Bottom bracket length ???

Hi, I'm ordering some bottom brackets... Can anyone tell me with 100% certainty what length of shimano square taper BB I need for each? Thanks!

Just incase you need to know, all will be on 68mm British shells...

1. Deore XT M730
2. XTR M900
3. RaceFace Turbine 94bcd
4. Syncros

Thanks!

122.5
107
107
107
(you can check all these in the archive as all the tech docs for each are there)

Thanks! Does this hold true for ALL frames? Including a Rocky Mountain experience?

Thanks!

It's not usual for me to disagree with Fluffy, but my RM Experience needed a 127mm BB when it should have been a 122.5. With the shorter axle the front mech couldn't move inboard enough to shift to the granny ring. With the longer axle it all worked fine. Probably due to the chunky seat tube, a couple of mm slimmer and it would have been ok.

As above, at doesn't hold true for all frames, but for the majority it does. Spec sheets are in the archive for each one though.

They should be fine on the bike but above shows the m730 probably isn't with, I assume, the m736 front mech?

It would then be
127.5
113
113
113
Which moves you to the alternative 50mm chain line.

Unfortunately, you're in the 'fit and hope' section :-(
The longer will tend to always work, but maybe not quite as nice a setup as the shorter one.
See if you can grab other Experience users and see what their raceface/syncros/m900 needed?

P.s. what are you doing with 4 of the best chasinsets made ;-)

Here is a good reference for Shimano Bb lengths:

http://www.shimano.com/publish/cont...tml/05) Crankset and BB Combination Chart.pdf

That would suggest that if my DX chainset needed 127 the m730 would need 127 and a M900 would need 113mm.

Thanks! Ill look through the linkie and do a little trial and error =)

Here's the intended usage:

XT M730 - Rocky Mountain Fat City Flyer
Race Face Turnine - Rocky Mountain Experience
Syncros - 1992 steel Rocky Mountain Vertex
M900 - Rocky Mountain Ti Bolt

The M900 pictured came on my experience and is near NOS but its 170.... So it's up for grabs.. I need a 175...

I have to measure the BB that's in there... It's a nice one so hopefully it's good for the turbine...

I'm still looking for a Syncros crankset... Eventually one will pop up on eBay for a good price...


Thanks!!

Other than the Experience, use the shortest length.

As for Why you may need to run the longer one my rule (and I think it's a general rule) is that
for 28.6 (small band) use the shortest, only try the longer one if you have a problem with it or if you are running the large band 34.9mm diameter.
Not sure what the experience band is but it's probably the larger, possibly the middle one.

For the reason's why, look at this document and the stroke range, you'll see it's different as the mech gets pushed further from the centreline. that's why the longer bottom bracket pushes it further from the centreline as well.
http://www.retrobike.co.uk/gallery2/v/M ... ewsIndex=3


If the bottom bracket on the experience is shimano , there will be MM107 or LL113 stamped on the axle and should be visible if you look for it. that's it's length.

If it's 107, then ace as you can use it to try the raceface/m900 on the bikes.

Thanks! The experience is 34.5 so ill start wider =)

I'm going to go through all my bottom brackets tonight and see what I have...

Is there anything wrong with using a 110?? Why jump from 107 to 113???