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Crank arm lengths

Clever PunClever Pun Posts: 6,778
edited December 2008 in Road beginners
I'm sure I saw someone else ask a similar question a while back so apologies if I missed it.

Does anyone have experience of different sizes?

I've just switched to 175 from 172.5 it feels different and I think it might have dropped my speed a litte, but I was off ill last week and the gym kicked my @ss yesterday so it might be in my mind.

I'm sure the extended rotation will make my legs work harder and be better for it once they are used to the extra motion?

Any links/experiences you be greatly appr

thanks
CP
Purveyor of sonic doom

Very Hairy Roadie - FCN 4
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  • Crank length (within the range of lengths typically available) has very little to no impact on our ability to generate power. Certainly not when comparing only a change of only a couple of mm (provided your position on the bike is suitable).

    The choice of crank length is more a matter of personal preference, type of riding, what feels right and a few other considerations, such as: impacts on aerodynamics (different crank length = different saddle height), toe/front wheel overlap and ground clearance.

    For the record, I ride 165s, 170s and 175s depending on the bike.
  • redddraggonredddraggon Posts: 10,862
    Clever Pun

    Aren't you stupidly tall? 172.5mm cranks I guess would be too short for you anyway.....I use 172.5mm and I'm 5'7ish.
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  • Clever PunClever Pun Posts: 6,778
    Clever Pun

    Aren't you stupidly tall? 172.5mm cranks I guess would be too short for you anyway.....I use 172.5mm and I'm 5'7ish.

    heh, I'm 6'5 if that's what you mean... it just feels a bit odd initially that's all as my legs are coming up a little higher than before... I suspect it's my tiny mind playing tricks on me
    Purveyor of sonic doom

    Very Hairy Roadie - FCN 4
    Fixed Pista- FCN 5
    Beared Bromptonite - FCN 14
  • bill57bill57 Posts: 454
    There have been plenty tales of riders having one crank a different length from the other and not even noticing - who says your legs are both the same length anyway?
    I would have thought that if you raised your saddle by the requisite amount you wouldn't notice your legs "coming up a little higher". I would also have thought that, for 2.5mm, if you left your saddle where it was, you'd be unlikely to notice much either.
  • It's generally the bottom of pedal stroke that people notice the change in reach and hence may need to adjust the saddle accordingly.

    Longer cranks = lower saddle height
  • no, i certainly notice it at the top. My Giant Defy alliance came with 175s. My knees feel like theyre round my ears and i just cant get the same power i could on my old bike.

    It feels like the saddles too low but ive got full leg extension on the bottom of the stroke. changing down to 170s and im 6ft.

    By the way, its not about height, its about inside leg.
    yep, my letter 0 key is bust
  • akcc05akcc05 Posts: 336
    didn't someone say that shorter cranks (165-170mm) are for people who rely heavily on cadence, like most climbers and the signature egg beater style of lance armstrong. while longer cranks (175-180mm) are for power riders like Cipolini and Boonen for better leverage?

    i might be wrong though.
  • Clever PunClever Pun Posts: 6,778
    akcc05 wrote:
    didn't someone say that shorter cranks (165-170mm) are for people who rely heavily on cadence, like most climbers and the signature egg beater style of lance armstrong. while longer cranks (175-180mm) are for power riders like Cipolini and Boonen for better leverage?

    i might be wrong though.

    better leverage makes sense as that's just physics...

    As mentioned earlier I can't move the seat as the bottom of the arc is now longer... guess I better just man up and get used to it :lol:
    Purveyor of sonic doom

    Very Hairy Roadie - FCN 4
    Fixed Pista- FCN 5
    Beared Bromptonite - FCN 14
  • bill57bill57 Posts: 454
    It's generally the bottom of pedal stroke that people notice the change in reach and hence may need to adjust the saddle accordingly.

    Longer cranks = lower saddle height

    Very diplomatic Alex. Should obviously have been in bed hours before.
  • akcc05 wrote:
    didn't someone say that shorter cranks (165-170mm) are for people who rely heavily on cadence, like most climbers and the signature egg beater style of lance armstrong. while longer cranks (175-180mm) are for power riders like Cipolini and Boonen for better leverage?

    i might be wrong though.
    Well, sort of.

    While cadence might tend to increase with a shorter crank, it is somewhat compensated for by a reduction in the distance the pedal travels around the circle (a reduced circumfrence) and hence actual pedal speed may indeed be very similar to a longer crank at lower cadence.

    In any case, it typically doesn't have an effect on cadence for sub-maximal efforts (such as hill climbing).
  • Clever Pun wrote:
    akcc05 wrote:
    didn't someone say that shorter cranks (165-170mm) are for people who rely heavily on cadence, like most climbers and the signature egg beater style of lance armstrong. while longer cranks (175-180mm) are for power riders like Cipolini and Boonen for better leverage?

    i might be wrong though.

    better leverage makes sense as that's just physics...
    Well, if it were torque that was a limiter, then I could believe you, but for most riding that's simply not the case. The forces involved in endurance cycling are simply too low for that to be the case.

    Power is the limiter, not torque applied.

    Indeed, if longer cranks were optimal for sprints, then why for instance would the world's fastest cyclists in track sprinting typically use crank lengths of 165mm, maybe 170mm?

    That's because even in sprinting, it is peak power production that is the limiter, not torque.
  • The choice of crank length is more a matter of personal preference, type of riding, what feels right and a few other considerations, such as: impacts on aerodynamics (different crank length = different saddle height), toe/front wheel overlap and ground clearance.

    You mention front wheel / toe overlap. Amazingly I only recently noticed this while doing a track stand at some lights. I have 175mm cranks, (due to a long inside leg and height) that were fitted on the bike when I bought it. I guess they just supplied it with long cranks / long stem as it was a larger sized frame. Anyway, is this something that should be corrected? Is it considered a bad thing? My bike has (apparently, by comparison with another bike that was reviewed in Pro Cycling) quite a long front center (BB to Front hub distance) anyway, and the pedal axle is right under the ball of my foot, so I don't see that I could correct it very much anyway.
  • octavoctav Posts: 50
    I noticed that Gilberto Simoni uses a 175mm crank(he is 1.70 m tall) and in general all the climbers use bigger crank arms . Lance also uses 175 mm cranks. So the reason is not only the height I assume.
  • derekwatts wrote:
    You mention front wheel / toe overlap. <snip> Anyway, is this something that should be corrected? Is it considered a bad thing?
    It rarely causes a problem, so I wouldn't worry about it. If your riding involves lots of slow speed technical work it might be an issue. If you are forced at speed to turn the front wheel to the extent that it hits your toes, then you have probably crashed already.

    If a bike frame is well fitted to you, then in most cases you won't have any, or a most only a very little, overlap. Unless of course you begin to ride with a mid-foot cleat position, but that is a whole 'nuther red herring.
  • dealdeal Posts: 857
    I have 172.5mm on all of my bikes, 2 road bikes, 1 f/s and 1 hard tail mtb. Tbh i doubt i wouldnt expect to notice any difference if they were a few mm longer/shorter but it makes sence to me to have a consistant size on all my bikes.
  • akcc05akcc05 Posts: 336
    What about thigh length? the ideal position is to have the knee joint directly above (in-line) the pedal axle right? so if your thighs are long but your cranks are short then you will have to move the saddle back to align the knee and the pedals, which in turn changes the weight distribution...so solution = longer cranks?

    am i thinking too much and making things more complicated than they really are?
  • derekwatts wrote:
    You mention front wheel / toe overlap. <snip> Anyway, is this something that should be corrected? Is it considered a bad thing?
    It rarely causes a problem, so I wouldn't worry about it. If your riding involves lots of slow speed technical work it might be an issue. If you are forced at speed to turn the front wheel to the extent that it hits your toes, then you have probably crashed already.

    If a bike frame is well fitted to you, then in most cases you won't have any, or a most only a very little, overlap. Unless of course you begin to ride with a mid-foot cleat position, but that is a whole 'nuther red herring.

    Alex,

    I'm just curious if you'd respond to your last statement about arch cleats being a "red herring"?? in this context of crankarm lengths? Your comment sounds as though you've
    seen or done some experimenting and have been diswaded.

    Let me preface by saying I have returned to cycling this past yr. recovering from DVT
    in my right calf precipitated by a knee injury and some "bad genetics" :-)...

    I'm using the arch cleat position totally from a comfort standpoint as it alleviates the cramping issues I was having with my old position and it works like a charm.
    I'm considering the prospect of racing again this coming year mostly in TTs and the occasional road race. and as I won't be going back to traditional cleat positions, fine tuning this arch position for more performance is something I'd like to pursue... Could you possibly point me to some info/ studies regarding this setup??
    Seems mainstream channels are a bit thin on arch cleat banter...

    Your time is most appreciated,

    Tod Oles
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