Framebuilding Time

Easton eccentric bottom bracket with the shell in Rene Herse/Alistair Spencestyle. Eccentrics are heavy, this setup weighs 425 grams.

Seat tube mitered and water bottle bosses brazed in.

3 hours down, lots more to go.


  1. Bryan Willman says:

    Alex – what’’s the point/advantage of an eccentric bottom bracket?

  2. AlexWetmore says:

    Bryan — It is used to tension the chain on a bicycle without a derailleur. This bike is being built for a Rohloff internal gear hub.

    The other options would be using a chain tensioner (ugly and inefficient), horizontal or sliding dropouts. I have a bike that was built for sliding dropouts and wanted to try something else this time around.

    Eccentrics are mostly seen on tandems where they are used to tension the timing chain (the chain between the front and back cranks).

  3. Jason says:

    The new (shown at interbike 08) niner eccentric bottom bracket is superlight in comparison. If I weren”t on my phone I would paste a link.

  4. Jimmy Livengood says:

    Jason, that Niner one looks sweet, and they say that alignment of the two sides isn”t an issue.

    I haven”t used an eccentric, but I notice Alex’’s has holes for a pin spanner to help adjust tension, the Niner one doesn”t. Is pressure on the cranks/bb alone enough to help rotate the eccentric in the shell?

    Alex, is the 425gms for eccentric and steel shell/bolts, or just the eccentric?

  5. AlexWetmore says:

    425 grams is for the eccentric insert and the shell with bolts. The shell and bolts are heavier than the insert (which is aluminum).

    It looks like the Niner eccentric would fit inside the shell that I”m building. I”ll have to weigh my insert, but I”m guessing that will save on the order of 100 grams, not much more.

    I don”t think it makes sense to talk about weight without including the shell. A 2 inch or larger EBB shell has twice as much metal as a normal BB shell. I could have machined out the middle to save some weight, but this is my first frame and I”m more worried about heat distortion than weight.

  6. AlexWetmore says:

    The Easton insert is 198 grams, so the Niner is only 80 grams lighter.