Hidden from sight, the bottom bracket is easy to ignore, but it is the heart of your bike’s performance and vital to both frame and component design. Cyclist helps you tell your BB30 from your BB90 and the rest
Not so long ago, your bottom bracket (BB) wasn’t something you’d give a lot of consideration to. Most bikes had standard fittings and as long as the bearings were in good order and well greased, you could quietly forget about it. But now the drive for performance and efficiency has created a host of different bottom bracket ‘standards’, all of which will have a direct effect on the way your bike is designed and how it will ride.
But it can all get rather confusing. When the blurb accompanying your prospective new bike says it has BB30, or press fit, or Hollowtech, are you any the wiser as to what that means or how it should affect your purchasing decision? Well, that’s what we’re here to explain.
First off – what is a bottom bracket? Simply put, it’s the system of axle and bearings that connects the left and right cranks to allow you to turn the pedals. Where the main differences between the various standards arise is in the thickness and length of the axle and the size and positioning of the bearings (and the materials used for both). Changing these factors will alter the rigidity, weight and dimensions of the bottom bracket, which will in turn affect how efficiently the power from your pedal stroke is transferred to the bike frame and translated into forward motion. So, it stands to reason – a good BB can give you more speed. Simple, right?
As always, there’s no perfect answer to the question ‘what is the best bottom bracket?’ because improvements in one area usually require a compromise in another. For what may seem like the simplest of components, it could well carry the most complicated lingo of the entire industry. But once you pull the bottom bracket apart, so to speak, it all becomes a bit simpler…
Back in the day
‘Before World War II press fit was very common,’ says Swift Carbon’s Boris Sirmanoff, demonstrating that some of the exciting new developments in BBs aren’t actually as original as we might think. ‘The threaded BB, originally produced by Birmingham Small Arms (BSA), got popular due to its wide distribution, so the BSA BB we know today is a post-war construction allowing relatively large tolerances in manufacturing,’ he adds.
This is a good insight as to why the BSA design worked, but as manufacturing techniques have improved and carbon has become king, the drive for the most efficient ‘system’ has changed the playing field. ‘It’s important we look at it as a system, meaning the stiffness is the sum of all parts, so the best result would be achieved looking at the weakest part,’ Sirmanoff says. Of course, he’s absolutely right – there’s no point in having the stiffest axle and bottom bracket if the deflection in the frame is so great it destroys any advantage gained. Each individual component is as important as the other.
Backtrack just a few years and bottom brackets were infinitely easier to decipher. But in the modern crop of frames there’s a mindboggling myriad of potential options thanks to key manufacturers all throwing their respective hats in the ring for what they believe is the best solution. The humble BB is no longer – it’s now part of a system to create the stiffest possible outcome.
Shimano and Campagnolo
Fundamentally, the BB is one area where component giants Shimano and Campagnolo see eye to eye, as both have stuck with their respective external BB designs. Shimano introduced Hollowtech II in 2003, the first of the modern era to space the bearings further apart by locating them outside the bottom bracket shell and increasing the diameter of the axle. It’s stood the test of time. Moving the bearings to the outside of the frame immediately meant more room within the BB shell, meaning it was possible to increase the diameter of the axle, and the distance between the bearings increased as well, providing greater lateral support too. Tim Gerrits, Shimano’s product manager, feels the manufacturer is right to have stuck with the system: ‘After the initial popularity of BB30 [we’ll explain more about this later], we’re currently seeing more and more frame builders move away from it again because its narrow shell has performance downsides, or they find preferable combinations with Hollowtech II and
a wider platform such as BB90 or BB386.’
Campagnolo has also remained faithful to its similar Ultra Torque system (introduced in 2006), as product manager Joshua Riddle reasons: ‘BB30 is torsionally stiffer thanks to its larger diameter of axle, however, having a narrower BB shell makes the overall unit less stiff,’ which is in agreement with Gerrit’s views.
In Riddle’s opinion, ‘BB30 offers an incomplete solution for stiffness’, and this explains Campagnolo’s reluctance to adopt the system. It does however offer its own solution by way of an adaptor, to retrofit its Hirth-jointed Ultra Torque cranks into a BB30 shell. ‘We’ve always pushed a doctrine of wider stance of the BB bearings along with a larger diameter axle,’ Riddle adds. As Campagnolo sees it, then, a combination of a 30mm axle and wide bearing stance would give the best of both worlds. There are now several companies producing frames in accordance with this way of thinking and yet another standard – BB386 – has been born out of this very idea.
Campagnolo is ready with the introduction of its new carbon fibre Comp Ultra Overtorque 11s and Comp One Overtorque cranksets. Expected later this year, Campagnolo’s new cranks are BB386 Evo compatible, showing the Italian company is fully behind this newer standard, but we’ll come back to that later. First, let us help you understand the main standards currently available.
Cannondale developed and introducedBB30 to the road market in 2006. Pushing for the design to become an industry standard, Cannondale left it open for other manufacturers to use. Although it has become widely adopted, it also seemingly opened the floodgates for several other fully integrated BB standards.
As its name suggests, it uses a 30mm axle diameter (6mm more than both Shimano and Campagnolo) and is made of alloy instead of steel for weight reduction, plus it houses bearings directly inside the BB shell. Cannondale’s engineers decided to stick with a narrower, 68mm shell width to help axle stiffness, and because the BB30 specific shell diameter is larger than standard, it provides a greater surface area for the down tubes, seat tubes and chainstays to connect to.
