The crank length thread

[backdoor]

Re:

Thanks for the link about crank length tests.

I don't understand the speculation about slower muscle contraction -
"may change mechanical advantage at the hip and knee allowing the muscle to contract slower through the pedal stroke"
even though the cadence remained about the same.
" Cadence and all ventilatory parameters were not significantly different between CL trials (p > .05)"

Can anyone explain why muscle contraction would be slower at the same cadence?
Is a larger portion of the crank rotation used for the 'downstroke' so the muscle contration rate is spread over a longer time period?

Jay Kosta
Endwell NY USA

http://www.cobbcycling.com/crank-length-coming-full-circle/

 

[JayKosta]

Re: Re:

...
http://www.cobbcycling.com/crank-length-coming-full-circle/

--------
Lots of thoughts and ideas there about shorter cranks, but I couldn't find anything discussing 'slower muscle contraction rate' at the same cadence.

I think that a slower contraction rate (at same cadence) can only occur if the amount of TIME for the contraction is increased - meaning a larger portion of the crank rotation is used for the contraction.

If a slower cadence is used, that also might give a slower contraction rate.

Jay Kosta
Endwell NY USA

 

[sciguy]

Re: Re:

...
http://www.cobbcycling.com/crank-length-coming-full-circle/

--------
Lots of thoughts and ideas there about shorter cranks, but I couldn't find anything discussing 'slower muscle contraction rate' at the same cadence.

I think that a slower contraction rate (at same cadence) can only occur if the amount of TIME for the contraction is increased - meaning a larger portion of the crank rotation is used for the contraction.

If a slower cadence is used, that also might give a slower contraction rate.

Jay Kosta
Endwell NY USA

Jay,

If the foot speed is slower, then the muscle contraction rate that drives that foot speed must be less. The foot speed must be slower when carrying the same cadence around a smaller circle. What's confusing about that?

Hugh

 

[JayKosta]

Re: Re:

Jay,

If the foot speed is slower, then the muscle contraction rate that drives that foot speed must be less. The foot speed must be slower when carrying the same cadence around a smaller circle. What's confusing about that?

Hugh

----
I think we're talking about 2 different things.

If I understand you correctly, you're talking about the physical distance that is involved in the contractions. Since the pedal circle is smaller the contraction distance is smaller, giving a slower 'fiber contraction velocity' (e.g. distance of movement per second).

The quote from the article that I questioned is -
"allowing the muscle to contract slower through the pedal stroke".
I thought this meant that the overall length of time of the contraction was longer, and was being called a slower contraction.

Jay Kosta
Endwell NY USA

 

[sciguy]

Re: Re:

Jay,

If the foot speed is slower, then the muscle contraction rate that drives that foot speed must be less. The foot speed must be slower when carrying the same cadence around a smaller circle. What's confusing about that?

Hugh

----
I think we're talking about 2 different things.

If I understand you correctly, you're talking about the physical distance that is involved in the contractions. Since the pedal circle is smaller the contraction distance is smaller, giving a slower 'fiber contraction velocity' (e.g. distance of movement per second).

The quote from the article that I questioned is -
"allowing the muscle to contract slower through the pedal stroke".
I thought this meant that the overall length of time of the contraction was longer, and was being called a slower contraction.

Jay Kosta
Endwell NY USA

Perhaps I'm assuming too much. You're looking for the way they increased the time while I'm seeing that they decreased the distance while maintaining the time. I still favor my interpretation as the only one that "jives" with what was done.

Added- Just a blip from some of Jim Martin's research - "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."

Hugh

 

[JayKosta]

This has been a good example of why 'word choice' is so important for accurate understanding.

Jay Kosta
Endwell NY USA

 

[thirtyeightinseam]

As a guy with a 38" insearm (96.5 cm) I am very inclined to agree with Frank. I'm 6'5" tall (195.5 cm) , so I have long legs for my height.

"It is inconceivable to me that bike frames vary from 48 to 62 cm (30% variation) whereas standard crank length vary from 170 to 175 (3% variation)".

