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Long-Term Test: Onyx Classic Hub

Sprag clutches are suave (and ridiculously reliable)

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Basics

-Sprag clutch
-Custom colors and configurations -Instant engagement -Silent when coasting -Hybrid ceramic bearings


Pros

-Durable and easily serviceable
-Completely silent
-Near-instant torque delivery
-Swappable freehub bodies
-You can say your hub uses a sprag clutch

Cons

-Pricy
-Heavy
-Expensive internals


Mountain bikers make purchases as much for performance as for emotional satisfaction. Prove me wrong. Especially right now, if all we wanted to do was ride a bike down a trail, there are plenty of sub-$3,000 rigs to satisfy every genre of rider. Bikes are good these days, and it’s becoming increasingly more difficult to justify shelling out top dollar on premium products when the economy package does darn near as good of a job. But of course, that’s not the whole story.

When it comes to, say, boutique hub offerings, not many can beat Onyx in terms of exotic design—I mean, who doesn’t want to roll up to a group ride—silently, I might add—and boast that they are running a sprag clutch. It just sounds suave, in the way that the best pieces of engineering are functional art that offer both function and art in equal measure. After all, we don’t buy bikes for the bikes—we buy them for the experience.

This is what fuels a large percentage of the innovation taking place in our industry.  Mountain biking is diversion based not in necessity but in pursuit of joy. And part of that joy comes from the tech and the gear—bikes are cool. And sprag clutches? They’re really cool.

See those two rows of little steel things inside the hub? Those are sprags. They allow the freehub to rotate friction-free, and silently, in one direction, then lock everything in place in the other direction to let you put the power down.

Now that I’ve mentioned sprag clutches three times, let’s talk about what they actually are. In simplistic terms, think of them like one of those finger traps, but for rotation. Put your finger in (turn the freehub counterclockwise, coasting) and it spins free. Pull your finger out (rotate clockwise, pedal) and the freehub body locks into place. The harder the pull, the harder it locks.

How does that work? Sprag clutches use, well, sprags, which are small, hourglass-shaped pieces of steel that wedge themselves between two steel races. It’s almost like a cartridge bearing, but replace the balls with sprags. The inner race is free to rotate one direction, that’s the freehub body, as it pushes the slightly leaning sprags out of the way and glides past them. In the other direction, the sprags catch and stand upright to wedge themselves between the two races. The harder you twist, the more force is applied to the sprags, making them grip harder.

The sprags sit between an axel (show here left) and the hub shell. When under load, the hub shell expands slightly, leading to a “wind up” feeling unique to Onyx hubs. It’ll never slip though, don’t worry—the Onyx has proven to be the most bullet-proof hub I’ve ever owned.

For that reason, sprag clutches are mostly used in the automotive and aviation industry—they allow free movement in one direction with very little friction or wear, and are instantly and forcefully resistant to movement in the opposite direction, as long as the system is stiff enough. On that note, let’s get one thing out of the way—the Onyx Classic hub does not slip. Even under the low gear ratios of modern 1×12 drivetrains, Onyx’s sprag clutch will never let go.

That being said, there are a few other key points to unpack. First, sprag clutches provide near-instant torque delivery, not instant. It does take a fraction of a degree to stand the sprags upright—in reality, it’s not enough to notice. However, what you do notice is that flex in the outer race and hub shell. As you apply torque to the system, that force is converted to outward pressure on the outer race as the sprags try to stand up straighter. That outer race does increase in diameter very slightly, enough that you can stomp on the pedals and feel a slight “wind up” give.

The Classic hub comes with outdated internals—you can run an XDR driver, but no Microspline. To upgrade, you’ll need new internals (pictured here, and another $180) that allow DT Swiss-style freehub bodies to be used.

Now, that probably sounds like a negative trait. To some, it might be. That solid, thwacking positive engagement of a pawl-driven hub is lacking in the Onyx system. By comparison, Onyx feels refined, like a deep southern drawl that makes most other accents sound harsh by comparison. And there are some circumstances on the trail where the Onyx has the edge in performance as well.

In tight trails where pedal strikes are imminent, ratcheting the pedals is a treat with the Onyx system. Power comes on exactly where you expect it—there’s no “float” to the system—so when you might only have a few degrees to work with, the Onyx is the most efficient way to go about things. That power also is delivered in a rising torque curve to the wheel, allowing the drivetrain to almost be preloaded and spring forward. I’ve found this aids slightly in traction management, as well as instances where getting the pedals started is helped by some momentum—it’s slightly easier to turn the cranks the first degree or so. 

Pricey? Heck yes. Delivers an entirely unique riding experience? Also, heck yes. And it’s dang reliable to boot.

And lastly, all of my personal bikes in the last four years have had Onyx hubs, and darn near every pawl-driven hub I ride now feels a bit clunky by comparison. That thunk of hard engagement sounds, and feels, unrefined. I may be a bit of an outlier here. Plenty of riders are into the “thunk,” but don’t need it in my life.

Which is a perfect sentiment to segue into how the Onyx hub sounds. Or rather it’s lack of sound. It’s completely silent, minus any worn bearing sounds (but we’ll talk about that later). Personally, I love a silent hub. It lets me listen to what the rest of the bike is doing—tire casings folding, oil circulating through dampers and cables rattling. Wait, cables rattling? The downside of a silent hub is that every other noise on the bike gets effectively amplified by lack of hug noise—any annoying creaks or rattles will drive you mad until you chase them down. That being said, when you finally 3M mastic tape your entire chainstay, zip-tie and shrink-wrap every cable and sticky-back-Velcro the entire interior of your downtube, you’ll feel like a gosh darn berm-slaying, root-floating, loam-surfing trail ninja. 

