Bosch Performance SX in the first test: Lighter, more compact... stronger?

Test / E-Bike: With the Performance Line SX, Bosch presents its first lightweight mid-engine. Weighing around two kilograms, it has a maximum torque of 55 Nm and an impressive maximum output of 600 watts. It is supported by a new CompactTube 400 battery and an optional range extender with another 250 Wh. We have already been able to test the drive extensively, measure the performance data on the test bench and gain initial experience on the trail.

Key data Bosch Performance SX

Weight: 2,0 kg
Max. Torque: 55 Nm
Maximum power: 600 watts,
Battery capacity: from 400 Wh

One could certainly ask oneself how long it might be before one of the big e-bike heavyweights enters the ring when it comes to the topic of light e-bikes. Today the Bosch Performance SX is ready. With a weight of around two kilograms for the motor unit, it is almost 100 g higher than the direct competitors from Fazua, TQ or Specialized, but it is still significantly lighter than regular mid-motors, which usually weigh 2,9 kg.

The low weight of the motor is not necessarily obvious, at least from the side - because it is significantly larger than many light-assist drives currently on the market. According to Bosch, this is because the gearbox inside is dimensioned in such a way that the electric motor itself does not need a high speed. The aim is to create a background noise that is as pleasant and quiet as possible. The motor is significantly more compact given its width: With a Q factor of 160 mm, it is one of the narrowest representatives here.

Of course, Bosch itself sees the motor particularly in the light e-MTB segment, which is so popular at the moment. In addition, however, one also has an eye on e-urban and e-gravel bikes. The latter is particularly important and the drive has even been given the new support level Sprint (in the display: SPRNT) on selected bikes. Here, the output power is even more strongly linked to the cadence in order to encourage the rider to pedal. A special version of the Mini Remote has also been adapted to the racing handlebar.

Combination with new CompactTube 400 battery and range extender

For the vast majority of bikes, the Bosch Performance SX should be combined with the CompactTube 400 battery, which is also new. As its name suggests, it has a capacity of 400 Wh and is much smaller and lighter than the well-known PowerTube energy storage. Weighing around two kilograms, it is more than twice as light as a PowerTube 750 - despite its capacity. This is made possible by the new cells inside, which also allow for its compact dimensions. In the future, compact frame designs with slim down tubes will also be possible for Bosch e-bikes. Whether the battery can be removed from the frame is up to the respective bicycle manufacturer.

On request, Bosch also states that the CompactTube 400 battery is also compatible with the existing drives in the Smart System. For example, nothing stands in the way of a powerful E-MTB with a CX motor but a light, compact battery. It is also possible to combine the light SX motor with larger batteries with more capacity. Alternatively, you can also use the new PowerMore 250 additional battery. This is the first real range extender in the Bosch e-bike portfolio. With a capacity of 250 Wh, it weighs 1,6 kg and, thanks to its compact dimensions, can be mounted on the down tube. The connection is made via cable to the charging port of the respective e-bike.

As part of the Smart System, the Bosch SX is compatible with all displays and controls. In most cases it should be installed with the minimalist combination of system controller in the top tube and mini remote on the handlebars. The Purion 200 is now also available as a further option; the combined control panel of remote and display could be a very good alternative for those who do not want to do without a battery percentage display, for example. Of course, the large Kiox displays and even the Intuvia 100 can also be coupled without any problems.

On the trail of the performance specifications: Really as strong as the Bosch CX?

At first glance, the performance data of the new drive looks promising, but raises a few questions. Bosch specifies a maximum torque of 55 Nm. This puts the Bosch Performance SX at about the same level as other Light Assist representatives. At the same time, however, the new drive unit from the Swabians is said to have an output of up to 600 W. For classification: This would put the Bosch SX at the level of the Bosch CX and other similarly powerful mid-engines. In order to achieve this performance, however, the general conditions must be right, such as the cadence.

In order to get to the bottom of this performance specification, which at first glance was almost contradictory, we took the Bosch Performance SX to the test again at PTlabs. For this purpose, M1 Sporttechnik provided us with a brand new M1.EN.400.SX - a big thank you for that at this point.

Bosch SX: Impressive maximum performance

In our regular measurement for the maximum power, we apply 250 W of input power to the crank for several minutes, keep the cadence in the range between 75 and 80 and then measure the power output at the rear wheel. With the Bosch SX, 538 watts arrive on the measuring drum. This puts the new Light-Assist motor at the top of our test field with light drives, but the difference to the EP8 RS and the Fazua Ride 60 (without turbo) is only a few watts. Adjusted for the power loss of the system, we arrive at a pure engine power of approx. 350 watts. Far from the 600 watts that Bosch itself claims.

