[Dmytro]

Hey experts,

I recently purchased a second hand frame. I transferred over the majority of my components from my Stumpjumper, though I bought a new bottom bracket, as per the previous owner’s size (113 x 73) My cranks are the Shimano FC-540, with the “custom, Octalink spline” The previous owner had a Race Face Signature XS bottom bracket, and a Race Face crankset.

I realized that the combo that I have installed leaves me with my cranks too far inboard. For example, the innermost parts of my small ring actually touch the frame’s bottom bracket shells!

I did a search, and some point out that since Shimano’s splines are deeper, a wider bottom bracket is required. Is their logic correct? If so, what would be a good starting point for moving up for me? Any other pointers?
Thanks a bunch!

 

[Speedub.Nate]

Shimano jacked up a good thing.

In order to force a "downspec" of the FC-M540, as well as the LX-level FC-M572, they machined deeper spline patterns on these two cranksets. Doing so requires the use of longer 121 and 126mm spindle lengths, which -- TA DA -- are only available in the relatively crappy ES-51 and ES-30 bottom brackets.

The ES51 is actually not a "junk" bottom bracket, per se, but it is heavier and has poorer quality bearings and seals relative to the pricier ES71 -- an XT level spec.

An ES51 in the 121mm length will get you a 47.5mm chainline with that particular crank, and a 126mm spindle will take it out to 50mm (which I wouldn't hesitate to recommend for a 73mm shell width).

Whatever you do, I doubt you'll be able to make the 113 work.

The unfortunate thing is that, before the 540 and the 572 came along, all ISIS and Shimano v2 Octalink cranks used either 113 or 118mm spindles, and that was that! Too many riders caught on to the value of mating their "cheap" LX crank with a nice XT-level bottom bracket, so Shimano quickly put an end to it!