Bottom Brackets Again

[Roy]

What is is advantage / disadvantage between square taper, octalink and hollowtech bottom brackets?

[LittleWheelsandBig]

Octalink is orphaned. Hollowtech are cheap and easy to replace but often die quickly. Square taper tends to be tough as nails but heavier and more flexible. It is easy to modify chainline with different axle lengths. YMMV

There are more variations on the theme e.g. ISIS.

[rogerzilla]

Most modern road racing bikes come with a press-in BB like BB30.  These have a mixed reputation and can creak insufferably, but can be sleeved down to BSC threading with an inexpensive adapter if you prefer HT2 or square taper.

[ElyDave]

HT2 very easy to replace, my experience is actualy pretty positive on the lifespan as well, still using the same bearings > 12 years on on a bike that has had a lot of use including winters, crankset replaced once, but that was due to wear on the teeth

[Brucey]

current hollowtech is HT2. Originally hollowtech and octalink were joined at the hip, so not all hollowtech is HT2.

That HT2 BBs can clap out at low mileage is arguably no big deal; they are cheap and easily replaced. Obviously they last longer if you cantually grease them properly, which is something that shimano seem unwilling or unable to do....

However one of the failure modes is that one or both bearings seize up and then spin on the BB spindle; this can wreck the spindle (in double-quick time if it is aluminium) and destroy the chainset.

ST was displaced originally from MTB use because it wasn't strong enough to withstand drop-offs and the like. HT2 can be stiffer and lighter but you can't get such a wide range of chainsets in this fitting (often at any cost) and it isn't so versatile (eg with adjusting chainlines and so forth). 

A lot of road riders (for training, commuting or touring) reckon that they spend less time and money on ST setups than they would on HT2 and I'd agree with that in most cases.  For a supposedly 'obsolete technology' ST (like 1" threaded headsets etc ) seems to be in rude health....

cheers

[rogerzilla]

HT2 likes the BB shell to be perfectly faced, something everyone thought was less necessary when cup-and-cone BBs went out of vogue.  Cartridge ST BBs aren't very fussy.

[yoav]

My nice road bike is HT2 but my commuting, winter and touring bikes are all square taper.

[Torslanda]

Without wishing to state too much of the obvious, you need to replace like for like. If you run square taper, that's what you buy.

If you want to run something different then you need the matching chainset.

Warning! Opinion based on having to fix the sodding things follows.

Square taper: Shimano UNxx, generally bombproof & fixable ANYWHERE with the right tools. Bearing failure is rarely VOR. Unless you grind on and on ignoring the creaking noises. Huge choice from clashed together cheap stuff thru exotica such as Royce.

HII/GXP etc. Lightweight & less flexible than square taper - hollow axle weighs less & is bigger diameter. Smaller bearings crap out quicker, especially in the UK climate. Fewer mechanical fastenings, easier to install (maybe). Compatibility between systems is zero. Like for like replacements.

BB30/PF30. Proprietary stuff invented by frame manufacturers to fuck your day up completely. BB30 is a chocolate fireguard. If it rains you will need a new one. OK to use if you're a peloton pro with the poor saps stripping and rebuilding the bike every night.

BB86 is Shimano's version of press fit. Seems to work OK, never changed one but installed a few.

Campagnolo. You're having a laugh . . .

[grams]

One problem with square taper is if the bolts come loose* and  you don’t have a 10mm Allen key handy you’re  buggered. And riding with them at all loose knackers the cranks.

(* yes yes,  proper maintenance, blah blah)

[Torslanda]

It's generally an 8mm hex or a 14mm slim socket but yes, I hear you...

[rogerzilla]

Most multitools now have an 8mm allen key, but getting enough leverage may be a problem.  My old Topeak Power 16's USP is that it can tighten 14mm crankbolts, now rarely seen except on vintage gear and BSOs.

[slohill]

Big advantage of taper BBs (JIS) is that you can still get high quality triple chain sets to fit them.
Most of the big manufacturers want to make them obsolete so we can run with ridiculous chain lines and knacker our knees!