Crank arm length on Compact Crank

Discussion in 'Cycling Equipment' started by Cusp, Jul 6, 2007.

  1. Cusp

    Cusp New Member

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    Hello,

    Little by little I'm leaning towards getting a shimano compact crank on my Specialized Allez.

    How can I find out what my OEM crank arm length is? I have no problems with it and would like to get the exact arm length.

    Or - what is the standard length for a 56cm frame from MOST bike companies?

    Thanks!
     
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  2. Pharaoh1

    Pharaoh1 New Member

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    Hi Cusp,

    Many cranks have the length stamp at the end of the crank arm. Typically it's on the inside face of the crank arm. If you can't find it you can measure it yourself.

    My guess is that most of the big manufacturers, like Trek and Specialized, put 172.5mm arms on when they come off the assembly line. If the customer wants to swap them shorter or longer it can be done at the point of sale or they can do it later on down the road (pun intended).

    I have the Shimano compact and love it. It's really helped with the hills and seems to be about equal to the Ultegra in quality. Good luck!

    Scott
     
  3. Cusp

    Cusp New Member

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    Scott,

    Which Shimano compact did you purchase? R4550? R600? R700?

    I have a 9-speed bike and apparently the R4550 is truly made for 9-speeds while the R600/R700 is 10-speed that 'works' with 9 speeds.
     
  4. Sikhandar

    Sikhandar New Member

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    Well, a 56x56 could also have a 175... check it on the inner arm! Or you can measure, with a caliber, the distance from the centre of the pedal-hole to the centre of the octalink hole (check only the left arm).

    In Italy we say: if you are able to shift gears with your right hand and to put the right gear in the right situation, you can take a 53/39 everywhere :p
     
  5. Cusp

    Cusp New Member

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    Thanks for the heads up on where to check for the length.

    I actually have a 170 length.
     
  6. Sikhandar

    Sikhandar New Member

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    Quite strange to have a 170 mm on a 56 centimeters frame... are you sure that your frame is a 56? I mean, 56 taken from: centre of crankset - centre of horizontal tube measured by following the seatpost-tube? Maybe it was a bike prepared for McEwen :D (sprinters love short cranksets)
     
  7. Cusp

    Cusp New Member

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    56cm frame. Sticker is still on tube.

    And 170 stamped on crank arm near where the pedal bolts are.
     
  8. gclark8

    gclark8 New Member

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    Sounds like an "entry level" bike, they don't go proportional with individual components until you get up market a bit. ;)
     
  9. Cusp

    Cusp New Member

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    haha. Heyyy now. 105 components. Be nice to my bike. j/k.
     
  10. Pharaoh1

    Pharaoh1 New Member

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    I've got the FC R700. I recently mated it with a 12-27 cassette. Not very macho, but I'm pushing 50 and am not too proud to use a little help!
     
  11. Halcyon1

    Halcyon1 New Member

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    Same here Pharaoh, and I love it. I'm 53 and who cares about being macho when struggling up a hill.
    Halcyon1
     
  12. Skittlebrau

    Skittlebrau New Member

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    Just got my Trek 2000 with an Ultegra compact crank. 170mm on a 52cm frame. Works flawlwssly (so far) with the new Ultegra groupset and the bike is a hell of a good climber. Previously had a stock 2300 which is the same bike with standard Ultegra parts. Very noticable difference accellerating and climbing with little loss of downhill speed. Try it. You'll like it
     
  13. kjbetz

    kjbetz New Member

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    I have a "stock" '05 Trek 2100, it has a Brontrager Crank, SRAM rear cassette, 105 FD, and Ultegra RD.

    I've been thinking about purchasing the R700 and have some questions:

    1) Do I need to buy anything else to replace the crank? Bottom Bracket - Does one come with it (or integrated?) or will the one I have already work?

    2) Will my 9-speed cassette, chain, etc... work fine with this crank?

    3) Is it worth upgrading, possibly with lower gearing, my cassette to an Ultegra?

    4) If replacing the rear cassette is an option for me, I can't go to a 10 can I? Not without getting new brifters, right?

    Thanks for anyone that can help me out!
     
  14. John M

    John M New Member

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    1) Do I need to buy anything else to replace the crank? Bottom Bracket - Does one come with it (or integrated?) or will the one I have already work?

    You will need the Shimano BB cups- The Truvativ (Bontrager ones won't work). The cups have to be purchased separately (about $35).

    2) Will my 9-speed cassette, chain, etc... work fine with this crank?

    Yes. You might need to shorten the chain a link or two, depending on the current length of the chain

    3) Is it worth upgrading, possibly with lower gearing, my cassette to an Ultegra?

    It is not worth the upgrade in and of itself. If you need lower gearing, then get a different cassette. SRAM 900 series cassettes (950,970,990) are comparable to Ultegra in quality.

    4) If replacing the rear cassette is an option for me, I can't go to a 10 can I? Not without getting new brifters, right?

    To go 10s, you WILL need new brifters (and a 10s chain, along with the 10s cassette). The crankset can go 9s or 10s. 9s derailleurs should work adequately with 10s, although a 10s front will work better than a 9s FD in the 10s drivetrain.
     
  15. artemidorus

    artemidorus New Member

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    Certainly, if you can climb 2000m with a cadence of 30/min, you can take a standard crankset anywhere! But if you are wanting efficiency with big climbs, you may choose a different option.
     
  16. oldbobcat

    oldbobcat Well-Known Member

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    These days 56s are usually fit with 172.5 cranks. No big deal. If your legs are longish, you might want longer cranks. On the other hand, you'll spin better with 170s.
     
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