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Bottom Bracket Standards

Chris King Bottom Bracket
James Spender
15 May 2015

BB30, BBRight, BB86, BB90. What ever happened to good old BSA? We delve into the murky world of bottom brackets.

Standards aren’t what they used to be – quite literally where bottom brackets are concerned. For years there was pretty much one available: threaded. Bottom brackets screwed into the bottom bracket shell on a frame, and in the main that shell was either 68mm wide, in the case of English threaded, or 70mm wide, in the case of Italian threaded. ‘Bottom bracket’ was a more straightforward term too. By the early 1990s these were mostly one-piece units, comprising of an axle – or spindle – mounted to two bearings. Today, things are a lot more complicated. 

For one, a bottom bracket doesn’t look the same. Instead, spindles are mounted directly to cranks, and the bearings either come ready-pressed into external threaded cups (such as the Hope unit pictured); pressed onto the spindles (such as with Campagnolo’s cranks) which then locate into threaded, external cups; pressed directly into frames such as with BB30, BB90 or BBright bottom brackets; pressed into replaceable cups mounted internally in the frame (that’s PF30, BB86 and 386 Evo), or even a mixture of both, such as with Colnago’s Threadfit 82.5, where internal cups screw into the frame before having the bearings press
fitted into place.

On top of that, the term ‘bottom bracket’ has been confused. Where it once referred to a single unit, it’s now often used to describe the whole system. A BBright uses the same diameter bearing (42mm) as a BB30, and also supports a 30mm spindle. Yet the former fits a 68mm BB shell, the latter a 79mm shell. Frankly, it’s a bit of a headache for the consumer, and as it turns out, for some manufacturers too. So why have we created such a minefield for ourselves? And is there even a ‘standard’ at all now?

Increase the piece

Enduro Ceramic Bottom Bracket

‘The catalyst for these new standards was the pursuit of more durable bearings combined with stiffer crank spindles,’ says Dan DePaemelaere, product manager of Wheels Manufacturing, whose job it is to make bottom brackets that harmonise the huge array of framesets with many types of chainsets. ‘Cannondale basically started it all in 2000 with its BB30 standard, at least as far as “press fit” bearing systems are concerned.’

Me? I’m biased as an old guy with lots of time on the bike, but BSA [English] threaded is still my go-to standard.

As Cannondale saw it, the weak links with bottom brackets were the interfaces between the crank and spindle coupled with the spindle width, and the small bearings used in an area subject to very high, repetitive stresses. An English threaded BB fitted into a 1.37-inch diameter BB shell, which meant the spindle widths of such units were around 17mm. Upping the ante, Shimano produced Octalink BBs and the rest of the industry ISIS Drive, which both had wider spindles of around 20mm, but still things were constrained by the BB shell diameter. As Cannondale saw it, wider diameter tubes are stiffer, hence it set about creating a BB shell that could support a 30mm diameter crank spindle (integrated into the driveside crank). At the same time, BB30 bearing diameter was increased to 42mm external/30mm internal to increase durability, as there was now more bearing, so to speak, to deal with the stresses a BB goes through.

Chris King Bottom Bracket cups

‘A little later Shimano and others started with the external threaded cup BBs supporting 24mm spindles,’ says DePaemelaere. Now the industry had three standards: internal threaded, BB30 and external threaded. BB shell width was unchanged at 68mm, however external threaded cups when installed pushed the distance between the bearings to around 90mm, edge to edge. This offered increased torsional stiffness about the crank, as putting the support points (the bearings) wider apart gave the system greater rigidity. This then encouraged frame designers to rethink the width of the bottom bracket shell.

‘People talk about crank stiffness and spindle stiffness, but after a point the frame is the limiting factor of stiffness in the system,’ says Ben Coates, product manager at Trek, which introduced the BB90 system in 2007. ‘The wider the system, the better. If you have a wider BB shell with larger diameter you can build a larger down tube and wider offset chainstays onto it and have a wider bracing angle of the stays. Think of this as your feet placed further apart for more stability.’

Trek pushed the BB shell width to 90.5mm, placing two press-fitted 37mm diameter bearings into the frame to support a 24mm spindle. This gave more surface area to attach wider, stiffer tubes and allowed the chainstays to adopt a wider, stiffer stance.

Wide boys

Hope Bottom Bracket

All this innovation has led to an array of BB options. DePaemelaere says, ‘The different standards now are BSA [English] threaded; BB30 (42mm wide bearings, 68mm shell, for 30mm spindle); PF30 (46mm bearings, 68mm shell, 30mm spindle); BB86 (41mm bearings, 86.5mm shell, 24mm spindle); BB90 (Trek standard only, 37mm bearings, 90.5mm shell, 24mm spindle); OSBB (Specialized’s “standard” which can be either 42mm or 46mm bearings, though is basically a BB30 – Specialized didn’t want to use the same name Cannondale had coined); 386 Evo (a joint venture between Wilier and FSA, 46mm bearings, 86.5mm shell, 30mm spindle) and BBright (Cervélo only! 46mm bearings, 79mm shell, 30mm spindle).’ Got that?

The question is, if bigger means stiffer, why aren’t we using 60mm bearings with 110mm shells and 45mm spindles? ‘Manufacturers can only push things so wide without affecting chainlines and Q-factors,’ says Cervélo project manager Graham Shrive. (The Q-factor is the side-to-side distance between the pedals.) ‘There is talk of going wider with the move to 135mm spaced rear ends [the width between the rear dropouts, up from 130mm to accommodate disc hubs], but for now we view 90mm spindle length as the widest we will go. We are working closely with the major component manufacturers on this issue.’

So, if there are no plans to make BBs wider, the next question is, which of the current crop is the best system? 

One size fits all?

‘What are the tangible differences? Wow, that’s a tough question to answer,’ says DePaemelaere. ‘Brands have muddied the waters as each tries to carve out their piece of the pie, claiming their BB standard is X% stiffer or Y% more compliant than a rival’s. Can the average cyclist notice that on their daily ride? And then all the crank suppliers are fighting for their piece of the pie too! Me? I’m biased as an old guy with lots of time on the bike, but BSA [English] threaded is still my go-to standard.

Enduro Ceramic Bottom Bracket cups

‘BB30 was a good attempt at a new standard, but Cannondale made it too tough for the different brands to hold the tight tolerances for the bearings to go directly into the BB shell. PF30 was designed – mostly by Sram – to alleviate these tight tolerances [by use of internally mounted nylon cups to take up the slack], but they created the creaking many people now hate. BB86, 386 Evo, BBright and OSBB are simply takes on the same standard, PF30.’ It’s almost enough to keep you up at night, isn’t it?

‘Well no, but it is kind of a headache,’ says Chris King. ‘I do think threaded BBs tend to work better than press-in stuff. The beauty is you can cut a thread into something and the thread itself doesn’t have to be perfect for it to work relatively perfectly. Whereas a bored hole [in a frame] has to be the right size otherwise it’s not going to work perfectly. Making components that have to go in that hole? That’s not easy for us!’. ‘The industry’s standard is: there is no standard!’ says DePaemelaere. ‘There are simply too many players who want to sell their product.’

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