Page 1 of 2 12 LastLast
Results 1 to 50 of 58
  1. #1
    mtbr member
    Reputation: vizsladog's Avatar
    Join Date
    Mar 2009
    Posts
    1,320

    Sram gxp 73mm bottom bracket h question...

    My lbs built my nickel and i have a x9 crankset gxp bottom bracket.

    The nickel has a 73mm bb and sram says no spacers should be used but he used a spacer on the non drive side and said it had to be done fro some reason.

    this sound right??

  2. #2
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,307
    Quote Originally Posted by vizsladog View Post
    My lbs built my nickel and i have a x9 crankset gxp bottom bracket.

    The nickel has a 73mm bb and sram says no spacers should be used but he used a spacer on the non drive side and said it had to be done fro some reason.

    this sound right??
    As long as you have enough chainring clearance, not a problem. The chainline is better, too.
    mtbtires.com
    The trouble with common sense is it is no longer common

  3. #3
    mtbr member
    Reputation: vizsladog's Avatar
    Join Date
    Mar 2009
    Posts
    1,320
    So the crank arm goes on enough??? won't mess with bearings??


    There was some sort of issue with the chainring so that might be what he was doing

    I got a north shore billett 2x10 104 64 spider so he may have been doing it to get the chainline right
    2 x10 104BCD Spider for SRAM X0 & X9 Cranks « North Shore Billet

  4. #4
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    2,958
    The splines will not be fully meshed if you use extra spacers. I am not sure how Shiggy got that wrong, but I guess nobody's perfect.

    Like I said in the thread you started in the Santa Cruz forum, GXP bottom brackets and SRAM cranks do not use any spacers on 73mm bottom bracket shells. Except this time, I'll prove it. It can be plainly read in their installation guide, here: http://cdn.sram.com/cdn/farfuture/o-..._cranksets.pdf

    An extra 2.5mm spacer is a LOT to lose from the mating surface on the NDS crank arm. It would be a great way to strip the splines and ruin the cranks. Now, on 68mm BB frames, you *can* use a combination of spacers of alternate thicknesses that add up to 5.0mm instead of a single 2.5 on each side to tune the chainline... like 2.5+1.0 on the DS and 1.5 on the NDS. That still adds up to the correct 5mm you need for the crank arm to fasten properly.

    Again, that doesn't fly with 73mm. No spacers.

  5. #5
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by ColinL View Post
    The splines will not be fully meshed if you use extra spacers. I am not sure how Shiggy got that wrong, but I guess nobody's perfect.

    Like I said in the thread you started in the Santa Cruz forum, GXP bottom brackets and SRAM cranks do not use any spacers on 73mm bottom bracket shells. Except this time, I'll prove it. It can be plainly read in their installation guide, here: http://cdn.sram.com/cdn/farfuture/o-..._cranksets.pdf
    An extra 2.5mm spacer is a LOT to lose from the mating surface on the NDS crank arm. It would be a great way to strip the splines and ruin the cranks. Now, on 68mm BB frames, you *can* use a combination of spacers of alternate thicknesses that add up to 5.0mm instead of a single 2.5 on each side to tune the chainline... like 2.5+1.0 on the DS and 1.5 on the NDS. That still adds up to the correct 5mm you need for the crank arm to fasten properly.
    Again, that doesn't fly with 73mm. No spacers.
    Actually, with Sram cranks, Shiggy's right, unlike Shimano cranks the Sram's "clamp" to the bearing race on the non drive side only. They don't pinch both bearings, there is a lip on the inside of the spindle that hits on the inside of the bearing race and the bolt/arm washer hit on the outside,...The Drive side bearing just floats and has no side to side restrictions... adding spacers to the frame/bearing cup wont make a diff to the splines unless the Drive side ends up hitting the bearing when you add too much, most Sram''s have a good bit of room on the drive side (usually more than the 2.5mm) so it's a non issue..

    I would check the drive side bearing/crank interface, the crank arm isn't supposed to come in contact with the bearing/seal, also check your chain line and make sure it hasn't moved too far in...

    but ,.. they shouldn't have had to for any reason other than they don't get the drive side seal/bearing floats and isn't supposed to be tight against the crank arm... many people see the small gap between the arm and the seal/bearing and think the thing isn't seated...
    Last edited by thomllama; 12-15-2012 at 05:02 AM.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  6. #6
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    here's an image I made quickly that may help those that don't get how it works with Sram.... It's FAR from accurate size wise but gives the idea on how the Non-drive side bearing holds the cranks from side to side motion... this is for the threaded GXP BB, I didn't add things like the actual bearing cups as they just add confusion to the image
    Attached Thumbnails Attached Thumbnails Sram gxp 73mm bottom bracket h question...-gxp-bb-image.png  

