Crank length ! How important !

Hollow-legs

I am struggling to get my head around why different size bike frames have different size cranks,,Its only few mms ,can some one enlighten me ,does it make a difference when turning the pedals.
I am 5 ft 8 " and have a small inside leg 29 1/2 "
I ride a medium frame !

Cheers!

drlodge

Bigger frame suits a bigger rider who has longer legs, and therefore needs longer cranks.

172.5mm is the "standard" these days, most medium frames with have this length crank. Large frames may go up to 175mm cranks, small frames probably have 170mm.

StillGoing

There are stacks of threads on here with the reasons why crank length is important. Some don't subscribe to the logic, but many do including a lot of bike fitting specialists. The simple reason is that if your crank arms are too long, your seat will need to be low enough to avoid over extending at the bottom of the stroke. As a consequence, when your foot is at the top of the stroke, your leg will be over compressed putting strain on the joints and reducing your ability to get your maximum power out as early as possible.

simon_masterson

I'm 6ft with 34ish" inseam (crotch to floor straight down; 32-33" in trousers) and as it happens just this weekend I switched to 175mm cranks, having always used 170mm.

It's definitely different. I'm not sure it's 'better'. What I've noticed so far is that I feel like I have more leverage and therefore find myself pushing harder gears, and spin a bit less.

Initialised

Find your optimal crank length with this handy calculator.

http://www.machinehead-software.co.uk/b ... lator.html

I'm a 33" and should be running a 170mm

mmacavity

http://www.cervelo.com/en/engineering/a ... ength.html

http://www.stevehoggbikefitting.com/bik ... which-one/

https://www.powercranks.com/cld.html

http://wbeauchamp08.serveronline.net/wi ... 0Power.pdf

dennisn

FWIW I switched from the 170's that I had been riding for years to 172.5's and never noticed a thing(well, the new ones were prettier). Don't even know why I decided to do it, other than why not. Or maybe the 172.5's were on sale? In any case I have zero to report on that issue. If in fact it is an issue.

andrewjoseph

My road bike has 170 cranks, my mtb 175. No problems switching between. I might notice going from 160 to 175.

My wife has 165 on mtb, 160 on road.

John.T

I have used 165s on the track, 175 and 180 on the road. After 5 minutes I could never notice the difference.
This is mainly about TT use but is interesting.
http://www.cervelo.com/en/engineering/ask-the-engineers/crank-length.html

StillGoing

There are plenty of people who can tell the difference and plenty of specialist fitters who support the theory.

http://bikedynamics.co.uk/FitGuidecranks.htm

John.T

Which of the many theories do the specialist fitters support? Usually the one supported by the system they have bought.
Leg length is a factor as are flexibility and how big your beer gut is. The only thing that matters is 'are you comfortable on the size you are using?'.

khisanth

blimey according to that calculator, my crank length should be 160mm ! (30" inseam)

However my beer gut is the main issue when in the drops !

NeXXus

I couldn't tell you what length the cranks are on either of my regularly ridden bikes.

dennisn

philthy3 wrote:

There are plenty of people who can tell the difference and plenty of specialist fitters who support the theory.

http://bikedynamics.co.uk/FitGuidecranks.htm

"Plenty" is the word I question here. :roll:

StillGoing

dennisn wrote:

philthy3 wrote:

There are plenty of people who can tell the difference and plenty of specialist fitters who support the theory.

http://bikedynamics.co.uk/FitGuidecranks.htm

"Plenty" is the word I question here. :roll:

Remember all those people who insisted the world was flat? :roll:

dennisn

philthy3 wrote:

dennisn wrote:

philthy3 wrote:

There are plenty of people who can tell the difference and plenty of specialist fitters who support the theory.

http://bikedynamics.co.uk/FitGuidecranks.htm

"Plenty" is the word I question here. :roll:

Remember all those people who insisted the world was flat? :roll:

Maybe I should re-phrase that. I'm thinking that ".. there are plenty of people who claim they can tell the difference..". Sort of a bragging thing, that they know cycling. Much like people who claim to be able to detect tire rolling resistance deviations or this wheel feels more aero than that one or people that can tell that Brand X components are better than Brand Y. You have read that people can tell the difference so therefore you can too. How would it sound if you said you couldn't. People would probably think less of you as a cyclist.

mmacavity

http://www.theroaddiaries.com/2013/08/2 ... h-options/

StillGoing

dennisn wrote:

philthy3 wrote:

dennisn wrote:

philthy3 wrote:

