar, boonen that run longer cranks and just put down a really fast sprint, but dont seem to have a quick snap of acceleration like cavendish, just my opinion on what I have seen in some races.....

 

[FrankDay]

titleshop, you ought to watch the video. According to it, your "short" cranks are way too long.

 

[mountaindew]

I can think of a couple of reason's.

It is true that the power increase on might surmise is very small moving from 170 to 145 cranks at the usual race power, say 1-2 watts and there is hardly any aerodynamic benefit when riding in a pack of 100 riders but:

1. Why would anyone pass up any power improvement, even a small one, when it comes so easily? and,

2. While the aerodynamic benefits are negligible while in the pack they certainly would offer an advantage if in a small group or solo breakaway or while trying to bridge a gap.

Because in a road race you slow and accelerate many times and short cranks would not be conducive to this kind of effort?

 

[Master50]

Well Frank I am not so sure this paper unequivocally supports your products claims.

Conclusions from the abstract summary your link provided.

"The optimal crank length was 20% of leg length or 41% of tibia length. These data suggest that pedal speed (which constrains muscle shortening velocity) and pedaling rate (which affects muscle excitation state) exert distinct effects that influence muscular power during cycling. Even though maximum cycling power was significantly affected by crank length, use of the standard 170-mm length cranks should not substantially compromise maximum power in most adults" Martin JC, Spirduso WW.

University of Utah, Department of Exercise and Sport Science, 250S. 1850E. Rm. 200, Salt Lake City, UT 84112-0920, USA. jim.martin@health.utah.edu

I looks to me that this thread is more of an infomercial ostensibly to generate sales of your crank. You also just joined this forum and I am thinking it was to make a sales pitch. I watched the video and wonder what it proves as it looks designed to make me feel stupid for riding longer cranks. Ie a lot of the content is aimed at an emotional response with very little support in facts. Maybe you could provide some of the power measurements supporting your conclusions?
I assume you used a power meter to measure the effectiveness? What about a wind tunnel test for the Aero claims? You did those when you built your prototype and made your marketing video?

Since I don't have any data to dispute your claims I just remain sceptical, not that I don't believe there are crank lengths that best match every body but your blanket shorter is better is no more credible than longer is better.

 

[FrankDay]

Because in a road race you slow and accelerate many times and short cranks would not be conducive to this kind of effort?

Well, you might have to change the gearing a bit to be riding at a slightly higher cadence with much shorter cranks, but if you do that I see no reason shorter cranks would have any affect on the ability to accelerate. Isn't acceleration all about power?

 

[FrankDay]

Well Frank I am not so sure this paper unequivocally supports your products claims.

Conclusions from the abstract summary your link provided.

"The optimal crank length was 20% of leg length or 41% of tibia length. These data suggest that pedal speed (which constrains muscle shortening velocity) and pedaling rate (which affects muscle excitation state) exert distinct effects that influence muscular power during cycling. Even though maximum cycling power was significantly affected by crank length, use of the standard 170-mm length cranks should not substantially compromise maximum power in most adults" Martin JC, Spirduso WW.

University of Utah, Department of Exercise and Sport Science, 250S. 1850E. Rm. 200, Salt Lake City, UT 84112-0920, USA. jim.martin@health.utah.edu

I looks to me that this thread is more of an infomercial ostensibly to generate sales of your crank. You also just joined this forum and I am thinking it was to make a sales pitch. I watched the video and wonder what it proves as it looks designed to make me feel stupid for riding longer cranks. Ie a lot of the content is aimed at an emotional response with very little support in facts. Maybe you could provide some of the power measurements supporting your conclusions?
I assume you used a power meter to measure the effectiveness? What about a wind tunnel test for the Aero claims? You did those when you built your prototype and made your marketing video?

Since I don't have any data to dispute your claims I just remain sceptical, not that I don't believe there are crank lengths that best match every body but your blanket shorter is better is no more credible than longer is better.

The only way my product is related to this thread is I happen to think this is of potential huge importance to many customers so I have made it easy for our customers to experiment with this and I put that in the video. For those of you out there who don't think PowerCranks have much to offer I doubt they are going to plunk down $1,000 USD just so they can experiment with crank length.

Martin's data provides the evidence to support the power claims at maximum power. At "normal" power I would expect the advantage to be so small that it would be difficult to "prove" as the expected advantage is only 1-2 watts. It would take a very large cohort study to prove such advantages. We have to infer that advantages seen at maximum power would also be seen at lower power.

