Originally Posted by
Bob Dopolina
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.
In bold is a great point and to help the 41 who may not be hyper focused on tech, my suggestion is run and don't walk from any frameset that has BB30 that doesn't have an insert molded 'one piece' BB30 bore cylinder. See a pic of the Specialized BB30 below for perspective to those interested.
What a single piece BB30 cylinder which connects both bores promotes:
1. Higher strength. Both bores connected ensures that both bores will stay in place and offer a stiffer BB.
2. Bore alignment. If BB30 bores are insert molded separately as you posit Bob, this sets the frame up for much higher tolerance and potentially higher crank spindle/bearing drag.
I would say most carbon frameset BSA aka English threaded BB's are very similar to the best connected bore BB30 framesets. Processing is very similar...both insert mold an alloy BB cylinder. Only difference other than I.D. is...a BSA English threaded BB has bores that are threaded. In fact these threads can easily be added to the BSA cylinder 'prior to' placing the cylinder in the mold for bonding to the carbon. So there is an added operation for BSA and if comparing the two, adding the thread creates an additional tolerance fractionally contributing to lack of bore center agreement.
I also included a pic of my English Threaded BB with Campy cups threaded in...which shows a 'thru cylinder' on my Roubaix just like how Specialized produces their more ubiquitous BB30 bikes.
OP, also provided a Specialized PF30 pic which OP is probably identical to what you have with your Foil...a virgin carbon thru hole.