Is 2023 the year of the ‘diet’ emtb? With Specialized dropping the new Levo SL and multiple brands joining the fold with new models there have been plenty of strong signs already, but if you’re still not convinced Bosch’s new Performance SX system is surely the 100ft tall, giant, wacky, waving, inflatable arm flailing tube man. You see, Bosch doesn’t do knee jerk trends. It makes safe, considered judgements about the products it introduces to market, and only with the knowledge that there will be a large, sustainable market to sell into. As such, Performance SX could very well be the tipping point for mid power e-bikes.

Check out our buyer’s guide to find out which are the best electric mountain bikes of 2023.

You can also find out how the Bosch Performance SX compares to other systems on the market with our guide to e-bike motors.

The new Bosch Performance Line SX eMTB motor looks a lot like a Performance CX that’s been put through a hot wash.

Need to know

• Compact, lightweight motor option from Bosch
• System weight of 4kg made up of 2kg motor and 2kg battery with 400Wh capacity
• 55Nm max torque and 600W max power
• Customisable modes and extended boost
• 250Wh range extender
• Uses Bosch’s existing System Controller and Mini Remote to display battery charge and select power modes

Weight

On paper it ticks all the boxes. Claimed weight is 2kg for the magnesium encased motor, which is competitive without being class-leading. That’s only 150g more than the TQ HPR50 and 50g heavier than the Specialized, Fazua and Bafang/Forestal. Packing 400Wh, the internal CompactTube 400 battery also weighs a claimed 2kg. Only Fazua beats it on capacity, with 430Wh, while the Specialized, Forestal, and TQ all make do with smaller 360Wh units. Bosch also has a generous range extender built and ready to go, providing an extra 250Wh for longer rides. Which is significant as only Specialized currently has a range extender you can actually buy and use – none of the others are available yet. 

The unit itself is not as compact as the TQ and Fazua, but it’s still smaller than the CX with a 15mm narrower Q-factor for more natural pedalling.

Power and torque

With 55Nm, torque is also right in the mix. A little down on the Fazua (60Nm) and Bafang/Forestal (60Nm) but above the TQ (50Nm) and Specialized (50Nm). When it comes to peak power though, Performance SX holds the Top Trump; a whopping 600W. That’s significantly higher than its rivals and in line with most full fat motors. Only the Fazua gets close with 450w for a maximum of 30 seconds using its overboost function. 

The wireless mini-remote makes it easy to switch modes and access walk mode and hill hold assist.

Control units

To control the power modes and check battery life the system is designed to work with the existing top tube integrated System Controller and bar mounted wireless Mini Remote. As such you can change modes with either unit, while the basic top tube display uses five LEDs to indicate power mode (using colour) and battery charge. As the battery drains first the chunk turns white to indicate 10% used, then the light goes out completely when 20% is used. This continues through each chunk until 40% is left and the two final chunks turn orange, followed by red at 20% remaining. It’s a simple yet effective design that is discreet and well integrated into the bike. And for more detailed information on battery life, it’s always possible to connect to the Bosch Flow app. 

On the top tube mounted System Controller, the upper LED shows which mode you’re in (here it’s eMTB), while the five LEDs below indicate battery charge. Each chunk goes from coloured to white once 10% has been used, giving a more accurate indication of battery remaining.

Bosch Flow app

The Flow app also allows you to customise each individual power mode as well as access security features and diagnostics and navigation/ride recording. As such you can tune how responsive the motor is to pedal inputs – making it more or less sensitive – as well as changing the level of support provided by the motor in each power band. 

The PowerMore range extender has a generous 250Wh capacity and a custom mount for the frame that’s interchangeable with a bottle cage. It uses standard Bosch connections and the same voltage as the other PowerTube batteries, so yes, you can use it with bikes running the Performance CX Smart System motor. Both batteries drain in parallel.

How it differs to Performance CX

If we compare SX to the full power Performance CX system, we’re looking at a total weight saving of approximately 3kg including controllers (Performance CX motor is 2.9kg plus a 750Wh battery weight of 4kg), no reduction in peak power, and 30Nm less torque. Target weights for complete bikes will be in the sub-20kg range depending on build, spec and target application. 

Performance SX also has a speed sensor in the back of the motor, so can be used with the valve mounted magnet. This eliminates wiring through the chainstay.

