Only Nine Speeds. Is Simpler Better? BOX Launches Prime 9 Drivetrain 26

An affordable, compatible contender in the 1x drivetrain market.

Box has worked hard to steadily grow as a legitimate drivetrain option in the mountain bike market over the last few years. Making inroads on the World Cup downhill circuit with the Polygon UR team running their 7-speed DH drivetrain and offering affordable-but-capable 11-speed systems, BOX has shown they're not just dabbling in the market. Today, the brand founded by legendary BMX racer, Toby Henderson, launched their new Prime 9 mountain bike drivetrain. Focusing on simplicity, durability and accessibility, the Prime 9 range with 11-50t cassettes can be found in the highest level Box One P9 X-Wide group (cassette, derailleur, shifter and chain) at $626 with an eye-catching unibody 11-50t cassette, all the way down to the  BOX Three Prime 9 X-Wide group at just $199.

BOX sent us the performance-oriented Prime 9 X-Wide Two drivetrain for testing. Retail price is $269 for cassette, derailleur, shifter and chain. BOX says this is the most durable group in their drivetrain lineup. We've spent about five weeks on the 9-speed drivetrain to get initial impressions and to see if there is merit to the "less is more" approach.

BOX Two Prime 9 X-Wide 9-speed Drivetrain Features and Spec

  • BOX Two Prime 9 Cassette: 11-50t, fits common Shimano HG freehubs, hardened steel cogs, aluminum spider, 11, 13, 15, 18, 22, 28, 34, 42, 50t, 650g listed (625g tested) - $99.99
  • BOX Two Prime 9 X-Wide Rear Derailleur:  Tri-Pack™ limited slip clutch, forged inner and outer cage, Pivot-Tech™ cable stay, sealed bushing pulleys, 3D-forged linkages, glass fiber/nylon composite, steel, aluminum construction, 290g - $109.99
  • BOX Two Prime 9 Multi Shifter: Die-cast top shell, hinged extruded clamp, two-piece pull lever, up to three gears per downshift, glass fiber/nylon composite, steel, aluminum construction, limited lifetime warranty, 138g - $49.99
  • BOX Two Prime 9 126-Link Nickel Chain: Compatible with modern 11-speed wide/narrow chainrings, nickel-plated protection, hardened alloy steel links, hardened solid pins, 350g - $24.99


  • Durability
  • Compatible with common Shimano HG freehub bodies
  • Compatible with any 9-speed chain
  • Easy to install and tune


  • Cassette weight
  • Gear selection in undulating terrain may be lacking

Initial Impressions and Installation

This was our tester's first time getting his hands on a BOX drivetrain. We'd seen the components at tradeshows and out of the "box" (get it?), the Prime 9 drivetrain had nice fit and finish details. Based on price, compatibility, and gear range, the BOX Two Prime 9 X-Wide system is a direct challenge to a SRAM NX Eagle drivetrain, but with three fewer gears. They both use standard freehub body interfaces and run 11-50t cassettes. The BOX group held its own in the aesthetics and presentation department compared to NX.

Installing the BOX Prime 9 on Race Face Turbine SL wheels with Vault Hubs

Installing the drivetrain was as easy as it gets. BOX had instructions for determining chain length, and the limit screws on the derailleur are standard fare for anyone used to tuning up their own bike. Flashbacks of working on our bikes 10 years ago entered our heads as we lined up the big 9-speed cassette with the keyed ribs of the "normal" Shimano HG freehub. Thanks to this cassette and hub interface, the BOX Prime 9 1x drivetrain is most likely ready to mount up to a wide variety of less-expensive or older mountain bikes that have drivetrains with front derailleurs. Riders making the 1x drivetrain upgrade, however, must remember to find a ramp-free, single-speed chainring for the cranks since their front derailleur is headed for the scrapyard. The BOX 9-speed chain works with today's newer narrow/wide chainrings, so options are easy and open while still eliminating the need for a chain retention device.

