If you've never heard of Bull bikes, you're not alone. Some of our testers had never seen or heard of them until the day they started riding our test model. The E-Stream EVO AM 4 we tested comes nicely equipped with a beefy enduro-ready build with 150mm of front and rear wheel travel, a stout RockShox Lyrik fork, and relatively modern geometry numbers. Wide rims and grippy 2.8 Schwalbe rubber help to maintain traction and tear through corners. This bike really comes to life at speed with a calm, stable, and confidence inspiring demeanor that begs to be ridden fast, although testers found it be a bit sluggish at lower speeds. The Brose motor system provides lots of smooth power with 4 customizable support settings and user-friendly controls. It also has a massive 650Wh battery that gives the bike a huge distance range, though it adds a bit of weight to this beefy rig. Overall, testers were impressed with the E-Stream EVO AM 4 and we awarded it with our Top Pick for Range and Battery Life.
Bulls E-Stream EVO AM 4 Review
Cons: Heaviest in test, sluggish at low speeds
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Our Analysis and Test Results
Bulls is a lesser known brand in the North American market, but that is likely to change as electric mountain bikes continue to grow in popularity. They produce a huge line of full suspension and hardtail e-MTBs as well as commuter and cruiser style models. The E-Stream EVO AM 4 model we tested falls roughly in the middle of their range of full suspension models and has a quality build for the price. It impressed our testers with its downhill prowess, stability at speed, impressive range and battery life, and smooth and powerful power output. It's the heaviest model we tested by a fair amount, but you'll be hard pressed to notice when you're riding this powerful model. Read on to find out how it compares to the competition.
The controls on the E-Stream EVO AM 4 are among the best in the test. There is a Compact Sports Interface (CSI) control unit mounted on the handlebar by the left grip which has a number of buttons for power, lights, changing power output, a small joystick, and an easy to read digital display. Turning the power on is as simple as pressing the power button on the top of the controller and it fires up almost instantly. This controller has decent ergonomics with the buttons you press most frequently while riding, to shift through the 4 power output settings, located closest to the thumb on the side of the unit. The display is somewhat small but it is bright and easy to read even in very sunny conditions. The main page displays your current speed in the center with 4 bars at the top of the screen that show which output setting you're using and 4 bars at the bottom of the screen that display remaining battery life. The small joystick on top of the unit allows you to scroll between pages to view your power output displayed in watts, ride distance, total distance, and remaining mileage range. Additionally, the control unit can be synced with your phone or heart rate monitor via Bluetooth to an app called Naviki that navigation and mapping features. You can also adjust the power output settings to your preferences. No other bike we've tested has this amount of information available on the display.
There is an additional battery display on the downtube which shows the remaining battery charge. When you press the button at the top of this display a number of small green lights illuminate depending on remaining battery life. Charging is done with a Rosenberger plug which is nearly identical the that used on the Specialized Turbo Levo Comp. This plug has a secure magnetic connection that holds it in place on the charging port. The charging port is located lower down on the downtube and covered with a magnetic rubber cap. The charging port itself is recessed within the frame about an inch and a half or so and it is difficult to see when you are attempting to attach the plug to it.
The E-Stream EVO also has a system called "Monkey Link" integrated into its design. This includes a magnetic water bottle system and magnetic mounts for lights on the bottom of the stem and on the back of the seat clamp. We didn't have the chance to test the lights, but this is an innovative system that allows you to quickly and easily mount or remove the lights with power supplied by the bike's battery, and turn them on and off with the button on the control unit. We did test the water bottle and we found it easy to attach and remove, it even stayed in place during the rowdiest of descents. Monkey Link makes a range of lights, reflectors, fenders, and bottles.
The controls on the AM 4 are most similar to those found on the Trek Powerfly which has a similar control and display unit mounted on the left side of the handlebar. The controls on the Bulls bike have a more ergonomically friendly layout and the display is easier to read. We think this is also a better system overall than those on the Haibike Xduro All-Mtn 8.0 and the Specialized Turbo Levo Comp which have buttons that are harder to reach. The Shimano Steps controls on the Commencal Meta Power Race still take the cake, however, with the best shifter style levers and an easy to read display mounted next to the stem.
The E-Stream EVO AM 4 is an all-mountain bike with a beefy build that performs well on the descents, especially at speed. Due the weight of the bike, the heaviest in the test at 55 lbs, nimble and agile aren't the first words that come to when describing its downhill performance traits. Interestingly, it isn't impossible to get this bike off the ground or manual as long as you are carrying some speed. This bike gets up to speed in a hurry with a stable and confidence inspiring feel complemented by a stout RockShox Lyrik fork, comfortable cockpit, and big 2.8" tires.
