crank length

jaffa666
jaffa666 Posts: 36
edited August 2012 in Road general
hi iv been riding a 172.5 crank now for10 years with out any probs but recently went for a bike fit and was told my ideal size is a 170.can anyone tell me would this make any difference at all to my cycling etc more power ,more comfort.is it worth me shelling out a 100 quid on a new chainset.
thanks.

Comments

  • BruceG
    BruceG Posts: 347
    none whatsoever save your money
  • styxd
    styxd Posts: 3,234
    none whatsoever save your money

    Obviously there is a difference, whether you notice it enough to justify the cost is upto you.
  • Hoopdriver
    Hoopdriver Posts: 2,023
    styxd wrote:
    none whatsoever save your money

    Obviously there is a difference, whether you notice it enough to justify the cost is upto you.
    Yes there will be a difference, a subtle one. If you're happy with your present crank and are having no troubles, i'd leave well enough alone. A hundred quid would be better spent elsewhere, me thinks.
  • danowat
    danowat Posts: 2,877
    Depends what sort of riding you do, and how you ride currently, there are gains to be made for people who race, don't think its worth a whole new crankset if you don't race though.
  • I find crank size makes a significant difference. I wouldn't go with a generic chart though - theoretically I should be riding 172.5 mm cranks but I prefer, and am faster with, 175 mm cranks. The only way to find out for sure is to actually try different size cranks and work out what's best for you.
  • P_Tucker
    P_Tucker Posts: 1,878
    I find crank size makes a significant difference. I wouldn't go with a generic chart though - theoretically I should be riding 172.5 mm cranks but I prefer, and am faster with, 175 mm cranks. The only way to find out for sure is to actually try different size cranks and work out what's best for you.

    No, the only way to find out is to do a well conceived scientific experiement, or read the findings of someone who has.
  • neeb
    neeb Posts: 4,467
    P_Tucker wrote:
    No, the only way to find out is to do a well conceived scientific experiement, or read the findings of someone who has.
    Do you do this when you're deciding what size shoes to wear?
  • oldwelshman
    oldwelshman Posts: 4,733
    styxd wrote:
    none whatsoever save your money

    Obviously there is a difference, whether you notice it enough to justify the cost is upto you.
    The difference will not be noticed riding. if it would you would notice it wearing different thickness socks :D
  • P_Tucker
    P_Tucker Posts: 1,878
    neeb wrote:
    P_Tucker wrote:
    No, the only way to find out is to do a well conceived scientific experiement, or read the findings of someone who has.
    Do you do this when you're deciding what size shoes to wear?

    No need; all my shoes are the same size.
  • Flexisurfer
    Flexisurfer Posts: 249
    I found a significant difference going from 170 to 172.5, my legs felt less restricted and easy of which I can sit at a higher pace an smoother cadence is noticeable. I needed a new chain set and one came up at 50% off in a sale so it wasn't a hard decision. I had been riding with the 170 for about 7 years.
  • smidsy
    smidsy Posts: 5,273
    I found a significant difference going from 170 to 172.5, my legs felt less restricted and easy of which I can sit at a higher pace an smoother cadence is noticeable. I needed a new chain set and one came up at 50% off in a sale so it wasn't a hard decision. I had been riding with the 170 for about 7 years.

    Surley that just means your saddle height was slightly wrong?
    Yellow is the new Black.
  • BruceG
    BruceG Posts: 347
    I found a significant difference going from 170 to 172.5, my legs felt less restricted and easy of which I can sit at a higher pace an smoother cadence is noticeable. I needed a new chain set and one came up at 50% off in a sale so it wasn't a hard decision. I had been riding with the 170 for about 7 years.
    If you are such an accomplished rider that this 2.5mm difference made such a profound affect on your riding, and assuming your saddle height as pointed out above was correct, then I suggest you get in touch with Mr Brailsford straight away, you could replace Cav or Froome depending on which one goes first.

    However I think you will find it is PLACEBO effect
  • styxd
    styxd Posts: 3,234
    BruceG wrote:
    I found a significant difference going from 170 to 172.5, my legs felt less restricted and easy of which I can sit at a higher pace an smoother cadence is noticeable. I needed a new chain set and one came up at 50% off in a sale so it wasn't a hard decision. I had been riding with the 170 for about 7 years.
    If you are such an accomplished rider that this 2.5mm difference made such a profound affect on your riding, and assuming your saddle height as pointed out above was correct, then I suggest you get in touch with Mr Brailsford straight away, you could replace Cav or Froome depending on which one goes first.

    However I think you will find it is PLACEBO effect

    What are you on about? Accomplished rider? Eh? Where did they say that?

    The fact is, some people are more sensitive to bike setup than others.

    If you've been riding with the same setup for seven years then a slight change to this will obviously be noticeable.

