These new BB90 etc Bottom brackets that are made of plastic, aka composite. They don’t seem very durable to me, anyone else found this? What is the alternative? Quick scan about shows some Hope etc Alu cups. Just wondering how these are when pressed into carbon frames, or if there is a good reason these Shimano BB are plastic?

Ie. do they squeak, expand, cease up?

Carbon frame will usually have a metal insert for the BB so shouldn’t be an issue being carbon.

But the ideal solution is stop using press fit! 😉

fair one. So bike is a BMC the BB is just a carbon shell. Think I am stuck with press fit.

a good number of carbon frames simply run a molded bb shell with no alu insert.

Shimano have made composite cups to help with any intolerance in the molding process.

What durability issues have you found?

My first developed a squeak, that we eventually found was a crack in the bearing shell, the second has only lasted a few months before it starts to wobble. The tolerances thing makes sense, which I suppose is what I was getting at, asking if the Alu ones from hope etc would cause more issues than they solve.