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Good Intentions: How the open-source ISIS Drive bottom bracket almost changed the world

The standard's design wasn't flawless, but the theory behind it was.

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The following story first appeared in the winter 2021 print issue of Beta. To get quarterly print magazines, sign up to be a Beta Pass or Outside+ member. Membership details HERE.

Some of the greatest movies of the modern era hinged on plot points that would not make sense today. If a single partygoer had tweeted about the storming of Nakatomi Plaza, the police would have been alerted much sooner, and the events of “Die Hard” would have turned out very differently. If the McAlister family had set their alarms on their cell phones like today’s humans, that fateful power outage wouldn’t have put them in such a frenzy, and little Kevin would not have been left “Home Alone.”

Times change, and the rules change with them. That’s why this very fond retelling of the story behind the ISIS Drive bottom bracket may seem a little odd. Not because of its unfortunate acronym (which stands for International Splined Interface Standard). And not because we shouldn’t remember ISIS Drive fondly. The then-new way of attaching crank to bottom bracket actually did a lot of good in its short lifespan. But that lifespan was indeed quite short and rather troubled. The introduction and near-immediate dominance of “two-piece” cranks meant that bottom-bracket spindles and crank arms would always be manufactured under the same roof, and the need for an International Standard for their Splined Interface suddenly evaporated.

But back in 2001, ISIS Drive was a light from the heavens. Our sport had somehow survived for decades on square-taper bottom brackets. It was barbaric. I personally broke two spindles in my teenage years, and that was before I even left the Midwest. There were only a handful of alternatives, and each had their flaws. BMX cranks were heavy, and not optimal for multiple chainrings. Shimano had Octalink, but pretty much only Shimano had Octalink. Then, a remarkable thing happened. A thing that had maybe never happened before, and probably has never happened since. A few competing brands got together, and they cooperated.

Truvativ, Race Face and Chris King all had an interest in designing an interface that would be more durable than square-taper, better suited for mountain biking than BMX cranks, and available to brands other than Shimano.

“Mountain biking was changing,” recalls Truvativ’s founder, Micki Kozuschek. “Mostly driven by the Pacific Northwest and Canada. It became clear that the square-taper interface was just not holding up.”

This was not earth-shattering news to anyone mountain biking in the late ‘90s. The second generation of XTR proved way back in 1996 that, if you use a big hollow spindle insead of a little solid one, the same crank could get you to the top of the podium at both the UCI Downhill Worlds and Olympic Cross-Country. Understandably, Shimano wanted to keep that technology to themselves. The people behind ISIS Drive had a different idea.

The concept of an open standard is rare in the bike industry, but not unheard of. When SRAM introduced the XD freehub body, it was free for anyone to manufacture. But they kept a tight grip on who could use their cassette design. Making the XD freehub body open-source was done to ensure there would be plenty of hubs out there to fit SRAM’s cassettes, not to gift the world with a useful new standard for hub/cassette interface. ISIS Drive, on the other hand, was a completely open book. It still is, in fact. Although the link to the schematic PDFs is no longer active, the website, is still up and running. For years it was where any brand could go for the data they needed to make their own ISIS spindle or cranks.

“If you wanted to be ISIS Drive you just had to send some pieces in to get checked,” explained Kozuschek. “That was done either by Race Face or Chris King.” Shapes and tolerances were carefully outlined, while exactly how the parts would be manufactured was left up to the individual brand. But the idea was for ISIS Drive cranks and bottom
brackets to be as easy to produce as possible.

A thing that had maybe never happened before, and probably has never happened since. A few competing brands got together, and they cooperated.

“Chris King consulted on the machinability side,” says Kozuschek. “What it should look like and how the interface would be made. Portions of it were supposed to be machinable, rollable, forgable, etc.” At the same time, Race Face was building and testing prototypes at its British Columbia headquarters.

The three brands behind ISIS Drive made up a pretty remarkable team. “We each represented a different part of the market,” remembered Kozuschek. “Truvativ held a lot of OEM business with a lot of big brands. Race Face was always the more aftermarket-driven company, and they were part of that freeride movement. And Chris King had that high-end, machined, Gucci, great quality and consistency.”

But Chris King famously never released an ISIS Drive bottom bracket. It takes time for King to do anything that meets their standards, and the ISIS Bottom Bracket was a particularly tough nut to crack. “The one thing we never changed was that BSA threaded BB shell, but the ISIS Drive spindle was rather large,” Kozuschek explains. “So, now we had a spindle that was very strong, but the bearings got very critical. So, we doubled them up on both sides.” Still, the bearings would prove to be ISIS Drive’s achilles heel. Especially given the types of riders ISIS Drive was attracting, the platform was notorious for its short bearing life. Chris King was producing prototypes that were promising, but they were heavy and, more importantly, expensive.

“The one issue was that a lot of our customers always wanted everything super fucking cheap.” Kozuschek is known for his frankness. So much so that, at the beginning of our call, I reminded him to lead any sensitive information with the phrase ‘off the record,’ but this was apparently not that sort of information. “And that’s on the record,” he added.

Truvativ, being the OEM player in the ISIS Drive supergroup, was fighting this battle the hardest. “If I were to raise my OEM customers from $6.00 to $6.01, it was like, ‘Oh my god!!’” As a result, most of the ISIS Drive bottom brackets that made it out into the wild had not successfully solved the problem caused by the limited space left for the bearings. They would often develop a wobble, and with no consistent or durable method for adjustment, ISIS Drive bottom brackets became somewhat disposable. It was better than breaking spindles, but ISIS Drive’s days were numbered. At some point, a new shell standard called “ISIS Overdrive” was experimented with, but never made it into use. Then came 2003, the year when Shimano released the M960 XTR group. With it came Hollowtech II, ushering in the era of the two-piece crank and outboard-bearing bottom bracket, and ISIS Drive as we knew it would soon be over. There was a short-lived three-piece outboard design called Howitzer, but it was mostly a mid-range OEM spec that was too heavy to compete. The two-piece crank was taking over, so ISIS Drive got on board. SRAM’s GXP crank used the ISIS interface to connect its non-drive crank arm to the spindle, and the 24mm / 22mm outboard-bearing system was on most SRAM cranks until the DUB spindle was released in 2018.

Still, ISIS Drive lives on. You’ll find the iconic 10-pointed star on e-bike motors from Bosch, Brose and Yamaha. Not only does this prove that the mechanical fundamentals are still sound, but that the business fundamentals are too. Motor manufacturers don’t need to design and produce their own cranks. And crank manufacturers don’t have to tool up for three different splined interfaces. And neither of them had to pay to use the standard that made it possible. As a model for bottom-bracket design, ISIS Drive may have been flawed, but as a model for cooperation among component manufacturers in our industry, it’s still unmatched.