Short Cranks vs Big Cranks, Which is Better?

[Citius]

Wow thats short! do you ride with a very high cadence or have a short inseam?

Let's not forget that for a given gear size, cadence is identical regardless of crank length.

 

[MichaelW2]

Let's not forget that for a given gear size, cadence is identical regardless of crank length.

How can you maintain your fastest cadence of you switch to a longer crank. Your feet will have to travel faster around a bigger circle.

At a constant power output, and constant pedaling force, you would rotate longer cranks more slowly, in a higher gear to ride at the same speed.

 

[FrankCrank]

....heh heh - indeed a can of worms. I use normal size on my MTB's, and 140mm on my bents. Can't be bothered to explain any rationale, just they work for me.......

 

[Citius]

How can you maintain your fastest cadence of you switch to a longer crank. Your feet will have to travel faster around a bigger circle.

I think you are over-estimating the effect that 10mm-20mm on the crank length would have on cadence. Think about it. Trivially though, your cadence for a given speed in a given gear is identical regardless of crank length. It has to be.

At a constant power output, and constant pedaling force, you would rotate longer cranks more slowly, in a higher gear to ride at the same speed.

Your legs may travel marginally faster around a bigger circle. But they still rotate one full circle in the same amount of time as a shorter crank, obviously. Which is why I said cadence is the same. Because it is.

Again though, I think you are over-estimating the effect that longer cranks can have.

 

[Dogtrousers]

Sheldon says: I think people really obsess too much about crank length. After all, we all use the same staircases, whether we have long or short legs. Short legged people acclimate their knees to a greater angle of flex to climb stairways, and can also handle proportionally longer cranks than taller people normally use.

I do remember some time back reading an article about Cav being very picky about his crank lengths, but at the time he was winning GT stages for fun, so he had the right to be picky about anything and everything.

 

[MichaelW2]

Work is distance x force. If your force is constant and your distance (circumference) s greater, you are doing more work. Your body cannot just output more power for longer cranks (otherwise it would output more power for smaller cranks as well). You don't go faster if you change crank length. What gives? The variable is not power, but cadence.
You are fixing the wrong factor. As you change crank you change gearing but your body's power output doesn't alter

 

[derrick]

A friend of mine has just recently put shorter cranks on and after a couple of rides her knees stopped hurting, She is quite short about 5ft. But she could not believe how much better she feels. So i would think if you have short legs and you are experiencing knee problems shorter cranks could be the way to go.

 

[derrick]

Sheldon says: I think people really obsess too much about crank length. After all, we all use the same staircases, whether we have long or short legs. Short legged people acclimate their knees to a greater angle of flex to climb stairways, and can also handle proportionally longer cranks than taller people normally use.

Does Sheldon spend all day climbing stairs. It normally takes me about 20 seconds to climb our stairs, I can spend 8 plus hours on a bike.

 

[A.Z.KOETSIER]

From what I can gather it seems situations with relatively constant cadence and resistance, like long climbs and the the Hour/TT, riders chose to increase their crank length.

Pantani (short rider) switching to 180s on climbs
Indurain (tall rider) switching to 190s in the Hour
Cancellera going up 2.5mm in TTs

In situations where leg speed and quick acceleration is more important riders decrease crank length, Like Wiggins who mostly rode on 177.5mm now he is on 170s as he prepares for Rio.

In my experience with trying different cranks (165-200mm) it has also worked out the same with my best climbing results on longer cranks and best sprints/crits and on shorter cranks. and as mentioned before i could go tremendously faster on rollers with short cranks.

shorter cranks are also more comfortable.

 

[Citius]

Work is distance x force. If your force is constant and your distance (circumference) s greater, you are doing more work. Your body cannot just output more power for longer cranks (otherwise it would output more power for smaller cranks as well). You don't go faster if you change crank length. What gives? The variable is not power, but cadence.
You are fixing the wrong factor. As you change crank you change gearing but your body's power output doesn't alter

Not sure who you are talking to, or what point you are trying to make.

 

[Citius]

From what I can gather it seems situations with relatively constant cadence and resistance, like long climbs and the the Hour/TT, riders chose to increase their crank length.

Pantani (short rider) switching to 180s on climbs
Indurain (tall rider) switching to 190s in the Hour
Cancellera going up 2.5mm in TTs

In situations where leg speed and quick acceleration is more important riders decrease crank length, Like Wiggins who mostly rode on 177.5mm now he is on 170s as he prepares for Rio.

In my experience with trying different cranks (165-200mm) it has also worked out the same with my best climbing results on longer cranks and best sprints/crits and on shorter cranks. and as mentioned before i could go tremendously faster on rollers with short cranks.

shorter cranks are also more comfortable.

Welcome to anecdote central.

 

[MichaelW2]

Not sure who you are talking to, or what point you are trying to make.

You claim that change in crank length has no effect on cadence. It does and you can figure this out by applying very basic physics. If you take the change in crank length to an extreme, compare say a 140mm to a 200mm crank, can you spin these at the same gear combination, at the same cadence?
Crank length is for fit and you select a gear accordingly.

 

[Citius]

You claim that change in crank length has no effect on cadence. It does and you can figure this out by applying very basic physics. If you take the change in crank length to an extreme, compare say a 140mm to a 200mm crank, can you spin these at the same gear combination, at the same cadence?
Crank length is for fit and you select a gear accordingly.

If you pedal 52x15 (other gears are available) at 90rpm (other cadences are available), you will still be doing 90rpm regardless of whether you are on 155mm cranks or 200mm cranks (other crank lengths are available). Whether that crank length is ideal for you is an entirely different matter.

I still think you're getting a bit too anal about something which makes zero practical difference in the real world. If you are sh*t on 170mm cranks, and you change to 150mm, or even200mm, you will still be sh*t.

 

[Arsen Gere]

Age could be a factor too. Since heart rate is proportional to cadence, older folks don't have the range of heart rate so spinning small cranks fast may not be as efficient for everyone. Similarly muscle types can be a factor.

 

[Citius]

Heart rate is generally proportional to physical effort. Pushing a big gear hard at a low cadence will still induce a high HR.