Crank arm length...

open topic, for anything cycling related.

Re: Crank arm length...

Postby Nobody » Fri Sep 20, 2013 7:49 pm

warthog1 wrote:
Nobody wrote:If I was racing, would it make my answer more valuable?

Well if you were tt ing over a set course a number of times and had a consistent trend in your times developing then yes, I think your results would be more valuable.
You seem to be seeing what you want to see. TLL posted above about that. Fitness and conditions change over time.

warthog1 wrote:I will soon get an idea over time which length of crank is faster for me. I dont expect a big change btw.
Haven't you been doing the long crank thing for about a year now? Surely the results should be well and truly in by now.

warthog1 wrote:
Nobody wrote:Average speed. Just as fallible as most other people's methodology.


Combine it with maximal effort and if your training load is relatively consistent you will establish a trend IMO
I did. It was no change.

warthog1 wrote:I don't see how doping or not affects the results. Would not doping make the same athlete choose shorter cranks to maximise their speed?
Maybe not, but it was funny and sad at the same time. I would dare to say that almost all would be taller than 173cm though.
Also here's a thought, maybe they all follow each other on what to get in the absence of any real data on the subject. Just like if you were to become a pro now. Then people would follow you and so on...

warthog1 wrote:
Nobody wrote:And yes, a possible gain might be there (although the science says no so far) but there are plenty of known advantages of shorter cranks (also listed previously).

The studies I have seen relate to short term maximal anaerobic (sprinting) power.
There is significant incentive for competitive cyclists at the highest level to win, evidence the amount who have doped :evil: . They tend to use longer cranks. Why? :P
Do all the sprinters also use long cranks, even though the scientific evidence says that shorter cranks accelerate faster? If so, why? :mrgreen:

This post is a concise argument for shorter cranks with a TT bike.
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by BNA » Fri Sep 20, 2013 11:59 pm

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Re: Crank arm length...

Postby warthog1 » Fri Sep 20, 2013 11:59 pm

Nobody wrote:Fitness and conditions change over time.

Haven't you been doing the long crank thing for about a year now? Surely the results should be well and truly in by now.


Those 172.5's were on a compact so the gearing was a bit different, but the 175's are faster over all my segments even though I'm getting even older :(

Nobody wrote:
warthog1 wrote:Combine it with maximal effort and if your training load is relatively consistent you will establish a trend IMO
I did. It was no change.

well thats what you get with your dodgy old knees :P

Nobody wrote:Do all the sprinters also use long cranks, even though the scientific evidence says that shorter cranks accelerate faster? If so, why? :mrgreen:.


I think they tend toward shorter cranks but who cares about those wheelsuckers anyway?

This post is a concise argument for shorter cranks with a TT bike.[/quote]
Thats a concise argument for why the 5cm saddle set back rule doesn't work. They all slide forward on the nose of the saddle to open up the hip angle again and run their faster longer cranks :P
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Re: Crank arm length...

Postby warthog1 » Sat Sep 21, 2013 12:04 am

winstonw wrote:
warthog1 wrote:Given the leg is lifted slightly higher with increased crank length, longer cranks increase leg flexion at the knee so that force is applied to the knee whilst it is hinged at a more acute angle. Can cause some people knee problems.




- masters cyclists with bodyfat over 15% +/- stiff spines have more difficulty getting a more efficient aero position via a larger hip angle, due to visceral fat pushing up on the diaphragm (which restricts breathing) and pushing on the femoral vein and inferior vena cava (which restricts venous return). To assist getting lower on the bars, and remaining comfortable there for longer, I'll recommend a shorter crank. I've done this for 4 people this year and it has made a significant difference. Their 57-58cm frames came with 175cm cranks, 3 of them are now on 170, and one on 172.5.


Tell the lard arses to get some gastric banding done, lose some weight and then come back to you :) (Joking about the gastric banding by the way)

Have you tried less set back on the saddle also, that might help? I have no experience at all in setting anyone else up on a bike so feel free to pay no attention :)
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Re: Crank arm length...

Postby Nobody » Sat Sep 21, 2013 7:52 am

warthog1 wrote:
Nobody wrote:Fitness and conditions change over time.

Haven't you been doing the long crank thing for about a year now? Surely the results should be well and truly in by now.


Those 172.5's were on a compact so the gearing was a bit different, but the 175's are faster over all my segments even though I'm getting even older :(
You poor old misery guts. :P
You aren't comparing like for like, because standard is going to be faster than compact unless you run out of gears at the low end. The science says bigger chainrings are faster. Yesterday I was pushing into a big headwind (I ride beside the water mostly) and when I dropped into the 34 and clicked up about 3 or 4 gears at the back (to save my knees) I really noticed how much less efficient the smaller chainring and sprocket are. If I had a 39, the gears would have been bigger at both ends and I would have had better efficiency. Same with 50 to 53. I think I might go back to a standard eventually.

So in reality I suppose that may be the real advantage of longer cranks, which is you are effectively gearing down so you can run bigger, therefore more efficient chainrings. There you go, you win, I agree with you on one aspect of why longer cranks are better. :) Whether that advantage is going to override the disadvantages with aero really comes down to the individual as to whether than can produce power lower.

warthog1 wrote:That's a concise argument for why the 5cm saddle set back rule doesn't work. They all slide forward on the nose of the saddle to open up the hip angle again and run their faster longer cranks :P
They would be doing that anyway, but don't let reality get in the way of your good story. :P
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Re: Crank arm length...