Bike and component manufacturers have a long history of stupidity. They are incapable of seeing the incredibly obvious. Look at the slow evolution in gearing. It's still changing after 75 years! These people are very slow learners and very poor listeners. If I sound angry it's because I am.

I admit I haven't read the Martin/Spirduso paper in complete detail, but they define leg length as the difference in sitting vs standing height? Am I missing something obvious? At the moment this makes zero sense to me. And in my opinion we shouldn't draw many conclusions based on a 6 second test.

Assuming this leg length is actually one's inseam I should be on 200 mm cranks using Martin's forumula. I was lucky enough to ride some 220 mm cranks (without having to buy them) and I admit it was freaky. The bike was owned by a Zinn fan/customer in Park City, Utah and we chatted for a minute while riding the same road and then he let me ride his bike. Of course there were other distractions such as his seat and riding position, and 3 minutes of testing isn't enough to adapt. I reduced my crank length wish from 220mm to 200 mm after riding his bike.

In my opinion logic dictates the entire bicycle should scale with size. For a guy my size riding a mountain bike with 26" wheels was a ludicrous endeavor. 29" wheels completely changed the game.

I recommend you state your inseam when you state your experience with various crank lengths. Without a correlation between the two the data becomes useless.

 

[PhitBoy]

Re:

In my opinion logic dictates the entire bicycle should scale with size.

Nothing in any of the series of papers from my colleagues and me says you should not scale your crank length with your leg length. All our findings indicate that crank length simply won't substantially influence biomechanics or metabolic cost. On the other hand, if you believe a longer crank will make a difference then it probably will influence your performance. Placebo can be very powerful (yes pun intended), so by all means choose the length that makes you happy.
Keep in mind that crank length is just one component of the overall gearing system. A longer crank is a smaller gear so you may want to go to larger chainrings. One thing you may not appreciate is that you are almost certainly able to get a horizontal torso because of your leg length to crank length ratio. When you scale up crank length you may compromise aerodynamics. Most of my rides include 2-3000ft of climbing and I ride 155s with (32 inch inseam). Doesn't hurt my climbing at all but allows me to get much more aero on the descents.
Cheers,
Jim

 

[Captain Serious]

Re:

As a guy with a 38" insearm (96.5 cm) I am very inclined to agree with Frank. I'm 6'5" tall (195.5 cm) , so I have long legs for my height.

"It is inconceivable to me that bike frames vary from 48 to 62 cm (30% variation) whereas standard crank length vary from 170 to 175 (3% variation)".

Bike and component manufacturers have a long history of stupidity. They are incapable of seeing the incredibly obvious. . I reduced my crank length wish from 220mm to 200 mm after riding his bike.
.

Are you still using 200s?

 

[Captain Serious]

I'm 182cm with an ~88.5cm inseam, and my regular cranks length is 172.5, for no great reason other than availability when I was decking out several bikes (I've said that before).

I have a short friend who's about 5ft4 and rides 170s, and he is ALWAYS complaining about, and tinkering with, his position.
I've begged him to try some of my 165s, but he's too stubborn. It drives me nuts

 

[sciguy]

Re:

I'm 182cm with an ~88.5cm inseam, and my regular cranks length is 172.5, for no great reason other than availability when I was decking out several bikes (I've repeated myself. Ha).

I have a short friend who's about 5ft4, and he rides 170s. The thing is, he is ALWAYS complaining about, and tinkering with, his position.
I've begged him to try some of my 165s, but he's too stubborn. It drives me nuts

At 6'1" I moved from 175s to 165s to help improve my aero position. With the 165s and at at 62 years of age I'm making more power riding aero than I did several years ago. As Jim says the hills are just about gearing.

YMMV,

Hugh

 

[Captain Serious]

^ Thanks. i might dust off my 165s again and give them another shot. Better for the knees, too... I've found

 

[shorter cranks]

Thought I would share what I have discovered after experimenting with ultra short cranks for a period of about just over 12 months, going down from 175mm to 120mm cranks.

