I have a specialized xc fsr pro, im not sure what year it is 2005,2006?

I bought it second hand was told it was a 2006 but cant seem to find the exact spec i got the bike with on the specialized webiste.

Anyway the BB is on its way out so i look on their website and it seems that the size was 68mm with 118mm spindle length from 2005 onwards.

I bought the 118mm spindle but have just pulled out the BB and its a 121mm spindle.

Can i use the 118mm instead of the 121 and what issues will i have?

I also assume this means my frame is a 2004

Cheers for any help

Ivan

What cranks do you have? Frame only dictates size of shell required, in your case 68mm. THe axel length will be determined by the cranks. Also, are you runnig double, triple or single?

I'd guess that the chainset might be an LX Octalink one, I think that they needed a 121mm axel whereas the Deore, XT etc. ones needed 113mm to give a 47.5mm chainline or 118mm to give a 50mm one. Frame design might dictate the need for a slightly longer axel for clearance reasons but 121mm seems a bit long.

Ahh thanks for the response guys.

It was an Ocatalink LX chainset with tripple rings.
I have upgraded the the cranks to XT ones and it says on the specialized website that the chainline is 50mm.

So does that mean I am good to go with the 118mm BB with the XT cranks.

Cheers

Ivan

I'm pretty sure that a 118mm axel will give you a 50mm chainline with the XT cranks, they should run on either a 47.5mm or 50mm chainline. I don't know though whether the LX cranks on a 121mm axel would be a 50mm chainline or a 47.5mm one, so you might need to fiddle with your front mech.

So am I correct in thinking that the frame is irrelevant in the whole chain line thing?

And am I correct in thinking that if you have an incorrect BB and crank combo its not the end of the world you will just need to adjust the front mech?

I have done a bit of research(googling) which may be of use to someone else if correct and found that the old cranks Deore FC M470 with a 121mm BB give a chainline of 47.5 and with a 126mm BB.

And the XT cranks M751 with a BB of 118mm give a chain line of 50mm and with a BB of 113mm give a 47.5mm chain line

Well, I'll have a go but I'm very much the amateur mechanic. Generally it's down to the crankset but, certain frame designs may require a certain axle length to give sufficient frame clearance – I've got a standard Inbred with XT M752 cranks on a 113mm axle (47.5mm chainline), the cranks are designed to work on a 47.5mm or 50mm chainline – 47.5mm was the prefered but certain frame designs needed more clearance. My 853 Inbred has very wide chainstays and needs a 50mm chainline to give anything like enough clearance between rings and chainstay, so the M752 XT cranks on that bike are on a 118mm axle.

Frame clearance allowing you should be able to run XT Octalink cranks on either a 113mm or 118mm axle. The point about maybe needing to fiddle with your front mech is this – in Octalink days 47.5mm seems to have been the prefered chainline, the LX cranks you had fitted on a 121mm axle may (I don't know) therefore have given a 47.5mm chainline and your front mech would have been adjusted to work with this. If you then put XT cranks on, fitted to a 118mm axle you'll have a 50mm chainline and the mech may be adjusting.

You can use the XT cranks on a 47.5mm or 50mm chainline because they've been designed to work with either so neither a 113mm or 118mm axle is wrong. If you fit a chainset to a BB with the 'wrong' axle length giving a chainline that it's not designed to work with then you could well have problems, for example you could fit the old LX crankset to an Octalink BB with a 113mm axle (in the sense that it would fit) but since it gives either a 47.5mm or 50mm chainline on a 121mm axle I suspect that you'd have no end of issue.

IFAIK modern external BB cranksets are all 50mm chainlines.