# Langster BB information needed.



## bdc88 (Apr 14, 2006)

I am building up a light weight Langster but I am having a hard time sorting out the BB information. According to the Specialized website, it appears that the bb size they use is 68 X 103mm and it is square taper. 

I really want to use a pair of the FSA Compact Carbon cranks that I have which are ISIS. I can not find a BB shorter than 108mm.

So any thoughts on this. FSA does track cranks in ISIS I would assume but on their website I do not see anything shorter than 108mm

Thanks in advance.


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## asterisk (Oct 21, 2003)

For the correct bottom bracket length you have to take your crank choice into account. The 103mm BB they spec is to put the chainring at 42mm from the center of the bike with the *stock crank*, not just any crank. 

A road double is spaced at 41mm for the inner ring and 46mm for the outer meaning if you use the intended bottom bracket for your carbon cranks with the chainring on the inner position, you'll come close to the 42mm chain line you need. If you want to use the chain ring in the outer position you would have to find a bottom bracket 8mm shorter (4mm on each side) and symmetrical which I don't believe most ISIS bottom brackets are.

Read more about chain line here at Sheldon Brown's bike pages.


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## Touch0Gray (May 29, 2003)

asterisk said:


> For the correct bottom bracket length you have to take your crank choice into account. The 103mm BB they spec is to put the chainring at 42mm from the center of the bike with the *stock crank*, not just any crank.
> 
> A road double is spaced at 41mm for the inner ring and 46mm for the outer meaning if you use the intended bottom bracket for your carbon cranks with the chainring on the inner position, you'll come close to the 42mm chain line you need. If you want to use the chain ring in the outer position you would have to find a bottom bracket 8mm shorter (4mm on each side) and symmetrical which I don't believe most ISIS bottom brackets are.
> 
> Read more about chain line here at Sheldon Brown's bike pages.


Then on the inside. couldn't he get the chainline with a shim on the rear then?..or would moving the cog out be moving it the wrong direction?


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## asterisk (Oct 21, 2003)

Shimming track cogs is not a great way to go, you really want all the threads engaged as there aren't many to begin with. There are some cogs that are narrower but that would just move it inward (toward the center) which is the wrong way if you want to use the outer ring.


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## Touch0Gray (May 29, 2003)

ok, i have a pretty much stock, 2005 Langster, and it came with the ring on the outside which proved to be the wrong chainline for a fixed cog, but ok for a freewheel. I tried shimming it ( I used a 1 mm which was still not far enough) So I pulled the shim out and moved the ring to the inside of the spider and it netted me a pretty close to perfect chainline. BUT even with the shim, and granted it was only 1 mm, I could wind the cog on all the way and get the lock-ring on all the way too. I'm not saying that a shim is a great idea, but then again, a straight Langster (especially a 2005 with an alloy fork) might not be the best bike to try to make a "light weight" either...naked, with no rack, mine goes 19 pounds.


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## asterisk (Oct 21, 2003)

As long as you get good thread engagement and the lockring threads on completely you're probably fine, usually however there isn't much room for adjustment on most track hubs. If you're talking a matter of 1mm you can put a shim behind your drive side bottom bracket cup to bump that out a bit but too much will mess with the pedal position.


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