Originally Posted by
Campag4life
Speaking of manufacturing Bob, some of the ardent supporters of BB30 claim that part of its performance advantage over English threaded aka external bearing BB is...co-axiality of BB30 bores can be held tighter than the threading of the cups used in an English threaded BB. If you think about it, the bores themselves of insert molded English threaded cups first have to be held as tight as BB30 bores...but then you have to roll a thread into those English threaded cups. This increases tolerance and makes the argument for threadless BB30. As you say it always comes down to process...a manufacturing control plan and quality control. Same argument you make for good versus bad carbon. Process, process, process.
I missed this. I was away over the weekend.
I understand your point and I both agree and disagree based on what I've seen. For instance, I had a 2008 Fuji in BSA where the two cups we molded in and then tack welded at the join, inside the shell. Guess what broke...But the real point is that the alignment came from the BB itself; It was rigid and as long as the threads were perpendicular to the frame it was good to go.
The problem with some press fit designs is that each bearing is oriented separately. If one is off then the whole system is compromised and there is no strength or guidance from the BB itself. PF30 is a bit better in this regard.
As a personal example of this we saw some frames that were fine out of the mold but after the paint was baked on a very, very small alignment issues developed that only surfaced once the bikes were built and ridden. I don't know why this wasn't caught in final QC (or maybe their go/no go gauges weren't up to the task?) but I know one vendor we worked with had this specific problem. I don't think this would have been an issue with BSA.
As I said, even if tighter tolerances are possible with press fit systems, it pushes that responsibility onto the frame factory and removes it from the component maker to a large degree.