Bosch boosts torque, tweaks eMTB mode of Performance Line CX motor

Increased torque and reactive eMTB mode should help riders tame technical terrain

Bosch electric mountain bike motor and display control unit

Bosch’s new electric mountain bike software update brings an increase of 10Nm torque, taking the motor up to a peak output of 85Nm, while a re-jigged eMTB mode is claimed to improve set-off sensitivity.


The update is compatible with its MY20 and newer Performance Line CX motors.

Like other electronic devices, such as phones, computers and, more recently, cars, new features and better performance can be unlocked via software updates without any physical change to the hardware it controls.

The era of software enhancing hardware has now filtered down to the world of electric bicycles and Bosch’s newest update.

Software updates enhancing hardware

It can be tricky setting off on a steep or technical climb on an electric mountain bike. The extra weight of the bike can sometimes make transitioning from standing to riding precarious, and putting the power down successfully, especially if you’re in the wrong gear, isn’t easy.

Bosch’s latest update hopes to address this problem by unlocking an additional 10Nm of peak torque from the Performance Line CX MY20 motor.

Bosch claims the rider can now “accelerate quickly and powerfully even at low cadences, as well as being able to perform standing starts on the steepest of terrains.”

Trek Rail 9 electric mountain bike
The update is available for Bosch’s MY20 Performance Line CX motors.
Alex Evans

Thanks to the increase in torque, Bosch says full power is now available over a wider range of pedalling cadences, too.

This should help reduce the number of times you’ll either feel like the bike is ‘bogging down’ and losing power or it needs to be in a different gear.

Bosch has also tuned the motor’s assistance to iron out jolts caused by it cutting power when the rider isn’t pedalling smoothly.

eMTB mode for all conditions

In the motor’s eMTB mode, it essentially mirrors the rider’s pedalling inputs; output is dictated by the pressure, and therefore power, put through the pedals.

The software discretely switches the motor’s assistance between Tour, Sport and Turbo modes depending on the rider’s needs.

Bosch claims that the refinements to eMTB mode combine sensor and motor control functions to generate a more natural-feeling ride over a higher range of pedalling cadences.

Bosch also says the tweaks to eMTB mode mean there’s more traction that’s easier to control and setting off on the bike is much more finely tuned with more sensitivity. This means your ebike should no longer feel like a bucking bronco when you’re getting going.

The Extended Boost feature, which is automatically activated when the bike’s in eMTB mode, cuts in when a rider puts a pre-defined amount of pressure through the pedals and provides “decisive thrust for negotiating an obstacle.”

Bosch hopes this extra power will help make technical sections of trail a breeze to master.

The software update can be installed by certain specialist retailers during the summer of 2020 and is only compatible with bikes with a Performance Line CX MY20 onwards motor.

The Cargo Line, Cargo Line Speed and Performance Line Speed drive systems will also receive an increase in Peak torque to 85Nm.

The upgrade is a no-cost option.

Bosch eMTB software update ride impressions

Trek Rail 9 electric mountain bike
The Rail is Trek’s enduro electric mountain bike.
Alex Evans

I tested the software update on a Trek Rail 9 electric mountain bike fitted with Bosch’s Performance Line CX 250w motor and a Bosch Power Tube 625 battery.

I rode a whole host of different trails ranging from undulating bridleways and fireroad slogs to very steep singletrack ascents and descents in a host of different weather conditions.

In general, the motor felt impressively smooth when applying its assistance and I didn’t experience any jerking or harsh pickup when putting power through the pedals to get going.

Up, up and away

This smooth assistance was particularly welcome on one of the steepest singletrack climbs I tackled. With an average gradient of 18 per cent over 1km, the motor responded well to my inputs and didn’t spin up the rear wheel or put out too much power when I didn’t want or need it.

In fact, I was surprised by how manageable the power was, even when I was in the 50-tooth lowest gear and wanted to set off from a complete stop on that 18 per cent climb.

This subtlety and control is reflected in how the power comes off, too. The motor’s cut-out feels tapered rather than abrupt. I found this is particularly useful when I mis-timed pedal strokes between rocks, with the motor continuing its assistance as I lifted a pedal or backpedalled to avoid a rock.

This meant I didn’t lose momentum or topple over when travelling at really slow speeds.

Imitation is the sincerest form of flattery

When I wasn’t climbing really steep trails I noticed how the motor mirrored my pedalling input. When I pedalled harder, below the 17mph cut-off speed, the bike surged forward with a decisive change in pace.

However, when I was just cruising along flatter sections at higher cadences and lower power, the motor backed off.

This intuitive reflection of rider input took the guesswork out of which mode I should be in. I found leaving the bike in eMTB mode gave me the most rewarding and hassle-free experience. The automatic changes between modes was discrete and I never thought the bike was in the ‘wrong’ mode.

On switchback climbs, the Extended Boost mode helped to keep speed up. Accelerating out of tight turns with some hard pedal strokes really made the bike surge, transforming usually-laboured climbs into technical wonders of pleasure.

Battery anxiety

The danger, however, of the eMTB mode is that because it encourages you to push hard to get the maximum amount of assistance, you’re basically forcing the bike to use its Turbo mode most of the time.

This means battery life depletes pretty quickly, especially when riding enduro and winching up fireroad climbs to enjoy the descents, but was less of an issue on more undulating trails.

I still managed to complete a 1 hour 45 minute ride with 1,471m of climbing over 34.41km on one single charge using eMTB mode exclusively, though. That’s quite impressive in my eyes.

However, the range calculator didn’t appear to be especially accurate. Most rides started out with an estimated range of 50 to 40km, but as soon as I started to climb, the predicted range would halve and sometimes even drop by three-quarters, while the battery indicator remained full.

Despite the estimated range going as low as 12km, even with a full charge, I still managed to break the 30km barrier on multiple occasions before I was out of juice.

An electric mountain bike will invariably provide a great day out regardless of which motor system it has installed, but Bosch’s latest software update seems to further refine the experience.


If you’ve got a compatible motor, I recommend you investigate getting the update.