I am 5ft 9", late forties, stocky build, 75kg, inseam measurement is 31", my flexibility is moderate to poor and I'm very lean for my height and weight. I probably should add I race at A grade level with my local club so I am an experienced moderately strong rider I guess!

My main reason for going shorter was,
1. Chronic low grade off and on issues with my hips, knees, back and dull aching buttock pain, nothing bad enough to stop me doing things, just annoying.
2. Being an open minded person I was keen to try shorter cranks after reading a lot of articles by Frank Day.

I first tried 155mm cranks which on the first ride (to be quite honest) felt terrible! At the time I guess my body and brain were so accustomed to using 175mm cranks for the last 40years I didn't really expect to feel so weird, literally to the point where I cut the ride short, road home to swap the cranks back again. Then I remembered Frank saying you need time to adapt, so I decided to persevere for a month to see if I could adapt. Best thing I ever did, withing about 2 weeks I felt completely normal on 155's, to my surprise I was not slower at all (despite people telling me I was just plain stupid) and interestingly some of the physical issues I had started to back off slightly, which gave me some real incentive to possible consider maybe going even shorter! So that's what I did over a period of about 12 months I slowly went shorter in length about 10mm jumps at a time until I reached 120mm. Interestingly each time I tried a shorter length I had that same "how could I ever get use to this feeling" but once adapted each length shorter I went the better I was riding, slightly faster but way more comfortable in the process! By the way all my physical issues completely disappeared by about the 135mm length, which was my initial incentive to try shorter.

Okay so after 12 months of experimenting down to my current length of 120mm, this is what I found. I can now ride on the flats at 50klm hr for short periods, where as before I could hardly handle more than 46klm which was a big one for me, that was probably where I was weakest. Hill climbing has changed in an interesting way I am climbing hills now seated almost the whole way where as before I use to stand up the whole time( I hated climbing sitting down) but now I love it, I would say my climbing is similar performance wise to before but I like having the option to stay seated rather than just stand all the time. The shorter hills I'm performing similar to before but over long mountain passes I'm definitely performing slightly better! Sprinting out of the saddle is an interesting one I find I don't quite have the initial jump I use to have on the 175mm cranks but I can hold the sprint for a lot longer without fatiguing and my top speed is always slightly higher. So I have to judge my sprints differently now, it took me a while but I'm starting to prefer that feeling!

Now my technique is were things have changed considerably, once I got down to about 140ish I started noticing pulling up a lot more on the up-stroke this not only helped me power wise but made the shorter cranks feel more natural to use and a lot smother while pedaling, once I got down to 120mm I now pull up almost as strong on the up-stroke as I do on the down-stroke. After reading a lot Frank Day's essay's on short cranks he made mention that once people get use to using Power Cranks they quite often start preferring shorter cranks because Power Cranks force you to pull up more on the up-stroke from what I gather, correct me if I'm wrong?

So generally I just feel strong now on the bike, much more comfortable in the aero position and all aches and pains have subsided!

Only real down side is finding cranks short enough, I use sinz square taper cranks they have a 110mm bcd spider and with a 103mm bb I have a Q-factor of 147mm and chainline almost identical to modern shimano cranks, they work perfectly. I have also drilled and tapped my own pedal threads in some Sram apex cranks they can easily be cut down to 125mm although I wouldn't cut them any shorter than that. Also I had to get a longer seat post as with the change in cranks length I had to lift my seat height a total of 55mm.

I actually ordered a set of sinz square taper cranks in size 115mm which I cant wait to try out!

Hopefully my findings inspire someone else to try going shorter, it's a fun eye opening experiment.

Regards.

 

[sciguy]

SC,

I'm interested in how you've modified your gearing to deal with the reduction in effective leverage of the system by ~ 29%. You mention riding up mountain passes seated so I'm expecting a really large rear cassette cog. Did you move to a mountain bike cassette?

