More Power & Flow from Bosch Performance Line CX Upgrade
More watts, more torque, and a brand-new eMTB+ mode
Photography by Clancy Kelly
When it comes to mountain biking e-bike systems, Bosch is one of the first names that comes to mind. Widely regarded as a benchmark in the category, Bosch has built a strong reputation for reliability, performance, and intelligent design in a no-nonsense package. The brand is renowned for powerful motor support, intuitive assistance modes, a robust ecosystem of components and a Flow app that works seamlessly – traits that have made Bosch systems a go-to choice for both recreational riders and serious trail enthusiasts alike.
With a raft of new competitors on the market, it became apparent that Bosch had to lift their game to remain competitive in the e-Bike market segment. Their new raft of backwards-compatible performance upgrades for the powerful fifth generation Performance Line CX system means that Bosch have committed to their existing customers.
I was fortunate enough to jump on a pre-release Cube Stereo One77 complete with the performance upgrades for the Bosch Performance Line CX released in September 2024 (BDU384Y). Having had extensive time spent on the Performance Line CX drive unit prior to the upgrade, I was keen to see how the upgrades translated on the trail.
Bosch CX Upgrades Put More Watts in the Tank
When the new generation of the Bosch Performance Line CX system was released, I was surprised to find the maximum power remained at 600W, and torque at 85Nm. While it’s certainly nothing to sneeze at, on numbers alone the system trailed behind other big releases in the market. Lo and behold, Bosch had a plan all along, with the most recent software update for the new generation CX unit pumping numbers up to 750W maximum power, 100Nm torque and a huge boost in assistance from 340% to 400%.
Accessing the software update is done via the Flow app, allowing you to manually scale power up to 750W as desired. Notably, the upgrade is available for the most recent generation of Performance Line CX only (BDU384Y) – the update isn’t compatible with older units.
Fresh eMTB+ Mode for a Racier Ride
In addition to the big whack of watts and torque granted by the performance upgrade software update, Bosch have launched the new eMTB+ mode. Described as bridging the gap between eMTB and Race mode (Race mode being available only with the recently released Performance Line CX-R drive unit), eMTB+ features generous assistance of up to 400% of rider input, in addition to progressing Extended Boost to feature the same overrun as the CX-R’s Race mode.
This is critically important for those racing E-Enduro with power stages, as the Extended Boost feature can really make or break cleaning savage uphill tech, with a small ratchet of power to the pedals. This is a significant increase from the 340% support offered by the existing Extended Boost-equipped eMTB mode, sitting far closer in power and performance to the Race mode than eMTB. eMTB and eMTB+ mode offer a more dynamic experience, even compared with Turbo mode, whereby user input, cadence and rider style determine the way in which power is delivered, compared to Turbo mode’s more static delivery of its 340% support.
Bosch claims that while eMTB mode is optimised for longer range – all day trail riding – eMTB+ is the mode to use if you toe the start line, or are looking for the top level of performance on your local Strava segments.
Display for Days: The New Kiox 400C Display Unit
When I had the Trek Rail+ on test earlier this year, I had a sneaking suspicion something was coming from Bosch when the System Controller was located upon a much broader backing plate. Suspicions were confirmed with the launch of the Kiox 400C display unit, available as an aftermarket purchase on selected bikes. Seamlessly located within the top tube, the new unit broadcasts a range of metrics such as power, cadence, heart rate and elevation. The new Kiox 400C allows for a dynamic display that alters with terrain, for example showing elevation when climbing and speed when descending.
For those of us with a preferred computer display set-up, the new Kiox 400C can be configured using the Flow app, and can also be manually operated using the tactile buttons.
Bosch have designed the new display to be visible in all light conditions, with an automatic brightness adjustment, and the display features a super handy USB-C charging socket, which can be used to power devices like your smartphone or USB-charged tyre inflator while you ride.
On The Trail: Riding with the Bosch CX Updates
For existing Performance Line CX riders with the fifth generation unit, downloading the upgrades is done through Flow App. From here, it’s a case of selecting the Customise Ride mode menu, which allows you to select what modes are operational. The default setting features Turbo, eMTB, Tour+ and Eco, so initially I replaced eMTB with eMTB+ to feature Turbo, eMTB+, Tour+ and Eco.
It wasn’t long before I realised that going from Tour+ to eMTB+ felt the equivalent of heading from Eco to eMTB – the jump was significant. I quickly readjusted modes to Turbo, eMTB+, eMTB and Tour+, though it was quickly apparent that eMTB+ can easily replace Turbo mode for all intents and purposes.
