The Bottom Bracket Breakdown

Be honest. When was the last time you had a stimulating conversation about your bike’s bottom bracket while you were out on a group ride? When was the last time you ran into your local bike shop full of anticipation to check out the latest in bottom bracket choices? It’s safe to say that few components have been as overlooked and disregarded in the marketplace as the bottom bracket. No more.

A bicycle’s bottom bracket sits inside the bottom bracket shell, and it is basically comprised of a set of bearings that support a spindle which the cranks attach to and spin freely on. For as long as we can (or need to) remember, the ‘standard’ road bike bottom bracket consisted of a squared, tapered spindle in a 68mm-wide shell with threaded-in cups. Over the past decade, crank and bottom bracket designs have radically altered the landscape of old with huge gains made in terms of stiffness, weight savings and bearing longevity.

Standard, by definition, means ‘accepted as normal.’ However, over the past few years, the concept of a true ‘standard’ bottom bracket norm has become anything but. After a second ‘bottom bracket standard’ was introduced this year alone, we decided it was time to take a closer look at it all.

It’s really not surprising that a bottom bracket revolution is upon us. Think about the advancements made on the rest of the bike; headsets are now tapered, seatposts have gone both integrated and aero, and frame tubes are shaped every conceivable way to gain stiffness and aerodynamics. Engineers are working on optimizing anything and everything on the bike, looking for any small advantage in weight savings and/or stiffness. As one engineer told us, ‘The low-hanging fruit has already been picked,’ meaning that they are now having to dig deep in their bag of tricks to achieve continued advancement. In reality, it’s surprising that it has taken this long for the bottom bracket to find itself in the engineers’ crosshairs. And after garnering so much attention as of late, changes have been aplenty.

In 2000, the aftermarket bottom bracket category took off when Truvativ, Race Face and Chris King introduced an ‘open’ bottom bracket standard that was available to anyone who wanted to use the technology. It featured a 21mm diameter, 10-splined spindle called ISIS (International Splined Interface Standard) Drive. Although a round spindle was nothing new in the two-wheel world from (BMX bikes had already been using them for years), it filled the need on the road for a stiffer, stronger and lighter spindle than what the previously historical ‘standard’ and current square-taper spindle could provide. The ISIS design was spurred on after Shimano developed their own proprietary spline system called Octalink (you guessed it, with eight splines). While these designs were stiffer and lighter due to their over-sized, hollow, chromoly spindles, they weren’t without fault. In order to fit the larger spindle into the confines of a standard 34mmdiameter, 68mm-wide bottom bracket shell, the bearings had to be smaller, which negatively affected their longevity.

The solution? Stick the bearings on the outside of the shell, of course! In 2003, Shimano introduced Hollowtech, the first external bottom bracket. It threaded into a 68mm shell and integrated a 24mm spindle into the driveside crankarm. The two-piece crank was new to the road, but once again, it was borrowed BMX technology from the ’80s. Within a year, FSA (Mega Exo) and SRAM/Truvativ (GXP) had their own outboard bearing, two-piece, 24mmspindle- diameter cranks. Campagnolo’s Ultra-Torque crank had a little different crank/spindle design than the others, but they still embraced the outboard bearing technology. The increased bearing and spindle size dramatically improved bottom bracket performance and has satisfied most of the industry for the past decade.

Around the time crank manufacturers were trying to figure out if they wanted the bottom bracket bearings inside or outside of the shell, one bike company saw the writing on the wall.

Cannondale, the Connecticut bike maker, had a history of doing things their own way. And so they developed their own 68mm-wide bottom bracket shell, but its key point of differentiation was its increased diameter of 42mm, which allowed cartridge bearings to press directly into the shell, eliminated the need for threaded cups. This largerdiameter shell made room for a 30mm alloy spindle that was both lighter and stiffer than the existing 24mm steel spindles. And with that, the BB30 ‘standard’ was born.

Cannondale had one thing going for them that many other companies did not: they made their own frames and cranks, so they were free to create their own standard without having to get anyone else on board. It took some time for the market to acquiesce to the BB30, but since Cannondale left it as an ‘open standard,’ competing frame and crank makers are able to use the system without penalty. The BB30 design has since become the most widely used non-threaded system.

In case you haven’t noticed, not only have carbon frames been getting lighter, but the frame tubes have also been getting bigger. Oversized tubes, of course, bring with them increased stiffness, and the bike companies quickly realized that using a bottom bracket shell wider than the standard 68mm width would allow them to use tubes up to 20mm larger in diameter. And so a new phase in both frame and bottom bracket design began.

Trek came out with a proprietary frame design on their Madone called BB90, which used a standard 24mm spindle and a 90mm-wide shell that the bearing presses directly into. Scott Bicycles and Shimano developed a system called BB86. It consists of a 24mm spindle in a 86mm shell (the same width as a 68mm shell with external cups installed). Look and Specialized followed the path of Cannondale and engineered their own frame/crank system: the ZED and OSBB, respectively. But, where Cannondale left the BB30 as an open standard for anyone to use, Look and Specialized based their bottom bracket systems on a proprietary crank design (a BB30 crank can be used in an OSBB shell). When asked why Specialized would want a proprietary design, head of road research and development Chris D’Aluisio said, ‘The brand managers would like everything to be compatible because it’s much easier, but from an engineering perspective, a standard system doesn’t necessarily mean it’s the best performing system.’