    Placebo effect or not, if it makes you faster/more comfortable then it doesnt really matter.
  • BruceG
    BruceG Posts: 347
    it does matter if you espouse such nonsense which ultimately misleads other people. So presumably if this guy is so sensitive to a couple of mm he was having to constantly alter his set up as he used socks of differing thickness, and as his cleats wore out
  • neeb
    neeb Posts: 4,467
    I certainly noticed going from 175 to 170, although when I went from 170 to 172.5 I couldn't say whether any subjective difference was due to that or other factors. However I can easily believe that it's something you could notice.

    Remember the 2.5mm is on each crank, so your feet end up a further 5mm apart when pedaling (the diameter of the pedaling circle increases by 5mm). That's quite a lot more than the thickness of a pair of socks, and besides, things like shoes, socks and stack height in general don't change the diameter of the pedaling circle, they just move the circle upwards - completely different thing. That said, when I got a 3mm wedge put under my left foot to partially compensate for a leg length difference it was REALLY noticeable at first, so I'm prepared to believe that that sort of level of difference in the pedaling circle could be noticeable too.
  • BruceG
    BruceG Posts: 347
    neeb wrote:
    I certainly noticed going from 175 to 170, although when I went from 170 to 172.5 I couldn't say whether any subjective difference was due to that or other factors. However I can easily believe that it's something you could notice.

    Remember the 2.5mm is on each crank, so your feet end up a further 5mm apart when pedaling (the diameter of the pedaling circle increases by 5mm). That's quite a lot more than the thickness of a pair of socks, and besides, things like shoes, socks and stack height in general don't change the diameter of the pedaling circle, they just move the circle upwards - completely different thing. That said, when I got a 3mm wedge put under my left foot to partially compensate for a leg length difference it was REALLY noticeable at first, so I'm prepared to believe that that sort of level of difference in the pedaling circle could be noticeable too.
    Really? I suggest you you might want to re think that. How on earth would incresing the radial length of a circle have any effect on the position of its rotating axis??? and why should it make any difference how the radial length is altered, ie crank length or sock thickness, it is still an alteration of the dimension.
    WOW its like the madness of king George in here sometimes
  • drlodge
    drlodge Posts: 4,826
    BruceG wrote:
    neeb wrote:
    I certainly noticed going from 175 to 170, although when I went from 170 to 172.5 I couldn't say whether any subjective difference was due to that or other factors. However I can easily believe that it's something you could notice.

    Remember the 2.5mm is on each crank, so your feet end up a further 5mm apart when pedaling (the diameter of the pedaling circle increases by 5mm). That's quite a lot more than the thickness of a pair of socks, and besides, things like shoes, socks and stack height in general don't change the diameter of the pedaling circle, they just move the circle upwards - completely different thing. That said, when I got a 3mm wedge put under my left foot to partially compensate for a leg length difference it was REALLY noticeable at first, so I'm prepared to believe that that sort of level of difference in the pedaling circle could be noticeable too.
    Really? I suggest you you might want to re think that. How on earth would incresing the radial length of a circle have any effect on the position of its rotating axis??? and why should it make any difference how the radial length is altered, ie crank length or sock thickness, it is still an alteration of the dimension.
    WOW its like the madness of king George in here sometimes

    Increasing the radial length does not affect the the position of its rotating axis, but it does change the radius/diameter of the circle that the pedals make. Unlike thicker socks which is the same difference as changing the seat height by the same amount - does not affect the radius/diameter of the circle that the pedals make.

    I'm going from 170mm (old bike) to 172.5mm (new bike), so the seat post on new bike will need to be 2.5mm lower in relation to the bottom bracket in order that the pedals at the lowest position give the same distance. But then each foot will travel 5mm higher and have a pedalling radius that is 2.5mm greater. I have no idea what difference it will make, perhaps it will lower my natural cadence slightly and give me a bit more torque going uphill.

    I was told by the bike shop that 172.5mm is now "the norm", I'm around 5'9" with proportionally longer legs/shorter torso than normal.
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  • jonomc4
    jonomc4 Posts: 891
    I had 175 for 2 years and changed to 172.5 - it did feel better to me and my cadence definitely went in the right direction. But I wouldn't buy a new chainset just for the change.
  • slowondefy2
    slowondefy2 Posts: 348
    Sole/sock thickness vs Crank length clearly have different effects on the pedalling action. Increase in sole thickness will lift the foot both at the bottom and top of the stroke, requiring an increase in saddle height to maintain the same leg extension (at all parts of the stroke). Increase in crank length will lift the foot at the top of the stroke, and lower the foot at the bottom of the stroke - you can lift the saddle to maintain the same leg extension at the top of the stroke, or lower the saddle to maintain the same leg extension at the bottom of the stroke.

