Crank arm length

jaybo1973
jaybo1973 Posts: 301
edited April 2011 in MTB buying advice
Hi

I am getting a deore M590 hollowtech 2 chainset. Didn't realise they came in 2 sizes though; 170 mm and 175mm. Not sure why. Hence, which would more suitable. Can anyone advise please? 5mm doesn't seem a lot.

Comments

  • nicklouse
    nicklouse Posts: 50,673
    the same size as you have now.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
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  • cooldad
    cooldad Posts: 32,599
    Will be staomped into the back of the crank arms.
    I don't do smileys.

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  • jaybo1973
    jaybo1973 Posts: 301
    Nice one. 175 then
  • The Rookie
    The Rookie Posts: 27,812
    Someone with shorter legs may want a shorter crank (so crank length to leg length ratio is similar), also single speeders often go for shorter cranks to reduce 'foot speed' when at max speed.

    For an average male 175 is fine, but unless your on the tall side if you can get 170's for less then get them!

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • jaybo1973
    jaybo1973 Posts: 301
    Cheers Simon. I am 6'1 but if 175 is the common size, ill go with that. Never knew there were different sizes so 175 as always been ok.
  • Uchiga
    Uchiga Posts: 230
    Also keep crank length consistant on all bikes, your body gets used to a certian crank length, I have 175mm SLX crabnks on my XC bike but my singlespeed Carrera came with 170mm cranks, i've been a bad boy and have been swapping between the two quite regularly and my body doesnt like it but since ive changed to my old M590 Deore cranks which came off my Scott and are 175mm my legs are happier. Not to mention the performance upgrade as a result was exceptional!
    Scott Aspect 45 (2008)
    Carrera Subway 1 Singlespeed
    2011 CR1 Comp
  • jaybo1973
    jaybo1973 Posts: 301
    So I need a cassette too. 2 options in this too. 11-32 and 11-34. Again. Don't know the difference
  • sniper68
    sniper68 Posts: 2,910
    jaybo1973 wrote:
    So I need a cassette too. 2 options in this too. 11-32 and 11-34. Again. Don't know the difference
    11-34 gives you a higher ratio in 1st.Unfit feckers like me prefer this to the 11-32.
    Lynskey R480

  • paul20v
    paul20v Posts: 267
    Uchiga wrote:
    Also keep crank length consistant on all bikes, your body gets used to a certian crank length, I have 175mm SLX crabnks on my XC bike but my singlespeed Carrera came with 170mm cranks, i've been a bad boy and have been swapping between the two quite regularly and my body doesnt like it but since ive changed to my old M590 Deore cranks which came off my Scott and are 175mm my legs are happier. Not to mention the performance upgrade as a result was exceptional!
    I asked this question yesterday
    are you really saying you noticed a 5mm difference in the crank length ?
    i ask as ive been running 175s and ive decided to go for 170s .
  • jaybo1973
    jaybo1973 Posts: 301
    ibbo68 wrote:
    jaybo1973 wrote:
    So I need a cassette too. 2 options in this too. 11-32 and 11-34. Again. Don't know the difference
    11-34 gives you a higher ratio in 1st.Unfit feckers like me prefer this to the 11-32.

    Unfit? I'm with you on that one ;)
  • cooldad
    cooldad Posts: 32,599
    Just swapped 11-32 to 11-34. Gives an extra ratio before you wimp out into granny.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

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  • jaybo1973
    jaybo1973 Posts: 301
    You would wimp to granny if you lived up my road lol. I understand now. But don't understand how the numbers work. Are there 34 teeth on the biggest ring and 11 on the smallest?
  • cooldad
    cooldad Posts: 32,599
    Yes, so you get a lower overall gear with the same highest gear.