Launching further into the modes on the Flow app allows you to dial up the assistance, dynamics, max speed and torque (though the maximum 100Nm torque becomes the default for both eMTB+ and Turbo modes). For most riders, changing the max speed from 25km/hr isn’t compelling, but you can increase the torque and assistance of eMTB mode to bring it closer in nature to eMTB+. Likewise, increasing support and dynamics (ie: rate at which assistance is delivered) to Tour+ mode became a good option to bring Tour+ a little closer to eMTB while maintaining the mode’s efficiency and slightly more subdued power delivery.
Driving the new KIOX 400C is a piece of cake, the bottom left button cycles through modes, the right flips through the display, the top left powers the unit on and the top right hides the integrated USB charger. As I was using the Mini Remote, use of the mode button was sparse.
The display cycles through several pages, featuring a phone connection page, speed, dynamic data page that adjusts from clubs, descents and flat terrain, and power data. This dynamic data page also features a range indicator using the four mode colours along the bottom of the screen – this is super handy to see while riding along and a huge upgrade from the at times nail-biting display of the System Controller’s 20% bars. Battery capacity is located at the top of each display, meaning there is no excuse to run out of juice on the trail.
My first ride on the updated Bosch Performance Line CX unit was a whole new eBiking ballgame. Coming from the integrated, natural assistance of the Performance Line CX, the upgraded power and torque of – in particular – the eMTB+ mode was initially a little wild, to the point where I was repeatedly flipping between Turbo and eMTB+ modes for a good 10km to feel the difference.
While Turbo’s default is 340% assistance, eMTB+’s is 400% and they both feature the peak torque value of 100Nm. Where they really differ is in the nature of that power delivery – eMTB+ mode really mimics the dynamic nature of power delivery on the trail, and delivers a varying output depending on what you’re doing.
For example, a strong stamp on the pedal with a lot of force is enough to engage some intense Extended Boost – a feature Turbo mode lacks. But it’s not just a power pedal that elicits that extended boost response, it’s also activated by moderate power, high cadence efforts – for example when spinning up a steep climb into a technical feature. This became super exciting when presented with technical features in low-speed sections of trail, or ‘unridable’ step ups in loose terrain.
Essentially, eMTB+ is giving you more support and torque than Turbo mode in default setting, in a nippy, race-ready package. Bosch states that eMTB+ mode closely mirrors ‘Race’ mode, which is only available on their Performance Line CX-Race units.
In my ride experience, it’s like eMTB mode on steroids. At times during grunty, tight switchbacks I found myself Extended Boosting into the void. It’s certainly a weird feeling having to brake uphill!
Just on that, compared to the Bosch Performance Line CX system, the Performance Line CX-Race units feature 1000x sensor inputs per second, magnesium housing and Race mode – Bosch’s mode that is the most rapid to hit peak speed and only features on the CX-Race units. Much of the performance of the CX-Race unit is attained with the update to the Performance Line CX, in a package many will already own.
The downside of the new upgrades from Bosch? Well, with big watts comes a cost – range. Heading out up a 1km offroad climb – steep and near-unrideable on an enduro bike but perfect fodder for an eBike, took me around 6minutes on eMTB mode, at a power of around 190-200w. For this effort, I used 4% battery. Heading back down and up again in eMTB+ mode saw climb time fall to around 5minutes at 190-200w, but churned through 7% battery (ouch!), pretty on par with Turbo mode.
Indeed, the range estimates displayed on the Kiox 400C confirmed this: eMTB is your friend for longer days out, while the range of eMTB+ is significantly less and consistently very close to that of Turbo mode. At one point late in a ride, the Kiox 400C indicated I had ranges of 14km in Turbo, 15km in eMTB+, 27km in eMTB and 40km in Eco.
This means that if you’re planning a longer ride, it’s definitely worth switching between desired modes to lengthen your battery life and ride time. Or you could just keep sending it on full power and instead purchase a PowerMore 250 Range extender. Up to you.
It’s notable that I have been testing a Beta version of the updated Flow app. I had a few issues with GPS data and elevation on my ride – with the Flow App and Kiox diverging in their elevation metrics but both offering 50 and 70% of the elevation on my concurrently run Garmin and Wahoo. I am waiting to hear from Bosch on this one. But one thing’s for sure, Bosch is committed to system upgrades to fight the scourge of inbuilt obsolescence.
I would also love to see increased third-party app integration, for example with TrainingPeaks and other options, at the moment you can upload to Strava and Upload/download to Koomoot and Apple Health.
Final Take on the Bosch CX Upgrades
Overall, I am stoked that Bosch have committed to backwards compatibility with this new upgrade to their Performance Line CX system. It certainly diverges in ride feel from that natural, integrated power delivery I’m used to from Bosch, to a punchier, racier unit when in eMTB+ mode.
