Do 26" race bikes use bottom bracket heights that are that low? Just curious.I wanted to keep the bb height lower than 11.25" and have a top tube angle no greater than 17 degrees. I ended up pulling the bb up to 11.33 to get the front deraileur to work better (running a brazeon IRD road compact with a 29/38 setup). Any higher on the BB and I would have pisspoor standover clearance, not to mention I was aiming for 74mm of drop...
74 works real well for me with 34c's, so I'm not going to have any issue with 47's or 50's.
With a 432 axle to crown fork with 48mm of offset that puts my center of mass pretty much perfectly distributed between the wheels. Any higher on the BB is going to move the weight bias toward the front of the bike, and is going to unweight the rear tire more than I'd like for out of the saddle climbing. I guess those who like to over-classify bikes would call it more of a "monster cross" bike, but I call it a fast bike for XC racing....