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.

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?

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).