    An increase in crank length makes the foot travel further, whereas increase in sole-thickness doesn't.
  • StillGoing
    StillGoing Posts: 5,211
    I went from 172.5 to 165 cranks and it is more comfortable for me with much less pain to knees and hip/lower back. My saddle was also raised as the shorter cranks mean I am no longer over extending at the bottom of the pedal stroke and as a consequence gain more clearance at the top. It was worth it for me but maybe not for everyone.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • neeb
    neeb Posts: 4,467
    Sole/sock thickness vs Crank length clearly have different effects on the pedalling action. Increase in sole thickness will lift the foot both at the bottom and top of the stroke, requiring an increase in saddle height to maintain the same leg extension (at all parts of the stroke). Increase in crank length will lift the foot at the top of the stroke, and lower the foot at the bottom of the stroke - you can lift the saddle to maintain the same leg extension at the top of the stroke, or lower the saddle to maintain the same leg extension at the bottom of the stroke.

    An increase in crank length makes the foot travel further, whereas increase in sole-thickness doesn't.
    Exactly. Increase in sole thickness raises the circle described by the foot when it rotates, without changing the diameter of that circle. The foot is effectively rotating around an (invisible) axis that is now slightly further above the centre of the bottom bracket. Increase in crank length, however, increases the diameter of the circle described by the foot.
    BruceG wrote:
    Really? I suggest you you might want to re think that. How on earth would incresing the radial length of a circle have any effect on the position of its rotating axis???
    It doesn't. But it's only the change in crank length that increases the radial length of the circle described by the foot, a change in stack height (i.e. socks etc) doesn't.
    BruceG wrote:
    and why should it make any difference how the radial length is altered, ie crank length or sock thickness, it is still an alteration of the dimension.
    No it's not, see above...
    BruceG wrote:
    WOW its like the madness of king George in here sometimes
    Sanity is overrated.. :wink:
  • dw300
    dw300 Posts: 1,642
    If you feel like youre stretching for the bottom of the stroke, but your thighs hit your chest when you're in your aero position, then crank lengths could make a difference.

    Also, if your seat is slammed forward and you can't quite get your knees over your cranks like you should, then shorter cranks would get your bikefit better. If you have short legs but a long torso this could be likely, and a smaller frame would not solve the problem.

    If you want more ground clearance in corners during crits so you can get the power down sooner with less risk, then shorter cranks could suit.

    People think that since power gains aren't there, there's no benefit to different length cranks.
    All the above is just advice .. you can do whatever the f*ck you wana do!
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  • oldwelshman
    oldwelshman Posts: 4,733
    dw300 wrote:
    If you feel like youre stretching for the bottom of the stroke, but your thighs hit your chest when you're in your aero position, then crank lengths could make a difference.

    Also, if your seat is slammed forward and you can't quite get your knees over your cranks like you should, then shorter cranks would get your bikefit better. If you have short legs but a long torso this could be likely, and a smaller frame would not solve the problem.

    If you want more ground clearance in corners during crits so you can get the power down sooner with less risk, then shorter cranks could suit.

    People think that since power gains aren't there, there's no benefit to different length cranks.
    Personally I dont think 2.5mm will make any difference to the thighs hitting chest and bottoming out on pedal downstroke, more likely to be incorrect stem length and stack height. Many people lowers their stack height too far thinking it will be more aero but often you end up with thighs into chest.
  • dw300
    dw300 Posts: 1,642
    dw300 wrote:
    If you feel like youre stretching for the bottom of the stroke, but your thighs hit your chest when you're in your aero position, then crank lengths could make a difference.

    Also, if your seat is slammed forward and you can't quite get your knees over your cranks like you should, then shorter cranks would get your bikefit better. If you have short legs but a long torso this could be likely, and a smaller frame would not solve the problem.

    If you want more ground clearance in corners during crits so you can get the power down sooner with less risk, then shorter cranks could suit.

    People think that since power gains aren't there, there's no benefit to different length cranks.
    Personally I dont think 2.5mm will make any difference to the thighs hitting chest and bottoming out on pedal downstroke, more likely to be incorrect stem length and stack height. Many people lowers their stack height too far thinking it will be more aero but often you end up with thighs into chest.

    Possibly, but it will make 2.5mm worth of difference, or 5mm or 10mm depending on what's on the bike as standard. It could makes things slightly more comfortable. But I think the fore and aft difference would be more significant.

    I'm thinking more of a senario of when you buy a bike, but might want a shorter crank version, when the one is the shop is a 175 as they always seem to be. If you're not paying extra for it, why would you choose an unsuitable one?

    Obviously i'd recommend anyone to think twice if they're upgrading a Dura Ace crankset, unless they're a CEO.
    All the above is just advice .. you can do whatever the f*ck you wana do!
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