Does crank length matter?

[Paulus]

What if any would be the difference between 172.5 and 175 length cranks, apart from the slightly greater circumference in the pedal stroke?

 

[Milkfloat]

2.5mm

 

[Deleted member 1258]

My geared bike has 170's on it, my fixed has 165's, they feel the same. On the fixed the difference between a 170 and a 165 is descending, the 165's feel more comfortable.

 

[Milkfloat]

Now being serious - very little, I doubt you would even notice. If you are hyper sensitive you may want to increase the saddle height by 2.5mm.

 

[Deleted member 26715]

It will depend on what level of cyclist you are, social, nothing, amatuer race, little, top flight sportsman possibly quite a bit. I also suspect that if you are riding huge distances then that extra 5mm per revolution might make it more comfortable.

When I had my bike fit, I was told I could do with the extra length, but it wasn't important, but if I were going to replace the cranks then he suggested I went with the longer ones next time.

 

[Racing roadkill]

The longer pedal stroke on a 175 mm crank will force the knee to do things it’s not designed to do, if your leg proportions don’t necessitate it. You lose a bit of leverage with the shorter cranks, but the physiological gains are far more beneficial than a bit of leverage. Most people who don’t need a long crank, find it easier and more comfy to maintain a more efficient high cadence with a shorter crank as well. The biggest difference most people notice when going short, is the effect when ‘pushing off’ from a standing start ( particularly on an incline ) you don’t get as much impulse, so you don’t get as much time to sort your feet out, before you grind to a ( usually ) undignified stop.

 

[Venod]

If you go from 172.5 to 175, assuming you have your seat at the optimum height with 17.5 you will have to lower it to maintain the same reach at the bottom of the stroke, its a minefield really, as I am a spinner I use 170 but have ridden 175 and can't say I notice the difference.

https://cyclingtips.com/2017/09/crank-length-forget-leverage-power-fit/

 

[Ajax Bay]

that extra 5mm per revolution might make it more comfortable . . . When I had my bike fit, I was told I could do with the extra length,

May I enquire on what basis you opine the first part? Why do you think longer cranks are more comfortable than shorter cranks? At the bike fit, how long were your cranks (which they suggested would be better longer) and what's your inside leg measurement?
And surely it'd be an extra 8mm anyway.
SteveHoggbikefitting.com/bikefit/2011/06/crank-length-which-one/
Rodale, 2005. 2005. Bicycling Magazine's Training Techniques for Cyclists

 

[Deleted member 26715]

May I enquire on what basis you opine the first part? Why do you think longer cranks are more comfortable than shorter cranks? At the bike fit, how long were your cranks (which they suggested would be better longer) and what's your inside leg measurement?
And surely it'd be an extra 8mm anyway.

If your natural length is to have 180mm over 175mm or whatever, then I would have thought that they would be more comfortable for you. As to what the cranks were compared to what are on unfortunately I can't remember it was about 5 years ago, but the bike was a 2013 Giant Defy 5 if you wish to google what are on it. As to 5mm over 8mm logic was 2.5mm at the bottom of the stroke & 2.5mm at the top, but if that is calculated wrong please enlighten me

 

[Ajax Bay]

If your natural length is to have 180mm over 175mm or whatever, then I would have thought that they would be more comfortable for you.

But why? What do you understand or mean by 'natural length'?
5mm > 8mm - I refer the honourable member to @vernon (late OTP)'s favourite dish / greek letter.

 

[Rooster1]

I went from a 175 to a 172.5 and I did notice initially that I had to work a little harder for some reason. The shorter length did not suit the way I had got used to turning the pedals. However, a few weeks later and I don't notice the difference as I have got used to it.

 

[Deleted member 26715]

5mm > 8mm - I refer the honourable member to @vernon (late OTP)'s favourite dish / greek letter.

Please stop trying to be clever if you want to say PI then just type it, however in this instance in my mind it has nothing to do with it as we are referring to the diameter of a circle not area nor circumference, but as I asked before if I am wrong please explain.

 

[glasgowcyclist]

I'm as curious as the OP because in another thread, where I was looking for a crankset to replace my old FC-M510 175mm, I was asked this:

As an aside, why do you want 175mm cranks - are you 1.90+m?

Is crank length choice to be made in relation to a rider's height? For what it's worth, 175mm cranks were fitted to the bike from new and I'm not even close to 1.9m tall.

 

[Ajax Bay]

that extra 5mm per revolution

Sorry - I thought you were talking about a crank revolution, not diameter.
'Natural length'?

 

[Racing roadkill]

Typically, with a shorter crank you can get a better lean angle without risking grounding the pedal as well, which is useful for tight, Crit circuits, and can’t hurt with being able to corner faster and being able to pedal through the corners in road rides either.