Enter BBright and BB386EVO for 2011. Each of these new ‘standards’ integrate a 30mm spindle with bottom bracket shell widths of 79mm (11mm wider than the BB30) and 86mm, respectively. BBright was introduced by Cervelo and is one of the most intriguing designs since it uses an asymmetric bottom bracket shell. The 11mm of extra shell width is all on the non-drive side of the frame, which accomplished their goal of adding surface area in order to use larger frame tubes without affecting the chain line.

The folks at FSA, BH Bikes and Wilier Triestina liked elements of the BBright design, but felt a symmetric 86mm shell was the best choice for allowing the greatest compatibility, and thus co-developed the BB386EVO, which was launched this past April. The BB386EVO open standard seems like the design that has the most potential to unseat the BB30 as the latest ‘standard’ due to its ability to work with most of the cranks currently on the market.

It depends on whom you ask. FSA’s Ivan Harms believes, ‘The 30mm spindle is here to stay. There will be a transition period, but in my opinion, the 24mm spindle will go away at the high-end level. The trend is definitely for wider bottom bracket shells, and it makes sense.’

Shimano USA’s vice president, Wayne Stetina, has a different take on things: ‘The BB30 is an optimized design for an aluminum spindle, and 24mm diameter is the optimized size for a steel spindle. But, after five to 10 years, an aluminum spindle will eventually fail. Neither of the designs are the ultimate.’

Even if Campagnolo, FSA and SRAM fully support a bottom bracket standard, it won’t be a true standard until the big S (Shimano) jumps in to support it. But, if history is any indicator, if and when Shimano makes a change, it’s going to be proprietary.

‘Basically, we make everyone’s stuff compatible with each other. If there’s a hole in a frame for a bottom bracket, chances are we’re going to have something to work. We’re not bringing out new cutting-edge technology as much as we’re playing cleanup, trying to make frames and parts work together,’ says Harms. Our guess is that FSA and others will be playing cleanup for some time still.

? Shell width: 68mm threaded (86mm with cup)

? Spindle diameter: 24mm

? Notes: The most ‘standard’ bottom bracket shell width is currently 68mm. Once the external cups are installed, it measures out to 86mm wide. Just about any crank can be used. FSA makes a bottom bracket that will even allow the 30mm spindle BB386EVO crank to be used.

? Shell width: 68mm

? Spindle diameter: 30mm

? Notes: Press Fit 30 (PF30) is a variant of BB30 and, while it uses the same shell width and crank compatibility, the shell diameter is slightly larger. Rather than bearings pressing directly into the frame like BB30, they press into nylon cups, which are then pressed into the frame. This gives more tolerance during manufacturing and allows the use of full carbon bottom bracket shells without any alloy inserts. A BB30 crank is only compatible with a BB30/PF30 shell. FSA and SRAM make BB30 cranks; Shimano does not, but FSA and Wheels Manufacturing make adapters that allow a 24mm spindle to be used in a BB30 shell. Campagnolo make adapters for their Ultra-Torque crank to work.

? Shell width: 86.5mm

? Spindle diameter: 24mm

? Notes: A Shimano-developed system and used primarily by Scott and Giant. The bearings are housed in plastic cups and pressed into the frame. Designed for Shimano Hollowtech II, but will also work with FSA Mega Exo, SRAM GXP, Campy Ultra-Torque cranks and other 24mm spindle cranks.

? Shell width: 90mm

? Spindle diameter: 24mm

? Notes: Used exclusively on Trek Madone bikes. The bearings are housed in plastic cups and pressed into the frame. Designed for Shimano Hollowtech II, but will also work with FSA Mega Exo, SRAM GXP, Campy Ultra-Torque cranks and other 24mm spindle cranks.

? Shell width: 86.5mm

? Spindle diameter: 30mm

? Notes: FSA is currently the only crank manufacturer making a BB386EVOspecific crank; however, it’s one of the most cross-compatible systems. And with the proper spacers from FSA, it will also work with SRAM GXP, Shimano Hollowtech II and FSA’s Mega Exo. The one crank this will not work with is a BB30, since that spindle is designed for a 68mm-wide shell.

? Shell width: 79mm (asymmetric)

? Spindle diameter: 30mm

? Notes: Cervelo is currently the only frame maker using BBright. But, we wouldn’t be surprised if it was adopted by other brands in 2012. Rotor and FSA make specific BBright cranks; these use a longer spindle than the BB30, but a shorter one than the BB386EVO. With the correct spacers, FSA Mega Exo, SRAM GXP, Campy Ultra-Torque, Shimano Hollowtech II and other 24mm spindle cranks are compatible.