Swap triple crank to double - outer ring hits frame

Discussion in 'Cycling Equipment' started by monkeyboy, Dec 20, 2004.

  1. monkeyboy

    monkeyboy Guest

    Hello,

    I recently purchased a bianchi axis for a commuter bike. It came with a
    175mm-triple. I would like to swap it with a shimano 600 or 105,
    172.5mm-double I currently have. When I try to mount the crank, the
    large chain ring rubs on the chain stay.

    I'm not sure what the best fix is. It looks like you can't find a
    172.5mm-triple unless your at the high end of the component range, and
    they are expensive. Could a new bottom bracket fix the problem? Are
    there different tapers on the bottom brackets that determine where the
    crank mounts?

    Thanks,

    Frank

    PS

    I want to make the change for a couple of reasons. I have two other
    bikes each with 172.5mm cranks, I'd like to keep things the same for
    all. Also, I have some road sized, 130 bcd, chain rings to use as
    spares. The triple came with a 48 as the largest and has a 110 bcd.
     
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  2. Weisse Luft

    Weisse Luft New Member

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    Get the double BB and all will be fine. Yes, triple BB's are narrower, making the outer ring too close to the chinstay on some bikes.
     
  3. davidd86

    davidd86 New Member

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    I think it depends on the brand as to whether the double's longer than the triple. But Weisse's right, get the next size up in BBs and you'll be set. I had the same problem as you do; using a Campy double with the 111mm BB, the big ring rubbed on the chainstay. I just swapped it out for a 115.5 that's supposed to be used with their triples. All is well. The 2.25mm on each side isn't enough to notice or materially foul up the chainline.



     
  4. monkeyboy wrote:
    > Hello,
    >
    > I recently purchased a bianchi axis for a commuter bike. It came with

    a
    > 175mm-triple. I would like to swap it with a shimano 600 or 105,
    > 172.5mm-double I currently have. When I try to mount the crank, the
    > large chain ring rubs on the chain stay.
    >
    > I'm not sure what the best fix is. It looks like you can't find a
    > 172.5mm-triple unless your at the high end of the component range,

    and
    > they are expensive. Could a new bottom bracket fix the problem? Are
    > there different tapers on the bottom brackets that determine where

    the
    > crank mounts?
    >
    > Thanks,
    >
    > Frank
    >
    > PS
    >
    > I want to make the change for a couple of reasons. I have two other
    > bikes each with 172.5mm cranks, I'd like to keep things the same for
    > all. Also, I have some road sized, 130 bcd, chain rings to use as
    > spares. The triple came with a 48 as the largest and has a 110 bcd.


    Well, you should be able to make the 600 or 105 fit, but you will
    probably need a longer BB. I couch this in "maybe" terms because the
    bike may well be designed in part around the particular crankset.

    Further, remember that you're increasing Q-factor by putting in a wider
    BB. The standard for 600/Ultegra cranks was 113mm, the standard for
    105sc cranks was 107mm.

    If clearance is tight, you could try something like a 105sc on a 115
    (or longer) BB...but you are paying for it in Q-factor.

    You might just want to try the stock cranks and see if they aren't OK
    for you as is...
     
  5. Luft writes-<< Get the double BB and all will be fine. Yes, triple BB's are
    narrower,
    making the outer ring too close to the chinstay on some bikes. >><BR><BR>

    I say-I don't get this. Triple BBs are always longer and a longer BB spindle is
    what this gent needs. He is going from a triple to a double, not the other way
    around. The way-wide chainstay on the Bianchi is the problem.

    Peter Chisholm
    Vecchio's Bicicletteria
    1833 Pearl St.
    Boulder, CO, 80302
    (303)440-3535
    http://www.vecchios.com
    "Ruote convenzionali costruite eccezionalmente bene"
     
  6. Terry Morse

    Terry Morse Guest

    Someone wrote:

    > Well, you should be able to make the 600 or 105 fit, but you will
    > probably need a longer BB. I couch this in "maybe" terms because the
    > bike may well be designed in part around the particular crankset.


    Another potential fix is to insert a spacer between the right side
    bottom bracket cut and the frame. This only works if you have enough
    clearance for the left side crank.

    You can purchase BB spacers of varying size at loosescrews.com.
    --
    terry morse Palo Alto, CA http://bike.terrymorse.com/
     
  7. Peter Cole

    Peter Cole Guest

    "monkeyboy" <[email protected]> wrote in message
    news:[email protected]
    > Hello,
    >
    > I recently purchased a bianchi axis for a commuter bike. It came with a
    > 175mm-triple. I would like to swap it with a shimano 600 or 105,
    > 172.5mm-double I currently have. When I try to mount the crank, the
    > large chain ring rubs on the chain stay.
    >
    > I'm not sure what the best fix is. It looks like you can't find a
    > 172.5mm-triple unless your at the high end of the component range, and
    > they are expensive. Could a new bottom bracket fix the problem?


    Ye, Sheldon Brown has a BB size index, you can look up your crank.
    http://www.sheldonbrown.com/bbsize.html
     
  8. Mark Janeba

    Mark Janeba Guest

    Qui si parla Campagnolo wrote:
    > Luft writes-<< Get the double BB and all will be fine. Yes, triple BB's are
    > narrower,
    > making the outer ring too close to the chinstay on some bikes. >><BR><BR>
    >
    > I say-I don't get this. Triple BBs are always longer and a longer BB spindle is
    > what this gent needs. He is going from a triple to a double, not the other way
    > around. The way-wide chainstay on the Bianchi is the problem.


