I need to change my bottom bracket and crankset. But I'm not sure what to buy.

I know it's an eccentric botton bracket and I still need one because I use the internal gear hub Shimano Alfine. My preferred crankset is the Shimano Alfine FC-S501.

What do I need to buy additional to the crankset? Can you suggest an eccentric bottom bracket? Or would you suggest a different crankset?

Picture of my bottom bracket

2 Answers 2


Your bottom bracket is screwed into the eccentric. You'll be replacing the bottom bracket. The fact that it's in an eccentric doesn't affect the part choice. The eccentric is more like part of the frame.

To install FC-S501 you need any Shimano road Hollowtech 2 BB, as indicated by BB-SM4600 being the model called out in the Shimano exploded view diagram for it.

  • The 4600 series has been discontinued, so finding a BB-SM4600 might be difficult. The replacement appears to be the BB-RS500. Sep 15, 2020 at 19:11
  • 1
    All road HT2 BBs are interchangeable. If 4600 will work, any other road one will. Sep 15, 2020 at 19:12

You have a square taper bottom bracket. Actually an eccentric one, they are used to tension your chain. You should be able to use any square taper crankset. However, various cranksets require square tapers of different width. We cannot see the width of your BB, but one typically also changes the bottom bracket when changing the crankset and one just buys the width the crankset requires. The bottom bracket is much cheaper.

However, the Alfine crankset you mentioned uses a completely different kind of bottom bracket. It is a two piece crankset, the axle is integrated in the left crank and therefore you cannot use the old bottom brackets that include an axle.

Or choose one of the many square taper cranksets. There are many, there is little point to recommend a specific product. Just remember they require bottom brackets of a specific width.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.