Using 110mm BB instead of 123mm

[Rouxenator]

I am in the process of upgrading from a 8 speed (Alivio/Acera) setup to a 9speed configuration. Currently I have 73x110mm BB-UN26 and I am worried it might not work with the new crank (FC-M391) which recommends a 123mm BB

 

Does it really matter that much? Should I get a longer BB before I can use the FC-M391?

[Vangar]

Not sure if it will work. But the bottom brackets are less than R200 by the looks of it. Might be well worth replacing.

[Rouxenator]

Hopefully it is not that big a train smash and the only thing affected will be the chainline.

[Flowta]

Hopefully it is not that big a train smash and the only thing affected will be the chainline.

 

The chain line will be different, of course. But you might be ok with that.

 

Provided you don't run into to any clearance issues it'll work.

 

Try it and if it doesn't work then get a new BB.

[JA-Q001]

ja, just check that the blades clears your frames and that the FD can set that low, otherwise you wont be able to shift to your granny.

[PeterF]

You get a spacer to use with the BB to increase the width. Your LBS should have some laying around. Not sure which side it goes on but I think it is the drive side.

[David Marshall]

I am suprised that you have a 110mm BB because that is usually only used on road frames with two chainring cranks. Road tripple BB's are often 118mm and MTBs longer. Just check the following before you make the change. 1) the bb shell width of your frame (68 or 73mm). 2) are there any spacers on the drive side of your BB? These will effectivly lengthen your BB.

I would try your new crank first on your current BB.

[Rouxenator]

It is a standard Shinamo BB UN26 73x110 that I specifically imported because on my Zaskar (designed to use an external BB) the chainline was way out when I use an Alivio/Acera 8speed crank with square hole.