Results 1 to 15 of 15
  1. #1
    Trucking & Extortion
    Reputation: RFXR's Avatar
    Join Date
    Dec 2003
    Posts
    56

    XX Cranks and Chainguide Fit Issue

    This is a crosspost from the Turner board but with no responses I'm giving it a shot here.

    Over the weekend I rebuilt my 2010 Sultan with some new parts. I went with an XX drivetrain setup, 166mm q-factor for the crankset, and a sram GXP Team BB. The guide I chose is the new truvativ (MRP) dual ring guide, BB mount.

    The sultan is a 73mm BB, the Truvativ BB comes with 2 2.5mm spacers on it to use it on a 68mm BB, and specifies to use 0 spacers for a 73mm shell. When I install the XX cranks with the BB mount X-Guide they do not tighten up all the way. When I install the cranks and BB without the guide they work fine. The X-Guide is 2.5mm thick, and I assume this extra width between the BB cups is causing my issues.

    My previous setup was a 2010 XT 9sp crank with an E13 BB mount guide and it fit just fine even though the crankset specified no spacers with a 73mm BB.

    Has anyone run across this issue? Is there a BB out there that will let me run the XX cranks and the X-Guide?

    Thanks.
    Seeking Lot Lizards and Rackets

  2. #2
    I do what I want
    Reputation: Guy.Ford's Avatar
    Join Date
    Oct 2009
    Posts
    1,015
    Edited: DOH, because Im a dumb@ss!

    Go read NoahColorado's explanation below and live in happiness!!
    Last edited by Guy.Ford; 01-25-2012 at 04:00 PM.
    Guy.Ford

    I'm not really an @sshole, I just act like one online.

  3. #3
    Desert Rat
    Reputation:
    Join Date
    Jul 2005
    Posts
    325
    This doesn't make sense. The GXP BB's fix the spindle/crank location with the non-drive side cup. There is excess spindle length for the drive side cup to move outboard with spacers, etc, during assy. If you shell is exactly 73mm, there is 3.3mm between the dust seal lip on the drive side and the face of the driveside crank that it would contact. Introducing a 2.5mm offset (spacer or backplate) beneath the drive side cup should leave you with space between the dust seal lip (or the drive side cup face) and the drive side crank.

    Measure the true width of your BB shell. The Sultan is anodized, so you should not have any paint build-up to contend with.

    Try your assembly with a single 2.5 spacer behind the drive side cup, and see if you get any binding (isolate the issue between spacing alone and possible guide issues).
    Last edited by Winans; 01-25-2012 at 08:27 AM.
    RapidCreekCycles

    Palisade CO Ride the Palisade Rim Trail
    Niner

    COPMOBA

  4. #4
    mtbr member
    Reputation: GTscoob's Avatar
    Join Date
    Apr 2009
    Posts
    2,151
    If you're deadset on that chainguide, you could take a facing tool and face 2mm off the driveside of the bottom bracket shell.

    If you dig around, there are plenty of folks that have done this in order to mount Hammerschmidts onto bikes with wide BB shells.

  5. #5
    GUIDANCE COUNSELOR
    Reputation: NoahColorado's Avatar
    Join Date
    Aug 2004
    Posts
    2,843
    Quote Originally Posted by GTscoob View Post
    If you're deadset on that chainguide, you could take a facing tool and face 2mm off the driveside of the bottom bracket shell.

    If you dig around, there are plenty of folks that have done this in order to mount Hammerschmidts onto bikes with wide BB shells.
    No you really shouldn't. This will only bring the guide inboard more, not the issue here.

    Check out Winan's advice. That guide was definitely designed to work with SRAM/Truvativ cranks and 73mm shells.
    NOAH SEARS
    MRP
    TECH QUESTIONS HERE: INFO@MRPBIKE.COM

  6. #6
    I do what I want
    Reputation: Guy.Ford's Avatar
    Join Date
    Oct 2009
    Posts
    1,015
    Quote Originally Posted by NoahColorado View Post
    Check out Winan's advice. That guide was definitely designed to work with SRAM/Truvativ cranks and 73mm shells.
    How is that possible when truvativs own documentation says it wont? Not to mention that there are several threads on the web regarding this issue? Sorry, not attacking you, just looking for "expert" advice.

    Would you say that the Lopes guide should also be able to work with a 73mm shell and Stylo Cranks?
    Guy.Ford

    I'm not really an @sshole, I just act like one online.

  7. #7
    GUIDANCE COUNSELOR
    Reputation: NoahColorado's Avatar
    Join Date
    Aug 2004
    Posts
    2,843
    Quote Originally Posted by Guy.Ford View Post
    How is that possible when truvativs own documentation says it wont? Not to mention that there are several threads on the web regarding this issue? Sorry, not attacking you, just looking for "expert" advice.

