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Box Components Box One Prime 9 drivetrain (with Box Two Prime 9 11-50t cassette) review

Box’s 9-speed drivetrain hopes to offer shifting performance and reliability

Our rating 
2.5 out of 5 star rating 2.5
GBP £400.00 RRP | USD $379.99
Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain

Our review

Heavy shifting and tricky setup make the Box One Prime 9 drivetrain fundamentally flawed
Pros: Consistent steps between cassette sprockets; 9-speed chain and cassette reliable; HG driver cassette requires no upgrade
Cons: Stiff shifting with a vague feel and too much paddle travel; poor chain control; price for performance; tricky set up
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Box Components’ Box One Prime 9 drivetrain was first launched in 2019, building on the brand’s experiences with its ebike-specific Box Two 9-speed system.

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As such, the Box One Prime 9 system has been designed with durability and shifting performance in mind, and although it only has nine gears, it still shares its wide-ratio cassette range with other brands’ 12-speed offerings.

Box Components Box One Prime 9 drivetrain headline figures

  • Total weight (including rear derailleur, 9-speed chain, 11-50t cassette and shifter): 1,375g
  • Total price (including rear derailleur, 9-speed chain, 11-50t cassette and shifter): £400 / $379.99

Although the Prime 9 looks good and is feature-packed, its on-bike performance isn’t as good as it should be for the price.

Shifts are stiff and vague-feeling, while the cable-pull lever has too much travel. The balance between chain control and shift performance isn’t quite right either.

I did like the steps between each of the 9-speed cassette’s sprockets and overall reliability was pretty good.

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The cable port is vertically positioned.
Alex Evans

Box Components Box One Prime 9 drivetrain details

Box’s Box One Prime 9 drivetrain can be bought as a full set, costing £400 / $379.99.

At the time of testing, the Box One Prime 9 cassette was unavailable, so my test sample was downgraded to use the lower-tier Box Two Prime 9 cassette instead, which is available to buy separately.

Box Components Box One Prime 9 X-Wide rear derailleur specifications

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
I thought shifting was a bit stiff, compromised by clutch tension.
Alex Evans

The Box One Prime 9 rear derailleur has been designed to work best with Box’s 9-speed 11-50t cassette. It has a Tri-Pack Clutch that sits behind a cap on the derailleur’s knuckle and can be adjusted using a 3mm Allen key. The clutch isn’t on/off switchable, though.

Its body and cage are made from a mix of carbon-nylon composite, stainless steel and hardened alloy steel.

Elsewhere, as the derailleur shifts gears the jockey wheels run on sealed cartridge bearings and cable-stay pivots to help maintain its position. However, because the cable port is vertically positioned, a large loop of cable is needed on some bikes.

The b-tension, limit screw adjusters and jockey wheel bolts all use the same 3mm Allen key size.

The Box One Prime 9 X-Wide rear derailleur weighed 291g on my scales.

Box Components Box One Prime 9 shifter specifications

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
My test sample wasn’t supplied with an I-Spec or Matchmaker adaptor, although these are available.
Alex Evans

The Box One Prime 9 shifter is available in two options: multi-shift (tested) and single-shift.

Its top shell and cable pull lever are made from cast aluminium and the machined bar clamp is hinged to make installation or removal easier. I-Spec II and Matchmaker adaptors are also available.

The Box One Prime 9 multi-shift shifter with factory-supplied cable weighed 142g on my scales.

Box Components Box Two Prime 9 11-50t cassette and Box One Prime 9 DLC black chain specifications

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The black finish resisted wear well.
Alex Evans

The Box Two Prime 9 cassette uses Shimano’s HG freehub standard which means the smallest sprocket size is limited to 11t while the largest cog is 50t – only one or two teeth away from the biggest offerings from SRAM and Shimano.

The Box Two cassette was originally designed for use with ebikes and uses sprockets made from stamped steel that are pinned to an alloy spider, to help deal with the extra stresses an electric motor dishes out. For the traditionally powered cyclist, this should mean increased longevity.

