Crankset Size

[Rich]

What difference does the size of the crank make in the bike set-up ie. 170 or 172.5 or 175mm? Does it affect power or overall bike size and what is preferable or does it depend on leg size and bike size?

[Johan Bornman]

It doesn't make much difference. The human body is pretty adaptable and we easily lengthen or shorten our stride or quicken our pace to adapt to different conditions. For instance, see how easily we adapt to stairs that are of different size. If this weren't so, taller people would find some stairs uncomfortable and shorties other stairs.

 

Some people here will argue that they can feel a difference of 2,5 mm but I question that. And even if they can feel a difference, what is the difference? I've played some tricks on friends where I had a long crank and short crank on the same bike and no-one noticed the extra 2,5mm.

 

Others will argue that they can recommend the right size by doing a set-up exercise. I question their arguments too.

 

Power is generated by your muscles  and no external gadget will increase that power.

 

A longer crank gives you more leverage, but so does a lower gear.

 

I ride whatever is fitted to the bike.

 

 

 

 

 

[The Saint]

Thanks Johan...notwithstanding my stupid question on the previous thread I could never understand why cranks are made in different lenghts. To my it was always all about raising or lowering the seat to compensate.

[Canaris]

To go against accepted knowledge.  It has been generally accepted (broad generalisation) that the leg loses the ability to generate power as soon as the knee is bent more than 90%.  Therefore, crank length is restricted by the length of key bones in the leg (read femur).  So yes, a longer crank will give you more leverage, but it may also give you knee problems as well.

[Johan Bornman]

To go against accepted knowledge.  It has been generally accepted (broad generalisation) that the leg loses the ability to generate power as soon as the knee is bent more than 90%.  Therefore' date=' crank length is restricted by the length of key bones in the leg (read femur).  So yes, a longer crank will give you more leverage, but it may also give you knee problems as well.[/quote']

 

I hope someone with a good knowledge of biokinetics and anatomy chips in here. I believe that the relative difference of a tall and short person's femur isn't as much as the relative difference between their overall lengths. Thefore, most of us shouldn't have a hassle whether we have a 170, 172,5 or 175mm crank. The extra 5mm in the pedaling radius doesn't change the angle of the femur at the top of the circle much.

 

I would however agree that a leg doesn't like to work at acute angles.

[Rich]

So if I had to choose between 170mm and 175mm I should choose 170mm and rather adjust the bike set up?

[TNT1]

 

 

So if I had to choose between 170mm and 175mm I should choose 170mm and rather adjust the bike set up?

 

http://www.machinehead-software.co.uk/bike/cranks/cyclist_crank_length_calculator.html

 

http://www.cptips.com/crnklth.htm

 

http://www.nettally.com/palmk/crankset.html

 

 

 

 

TNT12008-07-07 08:21:42