Help settle an argument about crank length.

[Cyclopathic]

I had a discussion with a friend concerning crank length. He seemed to think that a longer crank length (say 175) was harder to pedal than a shorter one (say 170). I think the opposite. I think a longer crank length will mean less force to pedal because it is shifting the same load over a greater distance.
Despite trying to explain this he still insisted that when he tried a longer crank that it was harder work.
I can't really argue against what he said was his personal experience but it does not make sense to me so I wonder if he just imagined it was harder work because he was so convinced that it should have been. I am assuming of course that all else is equal.
Am I right or have I got a helping of humble pie coming my way?

 

[Drago]

You're right.

 

[deptfordmarmoset]

Yup, a longer crank is a longer lever so easier. There was some genius or other who said something like ''Give me a lever long enough and I will move the world.'' Probably longer than 175cm in his case.

 

[Pauluk]

As Drago says, you're right. The longer crank length gives you an effectively lower gear/gain ratio.

http://sheldonbrown.com/gain.html

 

[mickle]

'Harder' is often used when someone means to say 'more difficult'. He could, conceivably, find it more difficult to turn his feet in the radius described by a 175mm crank. But i challenge anyone to detect how long a crank is from the saddle. I thnk he's lying to himself.

 

[Smokin Joe]

'Harder' is often used when someone means to say 'more difficult'. He could, conceivably, find it more difficult to turn his feet in the radius described by a 175mm crank. But i challenge anyone to detect how long a crank is from the saddle. I thnk he's lying to himself.

+1

I rode and raced for years without having a clue how long my cranks were, I probably rode all but 165mm track cranks.

 

[gaz]

It's simple...

Try to open a heavy door from close to the hinge, it is hard work.
Try to open a heavy door from the the side furthest away from the hinge, and it is easier.
It's the same principle.

 

[PaulSecteur]

Before people rush out to get new cranks to help with hills, remember crank length has an affect on bike fit too!

 

[Big boy]

A longer crank gives more torqe for hills etc.
A shorter arm is aparently better for peddling fast on the flat.
That is only what i was told some years back, made some sence as your legs wont have to move up and down so far . (to peddle faster)
None of this will be relavent if along with his shorter crank came higher gearing.
And as someone said it also effects the fit of the bike...

 

[the snail]

I think the opposite. I think a longer crank length will mean less force to pedal because it is shifting the same load over a greater distance.

Yep, presumably you would have to push 175/170ths harder, about 3%?

 

[totallyfixed]

What Bb said more or less, if you have raced on fixed in the same gear but different length cranks you can tell the difference. Longer cranks makes climbing easier but what goes up must come down and believe me hitting 200 rpm on 175's is bed wettingly scary. My mountain bike has 180's on and there isn't much you cannot get up on it and being as I'm not intending to spin my legs like a Kenwood mixer on this bike they work fine.

 

[Deleted member 1258]

'Harder' is often used when someone means to say 'more difficult'. He could, conceivably, find it more difficult to turn his feet in the radius described by a 175mm crank. But i challenge anyone to detect how long a crank is from the saddle. I thnk he's lying to himself.

My fixed has 165's on it, my geared bike has 172.5 on it, they don't feel different, on the fixed when I swapped the 170's for 165's the only difference I noticed was the shorter crank made spinning on a descent easier.

 

[Smokin Joe]

Have a look at a ruler and you'll see that a 5mm difference in crank length has bugger all effect on leverage.

 

[GrasB]

I had a discussion with a friend concerning crank length. He seemed to think that a longer crank length (say 175) was harder to pedal than a shorter one (say 170). I think the opposite. I think a longer crank length will mean less force to pedal because it is shifting the same load over a greater distance.

2 things can be going on here. Firstly larger cranks increase the foot speed & he's getting confused by his muscular feedback to says it harder to pedal. Also he may be riding on cranks which are extending his muscles further than he's used to which means it feels harder as he's utilising an extended range of his muscles.

There is a difference between perceived effort & actual effort. Just because you perceive that you're pushing harder on the pedals doesn't mean you actually are. A great example of this is moving from one riding position to another, you say make a radical fit change on your bike which makes you feel like you can up the effort further, however you look at a power plot & see you're actually pushing out less power. This is fairly typical when road bike riders do a TT bike fit.

Have a look at a ruler and you'll see that a 5mm difference in crank length has bugger all effect on leverage.

Maybe, maybe not. At the same power output & rpm 175mm cranks deliver a 3% reduction in require pedal pressure compared to 170mm cranks. That's about 1/2-1/3 of a 1t gear step. When pushing big gears riders can want sub-1t gearing steps.

 

[Cyclopathic]

Some good points here. I had thought some of these myself but had not been able to articulate them as well or even at all.