Crank arm length...

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Crank arm length...

Postby DoubleSpeeded » Mon Sep 16, 2013 8:26 pm

IM aware that there is a text book guide to selecting the right Crank arm length in comparison to the length measurement of your inside leg.


However, Ive heard longer crank arms can offer more leverage force with pedalling but can result in knee pain for some people...


I'm curious to know.. has anyone serious riders have gone higher than what is specified & achieved better results?
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by BNA » Mon Sep 16, 2013 8:52 pm

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Re: Crank arm length...

Postby Duck! » Mon Sep 16, 2013 8:52 pm

Longer cranks do provide a bit more torque, but because you're pedalling in bigger circles, they're not as easiy to spin at a high cadence. Really though, it depends how much longer you want to go. My two roadies have 172.5 mm cranks and the MTB has 175mm and I really don't notice the difference. Maybe it's overpowered by the completely different riding.

What is more noticeable is the 150mm cranks I have in the HPV..... Very easy to spin over at a high cadence, very responsive out of corners, as long as you're in the right gear. Get stuck in the wrong gear & it's a bit sluggish 'cos there's no torque.
I had a thought, but it got run over as it crossed my mind.
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Re: Crank arm length...

Postby DoubleSpeeded » Mon Sep 16, 2013 9:11 pm

Duck! wrote:Longer cranks do provide a bit more torque, but because you're pedalling in bigger circles, they're not as easiy to spin at a high cadence. Really though, it depends how much longer you want to go. My two roadies have 172.5 mm cranks and the MTB has 175mm and I really don't notice the difference. Maybe it's overpowered by the completely different riding.

What is more noticeable is the 150mm cranks I have in the HPV..... Very easy to spin over at a high cadence, very responsive out of corners, as long as you're in the right gear. Get stuck in the wrong gear & it's a bit sluggish 'cos there's no torque.


Im just curious..

Whats your inside leg measurement?

well my MTB/Hybrid i use for road is a 172.5mm.
The TT is 170mm... torque wise i do notice the difference as the TT has 54T large crank and the MTB is 48 from memory?... so it feels like a different ball game. But the circular motion/revolution feels great on the slightly longer crank arm.

i was just reading an article on Fabian Cancellara, he's crank is 177mm... and I'm certain his height and inner leg would not be suited to that.
Last edited by DoubleSpeeded on Mon Sep 16, 2013 11:37 pm, edited 1 time in total.
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Re: Crank arm length...

Postby ldrcycles » Mon Sep 16, 2013 9:21 pm

As with handlebar and saddle width, I think measuring inside legs/shoulders/cheekbones/whatever else can give you a guide as to what might work but in the end it comes down to personal preference. IME longer cranks are more comfortable for low cadence, shorter cranks for high cadence. So if you prefer a low cadence, it would be safe to assume you would prefer longer cranks.
Last edited by ldrcycles on Tue Sep 17, 2013 5:19 am, edited 1 time in total.
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Re: Crank arm length...

Postby Duck! » Mon Sep 16, 2013 9:25 pm

My inseam is about 855mm, give or take a couple. The cranks on my three "normal" bikes are stock.

Ever thought of going to a smaller chainring on the TT? Unless you're an elite rider, 56T is pretty over-geared.
I had a thought, but it got run over as it crossed my mind.
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Re: Crank arm length...

Postby warthog1 » Mon Sep 16, 2013 9:29 pm

DoubleSpeeded wrote:
i was just reading an article on Fabian Cancellara, he's crank is 177mm... and I'm certain his height and inner leg would not be suited to that.


They tend to go slightly longer on the tt than the roadie. Cancellara is fairly tall at 185 cm
Marco Pantani was not at 172 cm yet he was known to climb on 180's
Sprinters tend toward shorter cranks on the other hand.

If you search crank length on here you will find numerous entries.
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Re: Crank arm length...

Postby mikesbytes » Mon Sep 16, 2013 9:41 pm

Another way to look at it is foot velocity
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Re: Crank arm length...

Postby Nobody » Mon Sep 16, 2013 9:42 pm

Duck! wrote:Ever thought of going to a smaller chainring on the TT? Unless you're an elite rider, 56T is pretty over-geared.
Bigger is more efficient.
http://www.jhu.edu/news_info/news/home9 ... /bike.html
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Re: Crank arm length...