    I agree. Is the chainstay spreading at some really big angle?
    Everyone's talking about the *big* chainring hitting the chainstay - I'm
    used to seeing the little ring hit first.

    Mark Janeba
     
  9. Werehatrack

    Werehatrack Guest

    On 20 Dec 2004 05:29:16 -0800, "monkeyboy" <[email protected]>
    wrote:

    >Hello,
    >
    >I recently purchased a bianchi axis for a commuter bike. It came with a
    >175mm-triple. I would like to swap it with a shimano 600 or 105,
    >172.5mm-double I currently have. When I try to mount the crank, the
    >large chain ring rubs on the chain stay.


    This can be due to one of three things. The 172 crank may have a
    larger chainring, or the 172 crank may require a different BB with
    wider spacing, or the 172 crank may have a wallowed taper.

    >I'm not sure what the best fix is. It looks like you can't find a
    >172.5mm-triple unless your at the high end of the component range, and
    >they are expensive. Could a new bottom bracket fix the problem?


    Yes, if it's just a matter of the crank/chainring/frame combination
    needing a wider BB.

    >Are
    >there different tapers on the bottom brackets that determine where the
    >crank mounts?


    No. The shaft lengths are different.
    --
    Typoes are a feature, not a bug.
    Some gardening required to reply via email.
    Words processed in a facility that contains nuts.
     
  10. Jim Hall

    Jim Hall Guest

    monkeyboy wrote:

    >Hello,
    >
    >I recently purchased a bianchi axis for a commuter bike. It came with a
    >175mm-triple. I would like to swap it with a shimano 600 or 105,
    >172.5mm-double I currently have. When I try to mount the crank, the
    >large chain ring rubs on the chain stay.
    >
    >I'm not sure what the best fix is. It looks like you can't find a
    >172.5mm-triple unless your at the high end of the component range, and
    >they are expensive. Could a new bottom bracket fix the problem? Are
    >there different tapers on the bottom brackets that determine where the
    >crank mounts?
    >
    >Thanks,
    >
    >Frank
    >most shimano triples use a 118 mm width BB, while doubles need 109 mm
    >
    >



    >PS
    >
    >I want to make the change for a couple of reasons. I have two other
    >bikes each with 172.5mm cranks, I'd like to keep things the same for
    >all. Also, I have some road sized, 130 bcd, chain rings to use as
    >spares. The triple came with a 48 as the largest and has a 110 bcd.
    >
    >
    >
     
  11. Mark Janeba wrote:
    > > around. The way-wide chainstay on the Bianchi is the problem.

    >
    > I agree. Is the chainstay spreading at some really big angle?
    > Everyone's talking about the *big* chainring hitting the chainstay -

    I'm
    > used to seeing the little ring hit first.
    >


    The OP identifies the bike as a Bianchi Axis, but doesn't say what kind
    of crankset was originally on the bike. If the original crankset had
    smaller chainrings (typical in a newer bike), then switching to a
    double crankset with larger "road" chainrings might mean the chainrings
    and chainstay are trying to occupy the same space.

    A couple solutions come to mind: install a smaller outer chainring on
    the "road" double crank (48 tooth would match the original, I believe)
    or remove the small chainring from the original crank and install it on
    the shorter bottom bracket.

    Jeff
     
  12. On Mon, 20 Dec 2004 06:10:22 -0800, marchantshapiro wrote:

    >
    > Well, you should be able to make the 600 or 105 fit, but you will
    > probably need a longer BB. I couch this in "maybe" terms because the
    > bike may well be designed in part around the particular crankset.


    Nonsense. It's much more likely that the cranks he is trying to put on
    are simply designed for a longer bottom bracket. Simple thing to change
    out. The rest of the bike could not care less what brand crank is
    used.


    >
    > Further, remember that you're increasing Q-factor by putting in a wider
    > BB. The standard for 600/Ultegra cranks was 113mm, the standard for
    > 105sc cranks was 107mm.


    But the relationship between Q-factor and bottom bracket length is not
    that simple. It depends on where, relative to the pedal, the tapers are
    supposed to meet the crank. Some are further out, others are closer in.
    It also depends on the brand; if the original crank is Campagnolo, the
    Shimano will not fit right. Find what length bottom bracket you need
    (Sheldon Brown's site has the information), and replace the bottom bracket.

    --

    David L. Johnson

    __o | A mathematician is a machine for turning coffee into theorems.
    _`\(,_ | -- Paul Erdos
    (_)/ (_) |
     
  13. monkeyboy

    monkeyboy Guest

    monkeyboy wrote:
    > Hello,
    >
    > I recently purchased a bianchi axis for a commuter bike. It came with

    a
    > 175mm-triple. I would like to swap it with a shimano 600 or 105,
    > 172.5mm-double ...


    Thanks to all who responed. I took another look at the frame, it's not
    symetric. The drive side has a stiffening member welded in. The chain
    ring was rubbing on the weld bead. The current bottom bracket was a
    110.5mm, I pulled a 113mm from an old frame and all works fine. I'll
    probably get a 115mm for a little additional clearance.
    Thanks again,

    Frank
     
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