lightweight and its limits
Bulls Sonic Evo SX Review

Bulls is one of the brands boasting the most extensive EMTB lineup. With the Sonic Evo model equipped with a Bosch SX motor, the Cologne-based company is targeting the sportive e-bikers. But does it hit the mark?

Bulls Sonic Evo AM SX-I Review
The Bulls Sonic Evo AM SX-I: Outfitted with a carbon frame, equipped with a Bosch SX motor, and starting at €5999. Our model is the €9999 variant.

The brand Bulls is known for aggressive pricing strategies. Well-equipped bikes at competitive prices – that’s normally Bulls’ creed. But even a quick glance at the price tag of the Bulls Sonic EVO AM SX-I makes it clear: this bike has a different mission. Sporting a MSRP of 9,999 € and extravagant aesthetics, it aims to prove: Bulls can do more than just value for money. The question remains, does it deliver on that promise?

Bulls Sonic Evo AM SX-I on the Trail
Bulls is aiming to shift away from the price-performance principle with the Sonic Evo and target the high-end market. Will this gamble pay off?
Bulls Sonic Evo AM SX-I on light trails
The Bulls Sonic EVO AM SX shines on light trails. For more demanding terrain, other Bulls bikes are better suited.

The Quick Facts for the Bulls Sonic Evo AM SX I

  • Motor: Bosch SX
  • Battery: 400 Wh (compatible with 250 Wh Range Extender)
  • Travel: 140 / 130 mm
  • Frame Material: Carbon
  • Prices: 3 models from €5999 to €9999
  • Weights: 18.5 kilograms (top-tier model)
  • Special Feature: Integrated light, removable battery, drivetrain powered by the main battery, only 130 kg max. system weight
Sonic Evo AM SX-I on the Trail
Can the Sonic Evo AM SX-I impress on the trail?

Minimalist Design, Brutal Weight

With only 140mm of travel at the fork, low profile tires, and a small 400 Wh battery, the bike’s concept is stripped down to the bare essentials. Many manufacturers, since the motor hauls everything uphill anyway, stuff their EMTBs with hefty batteries, downhill tires, and usually 160mm of travel or more.

You could almost say that among EMTB product managers, a “better to have than to need” mentality is quite widespread. This mindset results in universally deployable, but also very heavy bikes. Even expensive Full Power EMTBs don’t break the 20-kilo mark.

The Bosch SX motor
No lightweight, but packed with power. The Bosch SX motor provides serious thrust when you as a rider deliver the needed input.

The Sonic Evo AM SX, with its minimalist approach, really hits where it hurts for many competitors. Our workshop scale stopped at a record-breaking 18.5 kilograms. Measured in size L, with tubeless tires mounted, without pedals, but with integrated front and rear lights. How much terrain can this lightweight handle?

Bulls Sonic Tires
Clumsy Combo: According to Mavic, tires mounted on the Crossmax XL R wheels should only be inflated to 1.5 Bar. An unrealistic pressure for Schwalbe's Nobby Nic and Wicked Will tires.
Bulls Sonic Battery
The 400 Wh Bosch battery can be removed from the side of the downtube—a rarity. Most bikes with the Bosch SX motor have an integrated battery that cannot be removed.

How does the Bulls Sonic EVO SX perform in real-world testing?

One thing’s for certain: you’ve got to take it off-road. The lightweight of this bike is not only a delight when lifting it but also when riding. At 18.5 kilograms and boasting a good, not-too-extreme geometry, the bike’s handling is on point.

On moderate trails with quick direction changes, the fun really kicks in. The bike’s typically stiff suspension plays into the sporty nature of the motor and the bike itself. The brakes, exclusively produced by TRP for Bulls, provide adequate stopping power without being absolute anchors. With their 2.3mm thick rotors, they offer impressive heat resistance. And when it’s a long downhill in the Alps, this brake system won’t run out of steam.

TRP E23 RX Brake
The TRP E23 RX brake has been specifically designed for Bulls. The lever feels great in the hand.
2.3 mm MTB brake rotors
The brake provides decent stopping power, but it's not an anchor. With 2.3 mm thick rotors, it holds up better on long descents than standard brakes equipped with 2.0 mm rotors.

