It’s been three years since the last big update to Bosch’s benchmark Perfomance CX motor. And with significant improvements to legacy rivals like Shimano’s EP801, innovative new options such as Pinion’s MGU, and outside industry disruptors like DJI and ZF introducing headline-grabbing motors, it couldn’t be a more critical time for Bosch to come up with something special to remain as one of the best e-bike motor brands on the market.

So it might come as a surprise that there are no massive increases in power, no big improvements in torque, and no crazy new drivetrain integrations. Instead, Bosch has focussed on giving its CX motor the best riding experience in e-mountain biking.

Doesn’t look different, but the devil is in the detail with the new Bosch Performance Line CX gen 5 motor.

Bosch Performance CX gen 5 need to know

• Fifth generation of Bosch’s highly popular, flagship motor
• Power or torque stay the same – 85Nm and 600W peak power
• Smaller and lighter (2.8kg) with new two-bolt frame fixture
• New 800Wh battery is lighter than the old 750Wh unit, plus 600W option
• New compact Purion 400 colour handlebar display in protected position
• Better rider experience through improved motor response – new sensors make this the smartest Bosch drive unit to date

Which is a bold move, as the most significant updates are difficult to distill into a list of bullet points or a snappy headline. You’ve got to actually ride it to really appreciate the difference. Which is exactly what I did recently at Bosch’s e-bike HQ near Stuttgart.

But before delving into the new features and tech that take the CX’s trail performance to the next level, let’s go through Bosch’s package of physical changes. And if you want to see some of the latest e-bikes to come with this updated motor, click here.

The latest Bosch Performance CX motor now attached to the frame at two points, rather than three, saving weight and freeing up engineers when it comes to frame design.

Bosch Performance CX gen 5 (BDU38 in Bosch nomenclature) motor updates

The first one being that the new CX motor is smaller and lighter than its predecessor. Not by much, but 100g is better than nothing. At 2.8kg it’s not as light as the DJI Avinox unit (2.5kg claimed) or the Bosch CX Race unit with its magnesium casing (2.75kg), but in the ballpark of the Shimano EP801 (2.7kg) and Brose S-Mag (2.9kg). And the reason it’s smaller is that it now uses the same two-bolt mounting pattern as Bosch’s mid-power SX motor. Which, as a rider, is perhaps neither here nor there, but the key advantage is that bike brands can now effectively make one frame and choose to fit either motor. The other big benefit is that there is now more freedom for designers and engineers to place main pivots, shock mounts, and even longer droppers and range extenders.

But we knew all that already, didn’t we? At Eurobike there were countless bikes with the new CX motor fitted and it was clear that there was a new mount and a smaller footprint. ‘Tell me something I don’t know’, I hear you cry!

No more rattle!

How about the fact that the new CX motor doesn’t rattle anymore? This may have been achieved by modifying the sprag clutch mechanism that allows the cranks to disengage from the motor, or it could be to do with the material of the transmission cogs, or how closely the teeth sit when there is no torque applied, but Bosch wouldn’t reveal what it has done to silence the rattle. Either way, that’s big news, and music to the ears of any aurally sensitive e-biker. It will be interesting if Bosch makes a similar running change to the SX motor, as this will be much more sensitive to any increase in friction. On that note, while Bosch made no mention of it during the press launch, I’ve heard whispers that this new CX motor boasts much lower friction than the old unit. I’ve asked Bosch for confirmation on this, and I’ll update this article when I’ve heard back.

New sensors make the CX smarter than ever

Another significant step forward in the performance of the new CX motor is down to a couple of new inertial sensors buried in the guts of the motor. These measure acceleration and movement in six axes, providing significant additional data – such as incline and trail surface – to the Bosch brain. With more info at its fingertips, the motor can meter out its power with far more control depending on the circumstances.

This extra sophistication gives Bosch the opportunity to take the CX performance to the next level, and ensure the right amount of power at the right moment to help you, as a rider, take on more challenging situations.

One example is the updated Extended Boost feature in eMTB mode. Sometimes described as overrun, this feature lets you power over obstacles like roots and ledges while keeping your cranks level for ground clearance. It’s also useful for getting a kick of power out of tight corners. On some systems it’s adjustable, but you need to go into an app to tune it. Bosch wanted riders to be able to control the extent of overrun simply through their feet. With the new system a short stab on the cranks gives a short overrun, while a longer ¼ turn ratchet gives the maximum 2m extended boost.

Also in eMTB mode is Hill Start Assist and Hill Hold. As the names suggest, these hold the bike from rolling back on climbs without applying the brake, and allow you to ride away without having to panic about getting your other foot on the pedal. There’s even a new intelligent walk mode that varies the power depending on the gradient and surface you’re pushing up.

