GXP bottom bracket confusion

Nautonier

Eats Squid
Does anyone know what the actual difference is between the 83mm and 68/73mm GXP bottom bracket cups? Is it just a case of the 83mm ones having a slightly longer threaded section to provide more strength in a wide BB housing?

I have some 68/73mm cups that I want to use in my 83mm frame and I want to know if the tolerances are exactly the same, or if I will run into issues. Sitting them side by side they look identical.
 
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mitchy_

Llama calmer
cups are the same, inner tube may be different (although not essential if you're stuck) main difference is obviously the crank spindle length.
 

moorey

Boom!
I've only used 68-73mm GXP, but they have had a sliding tube that accommodate up to 83mm, unlike shimano ones that only work at 73mm.
 

Nautonier

Eats Squid
I've only used 68-73mm GXP, but they have had a sliding tube that accommodate up to 83mm, unlike shimano ones that only work at 73mm.
Sorry, I meant 68-73mm. So it's just the length of the plastic tube that is different? I don't even use that and I don't even know what it's for - is it to keep water out of the cups or something? I can't figure out why Sram would make two different parts that are identical.
 

MrCove

South Shore Distribution
for 68/73 you set them up as 73 whatever your bb width
the only difference is that if you are running a 68mm shell you will have 2 spacers on the drive side and 1 spacer on the non drive
if you are using a bb mount guide or front mech then it'll replace one of the spacers
if you are running 73mm bb then just 1 spacer on the drive side (unless using bb mounted guide or front mech as described)

pretty much all threaded bb's are like this now, GPX/Shimano/Race Face/etc so the same part will fit any size bb

also gives you a bit more adjustment if you require a particular chainline
 

mitchy_

Llama calmer
Sorry, I meant 68-73mm. So it's just the length of the plastic tube that is different? I don't even use that and I don't even know what it's for - is it to keep water out of the cups or something? I can't figure out why Sram would make two different parts that are identical.
yep. a lot of frames will have drainage holes under the BB in case of water ingress. just keeps it away from bearings, etc.
 

moorey

Boom!
Sorry, I meant 68-73mm. So it's just the length of the plastic tube that is different? I don't even use that and I don't even know what it's for - is it to keep water out of the cups or something? I can't figure out why Sram would make two different parts that are identical.
The one I had, i run as 68-73, BUT, it has a rubber O ring that allows it to slide out or in 15mm, and can run a 83mm BB.
 

Gripo

Eats Squid
if you are running 73mm bb then just 1 spacer on the drive side (unless using bb mounted guide or front mech as described)

pretty much all threaded bb's are like this now, GPX/Shimano/Race Face/etc so the same part will fit any size bb

Looks like I might have misinterpreted the colorful diagram.....

Just switched over to SRAM DM cranks and I'm running 73mm BB without any spacers/chainguide etc. chain line and operation seem fine on a 1x10spd...

Better dig out the SRAM installation cartoon?
 

moorey

Boom!
Looks like I might have misinterpreted the colorful diagram.....

Just switched over to SRAM DM cranks and I'm running 73mm BB without any spacers/chainguide etc. chain line and operation seem fine on a 1x10spd...

Better dig out the SRAM installation cartoon?
Or, like my chumba, the frame shell is 73mm, and doesn't need a spacer?
 

mitchy_

Llama calmer
Looks like I might have misinterpreted the colorful diagram.....

Just switched over to SRAM DM cranks and I'm running 73mm BB without any spacers/chainguide etc. chain line and operation seem fine on a 1x10spd...

Better dig out the SRAM installation cartoon?
because the SRAM spindle has a lip on the non drive side, the spindle will stop at the bearing regardless of what's happening on the drive side. it's not essential, but putting the spacer in will just move the drive side bearing out a bit closer to the crank arm.

Or, like my chumba, the frame shell is 73mm, and doesn't need a spacer?
nert, still requires one. spacers are 2.5mm and cranks are actually designed for 75.5mm BB width

68 shell + 3 spacers = 75.5
73 shell + 1 spacer = 75.5
 
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Gripo

Eats Squid
Or, like my chumba, the frame shell is 73mm, and doesn't need a spacer?
That's the case Moorey the TRc and TB are 73mm, so all good then.....Mr Cove had me confused ....

EDIT: Going by mitchy_ then we are all confused....it works it's good theory will apply...
 
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moorey

Boom!
nert, still requires one. spacers are 2.5mm.

68 shell + 3 spacers = 75.5
73 shell + 1 spacer = 75.5
Nope, if I added even one spacer, the spindle would have been too short. Glad I didn't need a BB mounted chain guide on it.
 

Gripo

Eats Squid
Nope, if I added even one spacer, the spindle would have been too short. Glad I didn't need a BB mounted chain guide on it.
That was my observation also, hence why I thought I got it right....not much spindle for the LH crank to hold onto....
 

moorey

Boom!
That was my observation also, hence why I thought I got it right....not much spindle for the LH crank to hold onto....
I also had issues with the crank fowling on the BB cups on another bike when doing up the crank if there wasn't enough spindle. Buy that bike was a problem with everything I tried to do on it....
 
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