Postby Duck! » Mon Sep 16, 2013 9:53 pm

Nobody wrote:
Duck! wrote:Ever thought of going to a smaller chainring on the TT? Unless you're an elite rider, 56T is pretty over-geared.
Bigger is more efficient.
http://www.jhu.edu/news_info/news/home9 ... /bike.html

Yes, but mechanical efficiency is only one part of the equation. It's also actually having the leg power to turn the bigger gear ratios.
I had a thought, but it got run over as it crossed my mind.
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Re: Crank arm length...

Postby warthog1 » Mon Sep 16, 2013 10:05 pm

The pros use chainrings that big to get a straighter chain line. Mugs like us may be making it worse by running a dinner plate like that. Simply haven't got the sustainable power to run it.
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Re: Crank arm length...

Postby Nobody » Mon Sep 16, 2013 10:06 pm

Everything you want to know about the science of crank length is in the link below.
http://www.plan2peak.com/files/32_artic ... hnique.pdf
Basically it says there is no real advantage to crank length so run whatever suits you.

In the real world shorter cranks have many advantages:
Less knee problems.
Less pedal strike in corners.
Less heel strike on panniers.
Less toe overlap with front wheel.
More aero both in themselves and aiding a more aero body position.
As Duck! illustrated, they spin up slightly faster (which has been proven).
Lighter.

[You can tell we've done this before many times]

Now just waiting for the usual suspects to post on how wonderful long cranks are...Oh, one already has. :P
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Re: Crank arm length...

Postby Nobody » Mon Sep 16, 2013 10:12 pm

Duck! wrote:
Nobody wrote:
Duck! wrote:Ever thought of going to a smaller chainring on the TT? Unless you're an elite rider, 56T is pretty over-geared.
Bigger is more efficient.
http://www.jhu.edu/news_info/news/home9 ... /bike.html

Yes, but mechanical efficiency is only one part of the equation. It's also actually having the leg power to turn the bigger gear ratios.
I can tell that we both like to "discuss" things. :)
OK, well TTs are usually fairly flat. True?
So if you run the 56 to about the middle of a cassette, say 21 tooth. That's about a 71 inch gear. And since the rear cog is bigger, it is also more efficient.
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Re: Crank arm length...

Postby Duck! » Mon Sep 16, 2013 10:17 pm

This is taking short cranks to the extreme:

Image

Custom-drilled to 150mm. That's a 73T chainring. I know I suggested 56T is a tad big, but when you're only driving a 16" wheel, you need to compensate the tiny wheel roll-out with a massive gear ratio. The 73T is used on tighter, slower tracks, and I have an 80T ring on for more open circuits.
I had a thought, but it got run over as it crossed my mind.
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Re: Crank arm length...

Postby Nobody » Mon Sep 16, 2013 10:19 pm

warthog1 wrote:The pros use chainrings that big to get a straighter chain line. Mugs like us may be making it worse by running a dinner plate like that. Simply haven't got the sustainable power to run it.
Probably not where you live, but on the flat with a TT bike that can go 10% faster (at least) then 53 tooth X 1.1 is 58.3 teeth. So I would say 56 is fine for most. Depends on what crank length you're running too, because that is a form of gearing as well.
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Re: Crank arm length...

Postby human909 » Mon Sep 16, 2013 10:23 pm

Most definitely. Running on sub 14 tooth sprockets starts to get silly. Much better to use a large chainwheel for efficiency.
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Re: Crank arm length...

Postby Nobody » Mon Sep 16, 2013 10:24 pm

Duck! wrote:This is taking short cranks to the extreme:

...

Custom-drilled to 150mm. That's a 73T chainring. I know I suggested 56T is a tad big, but when you're only driving a 16" wheel, you need to compensate the tiny wheel roll-out with a massive gear ratio. The 73T is used on tighter, slower tracks, and I have an 80T ring on for more open circuits.
Reminds me of the link below.
Image
http://www.cyclingweekly.co.uk/news/lat ... -bbar.html
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Re: Crank arm length...

Postby warthog1 » Mon Sep 16, 2013 10:26 pm

Nobody wrote:Probably not where you live, but on the flat with a TT bike that can go 10% faster (at least) then 53 tooth X 1.1 is 58.3 teeth. So I would say 56 is fine for most. Depends on what crank length you're running too, because that is a form of gearing as well.


Tony Martin runs a 58 tooth but then he tts at over 50 kmh. No one on here comes close to that, 56 is well over geared for most.
Unless we have Cancellara or Wiggins posting on here that is.
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Re: Crank arm length...