Bosch’s latest PowerTube 800Wh battery boasts the best energy density of any in the Bosch range, and weighs less than the old 750Wh unit. Claimed weight is 3.9kg.

New 600Wh and 800Wh batteries with latest cell technology

Something that was impossible to see on those show bikes was the battery, and Bosch has got two new energy packs to power the latest CX motor. Both of these use 21700 cells, first introduced on the CompactTube 400 battery commonly used with the SX motor. Those new options are the PowerTube 600Wh and 800Wh, so now there is the choice of 400, 600, and 800Wh batteries with the latest cells, alongside 750Wh and 625Wh units with older and heavier cells. The 600 and 800 share the same overall length, too, but there the 800Wh is deeper, with an extra row of cells. Weights for the latest batteries are 3kg and 3.9kg respectively, which gives them an energy density of 200Wh/kg and 205Wh/kg compared to the 750Wh battery’s 170Wh/kg. In fact, the 800Wh battery is slightly lighter than the 750Wh as well as packing 7% more cells.

There’s also the lighter Bosch PowerTube 600Wh unit weighing 3kg.

Compare that to the competition, and that’s right up there with the DJI system on the Amflow PL Carbon (209Wh/kg for the 600Wh battery), but not quite as dense as TQ’s latest 580Wh unit which comes in at 216Wh/kg. It’s still considerably better than anything Fazua or Specialized currently has on the market.

Being entirely modular, theoretically there’s nothing stopping a manufacturer building a bike with the SX motor and the 800Wh battery, with an option to run the 250Wh range extender. Or, conversely, a bike with the CX motor and the 400Wh battery. Anything is possible. And, of course, most new bikes with the CX motor will have the opportunity to increase ride time by fitting the range extender.

The new Bosch Purion 400 display is neater and less vulnerable than the Kiox, but gives all the data you could need.

New compact Purion handlebar display – inspired by Shimano?!

On the display side, I was expecting a new colour touchscreen unit to sit inside the top tube – every bike with the new Bosch System has a larger hole cut in the frame and an adapter to size it down to fit the basic Top Tube Controller. So it’s obvious that there’s something new on the way, but for now Bosch is holding that particular update back. Instead there is a new compact MTB-friendly colour display with 1.6in screen that sits behind the handlebars in a similar fashion to the classic Shimano unit. And while there’s nothing new in that idea, the Purion 400 is actually a decent solution for mountain bikers, as it provides stacks of data and options for customisation, without the bulky vulnerability of the current Kiox unit. This is wired into the top tube controller and actuated by the wireless handlebar remote. Expect to see it on plenty of new models going forward, and Bosch will also be offering it for sale aftermarket to anyone with a Smart System-equipped Bosch bike.

Bosch is clearly working on a larger colour display to fit in the top tube, but for now it remains under lock and key.

How does it ride?

Smarter, quieter, more reactive, yet also utterly familiar; that’s how I would describe the performance of the new Bosch CX motor.

It has all the traits I’ve come to enjoy and expect from Bosch’s flagship motor – boat-loads of support (the difference between your input and the motor’s output), controllable power, good torque across a wide cadence range, and simple, intuitive controls. But with the added bonus of even better controllability and reactivity. Being able to modulate the amount of overrun with the cranks is simple and intuitive, making it a powerful tool for unlocking more technical climbs.

I could roll up to a climb up a short bank with a root step at the base just ratcheting the cranks back and forth, timing it so the last and longest stab gave me maximum overrun. This kept the forward momentum and drive while allowing me to unweight the bike, or even hop it, over the trail feature. Once on the other side, I could either resume pedalling, or add further prods on the crank to keep the bike moving forward.

With better trials skills, this could even be used to back wheel hop up sections of trail, feathering the brake and kicking the cranks to explode forward. Even if you don’t possess Danny McAskill’s abilities, it’s a seriously useful tool for climbs, that allows you to pause pedalling in a narrow rock garden, or if crank clearance is limited, and still maintain forward momentum.

Hill hold and hill start assist probably won’t be used that regularly by most riders, but they still have a place. On one climb during the test ride, I ran out of traction on the rain-soaked loamy surface, but hill start assist got the bike moving and kept it climbing while I got my back foot clipped into the pedal. Just hold the minus button down until the message appears on the screen, then start to pedal away.

My other favourite aspect of the latest CX is that it no longer rattles when coasting. Long a bugbear of Bosch users, that annoying clatter over small bumps and rattles varied from motor to motor in volume, but was always there to some degree. Now it has completely disappeared, and bikes will feel smoother and faster as a result. A small improvement, but a significant one. Bravo Bosch!

Bosch’s automatic eShift shifting has been developed in partnership with TRP, and will also work with Shimano.