    Last edited by thomllama; 12-15-2012 at 06:06 AM.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  7. #7
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    2,958
    Quote Originally Posted by thomllama View Post
    Actually, with Sram cranks, Shiggy's right, unlike Shimano cranks the Sram's "clamp" to the bearing race on the non drive side only. They don't pinch both bearings, there is a lip on the inside of the spindle that hits on the inside of the bearing race and the bolt/arm washer hit on the outside,...The Drive side bearing just floats and has no side to side restrictions... adding spacers to the frame/bearing cup wont make a diff to the splines unless the Drive side ends up hitting the bearing when you add too much, most Sram''s have a good bit of room on the drive side (usually more than the 2.5mm) so it's a non issue..
    thank you for the well-reasoned discourse. however, I strongly disagree.

    the spindle is a fixed length. the splines mate the spindle to the crank arm/arms at a known length. the bottom bracket, bearing cups, and any spacers simply need to fill that known length.

    in your picture, if you add the 2.5mm spacer to the DS, can the spindle get longer? no, of course not. putting the DS 2.5mm farther outboard will result in the spindle being 2.5mm too short on the NDS to properly mate with the NDS crank arm.

    it's not rocket surgery.

  8. #8
    mtbr member
    Reputation: vizsladog's Avatar
    Join Date
    Mar 2009
    Posts
    1,320
    Gonna take it back to him today. This is the second shop. I just moved here and the first shop had it freakin jacked up really bad.

    Guess i need to buy some tools and learn to do this myself...

  9. #9
    mtbr member
    Reputation:
    Join Date
    Nov 2011
    Posts
    3,504
    Quote Originally Posted by thomllama View Post
    here's an image I made quickly that may help those that don't get how it works with Sram.... It's FAR from accurate size wise but gives the idea on how the Non-drive side bearing holds the cranks from side to side motion... this is for the threaded GXP BB, I didn't add things like the actual bearing cups as they just add confusion to the image
    Cool, nice drawing. Never had my hands on a SRAM crank and always wondered how it worked.
    So since the drive side floats in the bearing, adding the spacer to the non-drive side makes the chainrings/crank pull 2.5 mm closer to the frame/bottom bracket. As Shiggy says, it will bring the chainline in as long as the rings don't hit the chain stay.
    And since the drive side has pulled over the 2.5mm, the non-drive side where the crank arm goes on hasn't changed - splines etc fit exactly the same as usual.

  10. #10
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by ColinL View Post
    thank you for the well-reasoned discourse. however, I strongly disagree.

    the spindle is a fixed length. the splines mate the spindle to the crank arm/arms at a known length. the bottom bracket, bearing cups, and any spacers simply need to fill that known length.

    in your picture, if you add the 2.5mm spacer to the DS, can the spindle get longer? no, of course not. putting the DS 2.5mm farther outboard will result in the spindle being 2.5mm too short on the NDS to properly mate with the NDS crank arm.

    it's not rocket surgery.
    Yes and no... all Crank manufactures have to leave play room for variances in BB shell widths, SRAM just leaves the bearing and seal spaced off the crank arm, Shimano uses a deeper cup splining so when you use the tensioning nut it has some room for adjustment,...
    in most cases, there is more than the spacer's room on the drive side open between the bearing seal and the actual crank arm,.. depending on "Actual" BB shell size, If it's been faced properly, or more than once, the size can very depending on the amount of material was needed to be taken off...

    My 68 BB shell is actually 68.7, and with spacers on both sides, still has around 1.5MM space between the drive side crank arm and the bearing seal...
    Edit- there is easily 2.5mm worth of space on my drive side between the seal and the crank arm...


    Quote Originally Posted by Slash5 View Post
    Cool, nice drawing. Never had my hands on a SRAM crank and always wondered how it worked.
    So since the drive side floats in the bearing, adding the spacer to the non-drive side makes the chainrings/crank pull 2.5 mm closer to the frame/bottom bracket. As Shiggy says, it will bring the chainline in as long as the rings don't hit the chain stay.
    And since the drive side has pulled over the 2.5mm, the non-drive side where the crank arm goes on hasn't changed - splines etc fit exactly the same as usual.
    yes and no,.. the non drive side still move over,.. but the whole crank assy moves as one, so the splines-to-crank arm interface stays the same,.. yes


    Again, there shouldn't have been a need to add the spacers thou unless the chain line was off, or the BB shell was actually smaller and they needed to push the bearing and seal up onto the raised lip of the crank spindle.
    Last edited by thomllama; 12-15-2012 at 09:56 AM.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  11. #11
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    hard to see as I'm going in from the side not straight down at, and the cam kept focusing in the bash guard not inside, but you can get the general idea...

    the 2nd image might give you a better idea....
    Attached Thumbnails Attached Thumbnails Sram gxp 73mm bottom bracket h question...-space.jpg  

    Sram gxp 73mm bottom bracket h question...-spacer-add-gxp-bb-image.png  

    Last edited by thomllama; 12-15-2012 at 11:13 AM.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  12. #12
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    here's the actual BB cups/bearings....

    Unlike Shimano the bearings themselves on SRAM'S are actually slightly diff, the Non drive side has a smaller inner race diameter...