With only nine gears, the spacing between each sprocket is larger than 10-, 11- and 12-speed offerings, which should improve shifting performance because derailleur indexing and cable tension don’t need to be as precise due to each shifting movement being larger.

The cassette has 11t, 13t, 15t, 18t, 22t, 28t, 34t, 42t and 50t cassette sprockets. The Box Two Prime 9 11-50 cassette weighed 624g on my scales.

Box Components recommends using the Box One Prime 9 chain with its cassettes. It has nickel plating that’s claimed to help reduce corrosion and is coated with its Diamond-Like Carbon (DLC) finish to improve hardness, reduce wear and increase smoothness.

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The chain is chunky and has nice detailing.
Alex Evans

The chain, made from hardened alloy steel, has chamfered shifting edges to increase shifting performance, and solid plates and pins to make it stronger.

The 126 link Box One Prime 9 DLC black chain and quick link weighed 318g on my scales.

Box Components Box One Prime 9 drivetrain compatibility

Conspicuously missing from Box Components’ line-up are cranks and chainrings.

The American brand says its Prime 9 chains are compatible with virtually all 9-, 10- and 11-speed narrow-wide chainrings, but specifically mentions Wolf Tooth Components, Race Face, One Up Components and Absolute Black.

However, it states its system isn’t compatible with 12-speed chainrings or non-narrow-wide offerings.

The cassette uses Shimano’s Hyper Glide (HG) freehub body which is different to SRAM’s XD Driver and Shimano’s Micro Spline system.

Arguably, the HG freehub standard is still the most common, especially on less expensive bikes, but that is starting to change and XD and Micro Spline systems are taking over.

Box Components Box One Prime 9 drivetrain set up

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The adjustment zone for optimal performance is very small.
Alex Evans

Box Components provides installation and set up guide videos on its YouTube channel to help with the finer details of getting the drivetrain installed and running smoothly. I followed the instructions to the letter to give the drivetrain the best chance possible of performing as intended.

Installation was relatively straightforward and I was particularly thankful for the shifter’s hinged bar clamp, which meant I didn’t need to remove the grips or brake lever from the bar to install it.

However, the shifter has one fixed position on its clamp which, coupled with its bulky shape, could be problematic for some setups if it interferes with brake levers, especially if you are unable to use SRAM’s Matchmaker or Shimano’s I-Spec adaptors.

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The bar clamp is bulky and limits the positions it can be set at.
Alex Evans

The cassette’s lockring appeared to be quite fragile and its splines had some visible scoring after one use with a cassette tool, so care should be taken when fitting and removing the cassette to avoid stripping the splines.

Because the derailleur’s cable stop is positioned vertically (similar to Shimano) a large loop of cable is required to avoid a sharp bend that could reduce shifting performance.

The cable clamp and cable stop don’t line up perfectly when the derailleur is in the highest few gears and the cable contacts the derailleur’s body. This didn’t appear to affect performance but did make fastening the cable in the clamp tricky.

The lack of on/off switch for the clutch meant that routing and joining the chain as well as inserting and removing the back wheel was much harder than derailleurs with an on/off clutch switch, such as Shimano’s 12-speed systems or SRAM’s cage lock.

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The clutch is adjustable (after removing this cover) but can’t be turned on or off.
Alex Evans

Although the derailleur’s limit screws and b-tension were easy to set, indexing the gears was much harder than I was expecting. Cable tension was very sensitive and there was an incredibly small sweet spot where the gears shifted well.

Outside of this zone, they skipped up or down from the selected sprocket. However, once that tension was found, no re-adjustment was required.

Box Components Box One Prime 9 drivetrain performance

I fitted the Box One Prime 9 to two different bikes – my Yeti SB165 long-term test bike and Marin Alpine Trail XR – and compared it back-to-back with a host of other drivetrains from SRAM, Shimano and other brands.