The E-Stream EVO AM 4 has good geometry numbers, but with a 67-degree head tube angle we wouldn't exactly call it slack. Once the rider adds weight to the bike and the rear suspension settles into its sag we would say that head tube angle decreases by a half to full degree, the front end of this bike doesn't really feel as steep as that measurement suggests. For comparison, all of the other bikes in this review, with the exception of the Trek Powerfly, have head tube angles in the 65-degree range. The AM 4 has a 74-degree seat tube angle, a moderate 435mm reach and a long 1230mm wheelbase. The moderate reach measurement is a good middle ground that doesn't feel too long or too short. The long wheelbase is partially due to the long 462mm chainstays and is one of the reasons this bike feels so stable at speed but struggles somewhat in low-speed technical sections of trail.
The 150mm RockShox Lyrik RC is an appropriate fork specification for a bike of this weight. It gives the front end a stout and solid feel and is highly tuneable with its air spring, compression and rebound adjustments, and bottomless tokens. The 150mm of rear suspension is handled by a RockShox Deluxe RT that feels well matched with the front end. The cockpit feels pretty dialed with a short Monkey link stem, 780mm handlebar, and KS LEV Integra dropper seatpost. The spec of 2.8" Schwalbe tires, Magic Mary in front and Knobby Nic in the rear, further inspires confidence and adds to this bike's smooth and stable feel. Once this bike gets up to ludicrous speed, slowing and stopping it is handled by Magura MT5 brakes with 203mm rotors both front and rear. These brakes provide heaps of power but testers weren't wild about their lever feel or the odd noise they make when you apply them.
The downhill performance of the E-Stream EVO AM 4 feels most similar to that of the Commencal Meta Power Race. Both bikes come to life at speed but struggle a bit in tighter technical sections of trail. In the case of the Bulls bike, this is due mostly to the long wheelbase and heavier weight. This in contrast to the Specialized Turbo Levo Comp which strikes a good balance with a more versatile performance on the descents.
The climbing performance of the E-Stream EVO AM 4 is surprisingly good, we might even call it fun. It has enough power on tap make climbing as exciting as the descents and it scrambles up just about anything. The drive unit's 4 support settings make it easy to dial it in for the trail, conditions, or workout you're after. The Brose Drive S unit provides very consistent power output that comes on very smoothly the moment the pedals start turning and continues for a second or so after they stop. This is especially nice in technical sections of trail where you may jockey your pedals to avoid striking them on rocks and makes it less likely to bog down under the weight of the bike. This extension of the power band was quite similar to that of the Commencal and just a tad longer than the HaiBike, all of which hang on notably longer than the Specialized which cuts off a bit more abruptly.
The E-Stream EVO AM 4's geometry plays into the way it handles on the climbs. The long wheelbase makes it a little tougher to get around tight switchbacks and through tricky rock gardens, although the steeper head tube angle helps keep the front end from wandering. The 74-degree seat tube angle isn't quite as steep as the competition, but it still puts the rider in a pretty neutral position above the pedals. The moderate reach feels good, neither cramped or too stretched out. The rear shock does have a dampening switch for use when climbing although, like with most pedal-assist bikes, it seems a bit unnecessary unless you're riding pavement for a long time. The large 2.8" Schwalbe tires also provide loads of traction for clawing your way over rocks, roots, you name it.
It is worth mentioning that the E-Stream EVO AM 4 is a bit of a bear if and when you do get to a section of trail that may be too steep to climb. This bike weighs 55 lbs and as far as we can tell it doesn't have a walk feature to assist you if you end up in a hike a bike situation.
Testers were very impressed with the performance of the Brose Drive S pedal assist system on the E-Stream EVO AM 4. Like most others, they claim a nominal power output of 250 watts, but one of the main things that was impressive was the smoothness of it, and this is due to the belt driven system. The drive unit engages with no jerkiness or twitchiness, just smooth pedal assistance the moment the pedals start turning. This is in contrast to other systems like the Yamaha drive unit on the HaiBike which feels twitchy and anxious to go, or the Specialized 2.1 motor which doesn't respond until the pedals turn about a quarter rotation. It is also pretty quiet, one of the quietest in the test, on par with the Specialized motor in that regard. The Bulls bike doesn't announce that you're riding an e-bike the way the louder motor noise of the HaiBike does. We also rode this bike with the motor off and it there wasn't any noticeable resistance which is nice considering the weight of this rig.