    On Shimano's you can actually take a non drive side bearing and pull it from the bearing cup and switch sides...

    this is one of the reasons I actually prefer SRAM cranks... the race it's self is "pinched" to hold the cranks in place.

    where with Shimano, both sides the inner race is pushed in, causing a constant un even wear on the races (thou they may have gone to an angular contact race to counter act that? ) But with Shimano you can get the cranks too tight or too loose and binding the bearing where with the SRAM's you can't.
    Attached Thumbnails Attached Thumbnails Sram gxp 73mm bottom bracket h question...-bb-cups.jpg  

    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  13. #13
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    2,958
    You appear to be looking at and taking pictures of the space on the DS under the spider. I assure you it is not an actual gap-- if it were, the cranks would be able to move side-to-side!

    The DS crank arm is either built into the spindle (most SRAM) or bolted on (some X9 and all XO, XX) but the center of it absolutely is in full contact with the DS bearing cup in what you think is a space. (See the second sentence of this post, above. It has to be in contact.)

    I don't know what you think is happening but I suggest two things:
    1) look at that link I posted to the SRAM pdf and note that there are no spacers on 73mm BB and one 2.5mm spacer on each side of a 68mm BB.

    2) realize that the crank arms and spindle assemble together at a fixed length.

    you can install extra spacers wherever you want, which does move the position of the chainrings if that is desired, but it will result in the DS crank arm not being fully seated on the spindle. I like a good chainline, but I like my cranks to stay attached even more.

  14. #14
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by ColinL View Post
    You appear to be looking at and taking pictures of the space on the DS under the spider. I assure you it is not an actual gap-- if it were, the cranks would be able to move side-to-side!

    The DS crank arm is either built into the spindle (most SRAM) or bolted on (some X9 and all XO, XX) but the center of it absolutely is in full contact with the DS bearing cup in what you think is a space. (See the second sentence of this post, above. It has to be in contact.)

    I don't know what you think is happening but I suggest two things:
    1) look at that link I posted to the SRAM pdf and note that there are no spacers on 73mm BB and one 2.5mm spacer on each side of a 68mm BB.

    2) realize that the crank arms and spindle assemble together at a fixed length.

    you can install extra spacers wherever you want, which does move the position of the chainrings if that is desired, but it will result in the DS crank arm not being fully seated on the spindle. I like a good chainline, but I like my cranks to stay attached even more.
    GXP cranks the spindle is pressed into the crank arm (as well as Shimano's external BB setup) But on the Sram's the space there is actually a space.... again, the bearing "floats on the drive side and the whole crank system is held side to side by clamping the race on the Non-drive side... Unlike Shimano's who clamp both races pushing inward...

    He stated GXP,...these are not Oct-link, or any of the other "internal" bearing systems where both cranks are bolted On... GXP the crank arm and Spider are both permanently pressed onto the hollow crank spindle... The crank arm/spider absolutely should NOT be in contact with the seal/BB cup or bearing...
    Last edited by thomllama; 12-15-2012 at 01:59 PM.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  15. #15
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    OK, one last image to try and get you to understand how GXP crank are held in place...

    instead of pushing in from both sides, the crank spindle and the compression seal "pinch" the inner race of the Non-Drive bearing... this takes the side to side forces, allows the races to sit square with the ball in the bearing and allows the Drive Side bearing to just deal with the forces up and down (when you pedal) and back and forth (chain pull) making the bearing last longer... theoretically anyway I do get 3-4 yrs out of GXP BB's where I usually have to rebuild or replace Shimmy's every yr or so, depending on use and terrain conditions..
    Attached Thumbnails Attached Thumbnails Sram gxp 73mm bottom bracket h question...-sram_shimmyspindle.png  

    Last edited by thomllama; 12-15-2012 at 02:46 PM.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  16. #16
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    2,958
    The only lip is the end of the splines on the NDS. Additionally, some SRAM/Truvativ cranks do unbolt from the spindle on the DS as I said before. Stop reading wikipedia...

    The floating you quoted earlier refers to the spindle floating inside the bottom bracket. It touches nothing but the external bearing cups.

  17. #17
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by ColinL View Post
    The only lip is the end of the splines on the NDS. Additionally, some SRAM/Truvativ cranks do unbolt from the spindle on the DS as I said before. Stop reading wikipedia...

    The floating you quoted earlier refers to the spindle floating inside the bottom bracket. It touches nothing but the external bearing cups.
    dude.. i own them... refer them to people, install them... believe me when I tell you the drive side bearing floats on the spindle and shouldn't have any direct contact with the crank arm.. this will push on parts of the seal and drag on the outer race areas... just be smart and look at the actual image of the two sides of the BB.. the drive side has no place for impact/touching of the crank arm to the seal... you'll wear/destroy the bearing or seals if you do press them tight...

    Oh ,.. let me guess, you think the crank arm should push on the raised area of the "GXP" logo on the seal or something... really, just look at it... you'll see there isn't a single place the crank arm can push/hold on that seal where it wouldn't distort...

    Now.. try actually putting a GXP crank set in your hands.. take the Non-drive side bearing and try and slide it down the spindle... it'll stop at the lip....
    Last edited by thomllama; 12-15-2012 at 03:47 PM.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  18. #18
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,307
    Quote Originally Posted by ColinL View Post
    The only lip is the end of the splines on the NDS. Additionally, some SRAM/Truvativ cranks do unbolt from the spindle on the DS as I said before. Stop reading wikipedia...