Test conditions ranged from icy cold and deep winter wet and mud to dry and sunny, over a mix of trail-centre style runs and more extreme off-piste runs in Scotland’s Tweed Valley – host to rounds of the Enduro World Series.

Box Components Box One Prime 9 X-Wide rear derailleur performance

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The derailleur resisted knocks and damage well.
Alex Evans

The factory setting for the derailleur’s clutch is stiff, which means its initial movement has a significant resistance peak before the cage is able to smoothly pivot forwards.

The clutch interferes with the derailleur’s ability to easily move into lower gears because of the mechanical coupling between the shifter and derailleur via the gear cable, leading to heavy shifter paddle operation.

Reducing tension on the adjustable clutch did lighten upshifting but increased the amount of chain slap and reduced overall chain stability, making the adjustment to a lighter setting a compromise not worth making.

At the clutch’s factory setting, there was significantly more chain slap than I was expecting and when pedalling in a high gear over rough ground, the gears had a tendency to skip around the cassette. Equally, when freewheeling, the chain would frequently drop down the cassette.

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The clutch wasn’t able to stop the chain from skipping down the cassette when freewheeling.
Alex Evans

However, general shifting was good and with a positive push of the lever (more on this below) the derailleur didn’t miss any shifts and wasn’t hesitant in its operation. It also happily shifted gears under power.

During the test period, the derailleur proved to be fairly robust, not bending or getting damaged, and the jockey wheels haven’t shown any signs of wear.

The parallelogram’s pivots have a small amount of play, though, especially compared to Shimano’s XT M8100 and SRAM’s Eagle GX derailleurs, probably Box One Prime 9’s closest counterparts.

Box Components Box One Prime 9 shifter performance

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The cable-pull shifter lever is stiff to operate.
Alex Evans

There’s a noticeable amount of vertical play in the shifter paddles from new and they have a plasticky feel, which is at odds with the £75 price tag, although this didn’t seem to interfere with operation.

Both the cable-pull and cable-release paddles are quite short, which made setting the shifter in my preferred position tricky, especially without a Matchmaker or I-Spec II adaptor. To help reduce this problem, left and right adjustment on the lever clamp could help, as seen on SRAM and Shimano offerings.

When lower gears were selected and chain length grew, the derailleur’s clutch tension caused the cage to be stiff pivoting forwards, so the cable-pull shifter lever was heavy throughout the lever’s throw.

The lever has a lot of travel before a shift is engaged, too, so a fair amount of sustained force was required to change each gear, which didn’t feel particularly natural.

The engagement of each shift wasn’t very positive, either, which lead to occasional missed shifts when I let go of the cable-pull lever before the shifter mechanism had fully engaged.

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The shifter housing has some nice detailing.
Alex Evans

The cable-pull shift lever moves the derailleur before the shifter ratchet engages the next gear, so if I missed a shift it caused the derailleur to shift back to a smaller cog on the cassette with a large clunk. This made the system feel rough and interrupted climbs where quick gear selection was essential.

The cable-pull lever can shift four gears at once if pushed far enough, but accessing the last shift is virtually impossible while riding because of the amount of travel required to engage the gear.

To access the fourth shift I needed to move my thumb more than was possible without rotating my wrist around the bar. It also required a lot of sustained strength.

The cable release lever was also quite stiff but felt way more positive. It was only possible to shift one gear at a time, though.

On the plus side, shifting operation was consistent and once I’d learned to push the lever the required amount to engage the next gear, the system was easy to use. No additional cable tension adjustment was required during the test period, either.

Box Components Box Two Prime 9 11-50t cassette and Box One Prime 9 DLC black chain performance

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The 9-speed cassette has large gaps between each sprocket, especially compared to 12-speed setups.
Alex Evans

The finish on the chain and cassette have shown little signs of wear during the test period and the teeth haven’t become hooked or the chain links stretched.