Postby insightt47 » Wed Jan 22, 2014 1:24 am

Sorry to resurrect and old thread but I have an important question. On my Look 695 I can adjust the crank arm length. I usually ride 172.5 but I thought id give 175mm a try. The first thing i noticed was its noticeably harder to accelerate and also harder to climb when seated. At first I thought it was due to my legs not used to working in the larger range but now Im beginning to wonder. So my question is should I continue struggling and will my legs come good or should I just give up and go back to the 172.5mm length.
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Crank arm length...

Postby toolonglegs » Wed Jan 22, 2014 1:55 am

How much can you adjust them by?... Sounds cool. Half of my club rides on Looks...we get them cheap from Cofidis... Never paid much notice to the cranks except they all bloody creak!.
On the length... 2.5mm is not much at all... But you do need to drop your saddle height when you change crank length, have you done that?.
Personally I am riding 172.5mm cranks at the moment with the bottom of stroke to saddle height at 1013mm... I race on 180mm and when I get on them I certainly feel I can push harder, I just struggle to make power on the shorter cranks...maybe it is because I can't spin... Or maybe it is in my head!.
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Re: Crank arm length...

Postby insightt47 » Wed Jan 22, 2014 2:18 am

toolonglegs wrote:How much can you adjust them by?... Sounds cool. Half of my club rides on Looks...we get them cheap from Cofidis... Never paid much notice to the cranks except they all bloody creak!.
On the length... 2.5mm is not much at all... But you do need to drop your saddle height when you change crank length, have you done that?.
Personally I am riding 172.5mm cranks at the moment with the bottom of stroke to saddle height at 1013mm... I race on 180mm and when I get on them I certainly feel I can push harder, I just struggle to make power on the shorter cranks...maybe it is because I can't spin... Or maybe it is in my head!.


Theyre adjustable from 170mm to 175mm. Haha I did my research and avoided the creaking by using some loctite.

Thats a good point, but I can't adjust my saddle height any more. Ive already used the maximum recommended 3cm of spacers plus a 2.5mm spacer. I bought the frame second hand so the seat post was already cut. Jeez now I know why your nick is "toolonglegs" haha. Looks like i'll need to adjust my saddle height if I wana be efficient on 175mm cranks, but thats not possible. Im definitely not buying a taller seat because my prologo scratch nack is the ultimate seat for me, so it looks like ill be going back to 172.5mm BTW the distance from the bottom stroke to the top of the saddle is 80cm for me (Im 183cm tall).

Thanks for your help toolonglegs!
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Re: Crank arm length...

Postby KGB » Wed Jan 22, 2014 6:24 am

Longer cranks = shorter saddle height. Why can't you remove spacer/s to adjust it down?
You wouldn't want longer cranks and a taller seat...
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Re: Crank arm length...

Postby Nobody » Wed Jan 22, 2014 8:15 am

insightt47 wrote:I'm definitely not buying a taller seat because my prologo scratch nack is the ultimate seat for me, so it looks like ill be going back to 172.5mm
As KGB said, as the cranks get longer you lower the saddle. It's to match the same leg bend you had previously at the bottom of the stroke.

insightt47 wrote:BTW the distance from the bottom stroke to the top of the saddle is 80cm for me (Im 183cm tall).
So is that from the top of the pedal (at the bottom of stroke) to top of saddle? If it is, then this appears to be a very low saddle height for your 183cm height. What is you inner leg measurement?

For example, I have a low saddle height for my height (172cm). I have an inner leg of 80cm and have a saddle height of 854mm. That height is measured from the top of the pedal platform to the top of the saddle with the crank at the bottom of stroke, measured along the seat tube. That's 106.75% of my inner leg. As you are 183cm, you should have a longer inner leg length than me, but you appear to have a lower saddle height of 80cm. This is using the "Hamley method" (according to the link below) with a starting point of 109% of inner leg length (PBH).
http://www.ecovelo.info/2008/10/16/more ... le-height/
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Re: Crank arm length...

Postby insightt47 » Wed Jan 22, 2014 10:43 am

KGB wrote:Longer cranks = shorter saddle height. Why can't you remove spacer/s to adjust it down?
You wouldn't want longer cranks and a taller seat...


oh yeah, stupid me, obviously....
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Re: Crank arm length...

Postby insightt47 » Tue Jan 28, 2014 11:44 pm

Just a quick update, my legs have gotten used to the longer crank arm and Im riding like normal, maybe even a little faster and I feel more comfortable on the bike. When the pedal is at its lowest point my feet are flat and my knee is slighty bent, probably not as much as it should be
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Re: Crank arm length...

Postby Percrime » Wed Jan 29, 2014 7:51 am

Heh. Probably not. You want the seat as high as you can get away with (to the mm) without rocking your ass as you pedal and without bottoming out your knees. So assuming that is so then you have effectively just managed to tweak your seat up a bit (in a complex manner) And its possible that that is all of your efficiency increase right there. and the crank change has done nada.

:P
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