This facilitates greater rigidity throughout this vital area and, as a further plus, it can be made very light too. The flip side is that much tighter manufacturing tolerances are necessary, which in turn ramps up build costs.
‘There has always been one kind of bike that uses press fit [PF] bearings – the BMX,’ says Swift’s Sirmanoff. Although the system is undoubtedly not a completely modern concept, its introduction to the road market was bolstered by SRAM backing it and releasing its version of the system in 2009.
While there are some technological similarities between BB30 and PF30 systems – the same size bearings housed in the same location – PF30 is different in that it’s a complete unit with bearings housed in composite cups that are pressed into the frame in a similar way to headset cups. By removing the need for any threading or bearing interfaces in the BB shell, a big plus for PF30 systems is the simplification of frame design.
Swift Carbon has always been a champion of PF30 shells, and Sirmanoff explains why: ‘The BB30 was initially designed for aluminum frames where the required tolerances could easily be achieved, but carbon frames became the top of the line. So with the PF system carbon frames found the perfect match, due to their lower tolerance demands.’ SRAM’s Geraldine Bergeron states, ‘With PF30 we are able to offer a system [cranks and BB combined] that has the highest performance and lowest weight, which ultimately is what the customer wants.’
Some might argue that it was in response to Cannondale’s BB30 that a year later, in 2007, Trek launched BB90, its own new standard for its top-end Madone bike. The big USP for this system is the huge 90mm shell width that creates a seriously wide platform for the adjoining tubes to interface and potentially create stiffer frames.
‘With BB90 the bearings press fit directly into the net moulded carbon BB shell,’ says Trek’s Jeremy Loftus. ‘BB30 is narrower and although you get a stiffer crank axle, it doesn’t really do as much for overall stiffness as the frame’s lateral rigidity does.’
A system that shares similarities to both PF30 and BB30 systems is Specialized’s OSBB (Over Sized Bottom Bracket). Using Specialized’s own carbon crank, OSBB creates a complete integrated package. Chris D’Aluisio, Specialized’s director of advanced research, explains, ‘The biggest advantage that comes from manufacturing your own frame and cranks together is the control that gives you. The window we work in is much better defined
when we limit the frame use to only our crank. For instance we can make the chain stays asymmetric without fear of conflict. This in hand creates a stiff and lightweight system, but one that we can still adapt to be compatible with other BB30 designs, if the user requires.’
Look is another brand, with its ZED monocoque carbon crank and BB system, which has developed a purpose built BB shell in the frame of its 695 model to accept its own hugely oversized carbon axle on the ZED cranks. In Look’s case, however, the frame is not compatible with other systems, only its own, but further highlights how the benefits are potentially largest when the whole thing
is designed as one system.
Cervélo has always been a little different in its approach to bike frame manufacture, and in 2010 it was another brand launching its own BB standard, working closely with Rotor. It called the standard (some might say rather cheekily) BBright.
BBright is essentially an amalgamation of threaded and PF30 designs with the drive-side cup remaining in the same location as other frames, but it’s the non-
drive-side cup that makes the difference. Located 11mm further out than a PF30 design, this places the non-drive-side bearing in the same location as it would be on a traditional threaded design, which Cervélo claims provides a significant increase in overall stiffness.
Just when you thought there couldn’t possibly be any more options, along comes another – BB386, developed by FSA and Wilier, which appeared on the scene in 2011.
‘The BB386 Evo standard is the system we have introduced co-operation from frame manufacturers BH and Wilier,’ says FSA engineer Jason Miles. The newest system to come to market, BB386 Evo is a formidable combination. ‘What makes this crank different is that it has a lighter 30mm alloy axle that’s longer than the axles found in BB30 cranks,’ says Miles. ‘Larger 30mm diameter crank axles are roughly 1.6 times torsionally stiffer than conventional 24mm axles. Wider BB shells allow frame manufacturers to incorporate oversized tubing, and this greatly increases frame rigidity.’
BB386 Evo locates the PF bearings in the same position as an external BB, with an 86.5mm wide BB shell. It looks, on paper at least, like BB386 provides the perfect mix, taking the best bits of all the other designs and combining them into a single new standard.
Will there ever be a single industry standard?
‘Good question,’ says Specialized’s D’Aluisio. ‘I think it comes down to differentiation and point of view as well as manufacturing expertise. I don’t think there was ever a move from the industry to have one standard.’
The bike industry has always struggled to agree on standards (think headsets and seatpost diameters) and Swift Carbon’s Sirmanoff isn’t convinced there is a need to: ‘I’m not sure you really need a standard as each system has now become an integral part of the frame design.’
Riddle at Campagnolo also explains the difficulty on agreeing to a standard: ‘With so many players in the marketplace it is difficult to put everyone on the same page and get everyone to coordinate and cooperate on a single standard. You have frame manufacturers that push for certain standards and component manufacturers that all push their own. It’s hard enough to get all your friends to agree on one restaurant that pleases everybody – it’s even more difficult to land on one standard to please the whole industry,’ he adds.
So there may never be one industry standard. Every manufacturer will have its own ideas in the pursuit of greater efficiency, continually evolving the bottom bracket. Still, the lack of an industry standard is a small price to pay for innovation.