Our system was used with the fast, trail-ready Race Face Turbine SL wheels that feature highly engaging Vault hubs. This wheelset is one of our favorites for the speedy, rolling Boise-area singletrack. Power is transmitted through the BOX drivetrain to the Vault hubs through the lightweight carbon Race Face Next SL cranks and chainring up front. The stiff, light cranks combined with the precision of the Race Face Vault hubs and Turbine SL wheels meant that we'd be able to notice all the intricacies of this BOX 9-speed system.

BOX Two Prime 9 Cassette Profile
SRAM Eagle Cassette Profile
Shimano XT 12-speed cassette profile
BOX Two Prime 9 11-50t cassette
SRAM Eagle 10-50t cassette
Shimano XT 10-51t cassette

Remember how we mentioned mounting the cassette? Well, it can't be ignored that we were pretty shocked by the weight of the BOX Two Prime 9 X-Wide cassette. It has an 11-50t spread with only has nine cogs, yet it weighs over 600 grams. BOX isn't shy and claims 650g. Our scale indicated 624g, and we'll gladly leave those 26g at the BOX office. A SRAM NX Eagle cassette tips the scales at 615g, but has 12 speeds, we were very curious to see how advantageous three fewer speeds could be for the same weight as a 12-speed system.

BOX Two Prime 9 cassette weight. 25g less than BOX claimed weight on our scale.

During set up, we can say drivetrain tuning was easier with the 9-speed configuration when compared to a 12-speed build. The 12-speed build isn't rocket science, but it takes a bit more patience and fine-tuning to get shifting dialed through the entire cassette range. Once the limit screws were set and the cable snugged up on the BOX system, it took a couple turns of the barrel adjuster on the shifter and we were dialed. The BOX 9-speed cassette is visibly narrower than a 12-speed cassette, making the chain line on the bike is less aggressive, especially in the 50t cog. BOX states this reduces wear on the system's components, as the chain and cogs will be grinding away with less friction between each other.

Left: SRAM 12-speed chain. Right: BOX 9-speed chain. The BOX chain is compatible with modern 11-speed narrow / wide chainrings.

The BOX cassette is made from hardened steel and the brand re-emphasizes it is their most durable cassette. When we sniffed around the BOX website, we found the cassette to be the same one they've been using in their 9-speed e-bike drivetrain. In fact, the entire BOX 2 Prime 9 X-Wide drivetrain, aside from the multi-shifter we received, is the same as their BOX Two e-bike drivetrain. Now, we understand that the cassette and system are built for some torque. E-bike motors put a big strain on drivetrain components, so much so, that BOX uses a single-click shifter in their e-bike drivetrain. Multiple downshifts (into easier gears) have been known to snap chains and fold cassettes when the motor is adding power, so BOX went big, burly and simple. We got to sample this durability on our mountain bike, but with multiple downshift options through the trigger shifter.

On the Trail

Since we had just a few weeks to wear the BOX drivetrain into the ground, we found ourselves shifting over and over and over again on our two-mile ride to and from the trails. Click, click, click, click...we must have shifted over a thousand times over the last couple weeks in the name of science. The ergonomics of the triggers are satisfactory. The shifting never faltered, and the mechanics of the drivetrain have worked well.

We wanted to feel guilty about what we're going to tell you, but we don't. After two rides and countless shifts without issue, we stopped in the middle of the trail, picked up a couple of handfuls of sandy dust and just dumped it onto the cassette. "That'll get ya," we thought. The next few minutes of shifting (which probably tallied up to 167 shifts up and down) was gritty and sounded like a machinist's worst nightmare, but the system never missed. In fact, after running through the entire gear range a few times, the system purged the dirt and returned to a relatively quiet state and again, never missed a shift. As you can see from the photos, we haven't lubed the drivetrain or cleaned it and wear is minimal. We just ran it through the dust, shifted until our fingers fell off and did our best to blow it up. We couldn't. We'll continue to abuse this system through the wetter winter months to see how it goes, but we're impressed with the solid nature of the BOX components.