    The floating you quoted earlier refers to the spindle floating inside the bottom bracket. It touches nothing but the external bearing cups.
    You may still disagree but that does not mean you are right.

    Read this, from Noah, a MRP tech and racer:

    XX Cranks and Chainguide Fit Issue

    As far as GXP crank bearings are concerned, adding a spacer to the NDS has the same (non-)effect as adding a BB mounted chain guide.

    The SRAM cranks that have the DS arm separate from the spindle are BB30, not GXP, and the OP specifically said he has GXP cranks.
    mtbtires.com
    The trouble with common sense is it is no longer common

  19. #19
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,307
    Quote Originally Posted by vizsladog View Post
    So the crank arm goes on enough??? won't mess with bearings??


    There was some sort of issue with the chainring so that might be what he was doing

    I got a north shore billett 2x10 104 64 spider so he may have been doing it to get the chainline right
    2 x10 104BCD Spider for SRAM X0 & X9 Cranks « North Shore Billet
    The splines are fully engaged because the spacing of the spindle end and the DNS bearing has not changed.

    If you had a spacing problem the crankset/rings would be rubbing on the driveside of the frame. No rubbing, no problem.
    mtbtires.com
    The trouble with common sense is it is no longer common

  20. #20
    mtbr member
    Reputation: vizsladog's Avatar
    Join Date
    Mar 2009
    Posts
    1,320
    Thanks for all the help.

    The lbs did exactly what shiggy said and his link said. He added the spacer to move the chain line in 2.5mm

  21. #21
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    2,958
    I did some research, reading a lot of crap here and around the web. I took apart one of my GXP-equipped bikes (all 3 have 68mm BB shells, though).

    I apologize to Shiggy and Thomllama. That is genius simplicity how GXP works. The chainline is very tunable because of it. Wow.

    Thanks guys. And no, this isn't because I got some anonymous negatiive rep... I'm glad to learn about it and I can man up.

  22. #22
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by ColinL View Post
    I did some research, reading a lot of crap here and around the web. I took apart one of my GXP-equipped bikes (all 3 have 68mm BB shells, though).

    I apologize to Shiggy and Thomllama. That is genius simplicity how GXP works. The chainline is very tunable because of it. Wow.

    Thanks guys. And no, this isn't because I got some anonymous negatiive rep... I'm glad to learn about it and I can man up.
    Believe me, you're not the first person who didn't understand the system,.. I've had tech's in shops that didn't get it even after I showed it to them

    Glad you figured it out
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  23. #23
    mtbr member
    Reputation: mack_turtle's Avatar
    Join Date
    Jan 2009
    Posts
    5,724
    I am glad I found this thread. I just ordered a BB-mounted MRP guide (the seat tube mounted ones were all out of stock) for my Karate Monkey to set it up 1x9. my frame has a 73mm BB shell and GXP cranks, so the MRP guide will not work. I am a bike shop mechanic, by the way, and I didn't think of this until this morning, before I put the guide on. we all make mistakes, but I would hope most mechanics at least think of these things before they start installing parts on your bike.

    now I need to find a way to keep my chain from popping off during the epic North Georgia ride I am doing TOMORROW. no time to order another chain guide and there's nothing else in stock at the shop.

  24. #24
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by mack_turtle View Post
    I am glad I found this thread. I just ordered a BB-mounted MRP guide (the seat tube mounted ones were all out of stock) for my Karate Monkey to set it up 1x9. my frame has a 73mm BB shell and GXP cranks, so the MRP guide will not work. I am a bike shop mechanic, by the way, and I didn't think of this until this morning, before I put the guide on. we all make mistakes, but I would hope most mechanics at least think of these things before they start installing parts on your bike.

    now I need to find a way to keep my chain from popping off during the epic North Georgia ride I am doing TOMORROW. no time to order another chain guide and there's nothing else in stock at the shop.
    umm it should work.. that's the whole point of the GXP BB as long as the drive side bearing seal isn't jammed up against the inner of the spider you should be OK.. remember spacing the drive side cup out does nothing to the cranks as far as chainline and such.

    take a look down inside and see how much the seal is spaced off the spider.. you should be able to guest-o-mate right off if there is enough room or not.


    if it wont work,.. and you just want something to hold the chain leading in the top and not so worried about leaving in the bottom,.. just take a cheapo front derailleur and slap it on there, adj the stops to where it doesn't move... done. might be a tad of weight if you're a weight weenie but I'd take a few grams over dropping a chain in a race any day
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  25. #25
    mtbr member
    Reputation: mack_turtle's Avatar
    Join Date
    Jan 2009
    Posts
    5,724
    Ah, I read it more carefully and that makes sense now:

    the spacers are not there to support the bearings so much as to insure chainline?

    the spindle requires at least 73mm of length, which is why you need spacers on a 68mm shell? so if I add a spacer to the drive side of a 73mm shell, it will work because the drive side of the spindle will just slide further into the drive side bearing to compensate. this might screw up my chain line, but I don't know how accurate my chainline is anyways. I'll check it when I am done.

    does that sound right?

