Crank length (can of worms).

[Hacienda71]

There's absolutely no way that 2.5mm on the crank will make any difference to your climbing ability.

There's a school of thought (and I have no reason to disbelieve it, particularly because Boardman thinks it) that shorter cranks (150mm) make the rider more aero. I expect this to be utilised in the next couple of years, probably by track riders first.

I have it on pretty good authority that Stannard is already using shorter cranks.

 

[nickyboy]

I can understand the aero argument for shorter cranks

But crank length in itself will not influence how quickly a cyclist can climb up a hill. A rider can produce X watts/kg. That's the main thing that influences climbing speed. Crank length doesn't alter your watts/kg

So if you maintain the same gearing, all that matters is can you maintain the same rpm of your cranks for different crank lengths? Of course longer cranks feel easier but you have to move the pedals more quickly to keep the same rpm as shorter cranks. These factors balance each other out

 

[Sharky]

I can understand the aero argument for shorter cranks

But crank length in itself will not influence how quickly a cyclist can climb up a hill. A rider can produce X watts/kg. That's the main thing that influences climbing speed. Crank length doesn't alter your watts/kg

So if you maintain the same gearing, all that matters is can you maintain the same rpm of your cranks for different crank lengths? Of course longer cranks feel easier but you have to move the pedals more quickly to keep the same rpm as shorter cranks. These factors balance each other out

Not quite,
Shorter cranks have less leverage, so you need to ride a lower gear, to give the same leverage. But because the pedal circumference is now smaller, the cadence increases, even though the pedal speed remains the same. Net result is that you travel at the same speed.

Another consideration is the rider's power output. This can't change, can it? Well consider the application of power. This is not the same throughout the 360 degree pedal rotation. When the knee is at it's most bent position, it is difficult to apply maximum power. This is somewhere on the down stroke as the knee is unbending. When you start riding with short cranks, you raise the saddle and end up with less bend at the knees, therefore the part of the pedal stroke at optimum power output can increase.

When it comes to the hills, it means you can stay in the saddle for longer and the hills do become easier.

For the record, I've been on 150mm cranks for a couple of years and really get on well with them.

 

[nickyboy]

Not quite,
the cadence increases, even though the pedal speed remains the same.

Not sure I understand this. When you increase cadence the speed your pedals are moving increases surely?

 

[Tigerbiten]

Not sure I understand this. When you increase cadence the speed your pedals are moving increases surely?

If you double the length of the cranks then you only need half the cadence to keep the same pedal speed.

 

[adscrim]

Not sure I understand this. When you increase cadence the speed your pedals are moving increases surely?

Only if the size of the circle the pedal is travelling remains the same. If you increase the cadence but shorten the crank length (radius) then the pedal completes the circle in less time but has travelled a shorter distance, so the speed the pedal is moving at is effectively the same.

 

[pvwnbroker]

So i just wanted to get peoples opinions,

During winter i ride a 1992 Dawes Impulse with 11 speed 105 crank length 170.

I recently purchased a Trek Emonda SL8 11 speed dura ace crank length 172.5. To ride in summer etc.

I seem to be able to climb better on the Dawes which strikes me as odd considering the Emonda is much much much lighter. I also seem to be more comfortable on the Dawes and get a lot of lower back pain on the Emonda.

The only difference in set up bar geometry etc is the crank length.

Could this be an issue stopping the Emonda perform? Or could it just be my fit on the Emonda. Or something else i have overlooked?

Thanks in advance,

Callum

Hello I have a quick question if anyone can help me

when I'm buying a left crank to match my right crank, all I'm concerned about is the length ?
is there other factors that will make my cranks uneven ? for example the bend on the crank and stuff?

thank you!