The grip of the tires tells a different story, though. On dry trails, there are absolutely no issues, but as soon as moisture enters the equation, the fun with the Wicked Will on the rear wheel ends rather abruptly, going both uphill and downhill. The tires roll well and have a well-defined limit range, but in terms of volume, tread pattern, and puncture protection, they are definitely intended only for light trails. Therefore, they match the concept of the bike perfectly. Riders looking to tackle more demanding terrain should consider other tires.

Apart from the characteristic gearbox noise typical of Bosch, the Bulls is completely silent on the descent. The dropper post offers a reasonable 150 mm of travel suitable for this bike’s suspension travel range.

Bulls Spice Dropper Post
The 150 mm travel of the dropper post is sufficient for riding on easy trails.
Bosch Mini Remote
Adjustment options are pleasantly minimalist in the cockpit.

The Bosch SX Motor - Between Light and Full Power

The motor, as the heart of every E-MTB, greatly influences the bike’s character. Bulls places its trust in industry leader Bosch for the motor question, yet doesn’t go for the powerful CX unit, but instead opts for the new Light Motor with the model code SX.

The Bosch SX motor is approximately one kilo lighter than its full-power counterpart and also has a smaller build. Although it matches the weight of competing motors from TQ and Fazua, the appearance of the rivals is considerably more understated. The Bosch SX is not a motor that hides behind the chainring. It’s smaller than the Bosch CX, but it’s no tiddler.

Bosch Control Hub
Bulls omits the use of a display on the Sonic Evo AM SX. Battery level and assistance mode can be read from the LEDs on the top tube.
Bulls Sonic Evo AM SX Bottle Cage
The bottle cage needs to be mounted on the top tube. Instead of a bottle, a 250 Wh Bosch Range Extender can also be installed.

The auditory backdrop is reminiscent of its big brother, with the distinct hum on the uphills and the rattling drivetrain on the descents. The sound isn’t a deal-breaker, but it’s noticeable enough that it can’t be ignored. If you’re in the market for a quiet, subdued e-MTB, the Bosch SX motor might not be your cup of tea. However, for those who don’t mind the typical e-MTB soundscape, you’ll be rewarded with a sporty motor that packs more punch than the light motor competitors.

Bulls Sonic Bosch SX Motor
The sonic soundscape of the Sonic: On the climbs, a hum is audible, and on the descents, it announces itself with slight rattling noises.

Motor Characteristics of the Bosch SX

The Bosch SX motor packs a solid 55 Nm of torque. To put that in perspective: Fazua’s Ride 60 cranks out 5 Nm more, while TQ’s HPR 50 delivers 5 Nm less. Bosch and Shimano’s Full Power units serve up 85 Nm. Even though those motors offer more torque, Bosch claims that the SX motor matches up with a peak power of 600 watts, nearly paralleling their performance.

On the trails, the Bosch SX motor genuinely delivers a strong push, provided your cadence is on point. While the Bosch CX provides full power across a broad rotational speed starting around 50 RPM, the SX, like a typical Light E-MTB, does relatively little at lower cadences.

The Bosch SX motor
With the right cadence, you'll make good headway with the Bosch motor.

The Bosch SX motor unleashes its full power only at a cadence of 90 RPM and above. If riders can maintain this pace, they are rewarded with a sporty feel and robust assistance. This calls for riders to be proactive and contribute significant input. Merely sitting in the saddle and letting your legs drop onto the pedals isn’t sufficient to bring the Bosch SX motor into its preferred operating range.

Topic Range - how far do 400 Wh get you

Packing 400 watt-hours, the Sonic Evo SX is not a range monster. Riders who frequently push the motor to its full potential in Turbo mode with a high cadence will be surprised how quickly the battery level drops.

We took the bike on several rides with 1200 meters of climbing, with a body weight just over 70 kilograms, and managed to complete them on a single battery charge despite heavy use of “Turbo mode”. However, the jersey was thoroughly soaked afterwards, indicating an aggressive riding style.

The range of the Bosch SX system surpasses many bikes equipped with a TQ motor and is roughly on par with what the Fazua motor offers. For those who need more than 1200 vertical meters, you can hook up a 250-watt Bosch Range Extender to the Bulls for a serious boost in range.

Bosch SX Motor Uphill
Climbing uphill, the Bosch SX motor hums along, as one would expect from the Bosch Performance Line CX. With high cadence and adequate input from the rider, it delivers similar performance figures.
Bosch SX Motor Range
The range is by no means scant, but the power unit isn't exactly a range monster. However, you can retrofit a range extender.

