Tuesday Tune-Up: BB Standards Explained

This was a request from a reader who is utterly confused by the number of different bottom bracket standards on the market – an easy situation to find yourself in given the ridiculous number of variations out there.  What follows is a bit of an overview on what they’re all called, what they each look like and why you might choose one over another…

Square Taper
What some still call the proper BB format.  The first, and only real, BB standard since cottered cranks. Use this on a classic build, a track build, or if you’ve got a set of beautiful square tpaer cranks that you just can’t let go of. Just don’t install them with anything more than the merest hint of a bit of grease or copper slip!

ISIS
The one that came after square taper, and the one with bearings made of cheese.  Generally best avoided unless, again, you have an ISIS chainset that you just cannot bear to let go of…

Octalink
Shimano’s version of ISIS.  Better, marginally; but this format limited you to only running Shimano cranks which, back then, were never that pretty!

External & GXP
Up until 2 or 3 years ago this had the potential to become the next ‘standard’, and it’s still what most people refer to when they talk about a ’24mm BB’ or a Shimano-compatible BB.  SRAM’s GXP format differs slightly in that is has a smaller hole on the non drive-side bearing, but Chris King and Hope both offer adaptors for their BBs if you prefer to run something more colourful than SRAM’s standard offerings.  And yes, it’s also another opportunity to get some Chris King bling on your bike!

BB30
Originally started life as a part of Cannondale’s ‘Si’ (or System Integration) range of technical features, this was the first of the BB ‘standards’ to mount the bearing directly into the frame.  Requires incredibly tight frame tolerances and careful installation, along with wave washers and other gubbins to work properly.  PressFit30 is sometimes mistakenly called BB30.  Here the ’30′ refers to the bearing inner diameter.

BB90 / BB86 (sometimes called ‘press-fit Shimano’)
Like BB30 in the the bearing fits into the frame, but here the ’86′or ’90′ refers to the fact that the BB is 86mm or 90mm wide.  Trek, Giant and Scott use these.  Generally designed for Shimano, these are not normally BB30 compatible.

PressFit30
A much simpler, perhaps more forgiving, version of BB30.  The bearings sit in Delrin or machined aluminium cups which are pressed into the frame.  Allows for marginally less tight frame tolerances whilst also providing a bigger BB shell to build onto (which is why many custom builders use PressFit30 now). Requires a 46mm BB shell diameter versus the BB30′s 41mm.  Often incorrectly referred to as BB30, although PressFit30 and BB30 cranks are interchangeable.

BB386 Evo
The latest ‘standard’ to emerge and the brain child (of sorts) of FSA.  Based on a cross between BB30 and PressFit30 (which I think is where the ’3′ comes from) but with an 86mm bottom bracket width (hence the ’86′).  It basically seems to employ a series of adapters to make any or all ‘current’ crank types work.  Sort of.  At one time it looked as though this might catch on as the rumour mill started hinting that Shimano would get on board with this.  The latest release of Dura-Ace shows they are sticking to their tried and trusted 24mm format crank axle though so BB386Evo is now reliant on frame builders taking it up in the hope that the likes of Shimano, SRAM and Campag might follow suit… which I think is unlikely.

There have been others along the way – Tune used to offer a crankset and BB which was like square taper / ISIS but with a hexagonal interface called the BigFoot. Look still offer their ZED system with something like a 60mm BB diameter to fit their massive crank format.

Some of the above are referred to by different names too – square taper is also known as JIS, external BBs are called ‘X-Type’ by Race Face (and other brands have their own name) and there are variations on the theme in almost all cases.

And then of course there’s the Italian threaded BBs… but you only need to worry about this if you intend to run a square taper, ISIS or external BB on an older frame these days.  That said, Dario Pegoretti still builds with Italian threaded BBs!

Bottom brackets are available that take two (or more) of the ‘standards’ above to allow you to run a different type of BB on a particular type of frame.  You want a BB for a PressFit30 frame designed to run your 24mm axle Shimano cranks?  No problem sir! Rotor and Praxis are two particularly good examples of companies offering solutions on this front.  If you don’t want to fit a specific BB then the likes of Wheels Manufacturing offer adaptors to change one BB format into another – typically BB30 / PressFit30 into 24mm, or BB30 / PressFit30 Campag adaptors (which actually result in you running 2 sets of bearing totally unnecessarily, but anything is better than Campag’s own BB30 and PressFit30 adaptors [which work their way out of the frame as they're not made to install deep enough!]).

SRAM even make a PressFit30 adapter that has threads in it so you could run a square taper BB (or your favourite external BB) on your PF30 frame.  I personally think this is the best way to fit Campag BB cups onto a frame designed for PressFit30.

One thing worth quashing right now is the thought that chainsets with 30mm axles can’t fit on a non-BB30 / PressFit30 / BB386Evo frame.  Again, Rotor have stepped up to the mark offering an external BB with a 30mm inner bearing diameter, and Zipp used to supply a similar setup with their Vuma Quad crank.  I think the only exception here is the SRAM BB30 cranks as they are designed for 68mm total width and therefore won’t allow for external cups to be fitted.

So there you have it.  Hopefully you’re less confused and more enlightened?…