Review: Box One Drivetrain

Is there room for a third combatant in mountain biking's drivetrain brawl?

Sometimes it seems like BMX racing technology is stuck in the bronze age. Maybe that's got something to do with it being an Olympic sport. Advancements we take for granted like tapered steerer tubes, thru-axles and 31.8-millimeter bar-clamp diameters are only just surfacing in the BMX world. Box Components has been leading much of that charge, and it must have them feeling their oats because they've started hurling stones at SRAM and Shimano.

They're entering the 1×11 market with Box One. The $175 Box derailleur and $75 shifter aren't here to undercut the competition, though the value-oriented Box Two cassette is evidence that there's a trickle-down in the forecast. Box is compatible with any 11-speed cassette, bookended by a minimum-size 10-tooth small cog and maximum 46-tooth large cog. So we used a 10-42 SRAM XO1 cassette and put the fancy new bits to the test.

The shifter is certainly fancy and new. Downshifting works just like you're used to, but you upshift with a forceful linear poke of the thumb, pushing the lever in toward the stem. The motion actually originates in the wrist, and that extra power allows for effortless, rapid-fire shifting. Cable replacement is also pretty effortless and rapid. No disassembly required.

Box One Drivetrain

And the shifter isn't even the most unique part. The rear derailleur takes a radically different approach to chain retention than SRAM or Shimano. Those systems produce immediate and constant friction, stiffening the motion throughout the entire swing of the cage. Instead, the mechanism on a Box derailleur offers progressive friction, and only introduces it when the cage is forced to swing especially far or especially quickly.

This design has a less dramatic effect on chain retention than traditional clutches. In fact, Box suggests using a front chainguide with the system. But, I spent my entire four-month test period guideless, and only once did I drop a chain off the front ring. Less problematic but more frequent was some nagging chain slap and a few rear-end derailments. If I was in a rough section and had to throw my front foot off in a turn or down a rut, that quarter backpedal would occasionally drop the chain to the next cog, and it would grind back up when I got back on the gas.

So, case closed, right? We gave up on dropped chains when one-by hit the scene. But we also gave up on something else. Bikes used to shift better. Traditional clutches inhibit the derailleur's ability to quickly adapt chain tension when moving to a larger cog. We have to put more force on the shifter and less force on the pedals. Especially after hopping back onto a few SRAM-equipped bikes, it was clear the Box took less effort, time and thought to downshift.

The One derailleur tucks its cable anchor hardware up, in, and out of the way. And there's a clever fold-away cable stop to help survive side-impacts. The rest of the construction is rather traditional. Like most derailleurs, the lower half of the body is a composite.  In my time with it, I never knocked the derailleur hard enough to break through the composite, but I did occasionally knock it. Most of those knocks were around the cover to the clutch mechanism, which is easily replaceable if a knock got a little too hard.

The pivots go through that same plastic, but after four months of abuse, there was no noticeable extra play in the derailleur. Of course, the shifter is far from the rough neighborhood where the derailleur lives, but it has the slow creep of time to guard itself against. Luckily, its guts are thick, robust, and most importantly easy to access, clean and replace. Box also has a fresh take on serviceability. Its website is stacked with exploded line drawings of small parts, nearly all of which are accessible and replaceable, including the clutch itself.

$250 (derailleur and shifter) / boxcomponents.com

Related
First Look: SRAM GX Eagle Drivetrain – 12 Speed for $500

Review: SRAM Eagle X01 Drivetrain