Regarding the aerodynamic advantages I did find this in an article published in triathlete magazine about this topic a couple of years ago.

John Cobb seems to know something about aerodynamics and the article says he saw a 30% reduction in drag from this simple change. I did not know this at the time I did the video or this would have been in it. That improvement alone seems worthwhile to me.

 

[Tibber]

The supporting study suggests this formula for calculating optimal crank length based on their data.

"The optimal crank length was 20% of leg length or 41% of tibia length. These data suggest that pedal speed (which constrains muscle shortening velocity) and pedaling rate (which affects muscle excitation state) exert distinct effects that influence muscular power during cycling. Even though maximum cycling power was significantly affected by crank length, use of the standard 170-mm length cranks should not substantially compromise maximum power in most adults."

Do the math, and this means a 145mm crank is optimal for someone with a 725mm (28.5") leg length. At 1.88m(6' 2") tall, I have a 36" leg length, which suggests an optimal crank of 183mm, meaning my 175mm cranks are too short!

So much for the data....

 

[TexasTom]

John Cobb isn't too far from me, and yes, he has some very specific thoughts regarding crank length. I've seen him put a 6'5" guy on 170's.

But I can't believe Tape hasn't jumped in on this.....he's got a study that says unless you're way off, then crank length has no big effect.

 

[FrankDay]

The supporting study suggests this formula for calculating optimal crank length based on their data.

"The optimal crank length was 20% of leg length or 41% of tibia length. These data suggest that pedal speed (which constrains muscle shortening velocity) and pedaling rate (which affects muscle excitation state) exert distinct effects that influence muscular power during cycling. Even though maximum cycling power was significantly affected by crank length, use of the standard 170-mm length cranks should not substantially compromise maximum power in most adults."

Do the math, and this means a 145mm crank is optimal for someone with a 725mm (28.5") leg length. At 1.88m(6' 2") tall, I have a 36" leg length, which suggests an optimal crank of 183mm, meaning my 175mm cranks are too short!

So much for the data....

I guess it depends upon how one defines or what one believes to be "optimal". I have looked at the study and I cannot find where Martin defines what he thinks is "optimal". It is hard for me to understand any definition of "optimal" as it relates to power that wouldn't be either "the most powerful" or "the most efficient".

But, then, of course, such a definition, which only looks at power, ignores the effects on aerodynamics. Of course, in this day and age of everyone being fixated on power such ignoring of these other aspects of racing seems commonplace. So, while something may be "optimal" based upon some academic definition concerned solely with power does not mean it would be "optimal" for racing.

 

[Oldman]

The supporting study suggests this formula for calculating optimal crank length based on their data.

"The optimal crank length was 20% of leg length or 41% of tibia length. These data suggest that pedal speed (which constrains muscle shortening velocity) and pedaling rate (which affects muscle excitation state) exert distinct effects that influence muscular power during cycling. Even though maximum cycling power was significantly affected by crank length, use of the standard 170-mm length cranks should not substantially compromise maximum power in most adults."

Do the math, and this means a 145mm crank is optimal for someone with a 725mm (28.5") leg length. At 1.88m(6' 2") tall, I have a 36" leg length, which suggests an optimal crank of 183mm, meaning my 175mm cranks are too short!

So much for the data....

Most riders will have the opportunity to mess around with crank length sometime in their competitive life and usually come to the same conclusion: different cranks for different efforts. Just as there is no one perfect position on a bike for all efforts there is also a corresponding difference in effective crank lengths. Too long and you will give up rapid acceleration. Too short and you'll compromise gear size in favor of rpm's.
One of the best Tt'ers I knew came from a BMX background and used long cranks and small gears. This was particularly potent for him in windy time trials and climbing. He couldn't sprint particularly well. I only concluded that he was particularly tuned to his setup.

 

[brianf7]

Over the past 50 years I have seen and heard so many different ideas and they are still comming but we always go back to 170 + or- 5mm.

Time trial cranks are longer as that will help you keep the bike going forward at a steady pace sprinters need slightly shorter also in Crits shorter will get you out the corners quicker with less power usage
I use 180 crank in TT that will help you maintain a steady power output that you need

I use 172.5 for crits I have seen power cranks bio pace mangle handle cranks and you name it they come and go but dont stay around.

Its good to have choice but be aware many are dreamed up over night. save your money.