After consulting Bosch, it also becomes clear where this big difference in performance comes from. The software of the Bosch Performance SX is designed in such a way that the engine only delivers its maximum power when it is really needed. It is, so to speak, an automatically triggered turbo. In order to simulate such a scenario on the test bench, we start a new measurement and initially only apply around 100 watts to the crank for a few minutes. Then we increase this to 250 watts within a few seconds. So we measure a power output of 580 watts at the rear wheel. Around 10% more than in our standard measurement, but we are still a long way from the promised 600 watts.

This is where the torque specification comes into play. Because despite the high specified maximum power, the Bosch SX only manages 55 Nm. So if you want high performance, the cadence must inevitably be increased. Accordingly, we repeat our measurement a third time. After the "break-in phase" with around 100 watts on the crank and a cadence of around 80, we not only increase the input power to 250 watts, but also switch to a lighter gear. Lo and behold, we end up with a cadence of 110 and an output of an impressive 729 watts. Encouraged by this success, we try our luck one more time, but shift to an even easier gear. At a cadence of 130, 756 watts finally hit the ground. Adjusted for the power loss, we arrive at a pure motor power of approx. 580 watts. So there you go!

So is the Bosch Performance SX just as powerful as a Bosch CX? There is no easy answer to this question. As we have seen, the conditions for achieving maximum performance must be right. A cadence of over 100 with a driver's power of 250 watts requires a lot of power in the legs. A "normal" mid-engine achieves similar performance values ​​with less effort and muscle power. We were also able to observe that the Bosch SX can only maintain this maximum performance for a limited period of time. After 10-15 seconds, the performance begins to drop slightly again. Nevertheless: This behavior is optimal for those for whom a motor that is not quite as powerful is sufficient for most scenarios, but who would like more power for a brief moment, for example on technical climbs.

Far less spectacular is the presentation of the Bosch newcomer with a relaxed average pedaling power of 100 W. Here it is also slightly ahead of the competitors from the light-assist segment, but shows significantly more "typical" values. The consumption measurements are very similar. Here, too, the Bosch Performance SX can shine with good values, but is not able to set itself apart from the competition that clearly.

The Bosch SX in practice

For half a day we were able to put the new drive to the test in real practical use. For this we were on our test trail with the M1.EN.400.SX. The first thing that stands out is the clearly noticeable support of the Performance SX, even in Eco mode. The additional power is gentle and easy to dose, but does not stay in the background as much as is the case with the TQ HPR50, for example. Otherwise, it quickly becomes apparent that you get the usual Bosch quality with the tried-and-tested Bosch features. A gentle pedal pressure is enough to get power from the system, you will look in vain for jerks when starting.

Especially in eMTB mode, the Bosch Performance SX shows its strengths on uphill terrain. In our opinion, it is somewhere between what you are used to from other light-assist or full-power drives. In order to tickle high performance from the system at key points, appropriate effort is required, which also includes anticipatory shifting in order to be able to pedal at a correspondingly high cadence in the right gear.

At times it almost feels as if the Bosch SX offers almost any amount of power, provided you hit the pedals properly. This encourages you to do more and rewards you with a great driving experience, which in parts actually comes close to the big in-house competition called CX. This is also due to the fact that you can also enjoy the eMTB mode with the light Bosch drive, which in 2023 is still one of the best things you could wish for on technical climbs. Can be dosed excellently via the pedal pressure, never too abrupt, but (almost) always powerful enough. Of course, there is also the Extended Boost, which triggers a short push of the motor via a targeted pedal kick, for example to overcome high levels.

It is very similar when you leave the trail and climb the uphill on asphalt. Here, too, a higher cadence is required for a corresponding performance. The Bosch Performance SX runs out of steam pretty quickly with higher gradient percentages and a heavy gear.

Slight drive rattle

We are ambivalent about the background noise. The motor itself can make very different noises depending on the assistance provided. With average pedaling, constant cadence and level ground, it is actually very quiet. However, as soon as you increase the cadence and the incline becomes steep, it is very noticeable. The volume in these moments doesn't quite reach that of the big brother CX, but it's not too far off either. It also inherits the changing pitch depending on the cadence from the Performance CX. On the descent, we could also make out a slight drive rattle. Significantly quieter than Shimano EP8 and Bosch CX, but still audible on the trail. We still put a cautious question mark behind this impression, since we have only tested one e-MTB and one drive unit so far. Should anything change in these impressions, we will update the article at this point.

Conclusion: Bosch Performance SX

It took a long time before Bosch came onto the market with a lightweight drive. However, the wait was worth it: The Bosch Performance SX combines the well-known advantages of the Smart System with a great driving experience, low weight and performance that is unique for the drive class. This means that the drive is probably the best choice on the market for many sporty e-bikers at the moment. Only those who want an even more natural support behavior could be better served with the drives from TQ or Specialized - but at the same time with significantly less power.

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