How it rides

Switching on the Performance SX system and toggling through the modes will be completely familiar to anyone who has ridden the full-fat CX system in the past. A button on the top tube gets the current flowing and pressing the +/- buttons on the handlebar remote or the top tube unit scrolls through the usual power modes – Eco, Tour+, eMTB, and Turbo. It’s easy to place the Mini Remote within reach of your thumb and the lack of cables adds to the unit’s flexibility while keeping clutter to a minimum. However, care is needed not to catch the back of the thumb pad, as it’s easy to bend or rip the cover away from the main unit.

Different mounting system

Visually the SX unit looks like a shrunken CX. It’s not a concentric system like the ultra compact TQ, or a worm drive design like the Fazua, so it’s not completely invisible. Bosch has engineered a two through-bolt mounting design – the Performance CX has six – with one bolt where the down tube usually meets the motor, and one low behind the BB axle, close to the rear wheel. Brands have the choice of building their own custom battery mounts or using off the shelf Bosch units. A lower motor cover/bash guard is also needed to protect the underside. All of this does add weight to a system in which minimalism is crucial, but it also plays an important role in protecting the motor from damage. 

Acceleration

A very brief 6km test ride, on a bike with the brakes reversed, wasn’t the perfect test for the Performance SX system, but it’s better than nothing. What’s immediately noticeable from the get go is how much SX likes a high cadence. It encouraged me to spin the cranks rather than grind a heavy gear – I prefer high cadences so it suits me – and if you can keep those legs pumping it rapidly accelerates up to the speed limiter on gradual climbs in eMTB and Turbo modes. As such it feels as quick and powerful as a full fat model, maybe even quicker because there’s less mass, less friction in the system and typically bikes will be running lighter, faster rolling tyres. As long as the gradient isn’t too steep, you could easily keep up with mates on full power e-bikes and not break a sweat. 

Technical climbs

Get into more technical climbs and experienced riders will want to increase the support and adjust the riding dynamics to make the motor as sensitive as possible. Then you can ratchet up steppy pitches with half cranks, or pause pedalling and use the 2m extended boost to prevent pedal strikes through narrow rock gaps. In that respect SX is an impressive tool for unlocking technical climbs. You can’t soft-pedal, leaching off the motor like you can with the CX, and it’s unlikely it will crawl up radical gradients like its more powerful cousin (I didn’t get the opportunity to try any super steep banks), but it leaves competent rider with few excuses for not cleaning a technical ascent. 

Drag

Approach the speed limiter and there’s a soft taper to the power, and once you’re on your own the resistance is not excessive. Bosch claims 50% less than the Performance CX, and only a fraction more friction than a regular BB, mostly because of the upgraded sealing needed to ensure durability. Turn the motor off, and I noticed the extra mass of the bike compared to an analogue model more than the drag in the system. Put it this way; running out of battery wouldn’t be fun, but it wouldn’t be as catastrophic as on a full fat e-bike. 

Range

Since we published this original first ride, we’ve now had time to do a few range tests on the Whyte E-Lyte 150 Works. The first ride was in mid-December, and the trails were reasonably dry. In Turbo mode, with a completely stock bike, we managed 776m of climbing. But the battery was only at 95% at the start. The second range test we did, we swapped the sticky Maxxis Minion DHF Maxx Grip front tyre for a faster rolling option and managed 842m of climbing/22.2km/1hr 26min moving time. Trail conditions were similar. The final range test we did was at Rogate Bike Park, using a Max Terra Minion DHF front tyre. Here we managed 752m of climbing/1hr 35min moving time. All three range tests were carried out exclusively in Turbo mode, without the range extender. That’s a lot less than the frugal Fazua, and the smaller capacity/lower power Specialized 1.2, but on par with the TQ HPR50. Obviously the Bosch SX has more power than any of these motors (but not more torque), so if you use Turbo and extract lots of power from the motor it stands to reason the range will be less. By using e-MTB or Tour modes, or customising the power, it should be possible to get a similar range to the other systems.

Noise

Personally I didn’t notice the volume of the motor on my ride, although maybe I was concentrating too much on not grabbing a handful of front brake by mistake. I don’t think it’s as quiet as the TQ, but it’s nowhere near as noisy as the whiny Bafang used on the Forestal. How it slots in amongst the Fazua and Specialized motor is TBC.