There are plenty of people who can tell the difference and plenty of specialist fitters who support the theory.

http://bikedynamics.co.uk/FitGuidecranks.htm

"Plenty" is the word I question here. :roll:

Remember all those people who insisted the world was flat? :roll:

Maybe I should re-phrase that. I'm thinking that ".. there are plenty of people who claim they can tell the difference..". Sort of a bragging thing, that they know cycling. Much like people who claim to be able to detect tire rolling resistance deviations or this wheel feels more aero than that one or people that can tell that Brand X components are better than Brand Y. You have read that people can tell the difference so therefore you can too. How would it sound if you said you couldn't. People would probably think less of you as a cyclist.

I know simply because the test I did to assess my ideal crank length was done with a power meter. The shorter length crank gave me improved power for less strain on the knees and a better overall fit on the bike once you take into account the various angles involved in a fitting.

cswitch

dennisn wrote:

philthy3 wrote:

dennisn wrote:

philthy3 wrote:

There are plenty of people who can tell the difference and plenty of specialist fitters who support the theory.

http://bikedynamics.co.uk/FitGuidecranks.htm

"Plenty" is the word I question here. :roll:

Remember all those people who insisted the world was flat? :roll:

Maybe I should re-phrase that. I'm thinking that ".. there are plenty of people who claim they can tell the difference..". Sort of a bragging thing, that they know cycling. Much like people who claim to be able to detect tire rolling resistance deviations or this wheel feels more aero than that one or people that can tell that Brand X components are better than Brand Y. You have read that people can tell the difference so therefore you can too. How would it sound if you said you couldn't. People would probably think less of you as a cyclist.

What a silly statement. Maybe you just have a very poor sensory perception.

dennisn

cswitch wrote:

dennisn wrote:

philthy3 wrote:

dennisn wrote:

philthy3 wrote:

There are plenty of people who can tell the difference and plenty of specialist fitters who support the theory.

http://bikedynamics.co.uk/FitGuidecranks.htm

"Plenty" is the word I question here. :roll:

Remember all those people who insisted the world was flat? :roll:

Maybe I should re-phrase that. I'm thinking that ".. there are plenty of people who claim they can tell the difference..". Sort of a bragging thing, that they know cycling. Much like people who claim to be able to detect tire rolling resistance deviations or this wheel feels more aero than that one or people that can tell that Brand X components are better than Brand Y. You have read that people can tell the difference so therefore you can too. How would it sound if you said you couldn't. People would probably think less of you as a cyclist.

What a silly statement. Maybe you just have a very poor sensory perception.

Of course you want to claim that you know all these things. You have sort of proven my point in that respect. If you didn't or couldn't tell about these things then you would have "very poor sensory perception", just like you think I do. The few of us out here who can't tell the difference in various tires rolling resistance are living in an absolute hell of denial and anger at our inabilities. You're the lucky one. :roll:

cswitch

I'm not the one making the bold claims.

Anyway back on topic
So philthy3 on the power test was self selected cadence used for differing crank lengths or did you specifically hit the same cadence for differing crank lengths such as in a stationary ramp test? If not the latter was cadence the same? I have heard smaller crank length can lead to higher self selected cadence.

Adam Topham's fly through the pain barrier book touches on crank length and explains some basic principals. I.e longer greater leverage, shorter = faster cadence, impact on saddle height and saddle fore aft. He states he uses a longer crank for greater leverage and also to lower the saddle to reduce drag due to bring a 'bulky rider'. Marginal gains no doubt but when a second may count.

A couple of other reasons for different crank lengths. shorter crank arms mean greater pedal to floor clearance when cornering though I wouldnt necessarily select a length based on that alone but it can be a bonus if crit racing. Also less toe overlap with shorter cranks, sometimes necessary if commuting on a single speed with track like geo.

cswitch

...maybe wasn't clear on the self selected cadence thing. What I mean is was the cadence across the different crank length selected by what felt comfortable for a specific crank length? As opposed to consciously hitting a specific rpm as in a ramp test.

StillGoing

The use of the power meter was to ensure I put the same power and cadence out for both tests. Rider feel was what determined which was the better fit coupled with detailed fitting measurements including the angles at the top and bottom of the stroke. There was no doubt in my mind that the shorter cranks felt much easier to achieve the same power at the same cadence due to less effort to overcome the dead spot at the top of the pedal stroke.