Prior to this test, we've been riding 11- or 12-speed drivetrains for a long time. The gear jumps are tight, the shifting is crisp, and aside from some proprietary parts (which don't mean much if you buy a complete bike), the modern 12-speed drivetrain is hard to beat. While the mechanics and durability of the Prime 9 drivetrain exceeded our expectations, there was a mental and physical hurdle to sort out as we dropped from 12 speeds to 9. Some hurdles positive, some negative.

The gear jumps throughout the 11-50t cog range (11, 13, 15, 18, 22, 28, 34, 42, 50 teeth) are consistent and spread out nicely. The jumps, however, are more drastic than 12-speed (duh).  The good thing about the larger jumps with the 9-speed system is the ability to quickly get into the right gear in dramatic terrain changes. If you're hauling ass into a gnarly uphill, push through the trigger to downshift three gears at a time. If you're at the end of a long granny grind and about to drop in, dumping two or three gears will net you some serious power. The fast-action upshift lever is a nice touch.

We almost never used the full three-gear downshift because it's such a big jump on the cassette. Our terrain doesn't warrant switching three easier gears at a time. It's also a bit of a reach to get that last click on the trigger, requiring us to roll our hand and thumb under the bar a bit. At the top of our climbs, we're normally hitting the 12-speed shifter four or five times to dump into a hard gear when we descend. With the BOX, we'd hit it just two or three times. The argument for efficiency and simplicity is validated with on-trail scenarios like this. One of BOX's arguments for a longer drivetrain life with their system is that shifting happens less often, therefore keeping components from wearing out as quickly. It is true, with this system, we didn't shift as much. The downside of not shifting as much, however, is that finding the perfect cadence can be tricky when the terrain is undulating or steady.

Running 12-speed has spoiled us. In certain situations where the trail went just a bit steeper or just a bit flatter, we had to decide between spinning faster than we wanted or stomping on the pedals more than we wanted. A shift up or down was felt more in our 12-speed-trained legs than we were wanting to deal with. Is this a deal-breaker? Tough to say. Eventually, our riding style tuned into the intricacies of the gear jumps, and we'd decide to go slower and increase cadence for longer sections or tough it out and smash it for shorter efforts. This was the biggest compromise we found with running the wide-range 9-speed system.

Things That Could Be Improved

From a mechanical standpoint, the clutch on the derailleur is STIFF, and it can't be adjusted. The cage and chain do stay put, and chain slap is minimized, but there is some effort required to make that downshift to easier gears. When you upshift under load to harder gears on the cassette, there can be a thud due to the big gear jump and snappy clutch. We were lucky enough to run new Race Face Turbine SL wheels with Vault hubs that have plenty of engagement, so our feet weren't bounced around. With a lesser-quality, less-engaging rear hub on a bike that may be getting a 1x conversion with the Prime 9, the gear dumps under load could be a bit jarring. Finally, the weight of the cassette can't be ignored. We understand durability is king and praise BOX for the seemingly bullet-proof nature of the cluster. However, it's a bit much for us, impacting the unsprung weight too significantly on our trail bike. We can't wait to get our hands on the BOX 1 unibody cassette that's 300g lighter. Yeah, it's expensive ($360), but for us to truly embrace a 9-speed drivetrain, that unsprung weight needs to come down.

What's the Bottom Line?

If you're a mountain biker who hates proprietary standards (don't we all?) and is looking for an easy, affordable 1x drivetrain conversion, consider the BOX Two Prime 9 X-Wide drivetrain. If you just want to simplify your life with fewer gears out back, you're in luck. If you like to be different (a motto BOX uses in some ad campaigns), the Prime 9 drivetrain is right up your alley. The 9-speed system works well, is easy to set up and uses commonly found standards to get the job done. Despite us literally throwing handfuls of dirt into the system and never cleaning or lubing it, shifting has been clean, crisp and hassle-free. Set-it-and-forget types on a budget, look no further. This could be your next wide-range drivetrain.

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