    Would you say that the Lopes guide should also be able to work with a 73mm shell and Stylo Cranks?
    No problem.

    First of all, understanding the GXP system helps.

    GXP works differently than Shimano, Raceface, FSA, or other similar external BB systems. Whereas those systems feature a spindle with a consistent 24mm OD, on GXP cranks the spindle steps-down slightly on the end. So essentially the ID of the non-driveside BB is smaller than that of the driveside. Thus, the spindle bottoms out on the inside of the non-drive side BB cups bearing. Therefore, spacers on the drive-side have ZERO effect on chainline (unless you have wayyyy to many spacers TOTAL and the spindle no longer bottoms out on the non-drive side BB cup).

    On a Shimano/Raceface/FSA style crank, installing a BB mount guide means REPLACING a BB spacer with the guide's backplate.

    On a SRAM/Truvativ GXP crank, installing a BB mount guide means ADDING the guide's backplate between drive-side cup and either the 1)BB shell (73mm) or 2) single spacer (found on a 68mm setup)

    Example of GXP 68/73mm cranks with various setups:
    68mm shell, no non-drive side spacers = chainline 2.5mm further outboard than standard
    68mm shell, 1 non-drive side spacer = normal chainline
    68mm shell, 2 non-drive side spacers = chainline 2.5mm further inboard than standard
    73mm shell, no non-drive side spacers = normal chainline
    73mm shell, 1 non-drive side spacer = chainline 2.5mm further inboard than standard

    maximum allowable "parts width" on 68/73mm GXP cranks is 75.5mm - no combination of spacers, bb shell width, guide, e-type derailleur, etc can exceed this or the crank will NOT bottom out on the non-drive side BB cup (you'll get binding, play, all kinds of problems).


    So, why doesn't SRAM/Truvativ call for a spacer on the drive-side of 73mm shells? It doesn't need one - makes no difference to the crank. But that doesn't mean you couldn't put one there (or install a e-type derailleur or BB mount guide) if you wanted to.

    Also, there really is no "preloading" the bearings on GXP system like on Shimano/Raceface/FSA system - you either have it tightened down all the way or not. There is virtually no way of crushing the non-drive side bearing. Think of it this way: on a Shimano/Raceface/FSA setup, tightening down the fixing bolt is essentially pinching the whole crankset together (no "hard" stop), with GXP you're just pinching between the spindle "step" and the left crank arm (a fixed distance with a hard stop).

    So yes, BB mount Lopes guide on 73mm shell is no problem.

    *The only combo that doesn't work, as far as I know, would be trying to setup a Truvativ X-guide on a CONVERTED triple crank (a standard triple crank with the "big" ring removed). The MRP 2x works for this, but the X-guide only designed to work with 2x10 cranks.
    NOAH SEARS
    MRP
    TECH QUESTIONS HERE: INFO@MRPBIKE.COM

  8. #8
    usually cranky
    Reputation: b-kul's Avatar
    Join Date
    Sep 2009
    Posts
    9,958
    i have a 73mm bb shell and a gxp crank. used mrps instuctions and it worked perfectly. from the bb shell out i went: bb shell, guide, 1mm or .5mm spacer (i dont remember, it was silver), bb cup, and finally crank. flawless. btw, noah, one complaint, the thin silver washer was pinched and crooked when i got it doubling the install time to 15 minutes, you guys need to step up your qc

  9. #9
    I do what I want
    Reputation: Guy.Ford's Avatar
    Join Date
    Oct 2009
    Posts
    1,015
    Quote Originally Posted by NoahColorado View Post
    No problem.

    First of all, understanding the GXP system helps.

    GXP works differently than Shimano, Raceface, FSA, or other similar external BB systems. Whereas those systems feature a spindle with a consistent 24mm OD, on GXP cranks the spindle steps-down slightly on the end. So essentially the ID of the non-driveside BB is smaller than that of the driveside. Thus, the spindle bottoms out on the inside of the non-drive side BB cups bearing. Therefore, spacers on the drive-side have ZERO effect on chainline (unless you have wayyyy to many spacers TOTAL and the spindle no longer bottoms out on the non-drive side BB cup).

    On a Shimano/Raceface/FSA style crank, installing a BB mount guide means REPLACING a BB spacer with the guide's backplate.

    On a SRAM/Truvativ GXP crank, installing a BB mount guide means ADDING the guide's backplate between drive-side cup and either the 1)BB shell (73mm) or 2) single spacer (found on a 68mm setup)

    Example of GXP 68/73mm cranks with various setups:
    68mm shell, no non-drive side spacers = chainline 2.5mm further outboard than standard
    68mm shell, 1 non-drive side spacer = normal chainline
    68mm shell, 2 non-drive side spacers = chainline 2.5mm further inboard than standard
    73mm shell, no non-drive side spacers = normal chainline
    73mm shell, 1 non-drive side spacer = chainline 2.5mm further inboard than standard

    maximum allowable "parts width" on 68/73mm GXP cranks is 75.5mm - no combination of spacers, bb shell width, guide, e-type derailleur, etc can exceed this or the crank will NOT bottom out on the non-drive side BB cup (you'll get binding, play, all kinds of problems).