My second bike currently has 170mm cranks fitted and after a longish ride today with quite a few hills, my legs feel like they've done it, whereas a ride of similar length with steeper climbs using the 165mm cranks on my main bike was hardly a problem. Now it could be that there are other factors to consider, such as weather and my own physical condition on the day, so the feeling is subjective. But for me, I'm happy that crank difference does make a difference to me and as a consequence I've been and ordered some 165mm Rotor 3D cranks for the second bike.

cswitch

Well if something feels good then totally agree thats what counts. Just wondered if they had affected cadence as I hear crank length often does. Would be interesting to see if overtime they do increase your cadence.

John.T

Disregarding the slanging match what you have found pretty much supports what I said some time back. It is what length you feel comfortable with that matters, not some silly 'method'. These will always be right for someone but wrong for many more. As the Cervelo tests showed within the normal band of lengths there was very little power difference but different riders preferred certain lengths.

pinno

In a moment of madness before the Caledonia Etape, knowing my legs were not as good as they should and the total amount climbing was going to test me, I switched to a compact 170mm crankset.
Despite completing the Etape with more ease than I thought, it was plain horrible having ridden 175's for years.

Prior to this, after numerous ops, I went to the gym to use the squat, leg press and leg curl machines to increase muscle and strength. No weights added, just the resistance of the equipment was sufficient for 15 sets plus of 40 reps at varying speeds. It worked, except the downside was decreased cadence. I hoped that the shorter crank arms would have helped counteract this.
After talking to a fitness instructor, he explained that by doing all that gym work, I would have shortened the muscle but increased my strength.
It took some 2 seasons to get the cadence back but assisted by going back to 175mm crank arms.

I was offered a Campag chainset for a good price, the downside is that they are 177.5's. I bought them on the reasoning that 2.5mm is negligible. They are fitted to my C40 . I haven't taken it out yet. We shall see...

balthazar

cswitch wrote:

Well if something feels good then totally agree thats what counts. Just wondered if they had affected cadence as I hear crank length often does. Would be interesting to see if overtime they do increase your cadence.

When I rode with accidentally mismatched cranks I found my left cadence was 0.29% higher than my right.

StillGoing

cswitch wrote:

Well if something feels good then totally agree thats what counts. Just wondered if they had affected cadence as I hear crank length often does. Would be interesting to see if overtime they do increase your cadence.

Cadence has increased from a normal average of around high 70's rpm to an average of high 90's rpm over the course. The nay sayers will argue this is merely down to more time on the bike, but I had almost a years lay off last season for one reason or another. It also doesn't take into account the different pedaling styles of spinning or grinding. Are shorter cranks going to benefit those who prefer to grind out big gears for instance at a low cadence?

I fully agree with John T in that power is not increased or decreased with shorter cranks; the crank is merely the lever that makes the pedal go around, but it is the feel for the effort to do it and the shortened dead spot at the top of the pedal action that matters. Using a power meter and cadence measure during the test simply guarantees that you're using the same efforts to be able to apply your feel for the different length cranks. If the test was a blind test, it would have been even better, but unfortunately I did know which length cranks were on the bike each time, which some would argue renders the test unqualified as an argument. I'd counter that by the fact that it was my money that was going to shell out for a shorter crank set so why would I say it felt better using shorter cranks and a £200+ bill if I wasn't genuinely convinced?

John.T

Talk of a shortened 'dead spot' is a red herring. Proportionally it does not change. What does change is the rotational foot speed relative to cadence. The only way to change the dead spot is by using non round rings.
If you stay within the more usual 170/175 length you will probably not notice any difference other than in the first 5 minutes of changing. All the formulae for calculating crank length are basically rubbish as if they were not then they would all agree. Shorter legs (not necessarily shorter riders) need shorter cranks. That is all you need to know.

mmacavity

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

John.T

mmacavity wrote:

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

I am always wary of claims attached to a product maker. They want to sell you something. I can not say about the power advantage he claims as other reports refute this. Mike Burrows is a big fan of short cranks but I see little evidence of them being taken up mainstream.
His aero claims are incomplete as he ignores the increase in frontal area from raising the saddle and getting too low at the front can make bike handling more difficult as well as causing neck and visibility problems. I regularly ride TT events with some of the best in the country and while there is considerable discussion about the merits of going shorter most are still talking in the 165/170 range as the shortest. When I see top riders using below 160s and improving their times I will take notice but not until then.