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175 to 172.5 crank

ghorswillghorswill Posts: 98
edited May 2014 in Road buying advice
My current crank is 175 on 58cm frame. Can anyone explain what the likely impact on riding performance would be to changing to 172.5 length?
2010 Specialised Sirrus Pro (drop bar conversion)
1993 Specialised Rockhopper A1
Voodoo Limba - for out with the kids

Posts

  • GrillGrill Posts: 5,610
    You may have to raise your saddle a couple mm but you won't really notice any difference whilst riding.
    English Cycles V3 | Cervelo P5 | Cervelo T4 | Trek Domane Koppenberg
  • Absolutely none I'd imagine.

    My winter bike has 172.5 and a Summer bike 175- not for any particular reason. My knees haven't exploded so far....
  • StillGoingStillGoing Posts: 5,199
    Jesus! Use the search function please. This subject has been covered umpteen times and we'll now have yet another to and fro from those who recognise it does make a difference and those who don't. :x
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • philthy3 wrote:
    Jesus! Use the search function please. This subject has been covered umpteen times and we'll now have yet another to and fro from those who recognise it does make a difference and those who don't. :x

    Jesus! Someone put too many testosterone patches on this morning!

    Are you going to copy n paste your outburst onto every:

    What frame
    What wheels
    What bib shorts
    What tyres
    What energy drink
    What saddle

    Thread?
  • BozmanBozman Posts: 2,570
    philthy3 wrote:
    Jesus! Use the search function please. This subject has been covered umpteen times and we'll now have yet another to and fro from those who recognise it does make a difference and those who don't. :x

    Jesus! Someone put too many testosterone patches on this morning!

    Are you going to copy n paste your outburst onto every:

    What frame
    What wheels
    What bib shorts
    What tyres
    What energy drink
    What saddle

    Thread?

    There's a search function? Won't that make the site really boring.
  • MarkjaspiMarkjaspi Posts: 729
    I've just gone the other way from 170mm to 175mm, just because I got a good deal of a site member on a crank for my new build.

    I've notice no difference, except for maybe a few mm difference on the seatpost.
    Cipollini Bond
    Pinarello GAN
  • luv2rideluv2ride Posts: 2,360
    Same here, using (or have used) 170, 172.5 and 175mm crank arms. Can't really tell much difference if I'm honest - went 175 on my last chainset as it was the only one left in stock at the heavily reduced price I paid :)
    Scott Solace 10 disc - Kinesis Crosslight Pro6 disc - Scott CR1 SL - Pinnacle Arkose X 650b - Pinnacle Arkose 1x11 "monster cross" - Specialized Singlecross...& an Ernie Ball Musicman Stingray 4 string...
  • ColinthecopColinthecop Posts: 996
    Are you going to copy n paste your outburst onto every:

    What frame
    What wheels
    What bib shorts
    What tyres
    What energy drink
    What saddle

    Thread?


    What about the,

    What bike for £300
    What bike for £600
    What bike for £1000
    What bike for £3000

    They surely deserve a mention...?
  • CaleidoCaleido Posts: 21
    It depends how your bike is set up, how close to your limits your fit is in terms of flexibility and range of movement.

    Crank lengths can have a massive impact on comfort and performance.

    All this "I changed and didn't notice anything so you won't" doesn't really mean anything to anyone else.
  • ghorswillghorswill Posts: 98
    Cheers guys...I'm gonna book myself a proper bike fit as I want to check stem length and bar width anyway, due to neck pain after an hour or so on the bike. So I'll ask about the crank length at the same time. I guess I didn't expect a 2.5 mm to make any difference but also thought I'd get some comments about power transfer, leverage, leg extensions etc.

    However, realistically is this going to make any difference to me as a newish club member...no not really.
    I'm just a perfectionist and if I can make it right then I'll try.
    2010 Specialised Sirrus Pro (drop bar conversion)
    1993 Specialised Rockhopper A1
    Voodoo Limba - for out with the kids
  • StillGoingStillGoing Posts: 5,199
    ghorswill wrote:
    Cheers guys...I'm gonna book myself a proper bike fit as I want to check stem length and bar width anyway, due to neck pain after an hour or so on the bike. So I'll ask about the crank length at the same time. I guess I didn't expect a 2.5 mm to make any difference but also thought I'd get some comments about power transfer, leverage, leg extensions etc.

    However, realistically is this going to make any difference to me as a newish club member...no not really.
    I'm just a perfectionist and if I can make it right then I'll try.

    http://bikedynamics.co.uk/FitGuidecranks.htm
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • odessoukyodessouky Posts: 264
    I'm very interested in this topic, as contrary to original poster, I want to go from 172.5 to a 175, as I want to lower the saddle a tiny bit....in THEORY giving me more room before I start flexing my knees too much..??