Thanks,

Hugh

 

[shorter cranks]

Hi Sciguy,

I'll be happy to explain, obviously I really should of mentioned my bike set up. Silly of me!

I actually have 2 bikes running a similar set up, my secondary bike is running 125mm cranks which I drilled and tapped myself, they are sram apex compact cranks 50/34 chainrings, and my main bike is running 120mm Sinz square taper cranks 50/34 with a 103mm square taper BB. Okay my main bike again is running 50/34 up front and I'm using a 11-28 cassette out the back, which sounds like my gearing would be to hard to push, so I will explain. The bike is a Ridley X-Trail gravel disc bike, frame weight is a tad over 1kg and the forks roughly 380g, so very light frame. To help lower the gearing I am using 26" Mavic sl pro crossmax MTB wheels with 28mm slick Michelin tyres, 225g each, the wheelset weight is only 1380g. It is a 7.5kg bike and is set up like a fast road bike. By using 26" wheels I have effectively lowered my gearing by roughly 10%, That's the advantage in having a disc bike!

Now the interesting part, as I have progressively started shortening my crank length once fully adapted( takes about a month) each length drop I relatively can handle larger gears, basically my knee at TDC is very low and I can easily push down with considerable more force than I could with the longer cranks, pulling up on the up-stoke as well as the down-stroke really helps the power, which is very hard to do on longer cranks , so for me the combination of the two, smaller diameter wheels and more powerful efficient pedaling stroke allows me to use that gearing comfortably. To be honest I never use the 28t out back I usually do mountain passes in my 25t cog the next one down. 26" wheels are very nimble when climbing I doubt I'll go back to using 700c wheels again. A lot of people say larger wheels are faster at speed, but I beg to differ, since using shorter cranks and smaller diameter wheels I can hold a minimum of 4 to 5klm faster upper end speeds on the flats every time, without a doubt!

If someone said this would be my bike set up 2 years ago I would of laughed! So I guess it would be hard to understand what I am trying to point out, unless people are willing to experimented with these ideas themselves, then they will always have trouble trying to put it all into perspective.

So to sum up, IMHO you don't need to effectively drop your gearing as much as the drop in crank length percentage wise when you progress to ultra short cranks, atleast that's how it is for me!

When I try the 115mm cranks I will probably drop my big chainring to 48t although I will see how I go with the 50t first, and if the 28t at the back doesn't cut it, I can easily change to 32t, I doubt I'll need it.

Regards

 

[Captain Serious]

I hurt my knee again, so I've been riding 165s for several months, and now they feel normal and good (I'm 181cm).
I'm not sure I'll switch back to 172.5s; I don't see the point, since the benefits of 7.5mm shorter cranks most likely outweigh any possible negatives.

I've put these anecdotes on here before, but, some of the most beastly riders I've encountered are taller guys who use relatively short cranks.
Perhaps their size is what gives them the power in the first places, however: one guy is 6ft"3 and kills people with his 172.5s, and another guy is 6ft5 and TOTALLY kills everyone using 175s.

To quote Max Rainsford (and drop a name ): "if ya're farking flyin', it doesn't matter WHAT ya farkin use"

 

[CoachFergie]

Re:

To quote Max Rainsford (and drop a name ): "if ya're farking flyin', it doesn't matter WHAT ya farkin use"

A bloody good rider!

What the science tells us, is that it isn't the crank length.

 

[shorter cranks]

115mm crank Update

I received my 115mm crankset a week ago and I've used them now on about 5 occasions, so I thought I'd comment on my experiences for anyone interested.

Dropping down to 115mm length cranks from 120mm was surprisingly quite seamless when in the past each time I dropped down in length it always felt really unusual at first, maybe because I only dropped 5mm this time and the fact that I'm starting to learn a pedaling technique that suites the shorter cranks, I think the combination of the two made it a fun and smooth transition.