Onyx hubs are meant to last years of hard riding. Bearing replacement is easy, but you’ll probably want to replace the stock hybrid ceramic bearings for standard steel ones as the former cost a small fortune and don’t always last as long.

But be warned, equestrian riders don’t like silent trail ninjas—just an FYI. Neither do bears. And I swear, neither of those points were learned by personal experience…

Silent and near-instant, the Onyx hubs also offer very little resistance when it comes to rolling. The sprag clutch is near friction-free, with the main source of drag coming from the dust seals and hybrid-ceramic bearings. Onyx originally designed the hubs for racing, and they’re actually some of the only hubs on the market that come stock with hybrid-ceramic bearings, which roll incredibly fast. How fast? I’m no scientist and there’s no research I could find that pits the Onyx against other contemporary hubs (although there was a study done by Duke University in 2016), but through my highly scientific method of turning the bike upside down and spinning the wheel really fast, I can tell you the wheel continues to spin really fast for a really long time. Take that as you will. 

Adjusting bearing preload on the Onyx hubs isn’t the easiest. It’s a nice feature to have, but used incorrectly can cause more problems than it solves.

Another thing you can take as you will are those hybrid ceramic bearings—they aren’t for everyone. Designed for maximum speed, they’ll roll fast for a while until the super-hard ceramic balls start to destroy the softer steel races under side loads and contamiation. For reference, I generally get about six months of hard riding before things start feeling a bit crunchy. That sounds pretty bad, but for reference,  I’ve killed two lesser hubs already this year, and they could not be repaired. Also for reference I kept riding the Onyx hub’s crunchy bearings for three years before finally replacing them. Also for reference, the bearings that seem to wear out the fastest are the non-drive-side and freehub bearings. 

The sprag clutch itself has always remained pristine, tucked away inside the hub—it’s behind the main seals and bearings. Even through deep water crossings and literally years of use, I’ve never seen a speck of dust on the sprags when servicing the hub.

When it does come time to service the Onyx hub, it’s one of the easiest hubs to rebuild. The system sounds like it’d be complicated, but I replaced everything using just Allen keys, a box wrench, a small mallet and a punch. Onyx, by no means, endorses my methods, but just saying, they’ve made a user-friendly hub. In fact, Onyx’s spare parts catalog is 20 pages long, and extends down to the tiniest c-clip and 0-ring, though the bearings are standard size and available elsewyere. You might have hard time finding new hybrid-ceramic bearings anywhere but Onyx’s site, but then again regular steel bearings are a more economical choice for replacement. 

With the new internals, swapping drivetrains is easy and fairly future-proof as well. Just make sure you choose a color you’ll still be able to live with in five years.

Speaking of replacement, the Onyx Classic has been around for quite some time—I’ve had mine for four years and plan on keeping it rolling for at least as many more. But we all know how standards tend to, well, not stay standard for that long. Onyx addresses this issue with an upgrade that converts the Classic’s freehub design to one closer to the more contemporary Vesper, which uses interchangeable DT Swiss-style freehub bodies. The upgrade kit cost $180 when I purchased it (darn near half a new Onyx hub and more than some other hubs), but it allows any DT Swiss-style freehub body to be used—Hyperglide, XD and Micro Spline. 

As convenient and reliable as the Onyx Classic hub is, there are two things about it that drive me bonkers. First, and worst, is the paint, or rather where Onyx put the paint. Which is inside the gosh darn spoke holes! Seriously, trying to thread spokes through when wheel building is a nightmare with my painted Classic (I have an anodized version as well, which is much better). For such an expensive hub, this should not be an issue. Second, and more minor, getting perfect bearing preload adjustment isn’t the easiest task, especially with the upgraded internals. The system is fiddly to use and it’d be easy to apply way too much preload and prematurely wear out bearings.

I could also note that the Onyx hub is about 100 grams heavier than other high-end hubs on the market. For myself, someone who rides a coil-sprung, DD-casing wrapped, 220mm-rotor rolling 29er—well, I don’t really care about weight. But I’m certainly not everyone, and 100 grams is more than just counting a few grams. Deal breaker? I don’t think it should be, but rather something to certainly keep in mind.

This particular Onyx hub is about to be laced to its fourth rim for its fourth bike. A bit battle-scared, it still has a long life ahead.

Those two annoyances aside, I should also note that Onyx offers some of the most customization options of any manufacturer—which should be the case for hub that runs $470. You can choose from a plethora of colors for the hub shell (painted or anodized), then match or mix the color of the end caps. Do you want 28, 32 or 36 spokes? How about freehub bodies? All options are on the table. Have a weird non-boost frame? Totally got you covered. And then there’s that collection of spare parts. There’s a list (with “add to cart” buttons) right below each hub configuration. Can’t find what you’re looking for? A real person will answer the phone. Few other hub manufacturers offer this level of customer experience and support. 

To take stock, the Onyx Classic is not a perfect hub. Objectively, it’s actually pretty hard to point to one thing that, by itself, serves as proof of superiority over other hubs. Yes, it’s a very fast rolling hub. Yes, it’s dead silent and makes you a trail ninja. And yes, it has (near-)instant engagement. But all of those things are a two-sided coin. And of course, for the price of one Classic rear hub, you could buy entire wheelsets from other manufacturers. But the Onyx hub is a hub that could, and should, be transferred from wheelset to wheelset, bike to bike, for many years down the road. It’s a piece of near-over-the-top engineering that is wildly cool and offers a riding experience unlike anything else on the market. Plus, I have an excuse to say “sprag clutch” any time I want, including 21 times in this review.