The Tandem Club



Discussion of anything related to Tandems. Opinions expressed on this discussion board are those of the contributors and not necessarily those of the Tandem Club. Postings or extracts may be published in the Tandem Club Journal.
To add a response or post a new message you need to have an account and be logged in. You can get emails sent to you by enabling the Send Forum Emails tick box in your user preferences. Note you need to login to the website to add replies. See our help information here for more information.
You can add to this discussion using the entry box at the bottom of this page, when logged in. Login

Chain ring catches on frame

Jordan Hawes2018-07-31 15:28:18


Recently I bought a mostly together tandem in the hopes that me and my fiancée could go riding together, and still be able to talk to one another, however this is my first time working on a tandem, and I've come across an issue with my cranks, the inner most chain ring on the 3x mounted to the back bangs into the frame, and I'm thinking that I need a new wider bottom bracket, however I don't know what width to buy, and having not put a chain on it yet (cant get the crank on) I don't know if this will mean I need 2 new bottom brackets so that the chainline would be OK. I was just wondering if someone could point me in the right direction so I can get it up and running. :D

Thanks in advance.

Mark Silver2018-08-01 12:15:12

A lot depends on the vintage of the machine. If it is old (roughly 1950's or older), then it'll have the old hard to find spindles that use 5/16" ball bearings. But if later, then much easier, solo size  1/4" bearings.

If you can post pictures, then can probably tell from these.

Jordan Hawes2018-08-11 00:22:34

Sorry for the late reply, hectic week, I've uploaded some pics of the problem on Imgur, link:

The smallest ring overlaps the stoker bottom bracket so it can't turn, I was just wondering if someone could give me a rough estimate of a bottom bracket length that might help, or failing that another fix to help it clears the frame, I haven't even played with chain line yet ;-;



Austen Wynne2018-08-11 10:30:27

Chain reaction do a shimano UN55 68mm wide 118mm BB which should give 2.5mm extra each end of spindle. austen

Austen Wynne2018-08-11 10:39:16

Hi again. 

I see you have a 73mm BB under stoker. Check width of B.B. shell/housing as you will prob need a 72/73mm wide B.B. and not a 68 as I mentioned above. austen

Jordan Hawes2018-08-11 20:58:56

Ok great! To recap for my own sake, go with a 73mm bb that has a 118 spindle? Would I need a similarly long front bb as well, for a straight chain line, or would the current 113mm be alright? 

Much appreciated on the responses though,


Austen Wynne2018-08-12 00:21:44

I would leave the 113 BB at the front as front chain line should be fine. The eccentric front B.B. prob has some lateral adjustability if needed.


Jordan Hawes2018-08-12 00:34:19

Ok, thanks ever so much, really appretiate all the help, ordering a new bottom bracket as we speak, so I'll let you chaps know how it goes.

again much appretiated,


Jordan Hawes2018-08-18 02:52:24

That worked a treat, it's on and everything is working smoothly so far, thamks very much for all the help!