Equipment: The Bulls is well-specked but not fully loaded.

The top-tier Bulls Sonic EVO SX will surely turn heads at your local ice cream parlor. This rig comes equipped with the XX Transmission drivetrain, offering the crème de la crème from SRAM’s lineup. The Pike Ultimate fork performs exceptionally well and, with its 35mm stanchions, it’s adequately robust for an e-MTB without being overkill. In line with the lightweight construction philosophy, the shock comes without a piggyback reservoir.

Bulls has outfitted this e-whip with an integrated taillight in the seat stays right out of the box. The front light, however, is an optional add-on, but the bike is ready for a click-mount system for easy installation. Like the SRAM drivetrain, the lighting system is also powered by the central Bosch battery. A huge plus, as it eliminates the headache of juggling multiple chargers for different batteries.

Bulls Sonic integrated taillight
Clever indeed. Not only the integrated tail light, but also the SRAM rear derailleur is powered by the central Bosch battery. This significantly reduces charging hassle for frequent riders.
Bulls Sonic Shock Absorber
The shock without a piggyback reservoir fits perfectly into the lightweight, performance-oriented build concept.
Bulls Sonic Drivetrain SRAM XX Transmission
SRAM's XX transmission shifts gears flawlessly even under full load. It is currently the best derailleur system for e-bikes.

You’ll have to forego a display. Battery status and assistance mode information are provided by the Bosch LED element embedded in the top tube. Common GPS computers can’t be paired with the system. Those who can’t do without range data or other info on the go will need to whip out their smartphone and use the app or retrofit a Bosch Kiox display. At just over €100, the price for this upgrade is reasonable. The removable battery is a highlight, something many Bosch SX models lack.

At a glance

The most importanten ratings of the SONIC EVO AM SX-I in comparison to the competitor bikes of following categorie: (10000) .

With a system weight of just 130 kg, limitations on tire pressure, and limited warranty

For heavier riders, it’s crucial to read the fine print because the Bulls Sonic Evo AM SX has a maximum permissible system weight of 130 kilograms. Subtracting the bike’s weight of 18.5 kilograms means the rider, including gear, can only weigh in at 111.5 kilograms.

The lightweight Mavic Crossmax XL R Carbon wheels can handle up to 150 kilograms, but according to the sticker on the rim, they should only be inflated to 1.5 Bar. This limitation is impractical not only for heavier riders but also considering the light Schwalbe tires that come fitted as standard. In this aspect, there’s a significant disconnect between reality and the specifications.

Bulls Sonic System Weight
With the permissible system weight, especially heavier riders should pay close attention.

As a customer, the combination of just a statutory two-year warranty on the bike doesn’t exactly inspire confidence. If you and your gear tip the scales over 100 kilos, you should carefully consider whether the Bulls Sonic Evo AM SX is the right rig for you.

During our review, we actually encountered a faulty front carbon rim. However, since we don’t have definitive proof that the carbon rim wasn’t pre-damaged from a prior test, we want to raise awareness without blowing the issue out of proportion.

Bulls Sonic EVO AM SX

Bulls nails a cohesive concept with the Sonic EVO AM SX for sport-orientated tour riders. Both the motor and the components appeal to riders who aren’t necessarily looking for that ultimate adrenaline rush on descents but want to engage in a physically active ride.

On light trails, the excellent weight really enhances the riding joy. For rougher terrain, Bulls has other bikes in its lineup with more travel. The limitations on system weight, tire pressure, and the modest warranty leave a slight aftertaste for a bike that’s been optimized for weight savings.

The Bulls Sonic Evo AM SX Lineup

The Bulls Sonic EVO AM SX is available in three spec levels ranging from 5999 to 9999 Euros. We took a close look at all the options. With the arrow icon Directly compare bikes, you can directly compare each model with any other bike from our extensive market overview.

About the author

Ludwig

... hat mehr als 100.000 Kilometer im Sattel von über 1000 unterschiedlichen Mountainbikes verbracht. Die Quintessenz aus vielen Stunden auf dem Trail: Mountainbikes sind geil, wenn sie zu den persönlichen Vorlieben passen! Mit dieser Erkenntnis hat er bike-test.com gegründet, um Bikern zu helfen, ein ganz persönliches Traumbike zu finden.

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