  26. #26
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by mack_turtle View Post
    Ah, I read it more carefully and that makes sense now:

    the spacers are not there to support the bearings so much as to insure chainline?

    the spindle requires at least 73mm of length, which is why you need spacers on a 68mm shell? so if I add a spacer to the drive side of a 73mm shell, it will work because the drive side of the spindle will just slide further into the drive side bearing to compensate. this might screw up my chain line, but I don't know how accurate my chainline is anyways. I'll check it when I am done.

    does that sound right?
    umm no or yes,.. or no LOLOL

    the spacers are there to insure both chainline and bearing width of the spindle. Yes you need (well should have) at least a 73 mm support width on the spindle. but chainline is adjusted on the NON DRIVE SIDE... adding or subtracting spacers to the drive side does nothing as it just floats over the spindle. all side to side movement is controlled by the clamping of the non drive bearing's inner race. I better described in on my little blog... Trailtiretv.blogspot.com scroll down one or 2 posts.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  27. #27
    mtbr member
    Reputation: mack_turtle's Avatar
    Join Date
    Jan 2009
    Posts
    5,724
    yes, that makes perfect sense now. thank you!

  28. #28
    mtbr member
    Reputation: honns's Avatar
    Join Date
    Sep 2011
    Posts
    552
    I learned something about my GXP crank and BB today, thanks all.

  29. #29
    mtbr member
    Reputation: GTscoob's Avatar
    Join Date
    Apr 2009
    Posts
    2,275
    So with all of this talk of using spacers to adjust chainline. If you put a 2.5mm spacer on the NDS cup, that will bring the drive side crank in 2.5mm put push the NDS crank 2.5mm outboard, correct? Seems like that would be funny having a different pedal spacing on either side of the BB.

  30. #30
    mtbr member
    Reputation: mack_turtle's Avatar
    Join Date
    Jan 2009
    Posts
    5,724
    true, but if you have to put a spacer behind your NDS cup to correct your chainline, you're either measuring your chainline incorrectly, or there's something else wrong with your setup. your chainring was poorly designed, your frame BB shell was welded in off-center, or something like that.

  31. #31
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,307

    Sram gxp 73mm bottom bracket h question...

    Quote Originally Posted by mack_turtle View Post
    true, but if you have to put a spacer behind your NDS cup to correct your chainline, you're either measuring your chainline incorrectly, or there's something else wrong with your setup. your chainring was poorly designed, your frame BB shell was welded in off-center, or something like that.
    All current mtb crank chainlines ARE poorly designed and ~5mm too far outboard from ideal. They were move outboard to gain chainring, front derailleur, and chain clearance when using short stays and big tires, not for best drivetrain performance. It decreases efficiency and increases chain drop.

    If you have the clearance moving the crank inboard is an advantage.
    mtbtires.com
    The trouble with common sense is it is no longer common

  32. #32
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by shiggy View Post
    All current mtb crank chainlines ARE poorly designed and ~5mm too far outboard from ideal. They were move outboard to gain chainring, front derailleur, and chain clearance when using short stays and big tires, not for best drivetrain performance. It decreases efficiency and increases chain drop.

    If you have the clearance moving the crank inboard is an advantage.
    what he said... I'm using a 3x9 crank set as 2x9 with the common setup bash guard in place of the monster ring. Never moved my chain line but can easily run any gear out back and have never once dropped the chain no matter if I'm using the 22 or the 32 up front. Thou i did lower the front derailleur which helps
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  33. #33
    mtbr member
    Reputation:
    Join Date
    Aug 2007
    Posts
    279
    Hey Guys,

    I have found this thread to be the single most useful thread in a long time on MTBR.

    So I have a 29er hardtail with a 73mm BB. I have an 2011/12 (i think) X9 GXP crank with an XO spider (42/28T).

    After my trial and error, I couldn't get the crankset set-up until I read this, and then felt much more comfortable with the fact that there is a very slight "space" between the DS sleeve and the bearing.

    BUT!! I put a 2.5 space on the NDS, because without it, the spindle would bottom out against the NDS bearing, preventing me from tightening it down to eliminate play. However, I can get the crank tight now, but there is still a very small amount of side to side play in the crank arms, but only when horizontal (to the ground). When vertical, there is no play. And when I say small amount of play, I mean MAYBE .5-.75mm at the end of the crank arm (if that makes sense).

    I figure it could just be a slightly worn out bearing. But is this play normal? How can I get rid of it? Should I be worried about it? Putting another 2.5 spacer in causes the spider to bind against DS bearing.

    What do you guys think? Thanks again for this thread!

  34. #34
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    BigMike969, something sounds wrong here. Adding spacers behind the cups should have zero change on the arm clamping down to the spindle and preventing or helping it to get tight. the only thing adding spacers to the NDS should do is pull the chain line in 2.5mm.

    the "shelf or lip" in the spindle should tighten right up against the inner bearing race and the crank arm should butt right up against the seal which traps the race on the out side. padding/spacing the cups to the frame has nothing to do with how it holds.