General operation was quiet, too, and shifting under power was good – as long as the shift lever was pushed far and hard enough.

Despite the 9-speed cassette offering fewer gears with larger steps between each cassette sprocket, I was pleasantly surprised by the range.

Box Components Box One Prime 9 with Box Two Prime 9 11-50t cassette mountain bike 9-speed drivetrain
The 50t largest cog nearly matches SRAM and Shimano’s biggest offerings.
Alex Evans

I didn’t find myself stretching lower gears out with increased cadences on flatter sections or grinding up steeper hills in higher gears for longer because the gear ratios were too far apart.

The maximum jump between gears is eight teeth (consistently between the lowest three gears), with the jumps decreasing as the gears become higher. The consistency of the gaps makes adjusting cadence to a gear change more gradual.

Box Components Box One Prime 9 drivetrain compared to SRAM NX Eagle, SRAM GX Eagle and Shimano SLX, XT and XTR

From a pricing perspective, Box Components Box One Prime 9 drivetrain is comparable to SRAM’s GX Eagle level (once you’ve removed the cranks and chainring from the GX groupset).

It is significantly more expensive than NX Eagle‘s £365 / $375 / AU$563 / €410 asking price, even with NX’s cranks included.

SRAM NX Eagle mountain bike groupset
SRAM NX Eagle mountain bike groupset.
Ian Linton / Immediate Media

Performance-wise, GX Eagle is significantly better with crisper shifts, a lighter shifter actuation and a wider-ranging – and lighter – cassette.

The Box One Prime 9 drivetrain might last longer than SRAM’s offerings – thanks to the chunkier chain and cassette – but I don’t think you’d be able to live with the high-resistance shifter lever once you’ve experienced a lighter system.

Compared to Shimano, pricing for Box One Prime 9’s derailleur and shifter sits in a middle ground between XT and XTR, while the cassette price is similar to Shimano’s SLX-level.

I wouldn’t choose the Box One Prime 9 system over a Shimano SLX, XT and XTR mix though, and couldn’t even justify buying it over Shimano’s significantly less expensive 12-speed Deore M6100 system. The Shimano groupsets offer much better performance for the cash.

Shimano Deore XT M8100 12-speed mountain bike drivetrain
Shimano Deore XT M8100 12-speed mountain bike drivetrain.
Ian Linton / Immediate Media

Weight-wise, the full 1,375g Box One Prime 9 setup I’ve reviewed is roughly equivalent to SRAM NX Eagle’s 1,362g weight and Shimano Deore M6100’s 1,330g.

Compared to SLX M7100 (1,221g), XT M8100 (1,153g), XTR M9100 (996g), and GX Eagle (1,163g) it is significantly heavier.

Like the SRAM systems, Box’s reliability might be better in the long run, but its performance is so compromised it’s hard to vouch for it.

Box Components Box One Prime 9 drivetrain bottom line

The main pitfall of Box One Prime 9’s drivetrain is its dominatingly heavy shift operation caused by its stiff and slightly sticky clutch. Winding down clutch resistance improved shift feel but further impacted already compromised chain stability.

Because set up was also tricky and the purchase price is quite high, the Box One Prime 9 has few advantages over more mainstream – and other less well-known – competition.

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I can’t personally recommend this drivetrain, but some people might be attracted to its 9-speed simplicity.

Product Specifications

Product

Price GBP £400.00USD $379.99
Weight 1,375g – Total weight including rear derailleur, 9-speed chain, 11-50t cassette and shifter
What we tested Box Components Box One Prime 9 drivetrain (with Box Two Prime 9 11-50t cassette)
Year 2021
Brand Box components

Features

Features Compatible with HG Freehub Bodies. Compatible with Standard Derailleur Hangers (Non Direct-Mount). Compatible with most 10,11, & 12-speed wide / narrow chain rings. Prime 9 chain must be used.
Cassette options 11-50t
Speed 9