Reddit mentions of SHIMANO SM-BB51 Deore Hollowtech II Bottom Bracket (68/73-mm BSA)

Hey everyone, due to the end of the world sale by on-one, my plans on getting a new frame might have accelerated a bit.

I bought a 2015 Cannondale F29 last December in Ohio and then moved to Seattle a few month later (wasn't expecting to). The F29 would have been all I ever needed for the Ohio trails, but the trails in Washington are a bit more exciting (I mostly ride Tiger Mountain), and I end up going over the bars fairly frequently with the 71° HTA. I have been thinking about getting a 29er all mountain hardtail, looking at the TransAm, Honzo, Big Wig, and Yelli/EPO. I haven't heard much about the Titus Fireline Evo, and wondered if it would also be a good fit.

It looks like I can transfer over most of my parts from the F29 as well, but I would appreciate if someone took a second look.

Fork: replace 100mm damper with 120mm. I have an email from Cannondale saying this is possible, even for 29er, but I can find no info on this anywhere. Definitely going to follow up before making any purchases.

F29 headtube: 134mm (for fork crown spacing)
Titus headtube: 119mm
Lefty-for-all type 1-1/8" adapter steerer tube with internal headsets required to meet stack height. 1-1/8" stem required to replace 1.5" stem.

F29 seat tube: 27.2
Titus seat tube: 31.6
Shims would be required for my gravity dropper.

Bottom bracket:
F29: BB30
Fireline: BSA 68mm
Would this bottom bracket work to use my existing cranks? Am I correct in thinking all Hollowtech II cranks and BB are cross compatible?

F29 rear axle: 10mm QR
Fireline rear axel: 135mmx10mm QR

F29 brake mount, rotor size: IS, 180mm rotor
Fireline brake mount, rotor size: Post, 160mm min
Will need adapter from IS to post mount.

If I use it, the front derailer may need a clamp on cable stop.

Did I miss anything? Kickstand compatibility? :P

BB standards and headest standards are retarded as fuck.

Brief lesson on BBs:

• Basically, most common standard that was on most bikes is the threaded bottom bracket, with a shell width (ie the left right edge to edge distance of the hole that holds the bottom bracket) of either 68 or 73mm. 68 was common for road bikes, while 73 was common for mtb. You would get something like this, which you would thread into the hole from one side and the cup from the other, and then mount the cranks.
  
  
• Shimano then figured out that you can make the cranks stronger by having bearings wider from each other. So what they did is made a threaded bottom bracket, except the bearings would sit in the external cups. The inner diameter of the BB is 24mm, designed for the 24mm crank spindles, (known as Shimano Hollowtech2). Note that the distance from the inner edges of the cups is 73mm as the wider standard is use on most mountain bikes, and the BB comes with the spacers to make it fit a 68mm width shell for the road or smaller width bikes (some modern dirt jumpers use a 68mm shell). However, the cups themselves are about ~10mm wide.
  
  
• Then bike makers found out that you can make the system even stiffer if you make the cups go in the frame, and thus was born the concept of press fit bottom bracket. Because the cup width was integrated into the shell, the shell width grew by about 20mm (the width of the 2 cups as before). So a bike with the 68 mm shell grew to the 86-90 mm range, and the bike with the 93mm shell grew to the 92-95mm range.
  
  
• The first way of doing the press fit bottom brackets was simply pressing the bearings into the shell. This is the BB90/95 standard and is the widest because of the support structure needed for the bearing. The bearings would be pressed in and fit flush into the frame.
  
  
• The next iteration of that was to include a sealed bearing type that was placed in cups from the factory, and these cups would be press fit into the frame. The cups themselves have a small ~2mm lip on them that acts a stopper against the shell edge when you push them in, so the shell width got smaller for these bottom brackets. So the BB95 became the PF92 (which is what yours is, sometimes called BB92), and the BB90 became the PF86. The advantage of this is that the unit was a sealed type, which meant less contamination, and the cups took up the compression stresses, which means less of a chance of overpressing the bearing during installation, which would lead to a reduce bearing life.
  
  http://problemsolversbike.com/files/tech/Bottom_Bracket_Standards_Reference.pdf
  
  So to answer your question, most shimano hollowtech2 crank will fit, as it is 24 mm and is the correct width for all of the above. The replacement bottom bracket from shimano for yours is called the shimano xt m800 press fit bottom bracket. A lot of them will say shell width of 68/73mm, which is fine because the "true" shell width from bearing to bearing is still 68/73mm.