Well, I'm immediately over my head. This is a new bike, Specialized Roubaix...all I know is it is a 10 speed Tiagra compact, not sure of the model. I have the opportunity to pick up an inexpensive ultegra crankset but never thought of all the complexities. I'll do some more digging to see exactly what I have. I've emailed Specialized to find out bottom bracket specs. Thank you, all for the fast response and great information!