    Sounds to me like you have a bad BB or at least a bad bearing in one cup, but without actually looking I can't say for sure.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  35. #35
    mtbr member
    Reputation:
    Join Date
    Aug 2007
    Posts
    279
    Hey,

    Yeah, something doesn't seem right with it. Here's the things I did and the result:

    1) 2.5 spacers between cup and frame on both DS and NDS (thought frame was 68mm originally) --> caused spider to bind against cup

    2) 2.5mm spindle spacer (tried it on both sides) --> still caused binding, but I wasn't sure where, regardless of which side the spacer was on, DS or NDS

    3) Confused, so measured BB shell, came out to 73mm, so as per SRAM's manual, removed all spacers --> spindle bottoms out against NDS bearing, leaving -+2.5mm between DS bearing and crank arm with significant lateral play

    4) even more confused, put 2.5 spacer between NDS cup and frame, can tighten down fine, no binding, crank spins well and smooth, DS crank/sleeve is not totally flush to bearing, but out maybe .5mm (which sounds like is ok for the GXP set-up), but as I mentioned, have a very small amount of lateral play, but only when cranks are horizontal to ground, and actually slightly more on one side than the other (as in, when the DS crank arm is horizontal to ground but towards rear of bike, has slightly more play than when towards front of bike).

    As I said, I figure it's a bad bearing, but the BB is new'ish (although I did buy it used, but without it being on a bike, I couldn't tell that there was a bearing issue).

    I might try and track down a new/other BB and see if that fixes it, but I don't know that I will be able to.

    Thanks again!!

  36. #36
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by bigmike9699 View Post
    Hey,

    Yeah, something doesn't seem right with it. Here's the things I did and the result:

    1) 2.5 spacers between cup and frame on both DS and NDS (thought frame was 68mm originally) --> caused spider to bind against cup

    2) 2.5mm spindle spacer (tried it on both sides) --> still caused binding, but I wasn't sure where, regardless of which side the spacer was on, DS or NDS

    3) Confused, so measured BB shell, came out to 73mm, so as per SRAM's manual, removed all spacers --> spindle bottoms out against NDS bearing, leaving -+2.5mm between DS bearing and crank arm with significant lateral play

    4) even more confused, put 2.5 spacer between NDS cup and frame, can tighten down fine, no binding, crank spins well and smooth, DS crank/sleeve is not totally flush to bearing, but out maybe .5mm (which sounds like is ok for the GXP set-up), but as I mentioned, have a very small amount of lateral play, but only when cranks are horizontal to ground, and actually slightly more on one side than the other (as in, when the DS crank arm is horizontal to ground but towards rear of bike, has slightly more play than when towards front of bike).

    As I said, I figure it's a bad bearing, but the BB is new'ish (although I did buy it used, but without it being on a bike, I couldn't tell that there was a bearing issue).

    I might try and track down a new/other BB and see if that fixes it, but I don't know that I will be able to.

    Thanks again!!


    the spindle should bottom out on the bearing,.. it's how they work, the spindle traps the bearing smaller race and the crank arm pinches it on the outside (with the bb seal which has a thick metal washer/spacer build in) Soinds to me like you have something binding the crank arm from going onto the spindle all the way.

    are you using a threaded BB or a Press fit? I haven't played with the press fit yet as most of the stuff I deal with is older and before it's time. (hell my cranks are 2006 Stylo's which are still awesome and lighter than many current models )

    I do know when the went to "X-#" cranks from stylo they added a little goofy wrinkled looking washer thingy that acts as a filler and contact point on the Non drive side.

    sounds to me like you are missing it as you shouldn't need any spacers between the crank arm and the spindle...
    Attached Thumbnails Attached Thumbnails Sram gxp 73mm bottom bracket h question...-crank.jpg  

    Last edited by thomllama; 02-22-2013 at 02:26 PM.
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  37. #37
    mtbr member
    Reputation:
    Join Date
    Aug 2007
    Posts
    279
    hey,

    Thanks for the reply.

    The frame is a standard threaded BB.

    I do still have that spacer in there, as well as everything else in the exploded diagram. I really think it's a bearing, but what confuses me is that given my BB width, and the fact that I have all the parts (according to the exploded diagram), I should be able to make it work without any cup spacers, but it bottoms out. And, I measured and re-measured the BB shell, and it is definitely 73mm.