Anyway to my surprise again I haven't noticed any drop in power at all. Speed across all facets off my cycling has not declined at all, my flat road riding at speed is about the same but I again just feel so comfortable and strong in the aero position I can hold my speed for longer before fatigue sets in. Sprinting again is fine similar to before but very strong once up at max speed. Hill climbing I am really starting to notice a difference with the really short cranks I am definitely performing better now at this length than I did on the 175mm cranks, standing or sitting makes no difference I am strong at both, where as with the 175's I had to stand to be strong and once seated I would loose power very quickly. So how well I'm hill climbing has been the biggest eye opener to me because I use to believe you needed longer cranks for leverage to climb well, I now know that is a fallacy, it's all about gearing, comfort and how much torque your legs can produce at the pedals, which I find much easier on the shorter cranks.

Again as I mentioned in one of my earlier posts, the shorter I go, the harder I pull up on the upstroke, there are no dead spots in the pedaling stroke, just strong through the whole circle. The other thing I haven't mentioned is my ability to spin at high cadence now(if I need to) is unbelievable, I was useless at spinning with 175's.

Anyway to wrap up I am starting to wonder how short I would have to go before power starts to drop of, because it definitely hasn't at 115mm length.

To go any shorter than 115mm I would have to find a different brand of cranks, Turn3 racing apparently make them in lengths down to 100mm in square taper, not cheap but good quality.

Although I think in the mean time I will continue with the 115's as I am really enjoying them.

Cheers.

 

[sciguy]

115mm crank Update

Anyway to my surprise again I haven't noticed any drop in power at all. .

So you're using a power meter and actually measuring your power? How's your mean maximal power at 1 minute, 5 minutes, 20 minutes and one hour compare to the longer cranks?

Thanks,

Hugh

 

[backdoor]

115mm crank Update


Again as I mentioned in one of my earlier posts, the shorter I go, the harder I pull up on the upstroke, there are no dead spots in the pedaling stroke, just strong through the whole circle.


Cheers.

In your estimation when at maximal power application, what percentage of your torque at 3 o'c are you applying at 9 and 10 o'c, and what do you mean by "no dead spots in the pedaling stroke" ?

 

[shorter cranks]

115mm crank Update

Anyway to my surprise again I haven't noticed any drop in power at all. .

So you're using a power meter and actually measuring your power? How's your mean maximal power at 1 minute, 5 minutes, 20 minutes and one hour compare to the longer cranks?

Thanks,

Hugh

No I don't have a power meter, although I would like to own one. All my findings are based on my cycle computer's speed and average speeds, most of the time I am comparing my speeds on a 20klm loop I do to work and back that I've been doing for 20 years, so I know the road, my top speeds my average speeds like the back of my hand. Part of the ride has a fairly tough hill that climbs for about 2klm reasonable steep and constant, my good friend said his GPS averaged ihat at 11- 12%, so a good test. I have timed myself many times over the years on that hill, the best time I have ever done is on the 120mm cranks, I haven't timed myself on the 115's yet but 3 days ago I'm almost certain I was faster based on speedo readings the whole way. On that same ride there is a very long flat section about 7klm, that's where I noticed my biggest improvements, I could never hold it much above 46klm on the 175's, but since going below 130mm I can handle 50klm for quite a bit of that distance. Again flat riding holding high constant speeds(TT) is where I have improved the most. Hill climbing is only slightly faster, but seems to be at it's best on 115's. Sprinting top speed I always do on the same section of road(fairly flat and smooth), I have done it many times on the 175's and my highest ever was 56klm, my highest speed on the short cranks is 59klm that was on 130mm cranks, on the 115's my top speed is almost as good 58klm but I can hold it longer at higher speeds. I will say my initial of the mark sprint speed is definitely snappier on the longer cranks like 155mm-165mm.

All my findings are obviously not results down on paper but I have no doubt myself that I am performing considerably more efficient on the shorter cranks(I wont go back to anything longer than 130mm). And as I have mentioned before I don't suffer with chronic low grade pain like I did with the 175's.

 

[shorter cranks]

115mm crank Update


Again as I mentioned in one of my earlier posts, the shorter I go, the harder I pull up on the upstroke, there are no dead spots in the pedaling stroke, just strong through the whole circle.


