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Old 02-11-12, 02:26 PM   #1
cyclekolo
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Sram crank/ultegra cassette

I will be installing a double Sram double crank/68 gxp bb and using an Ultegra 6700 10 speed cassette on my setup this season (all the other components are Ultegra 6700). I have researched as for compatibility and that setup seems fine. The only thing I could not find out is if you can install the gxp bb as is or do you need to use shims/spacers under the bb cups to have to have the correct chainline between the Sram crank/rings and the Ultegra 6700 cassette? Thanks
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Old 02-11-12, 02:50 PM   #2
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I can't answer the specific BB question. But chain line is chainline and the brand of cassette or crank doesn't change that since the cassette position is determined by the frame's dropout width, and the crank must line up with that.
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Old 02-11-12, 03:11 PM   #3
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GXP BB is designed for 73mm BB shells, so the spacers are necessary for 68mm shells.

if you don't use the spacers, either of two things can happen: a) the threads will bottom out, or b) your right side will sit further outside, because the cranks are aligned to the left side.
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Old 02-11-12, 03:38 PM   #4
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Thanks for the replies. AEO- would you be able to tell me the amount of spacers and their thickness (should it total 5mm to make up the difference between the 68 and 73) and which side to install (drive non drive) them on to? Thanks
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Old 02-11-12, 03:53 PM   #5
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you put one 2.5mm spacer on each side. It's on the poorly written documentation that comes with the GXP BB package.

or it should be like that, at least. The manual is poorly written, like I've said. I had to use one 2.5mm spacer on each side with my truvativ touro triple with a 68mm shell.
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Old 02-11-12, 06:51 PM   #6
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Originally Posted by AEO View Post
GXP BB is designed for 73mm BB shells, so the spacers are necessary for 68mm shells.

if you don't use the spacers, either of two things can happen: a) the threads will bottom out, or b) your right side will sit further outside, because the cranks are aligned to the left side.
This is true for a triple or MTB crank, but not a road double. You do not use spacers for a road double, if you did, when you tighten down the crank arm the crank will not spin because the chain ring side will bottom out on the bearing.

GXP is designed such that lateral position (chainline) is determined by the capturing the left side bearing between the spindle and left crank arm. The right side bearing floats on the axle to allow for frame width variation.

OP, you should assemble with no spacers and check the chainline, If for some reason, you need to shift the chain line to the left you can put a spacer between the left side bearing and frame. I have built many bikes with SRAM double cranks and GXP bottom brackets and have never required a spacer.
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Old 02-11-12, 09:22 PM   #7
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no issues, don't use the shimano spacer if you have one
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Old 02-12-12, 09:18 AM   #8
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This is true for a triple or MTB crank, but not a road double. You do not use spacers for a road double, if you did, when you tighten down the crank arm the crank will not spin because the chain ring side will bottom out on the bearing.

GXP is designed such that lateral position (chainline) is determined by the capturing the left side bearing between the spindle and left crank arm. The right side bearing floats on the axle to allow for frame width variation.

OP, you should assemble with no spacers and check the chainline, If for some reason, you need to shift the chain line to the left you can put a spacer between the left side bearing and frame. I have built many bikes with SRAM double cranks and GXP bottom brackets and have never required a spacer.
Ok. I have the crank on, no spacers, torqued and spining nicely without any lateral movement. I just have one more question now, and that is how to properly check the chain line? Thanks all for taking time to answer my questions.
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Old 02-12-12, 10:07 AM   #9
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Originally Posted by AEO View Post
you put one 2.5mm spacer on each side. It's on the poorly written documentation that comes with the GXP BB package.

or it should be like that, at least. The manual is poorly written, like I've said. I had to use one 2.5mm spacer on each side with my truvativ touro triple with a 68mm shell.
only use spacers for mtn crank. the spindles are different lengths between mtn and road. not so much poorly documented but the bb is the same between road and mtn
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Old 02-12-12, 10:20 AM   #10
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Ok. I have the crank on, no spacers, torqued and spining nicely without any lateral movement. I just have one more question now, and that is how to properly check the chain line? Thanks all for taking time to answer my questions.
It seems like you have it together correctly,chain line shouldn't be a problem. If you want to check it, the chain line should be 44.5mm from the center of the down tube to the center between the two chain rings.
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Old 02-12-12, 07:23 PM   #11
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It seems like you have it together correctly,chain line shouldn't be a problem. If you want to check it, the chain line should be 44.5mm from the center of the down tube to the center between the two chain rings.
I meassured the chain line as accurately as possible and it seems very close to that of 44.5mm. Thanks again for your help.
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