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Standard Issue: Why the 31.8-Millimeter Handlebar Was Never Meant To Be


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The 25.4mm bar clamp diameter made sense. Sure, it wasn’t optimal–or even adequate–for what mountain bikes grew up to be. But the number 25.4 made sense because 25.4mm is exactly one inch. Or, it has been since 1959 when the world agreed to stretch what we then called an inch by .000044 millimeters to get a clean 25.4. The 31.8mm clamp diameter does not make sense; 31.8 is close to one-and-a-quarter inch, but apparently, that has nothing to do with it.

“How 31.8 came about was an absolute fluke,” says Gavin Michael Vos. Vos is one of those people who you’ve probably never heard of, but our sport would not be the same without. He lives in Taiwan where he runs, among other things, Spank Industries, The Gravity Cartel, Fratelli Industries and Anvil Industries. As we spoke over WhatsApp, I could hear an orchestra of voices in the background, punctuated by the sounds of heavy equipment, slamming doors and the unmistakable clang of metal tubing hitting concrete. After 35 years in the industry, Vos still prefers to be close to the action.

“We started selling mountain bikes out of our surf shop in the mid to late ’80s,” he says. Vos grew up in South Africa and went on to help build one of the strongest mountain biking scenes on the planet. “We brought a team to the World Champs in France in 1993, and in 1997 we had the first World Cup race in Cape Town.”

Later, Vos founded Funn, a component brand focused exclusively on freeride and DH. It was a pivotal time in the industry. “All the frames became oversized, the Kleins, the Proflexes, the Cannondales. A 25.4 handlebar just looked so puny.” So, Funn designed a bar with the very late-90s name Fatboy Slim. “The handlebar was supposed to be 32mm. It looked good on paper with the 32mm stanchion size emerging.” So, they set to work.

Before bars are bent to create rise and sweep, they are shaped through butting and swaging. Butting is the manipulation of a tube’s wall thickness and swaging is the manipulation of its diameter. But that’s over-simplifying it.

All the frames became oversized, the Kleins, the Proflexes, the Cannondales. A 25.4 handlebar just looked so puny.

“There’s a lot of kung fu,” as Vos puts it. “You end up working the material, and you put it under a lot of stress. Then, when you bend, you get expansion and contraction, outside and inside, and that causes some form of distortion on the material. You have something called ‘orange peel,’ which is a wrinkling. We had to increase the wall thickness so we could grind away the faults.” Going from 25.4 to the 22.2mm at the grips was relatively easy, but from 32mm was uncharted territory. “This is more of an understanding than a strict engineering discipline. It is quite manual to some degree.”

Eventually, they produced a bar that had the right shape, wall thickness and finish, and went into production, expecting to create the first 32mm bar. But that’s not how it went. “Our first 250 or 500 bars had all suffered some shrinkage, which was just a flaw in our manufacturing … but we hadn’t machined our stems yet.”

Thus, 31.8 was born. Vos can’t point to a specific reason why the Fatboy Slim gained enough of a following to launch a new standard. There was a competing oversized bar at the time from Azonic, but it used a clumsy three-piece design instead of tapering, which actually makes sense now. Also, it was called the Chubby.

Ironically, Vos is skeptical of new standards. “I think it’s the industry stretching to create interest among consumers. A lot of these things are meaningless, and create a lot of waste.” But 31.8 is not meaningless. It has clearly made an impact on how we ride. A measurable impact.