Cheers.

In your estimation when at maximal power application, what percentage of your torque at 3 o'c are you applying at 9 and 10 o'c, and what do you mean by "no dead spots in the pedaling stroke" ?

I will try my best to explain.
Once I progressed down to about 140mm, I started to notice to achieve good power at that length It was almost natural to pull up to a certain degree through what felt like about 8 to 10/11 during the upstroke which then makes the down stroke from about 1/2 to 5/6 feel more lively I guess. But once I dropped below 125mm this pedaling technique/sensation becomes almost instinctive and very easy to achieve. On 175's I never pulled up on the upstroke, I found it hard enough to get my foot over the top of the stroke (12) little own pull up!

Now what I mean by no "dead spots" is with lengths below 130mm it feels like I am not only pulling up and pushing down hard but I also feel like I push the pedal forward with force over the top of the stroke 11 to1/2 and pull back through the bottom of the stroke as well from 5 to 7/8 again with force. So no dead spot where not torque is applied to the pedal.

Obviously, well I assume in reality peak force would be at it's greatest on the down stroke 3 to 5. But it feels like I am Pulling up and around the back as hard as I am pushing over down the front.

So I am certain that I apply more even torque around the entire pedal stroke than I can with longer cranks (only pushing hard through the down stroke).

I hope I didn't confuse you?

 

[backdoor]

115mm crank Update


Again as I mentioned in one of my earlier posts, the shorter I go, the harder I pull up on the upstroke, there are no dead spots in the pedaling stroke, just strong through the whole circle.


Cheers.

In your estimation when at maximal power application, what percentage of your torque at 3 o'c are you applying at 9 and 10 o'c, and what do you mean by "no dead spots in the pedaling stroke" ?

I will try my best to explain.
Once I progressed down to about 140mm, I started to notice to achieve good power at that length It was almost natural to pull up to a certain degree through what felt like about 8 to 10/11 during the upstroke which then makes the down stroke from about 1/2 to 5/6 feel more lively I guess. But once I dropped below 125mm this pedaling technique/sensation becomes almost instinctive and very easy to achieve. On 175's I never pulled up on the upstroke, I found it hard enough to get my foot over the top of the stroke (12) little own pull up!

Now what I mean by no "dead spots" is with lengths below 130mm it feels like I am not only pulling up and pushing down hard but I also feel like I push the pedal forward with force over the top of the stroke 11 to1/2 and pull back through the bottom of the stroke as well from 5 to 7/8 again with force. So no dead spot where not torque is applied to the pedal.

Obviously, well I assume in reality peak force would be at it's greatest on the down stroke 3 to 5. But it feels like I am Pulling up and around the back as hard as I am pushing over down the front.

So I am certain that I apply more even torque around the entire pedal stroke than I can with longer cranks (only pushing hard through the down stroke).

I hope I didn't confuse you?

As cadence increases your upstroke muscles are only capable of eliminating negative torque and this will result in a weaker downstroke. The dead spot can only be eliminated by using a combination of equally powerful muscles in that sector as those used around 3 o'c.

 

[PhitBoy]

Hi Shorter Cranks:
Thanks for sharing your experiences. I have a question about your approach to changing seat height. When you change to a shorter length do you raise the saddle so as to maintain maximum leg extension? In other words, when you change to a 10mm shorter crank do you raise the saddle by 10mm? That's how we did the studies in my lab.
Another approach would have been to leave the saddle at the same height. This would give the same extension in the middle of the cycle (3 o'clock) but less extension at the bottom.
Anyway, would you share how you adjust your saddle?
Thanks,
Jim

115mm crank Update

 

[talbet]

I definitely feel more energy efficient when I climb stairs one at a time (like with extremely short cranks), but I jump 3 at a time when I'am in a hurry. Probably somewhere in the middle is a place with reasonable balance between speed and endurance and since I need both on a bicycle then I feel that small differences around this middle aren't worth investigating.