  38. #38
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    don't know what else to tell you,.. all I can think of is that you have something stuck in the splines so the crank arm isn't going all the way on,.. or you're using a non GXP crank or something... ? if ya lived in the CT area I'd say bring it over and I'll take a look.

    last idea I got without getting my hand on it is to take the whole thng off the bike, take just the non drive bearing cup and slide it onto the spindle... examine the from the inside and make sure the spindle is bottoming out on the bearing's race, slide the crank arm on and examine how far it goes... if something gets inside the crank arm you may want to pull the 2 bolts (the main bolt and the back out bolt) and make sure nothing is in there .. stopping the arm for going on all the way...

    hey,.. thought ,.. you don't have the attachment bolt OUTSIDE the back out nut? it supposed to be trapped inside!



    take pictures will help
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  39. #39
    mtbr member
    Reputation:
    Join Date
    May 2012
    Posts
    1
    I'm soooo thankful I came across this thread after reading tons of garbage for the past couple days. I was really scratching my head at a bike I purchased that has a 73mm BB cup and a spacer on each side of a GXP BB. I'm about to replace the BB and install a Blackspire Stinger, so this is just the post I needed to see. Thanks!

  40. #40
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by salsinator View Post
    I'm soooo thankful I came across this thread after reading tons of garbage for the past couple days. I was really scratching my head at a bike I purchased that has a 73mm BB cup and a spacer on each side of a GXP BB. I'm about to replace the BB and install a Blackspire Stinger, so this is just the post I needed to see. Thanks!
    glad it worked out for ya
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  41. #41
    mtbr member
    Reputation: Ramjm_2000's Avatar
    Join Date
    Jan 2005
    Posts
    1,117
    So if I understand this and the link XX crank link the max allowable width for GPX is 75.5mm, if I was running a GXP system on a 68mm BB with 2.5 or each side and decided I wanted to widen/adjust the q factor by 2mm would adding a 1mm spacer on each side do it? or would it bring the chain line in by 1mm because of the floating DS?

  42. #42
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,307
    Quote Originally Posted by Ramjm_2000 View Post
    So if I understand this and the link XX crank link the max allowable width for GPX is 75.5mm, if I was running a GXP system on a 68mm BB with 2.5 or each side and decided I wanted to widen/adjust the q factor by 2mm would adding a 1mm spacer on each side do it? or would it bring the chain line in by 1mm because of the floating DS?
    The width of the crankset (Q factor) is fixed, can not be changed. Using/moving spacers on the non driveside changes the chainline.
    mtbtires.com
    The trouble with common sense is it is no longer common

  43. #43
    mtbr member
    Reputation: Ramjm_2000's Avatar
    Join Date
    Jan 2005
    Posts
    1,117
    I understand in theory the q factor is fixed and should be related to the spindle length but what I'm asking is if 1mm is added on each side (not NDS only) would you not by virtue increase the total width to 75mm when completely tightened (vs. 73mm)? I'm assuming the q factor is calculated based on the pedal eye to eye width completed cinched down.

  44. #44
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,307

    Sram gxp 73mm bottom bracket h question...

    Quote Originally Posted by Ramjm_2000 View Post
    I understand in theory the q factor is fixed and should be related to the spindle length but what I'm asking is if 1mm is added on each side (not NDS only) would you not by virtue increase the total width to 75mm when completely tightened (vs. 73mm)? I'm assuming the q factor is calculated based on the pedal eye to eye width completed cinched down.
    You really need to read this whole thread and learn how GXP cranks/BBs work.

    Spacers on the drive side have ZERO affect on chainline or Q factor.

    Additional spacers on the NDS reduce the chainline and have ZERO affect on the Q factor.

    The spacers only affect the distance between the bearing cups. The crank still just tightens against the NDS bearing. Nothing else. period.
    mtbtires.com
    The trouble with common sense is it is no longer common

  45. #45
    mtbr member
    Reputation: linguinee's Avatar
    Join Date
    Jun 2013
    Posts
    11

    Some Photos

    Quote Originally Posted by thomllama View Post
    Believe me, you're not the first person who didn't understand the system,.. I've had tech's in shops that didn't get it even after I showed it to them

    Glad you figured it out
    thomllama, your explanations and analyses are spot on; we could use more threads such as this.

    I've uploaded two photos of my GXP Truvativ Rouleur crankset and (BSA spec'ed) BB cups that demonstrate what you've so capably detailed.

    Photo 01: The spindle of the Roleur crankset focusing on the shoulder that abuts the NDS BB bearing.

    Photo 02: An installation mockup. The GXP BB cups–with 2 spacers (as per 68mm BB shell width installations–fitted over the spindle. NOTE: the NDS cup is resting on the shoulder of the spindle while the DS BB cup's bearing, having a slightly greater inner diameter, slip fits, past the shoulder all the way to the crank's spider without engagement or hindrance.

    Compliments on an edjumacating thread.
    Attached Thumbnails Attached Thumbnails Sram gxp 73mm bottom bracket h question...-01.jpg  

    Sram gxp 73mm bottom bracket h question...-02.jpg  


  46. #46
    mtbr member
    Reputation:
    Join Date
    Oct 2012
    Posts
    82
    Quote Originally Posted by thomllama View Post
    the spindle should bottom out on the bearing,.. it's how they work, the spindle traps the bearing smaller race and the crank arm pinches it on the outside (with the bb seal which has a thick metal washer/spacer build in) Soinds to me like you have something binding the crank arm from going onto the spindle all the way.

    are you using a threaded BB or a Press fit? I haven't played with the press fit yet as most of the stuff I deal with is older and before it's time. (hell my cranks are 2006 Stylo's which are still awesome and lighter than many current models )

    I do know when the went to "X-#" cranks from stylo they added a little goofy wrinkled looking washer thingy that acts as a filler and contact point on the Non drive side.

    sounds to me like you are missing it as you shouldn't need any spacers between the crank arm and the spindle...
    Thanks for this great thread. Saved me lots of headache. I panicked when I saw about a 2mm gap between the DS spindle and the bearing. My setup is a 73mm BB shell using threaded GXP on an Epic.