    So, why doesn't SRAM/Truvativ call for a spacer on the drive-side of 73mm shells? It doesn't need one - makes no difference to the crank. But that doesn't mean you couldn't put one there (or install a e-type derailleur or BB mount guide) if you wanted to.

    Also, there really is no "preloading" the bearings on GXP system like on Shimano/Raceface/FSA system - you either have it tightened down all the way or not. There is virtually no way of crushing the non-drive side bearing. Think of it this way: on a Shimano/Raceface/FSA setup, tightening down the fixing bolt is essentially pinching the whole crankset together (no "hard" stop), with GXP you're just pinching between the spindle "step" and the left crank arm (a fixed distance with a hard stop).

    So yes, BB mount Lopes guide on 73mm shell is no problem.

    *The only combo that doesn't work, as far as I know, would be trying to setup a Truvativ X-guide on a CONVERTED triple crank (a standard triple crank with the "big" ring removed). The MRP 2x works for this, but the X-guide only designed to work with 2x10 cranks.
    HOLY SH#T GOD D@MN! Now thats an explanation!! You are the man, thank you very much!!! Rep points x1000
    Guy.Ford

    I'm not really an @sshole, I just act like one online.

  10. #10
    Trucking & Extortion
    Reputation: RFXR's Avatar
    Join Date
    Dec 2003
    Posts
    56
    This still does not work. With the chainguide installed the non-drive side arm will not seat properly. When the guide is removed it sits tight with no side to side wobble. The same results occured when using a 2.5mm spacer instead of the guide. Maybe some GXP cranks are different, but with this XX setup it does not want to let you put that extra 2.5mm of width into the BB.
    Seeking Lot Lizards and Rackets

  11. #11
    Trucking & Extortion
    Reputation: RFXR's Avatar
    Join Date
    Dec 2003
    Posts
    56
    This still does not work. With the chainguide installed the non-drive side arm will not seat properly. When the guide is removed it sits tight with no side to side wobble. The same results occured when using a 2.5mm spacer instead of the guide. Maybe some GXP cranks are different, but with this XX setup it does not want to let you put that extra 2.5mm of width into the BB.
    Seeking Lot Lizards and Rackets

  12. #12
    mtbr member
    Reputation: Slurry's Avatar
    Join Date
    Dec 2008
    Posts
    607
    Hrm, with the GXP system, the NDS crank arm bottoms out on the spindle (with 50 NM or so of torque) and the NDS bottom bracket cup's bearing is a floating bearing (this is why this system works without having a split NDS crank arm with pinch bolts and a pre-load cap, ala Shimano, FSA, etc). Correct (within 1mm or so, from my experience) BB shell width is critical in order to have enough of the BB spindle sticking out of the NDS so that the NDS crank can be securely attached without it pressing against the NDS bottom bracket cup's bearing and overloading it.

  13. #13
    mtbr member
    Reputation: Snfoilhat's Avatar
    Join Date
    May 2010
    Posts
    441
    I am running 2010 XX cranks (q166), GXP BB, and MRP 2x guide (BB mount).
    73 mm BB shell. No spacers. Installed easily and no problems. I suggest taking some measurements rather than taking the published numbers for granted. Something (e.g. BB width, spindle length, the total width of the installed BB cups plus backing plate) could be off. Good luck.

  14. #14
    usually cranky
    Reputation: b-kul's Avatar
    Join Date
    Sep 2009
    Posts
    9,958
    this may be a really dumb suggestion but are you just not pushing the crank onto the spindle enough to get the bolt threads to engage? once you can make that happen you should be set.

  15. #15
    Desert Rat
    Reputation:
    Join Date
    Jul 2005
    Posts
    325
    Quote Originally Posted by Snfoilhat View Post
    I am running 2010 XX cranks (q166), GXP BB, and MRP 2x guide (BB mount).
    73 mm BB shell. No spacers. Installed easily and no problems. I suggest taking some measurements rather than taking the published numbers for granted. Something (e.g. BB width, spindle length, the total width of the installed BB cups plus backing plate) could be off. Good luck.
    Yes, measure your hardware. That being said, Sram doesn't publish the length of the spindle as far as I know, but you could assemble the NDS arm to the DS/Spindle and measure the distance between the interior arm faces to find that value (off of the bike of course). And measuring BB shell width is straightforward (likely culprit if I had to guess).

    Like your name by the way, Snfoilhat - one can't be too careful with ones thoughts.
    RapidCreekCycles

    Palisade CO Ride the Palisade Rim Trail
    Niner

    COPMOBA

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •