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  1. #1
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    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??

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    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.
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  3. #3
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    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

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    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
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    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 04:02 AM.
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    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 05:06 AM.
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  7. #7
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    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.

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    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...

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    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.

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    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 08:56 AM.
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    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 10:13 AM.
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  12. #12
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    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  

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  13. #13
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    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
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    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 12:59 PM.
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    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 01:46 PM.
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    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.

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    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 02:47 PM.
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  18. #18
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    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.
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  19. #19
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    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.
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  20. #20
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    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

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    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.

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    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
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    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
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    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
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    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?

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