    I still wimp to granny a lot, just get a few yards further up the hill.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • Deputy Dawg
    Deputy Dawg Posts: 428
    paul20v wrote:
    Uchiga wrote:
    Also keep crank length consistant on all bikes, your body gets used to a certian crank length, I have 175mm SLX crabnks on my XC bike but my singlespeed Carrera came with 170mm cranks, i've been a bad boy and have been swapping between the two quite regularly and my body doesnt like it but since ive changed to my old M590 Deore cranks which came off my Scott and are 175mm my legs are happier. Not to mention the performance upgrade as a result was exceptional!
    I asked this question yesterday
    are you really saying you noticed a 5mm difference in the crank length ?
    i ask as ive been running 175s and ive decided to go for 170s .
    I noticed the difference in leverage going up hills. Admittedly it wasn't much but every little helps ;)

    170's will give you better ground clearence if your prone to bottoming out though so its all subjective to your reqirements.
    Statistically, Six Out Of Seven Dwarves Aren't Happy
  • Uchiga
    Uchiga Posts: 230
    paul20v wrote:
    Uchiga wrote:
    Also keep crank length consistant on all bikes, your body gets used to a certian crank length, I have 175mm SLX crabnks on my XC bike but my singlespeed Carrera came with 170mm cranks, i've been a bad boy and have been swapping between the two quite regularly and my body doesnt like it but since ive changed to my old M590 Deore cranks which came off my Scott and are 175mm my legs are happier. Not to mention the performance upgrade as a result was exceptional!
    I asked this question yesterday
    are you really saying you noticed a 5mm difference in the crank length ?
    i ask as ive been running 175s and ive decided to go for 170s .

    I definatly felt the differance, for a start it was a lot more comfortable to cycle despite both bikes being set up correctly for their respective crank lengths. It just felt more natural and something my legs are obviously used to. Also the extra leverage on a singlespeed was a nice touch up the hills and to get started because of the relatively tall gearing i ride. (44-16 which has since been changed to a 36-13 the 36-13 being only 0.02 bigger a gear)
    Scott Aspect 45 (2008)
    Carrera Subway 1 Singlespeed
    2011 CR1 Comp
  • peter413
    peter413 Posts: 4,909
    Uchiga wrote:
    Also keep crank length consistant on all bikes, your body gets used to a certian crank length

    Not always, I run 175mm cranks on the 456 and 165mm cranks on the 224 and I am just as comfortable on either bike, don't notice the difference if I'm honest
    Transition Patrol
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  • cavegiant
    cavegiant Posts: 1,546
    The size differences are so subtle you will doubtfully notice any differences (unless you ride road at a high level). I am 6'7 and the only difference I could spot between my wife's deore 160 and my atlas 180 is that the deore is really really flexy. (I borrowed her cranks while mine were being repaired).
    Why would I care about 150g of bike weight, I just ate 400g of cookies while reading this?
  • cat_with_no_tail
    cat_with_no_tail Posts: 12,980
    cavegiant wrote:
    The size differences are so subtle you will doubtfully notice any differences (unless you ride road at a high level). I am 6'7 and the only difference I could spot between my wife's deore 160 and my atlas 180 is that the deore is really really flexy. (I borrowed her cranks while mine were being repaired).

    I agree with this. I changed my old 170mm cranks for 175mm and other than the stiffness thing felt no discernible difference whatsoever.
    "Avan-TT"
    F*cking Fast 29er
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  • meesterbond
    meesterbond Posts: 1,240
    I'd go with Michael Hutchinson's opinion on crank length..... "I don't think crank length makes a flying toss of difference"

    I checked mine last night and the road bike is on 172.5 and the mtb on 175mm. Can't tell the difference in the slightest.
  • CharlieH
    CharlieH Posts: 410
    I went from the standard 175 on both my bikes to 170 SLX and I'm much happier. I don't have the strongest legs and tend to spin easier gears rather than mashing the cranks. The shorter cranks just felt much easier on my legs and shortly after I changed, my riding buddy mentioned that I seem much better on hills than I used to be (but still sh1t slow, lol)

    FWIW I'm 5'8" tall
  • Anonymous
    Anonymous Posts: 79,666
    meesterbond wrote:
    I'd go with Michael Hutchinson's opinion on crank length..... "I don't think crank length makes a flying toss of difference"

    I checked mine last night and the road bike is on 172.5 and the mtb on 175mm. Can't tell the difference in the slightest.
    ^^Very much that. Uchiga has been talking a lot of grandiose nonsense recently. Frankly, if the worl'd top road racers can't tell a difference, even when they're analysed to the nth degree for every possible performance gain, then I call BS.

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