Postby Nobody » Mon Sep 16, 2013 10:31 pm

warthog1 wrote:Tony Martin runs a 58 tooth but then he tts at over 50 kmh. No one on here comes close to that, 56 is well over geared for most.
Unless we have Cancellara or Wiggins posting on here that is.
Well 4 out of 5 are visitors, so they could be lurking. :mrgreen:
A 53 is only 3 teeth smaller or 94.6% of a 56, so most roadies must be over-geared too. Especially since they are generally less aero (when riding alone).
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Re: Crank arm length...

Postby warthog1 » Mon Sep 16, 2013 10:38 pm

I think I've seen this list before on here.


Jacques Anquetil 175mm
Lance Armstrong 175mm
Magnus Backstedt 177.5mm
Chris Boardman 170mm
Santiago Botero 172.5mm
Angel Casero 175mm
Mario Cipollini 172.5mm
Fausto Coppi 171mm
Malcolm Elliott 172.5mm
Tyler Hamilton 172.5mm
Bernard Hinault 172.5mm
Miguel Indurian 180mm (190mm for second Hour record!)
Laurent Jalabert 172.5mm
Greg Lemond 175mm
Brad McGee 175mm
Robbie McEwen 175mm
Eddy Merckx 175mm
David Millar 175mm (180mm in TT)
Francesco Moser 175mm
Marty Northstein 167.5mm in Keirin (170mm in kilo)
Graham Obree 175mm
Marco Pantani 170mm (180mm in mountains)
David Rebellin 172.5mm
Roger Riviere 175mm
Jean Robic 170mm
Tony Rominger 172.5mm (175mm for Hour record)
Oscar Sevilla 175mm
Jan Ullrich 177.5mm
Rik Verbrugghe 175mm
Erik Zabel 172.5mm
Alex Zulle 175mm (180mm in mountains)
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Re: Crank arm length...

Postby Nobody » Mon Sep 16, 2013 10:40 pm

Well you are one of the "usual suspects". :P
Just waiting for TLL now.

Also you never seem to be able to find a list for the track riders, why is that? :roll: :P

Actually I just noticed on by the description which looks to be also the shortest:
Marty Northstein 167.5mm in Keirin (170mm in kilo)
Last edited by Nobody on Mon Sep 16, 2013 10:45 pm, edited 1 time in total.
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Re: Crank arm length...

Postby warthog1 » Mon Sep 16, 2013 10:44 pm

Nobody wrote:
A 53 is only 3 teeth smaller or 94.6% of a 56, so most roadies must be over-geared too. Especially since they are generally less aero (when riding alone).


Roadies need the bigger gears to sprint in. If you have paced your tt right there is nothing left for a sprint.
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Re: Crank arm length...

Postby toolonglegs » Mon Sep 16, 2013 10:49 pm

Meh... run what works for you.
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Re: Crank arm length...

Postby warthog1 » Mon Sep 16, 2013 10:51 pm

Nobody wrote:
Also you never seem to be able to find a list for the track riders, why is that? :roll: :P

Actually I just noticed on by the description which looks to be also the shortest:
Marty Northstein 167.5mm in Keirin (170mm in kilo)


I have never ridden track but try this. Chris Boardman mght have had osteoarthritic knees like yourself but the rest weren't hobbling old cripples :mrgreen:
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Re: Crank arm length...

Postby Nobody » Mon Sep 16, 2013 10:52 pm

warthog1 wrote:Roadies need the bigger gears to sprint in. If you have paced your tt right there is nothing left for a sprint.
True, but even lowly, overweight, middle-aged me with a heavy steel bike and no real sprinting ability is still happy to run a 50 which is almost 90% (89.2) of a 56. That's because it's mainly flat where I ride. Somewhat like a TT race really...
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Re: Crank arm length...

Postby warthog1 » Mon Sep 16, 2013 10:58 pm

Nobody wrote:True, but even lowly, overweight, middle-aged me with a heavy steel bike and no real sprinting ability is still happy to run a 50 which is almost 90% (89.2) of a 56. That's because it's mainly flat where I ride. Somewhat like a TT race really...


Are you regularly finding yourself in the 50-11 though? It is about a straight chainline where you spend the bulk of your time. Unless you are tting at 50kmh a 53 is more than adequate to achieve that.
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