    I was able to torque down the NDS bolt to 48 nm and have no side to side play using no spacers. However, my crankset did not come with the "washer" that you labeled "this thing", so I'm wondering either it was shipped missing or because its a newer MY that SRAM did not update the documentation?

    Other than the missing "washer", everything seems to be functioning and again no lateral play. It was just the gap on the DS that had me worried as I'm used to either Shimano BB or SRAM PF30 BB being fully seated against the bearings.

    So question is do I still need the NDS "washer" or not?

  47. #47
    mtbr member
    Reputation: linguinee's Avatar
    Join Date
    Jun 2013
    Posts
    11
    Quote Originally Posted by nsxtc View Post
    I was able to torque down the NDS bolt to 48 nm and have no side to side play using no spacers. However, my crankset did not come with the "washer" that you labeled "this thing", so I'm wondering either it was shipped missing or because its a newer MY that SRAM did not update the documentation?
    I've two GXP cranks: the ~5 year old Rouleur pictured up thread and a year(?) old 10spd SRAM Apex Compact crank and BOTH require the NDS compression washer. Once I installed the Rouleur without the washer between the crank and the BB and it was immediately apparent by the crankset's increased drag/play that it wasn't an optional component.

    Please see the photos for clarification:

    Photo 1: the outside of the compression washer and a bearing cup. Note the outboard surface of the washer is basically flat. (I mistakenly used the DS bearing cup in the photos. Ooops.)

    Photo 2: the inboard side of the washer, the one that abuts the BB bearing. It's difficult to see from the photo but there's a shoulder encircling the splined hole of the washer that interfaces with the BB bearing's inner race, thus pinching bearing against the crank spindle's NDS shoulder.

    In this case, without that compression washer the torqued NDS crank would contact the BB bearing races. Not good.

    You're saying that your crank did not ship with the something akin to the compression washer pictured?
    Attached Thumbnails Attached Thumbnails Sram gxp 73mm bottom bracket h question...-photo-1-outboard.jpg  

    Sram gxp 73mm bottom bracket h question...-photo-2-inboard.jpg  


  48. #48
    mtbr member
    Reputation:
    Join Date
    Oct 2012
    Posts
    82
    Thanks for taking the time and digging out old parts and taking pics for illustration and clarification.

    Yes, no compression washers. I guess I'll see if my LBS has one. Otherwise I'll have to contact the shop I ordered from and have them ship a replacement.

    Quote Originally Posted by linguinee View Post
    I've two GXP cranks: the ~5 year old Rouleur pictured up thread and a year(?) old 10spd SRAM Apex Compact crank and BOTH require the NDS compression washer. Once I installed the Rouleur without the washer between the crank and the BB and it was immediately apparent by the crankset's increased drag/play that it wasn't an optional component.

    Please see the photos for clarification:

    Photo 1: the outside of the compression washer and a bearing cup. Note the outboard surface of the washer is basically flat. (I mistakenly used the DS bearing cup in the photos. Ooops.)

    Photo 2: the inboard side of the washer, the one that abuts the BB bearing. It's difficult to see from the photo but there's a shoulder encircling the splined hole of the washer that interfaces with the BB bearing's inner race, thus pinching bearing against the crank spindle's NDS shoulder.

    In this case, without that compression washer the torqued NDS crank would contact the BB bearing races. Not good.

    You're saying that your crank did not ship with the something akin to the compression washer pictured?

  49. #49
    mtbr member
    Reputation: linguinee's Avatar
    Join Date
    Jun 2013
    Posts
    11
    @ nsxtc

    My experience with GXP configurations only extends to Rouleur and Apex cranksets. Perhaps your left crank spindle interface has a specific profile that negates the compression washer. You may have everything you need already.

    In any event please update the thread with your progress. (Valuable for future reference.)

    Keep on rolling.

  50. #50
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,232
    Quote Originally Posted by linguinee View Post
    @ nsxtc

    My experience with GXP configurations only extends to Rouleur and Apex cranksets. Perhaps your left crank spindle interface has a specific profile that negates the compression washer. You may have everything you need already.

    In any event please update the thread with your progress. (Valuable for future reference.)

    Keep on rolling.
    most of the MTB (stylo, X9,X7..bla bla bla) have the compression washer built into the BB cup seal..but not all... it's very obvious if you need it and if you got the torque on the bearing and it's not dragging really bad you probably don't need it... it's quite obvious on the bearing seal also.. if you read the write up on TrailtireTV there is a picture of the BB cups and bearing seal diffs...
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

Page 1 of 2 12 LastLast

Posting Permissions

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