    Most of the responses here sway towards absolutely NO DIFFERENCE between 170, 172.5 & 175...

    If so, why do the manufacturers even bother doing different lengths cranks? Why don't they just do 172.5s?
  • mr_evilmr_evil Posts: 234
    odessouky wrote:
    ...If so, why do the manufacturers even bother doing different lengths cranks?..
    Because people buy them.
  • StillGoingStillGoing Posts: 5,199
    odessouky wrote:
    I'm very interested in this topic, as contrary to original poster, I want to go from 172.5 to a 175, as I want to lower the saddle a tiny bit....in THEORY giving me more room before I start flexing my knees too much..??

    Most of the responses here sway towards absolutely NO DIFFERENCE between 170, 172.5 & 175...

    If so, why do the manufacturers even bother doing different lengths cranks? Why don't they just do 172.5s?

    Having longer crank lengths isn't going to give you more room. If the angles for your leg at the bottom and top of the stroke are supposed to be around 143' and 70', longer cranks will mean the bottom angle stays exactly the same as the leg extension will be set as normal, but the angle at the top of the stroke becomes more compressed due to the seat having to be lowered.

    It isn't that most of the responses sway towards it having no effect, it's that some people simply don't have the ability to notice these things or more often than not, because they haven't tried it they won't buy into the idea that it could possibly have any benefit. As someone who has tried it and found it works for me and I can notice the difference, I'm behind the theory enough to have bought shorter chainsets for both road bikes.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • odessoukyodessouky Posts: 264
    philthy3 wrote:
    odessouky wrote:
    I'm very interested in this topic, as contrary to original poster, I want to go from 172.5 to a 175, as I want to lower the saddle a tiny bit....in THEORY giving me more room before I start flexing my knees too much..??

    Most of the responses here sway towards absolutely NO DIFFERENCE between 170, 172.5 & 175...

    If so, why do the manufacturers even bother doing different lengths cranks? Why don't they just do 172.5s?

    Having longer crank lengths isn't going to give you more room. If the angles for your leg at the bottom and top of the stroke are supposed to be around 143' and 70', longer cranks will mean the bottom angle stays exactly the same as the leg extension will be set as normal, but the angle at the top of the stroke becomes more compressed due to the seat having to be lowered.

    It isn't that most of the responses sway towards it having no effect, it's that some people simply don't have the ability to notice these things or more often than not, because they haven't tried it they won't buy into the idea that it could possibly have any benefit. As someone who has tried it and found it works for me and I can notice the difference, I'm behind the theory enough to have bought shorter chainsets for both road bikes.

    Thanks for your reply

    I like your DEGREES theory and understand what you mean...

    Am I to assume that for different sizes, ONLY the crank arms are different, and the rest of the chain rings etc are the same?

    Are crank ARMS sold separately?

    Thanks
  • bernithebikerbernithebiker Posts: 4,148
    170 to 175 doesn't sound like a big difference.

    But consider this; the circumference of the circle scribed by your pedal axle is 1099mm with 175mm cranks, and 1067mm with 170mm. Suddenly doesn't seem quite so small…….

    I am an advocate of smaller cranks; you can spin better, less strain, and get more aero.
  • mpiempie Posts: 84
    170 to 175 doesn't sound like a big difference.

    But consider this; the circumference of the circle scribed by your pedal axle is 1099mm with 175mm cranks, and 1067mm with 170mm. Suddenly doesn't seem quite so small…….

    I am an advocate of smaller cranks; you can spin better, less strain, and get more aero.

    Except that with shorter cranks you have to push harder (more strain) just to generate the same power (for a given gearing). You can drop the gearing to reduce the strain, but then you have to maintain a faster cadence just to get the same power.The higher cadence is not an advantage, it's a requirement to maintain speed. The only real variable is the muscular efficiency over difference ranges of motion.
  • ghorswillghorswill Posts: 98
    now that's more like what I expected...thanks. Based on the bike dynamics website I'd say I should be using a 175.

    Like I said I'm gonna organise a bike fit to get it all checked out.
    2010 Specialised Sirrus Pro (drop bar conversion)
    1993 Specialised Rockhopper A1
    Voodoo Limba - for out with the kids
  • odessoukyodessouky Posts: 264
    ghorswill wrote:
    now that's more like what I expected...thanks. Based on the bike dynamics website I'd say I should be using a 175.

    Like I said I'm gonna organise a bike fit to get it all checked out.

    Funny thing is a close friend of mine is kind of OCD with his cycling, wasn't happy with his riding position, had a bike fitting session for around £100, still wasn't happy, did another fit outside London (drove 75 miles for it), and they gave him VERY DIFFERENT NUMBERS AND SUGGESTIONS!!!!
    :)
    And he's still unhappy...
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