Automatic shifting – Bosch eShift with TRP EASI A12

A new development for Bosch in partnership with TRP is eShift. It’s an automatic shifting option to rival SRAM and Shimano’s similar e-bike auto shift systems, but from my (admittedly short experience) it could be the best version yet.

The bike I rode was equipped with the TRP EASI A12 12-speed system, which consists of an electronic rear derailleur hooked up to the main e-bike battery, a wireless shifter, and 12-speed cassette and chain. A small button on the rider facing side of the shifter pod toggles between auto mode and manual mode, and pressing either of the shift paddles in full auto mode will override the computer for a short period of time, after which the system reverts to auto mode.

To set up the eShift, you need to input your optimum cadence. One of the screens on the Purion 400 display (and presumably the Kiox as well) lets you go into the settings, where you can select your cadence in 5rpm increments. I went for 80rpm. This isn’t a hard goal for the system, but more of a window that it aims to stay within, depending on what information it’s receiving from the sensors.

When cruising along fire roads or gradual climbs, the bike will quietly work away in the background, dropping down to a harder gear as you accelerate, and an easier gear if your cadence starts to fall. These situations don’t tend to be very dynamic, and the force applied through the pedals is relatively low, so the system is barely taxed.

TRP’s wireless shifter is intuitive to use compared to SRAM’s AXS Pod found on its T-Type Transmission.

While slowing down to a halt, the system automatically shifts into an easier gear, so you’re always in the right gear when you come to pull away again. This is a really nice feature that I found useful when approaching a road junction, slowing down for hikers, or even pulling up at the top of a climb to wait for your mates.

So far, so good, but my experience is that other systems trip up when you get to a proper mountain bike trail, particularly one where you have to make rapid accelerations out of a corner, into a jump, or on the approach to a steep bank. It’s here that rival systems will detect the increase in cadence and start to dump gears. But the clever part of Bosch eShift is that it reads the information from the torque sensor, so it knew when I was putting serious power through the pedals. If I was sprinting for a trail feature, it would hold the bike in the same gear accordingly. As such the system never dumped me into a big gear and killed my momentum at a crucial moment.

The only place where it didn’t do exactly what I wanted was riding up one of the singletrack descents, which ebbed and flowed through gullies and bombholes, over roots and stumps. Here the bike held a slightly higher gear than I would have liked, and resolutely refused to shift into an easier sprocket. I couldn’t back off the pedals or I would have lost momentum, and my cadence wasn’t high enough to get sufficient support from the motor. The solution, of course, would have been simply to manually override the computer, but I wanted to see if it would look after itself. Which it didn’t. But this was the only glitch, and could have been solved with a manual shift or possibly a tweak of my cadence setting.

While I’m covering the negatives, I also found the shift quality to be nowhere near as slick as SRAM’s T-Type Transmission or Shimano, although it was absolutely hosing down with rain the entire ride, so just about the worse conditions it could have encountered.

Overall I was extremely impressed with the performance of Bosch’s eShift. It’s the first of its type that I could genuinely leave alone and let it do its thing without constant intervention (which defeats the purpose of automatic shifting in my opinion). I’d like to get more time on it, but first impressions are very positive. Let’s hope some brands take the plunge and spec it on their bikes so more riders can get to experience it.

Bosch’s latest ABS braking system has been developed on the e-bike enduro race circuit.

ABS Pro braking

The final piece of Bosch’s tech puzzle that’s integrated into the new CX motor is ABS braking. Yes, that’s nothing new – Alan tested a bike with it fitted a couple of years ago – but this latest iteration has been refined through a development process that includes racing at the highest level on the E-EDR circuit.

And the result is two new modes that propose to offer high performance braking that’s aimed at skilled riders and gnarly terrain, rather than commuters and urban tourists on hire bikes.

Two modes are offered in the new ABS Pro system (available on the Magura MT7 and TRP DHR Evo) – these are Trail Pro and Race. In brief, the upgrades boil down to faster intervention and optimised pressure modulation, both designed to improve performance at the limit of braking. Which even includes the ability to let the rear wheel come off the ground, when endo-turning into a corner, for example.

There’s still a box on the fork, special rotors, and additional wiring, so it’s not a sleek system visually. And for many riders, that will be an instant turn-off. For me, there needs to be a lot of work making it smaller and better integrated before I would consider it on my bike.

That’s all well and good, but how does it perform? Honestly, I didn’t get to grips with it at all, and I’ll put that squarely down to not having enough time on it. Years of sensing grip and braking traction put up an instinctive barrier that prevented me from ever pulling the brakes hard enough to get the ABS to intervene. I needed to take the plunge, yank on the brakes and trust in the system to sort out the grip, but I couldn’t do it.

A couple of car park tests, on gravel, and wet metal, revealed what the system was capable of, but I need more focussed time on it to make the commitment and assess how it works. One for a later date, then.