E-MTBs can rack up a lot of extra mileage often with more stress on components. It’s not surprisingly component makers are now looking to create e-bike specific parts that will stand up to their accelerated wear & tear. Along those lines Box Components returns to 9-speed in the name of simplicity & durability for their new Box Two-E 9S drivetrain.

Box Two-E 9S, 9speed eMTB drivetrain

Box Two-E 9S E-MTB drivetrain, wide range 9 speed cassette

The heart of the e-bike specific drivetrain is of course the first new 9-speed mountain bike cassette we’ve seen in several years, still fitting on a current standard Shimano freehub. Despite having just nine cogs, the Two-E 9S cassette still provides the same generously wide gearing range of 454% with its 11-50T cogs, like you would find in the budget Box Two 11-speed mountain bike drivetrain.

Gearing steps are still nicely spaced out through the range. Box says the fewer gears actually work to the e-biker’s advantage, since pedal-assisted riders don’t have to shift as much as regular riders. They can rely on their motor to kick in and help them tackle tough climbs. Less shifting brings less wear & tear. So Box could be on to something with their ‘fewer gears for E-bikes‘ approach.

With the cassette comes a new Two-E 9S rear derailleur and shifter. The 9-speed derailleur itself looks functionally identical to the Box Two X-Wide 11-speed derailleur with 3D forged linkages to resist rock strike damage, and a preset Tri-Pack limited slip clutch.

The Two-E 9S trigger shifter also looks just like the 11-speed version with a different label as well. Besides fewer gear steps, the internals are also limited to just one shift per lever pull for more simple operation.

Of course, it also gets a beefed up & wide nickel-plated Two-E 9-speed chain to put that e-MTB power down and deliver on extended life of your e-bike drivetrain.

For those mountain bikers thinking upgrade when they see a budget, durable groupset, individual component pricing is exactly the same for this 9-speed Two-E groupset as is Box’s budget 11-speed Two group (with the same 11-50T cassette spread). If you are thinking of putting that mega 9-speed cassette on some old 9-speed mountain bike lying around as an upgrade… we don’t yet know if it is a different 9-speed cog spacing and two, good luck getting an old mountain bike derailleur to clear a 50 tooth cog.

Update: Cog spacing is the same at old 9-speed, but it uses thinner cogs that work with a thinner chain, again to work with existing, modern 1x chainrings.

The complete Box Two-E 9S drivetrain can also be purchased at a bundle price of $280 to save ten bucks, but each component is available separately as well. Check out our detailed look at the new eMTB group on e-Bikerumor if you want the full details, pricing & claimed weights.



  1. SRAM’s 8-speed EX-1 cassette, specifically for e-bikes, has been on the market for over two years, as well as cranks, derailleur, shifter and chain to go with it.

    • Trouble with the SRAM cassette is that it’s $500, assuming you can get a hold of one aftermarket at all. As for fitting this to an olde 9sp bike, Sunrace sell 11-40t 9 speed cassettes and they’re ace. Just about clears the XT medium cage mech on my now very old hard tail.

  2. Yes, SRAM offers a 8-speed E-Bike specific set since quite a while, but it’s based on 11-speed components. Chain, sprocket thickness and -spacing is all 11-speed. The lack of three cogs is just compensated by a thick spacer at the cassettes back. A cheap trick and not helpfull against wear and tear!!!

  3. So why is this better than ant Shimano 10 or 11 spd system? I don’t see anything inherently more durable especially when you consider the narrow chain and cogs.

    I definitely don’t need that much range on any ebike I’ve tried or own. Such a low gear is useless when you have the assist of the motor and you are top speed limited so you don’t need much on the top end.

  4. E-bike purpose aside, this seems like a good upgrade option for people who still have 9-speed shifters but want a beefier non-assisted drivetrain. Bicycle tourers come to mind, especially since in theory, these should be compatible with 9-speed Shimano Sora STI levers too.

    Outside of Box’s own chain, compatible third-party chains are perhaps a question mark, though? Cassette cog spacing is 9-speed, but the cogs themselves are narrower, so I wonder what alternative chains will fit and work fine.

    • Or you could just go for the Microshift Advent, it’s something like $125 I think for the cassette (11-42t), rear derailleur and shifter.

  5. Will the cable pull of the derailleur be compatible with Shimano or with SRAM 9-speed? Having a 9 speed clutched derailleur could be quite cool!

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