What's in a bottom bracket?? (How important is it after the frame???)........
 

Long story, short, I feel I'm approaching power/efficiency limits on my hybrid. I love (and I mean LOVE) this bike. Cannondale Quick 4. And to me it's a very rigid, lightweight, smooth, nimble and joy of a ride! (No joke) Last road bike I rode was back in the mid 80's. (SR steel 10-speed) So this feels like a feather on wheels in comparison.

That said.....I've heard suggestions that to get to the next level, I really need a road bike. Specifically, my frame & bottom bracket hold me back. (components are arguably pick/choose & better wheels are always better but generally speaking it's frame & BB)

So I get the frame part. More rigid, more agressive geometry, etc. but why the bottom bracket??? What's in a bottom bracket that it matters?? Bigger diameter?? For what?? And why do some people say BB30 sucks?? (flame suit on)

;)

I doubt the bottom bracket is holding you back. Most of the time I hear people discuss bb, it's really the bb shell of the frame and how stiff it is. Stiffer bb shell/stiffer frame will in theory give you more efficient power delivery form pedals to wheels.

When you asked the people you heard that from, what did they say?

Not much, to be honest. Some (mostly roadie folk) say "rigidity" but don't say how. Thus, rms13's comments make sense to me. I understand the idea behind architectural geometry lending itself toward rigidity as it pertains to 2 angles coinciding with an arc but I don't know how the BB itself is supposed to be as significant. However, I feel I must be missing something cuz BB30 (and others) appear to be the only thing available on higher-end bikes. Otherwise, they'd all have the same diameter & parts, no?

(I read thru the thread here a while back that asked, "Is BB30 fixed yet?" and wondered what's wrong?)

The advantage of a road bike is the position. If you are flexible enough to ride in the drops with a flat back you can go fast if you have the engine for it. The bike has always been an efficient way to travel. The multiple triangles in the frame makes for a bike that is a rigid as it needs to be.

BB30 in theory is supposed to be more efficient than other bb standards:

Innovation - BB30

In practice I think a lot of people have had problems with the bottom bracket not sealing tightly and leading to creaking. I have a BB30 frame with an adapter to use a standard 68mm bb and I have had to battle some creaks since I built this bike. But I think a lot of problems i.e. people complaining on forums probably equals problems with 5% of the frames out there in reality. And most of the problems are probably related to components that were not properly installed.

It's true that BB stiffness affects power transfer. But unless you have a real "wet-noodle" frame, the power levels at which this becomes a significant discriminator are pretty high. It's far more likely that what's holding you back on your hybrid (aside from the engine), is aerodynamics and position on the bike. Those are the primary reasons to upgrade to a true road bike.

If I had to rank things in order of their impact of speed or endurance it would be something like this

1-engine
2-fit and position
3-tires and tire pressure,

.....

99-bottom bracket.

I don't believe that the quality of the BB, running from best to worst, would have any measurable impact in the general scheme of things,

What's in a bottom bracket that matters?? Seriously? You match the BB to the crankset and the frame. Stiffness or power transfer differences between the different 'standards' are insignificant.
I put a quote around 'standards' because we have about a dozen of them right now. 30 years ago there was basically one shell standard (French was gone, and Italian a small share of the market), with different widths of bottom brackets to match the crankset requirements.
Now we have chaos that local shops cannot stock for, or even keep track of. The old square taper standard was more than 'stiff' enough for sprinters or track specialists who could crank out 1,500 watts.

This demonstrates the sad slavishness to trends in the bike industry, which has unfolded as follows:

1. About 20 years ago, some marketer (obviously not an engineer) decided that bottom brackets needed to be 'stiffer'. Translation: no technical problem to be solved, but we needed something new to create some sales buzz, and to lock consumers into only buying our stuff by creating a propietary system.
2. The solution was to make the spindle larger. Which meant that the bottom bracket bearings had to be correspondingly smaller to fit inside the frame
3. This resulted in rapid failure of the BB bearings
4. Then, to get around the frame standard, the bearings were put on the outside of the frame.
5. This meant that cranksets had a wider width, which is biomechanically less efficient
6. It also meant that bottom bracket bearings were more exposed to the elements.
7. Start all over - make spindles even bigger, but increase the bottom bracket hole size so everything gets put back into the frame - where it belongs.
8. This then proliferates a multiude of new frame 'standards' leading to confusion and headaches for shops and consumers.

A mess!

OK, it's not quite that dismal, at least for newer design bottom brackets the used the "standard" English threaded 68 mm (or 73mm for MTBs) wide bb shell. Taking your numbered points:

1. I agree, square taper was plenty stiff enough and stiffness in and of itself isn't a big deal. The stiffer and stiffer claims were indeed mostly marketing hype as to their effect on the rider.

2 and 3. There were two larger diameter splined hollow spindles; Octalink and ISIS. Octalink worked. I have 35,000 miles on a BB-6500 and thousands and thousands of miles on a BB-550 used on a "rain bike" with no problems at all and my experience isn't unusual. The Dura Ace version was a pain since it was adjustable, not sealed, and required routine maintenance. The other design was ISIS and many ISIS bottom brackets were cheaply and poorly made and gave the entire design a deservedly bad reputation. So, done properly the larger hollow spindle was satisfactory.

4, 5 and 6. External bearings are a bit more exposed but well sealed and the cranks are designed to "wrap around" them so the Q-factor doesn't have to be any wider. I have FC-5703 105 triple cranks with external bearings on two bikes and the above mentioned Octalinks fitted with FC-6500 Ultegra triple cranks on two others and the Q-factors are absolutely identical.

7 and 8. +1 Total agreement there except the "where it belongs" part. The multitude of new and unnecessary "standards" solves no problem and only adds difficulty and complexity.