In addition to the smoothness of the engagement of the pedal assistance, testers also appreciated the lack of abruptness when the pedals stop turning. The extension of the power band for a moment after you stop pedaling really makes a world of difference and helps to prevent this bike from feeling like dead weight. The drive motor has 4 output settings, Cruise, Tour, Sport, and Power, and those settings are customizable to match your preferences. The drive unit also boasts 90Nm of torque, the most of all models we tested, and it has no problem hitting its top assisted speed of 20mph. The HaiBike has a claimed torque of 80Nm, but feels a little more torque-y than the Bulls due to the surging nature of its power output. It's fair to say that both bikes feel like they put out roughly the same power, although the Bulls bike does so in a more refined feeling way.
The simple fact that the E-Stream EVO AM 4 comes with a 650Wh battery automatically gives it a longer distance range because it has more storage capacity. This is nearly 30% more battery life than the other competitors in this review which have 500Wh or 504Wh batteries. In theory, this would result in approximately 30% more distance range, but that varies with factors like rider weight, output setting, trail conditions, weather conditions, etc. Bulls claims a range of 137 miles under optimal conditions, and while that really sounds impressive it would be nearly impossible to achieve that kind of mileage while on a normal mountain bike ride. To test the range on the Bulls we took it for a not so casual 24-mile ride with over 4,600 vertical feet of climbing. During the ride, it was used primarily on the highest output settings, Sport and Power, and when we were finished it still had a bar of battery charge remaining on the display. We feel this is quite impressive.
It's not exactly fair to compare the distance ranges of the other bikes we tested to that of the Bulls E-Stream since the storage capacities of the batteries are quite different, but we'll do it anyway. The Commencal Meta Power Race 650B+ traveled 17.1 miles and 3,100 vertical feet, the HaiBike went 17.8 miles and 3,200 vertical feet, and the Specialized Turbo Levo Comp traveled 20.6 miles and 3,455 vertical feet. Based on those numbers it's clear that the Bulls can travel at least 30% farther than the Commencal and the Haibike, and about 20% farther than the Specialized, and that's without depleting the battery. If you're looking for the most battery life and longest distance range, the Bulls is the best that we've tested. While most models come with 500Wh batteries there are a number of options that come with 650Wh and even 750Wh storage capacities. Batteries are heavy, and the larger the battery the more it and your bike weighs.
The component specification on the E-stream EVO AM 4 is nothing mind-blowing but it is definitely nice for the price. It all starts with their 7005 Aluminum frame which is beefy and stout from front to back. The Brose Drive S pedal assist motor is integrated into the frame at the bottom of the down tube and around the bottom bracket. Above that, the 650Wh powerpack is also built into the downtube for a super clean look. RockShox parts were chosen to handle the suspension duties with a 150mm Lyrik RC Solo Air fork and a 150mm Deluxe RT in the rear. Testers had no qualms with the suspension on the Bulls, it is highly tunable and felt sturdy enough to handle this heavyweight machine.
Shifting responsibilities were left to an 11-speed Shimano XT derailleur and shifters. Shifting was precise as expected and the Shadow clutch on the derailleur plus a chain guide helped prevent any unwanted chain drops. It has an FSA crankset with a 38-tooth ring and an SLX 11-42 11-speed cassette that provides plenty of range given the pedal assistance available.
Braking is handled by a powerful set of four-piston Magura MT5 brakes with 203mm rotors front and rear. Testers didn't love the lever feel or the interesting sound of the Magura stoppers, but they did work well. The cockpit consists of a short Monkey Link stem attached to a modern width handlebar with Ergon grips. There is the addition of a KS LEV Integra seat post to drop it down and out of the way on descents. One thing we didn't love about the cockpit was the fact that the seat post remote wasn't the undermount 1x shifter style. This is likely due to the fact that the e-bike controls take up a fair amount of real estate on the left side of the bar and they would conflict. Our test model had the KS Polycarbonate remote on the right side of the bar, not a deal breaker but it takes a little getting used to if you're accustomed to something else. Rounding out the cockpit is a Selle Royal saddle with Bulls branding. Not the most comfortable saddle in the world, but not horrible either.
Rounding out the build are nice wide Bulls rims laced to Formula hubs with boost spacing and thru-axles front and rear. Mounted to those rims are some 27.5 x 2.8" Schwalbe tires, Magic Mary in the front and a Nobby Nic in the rear, which provide plenty of traction both climbing and descending.
The E-Stream Evo AM 4 is a great option for the rider looking for a stable, confident descender with plenty of power, and a longer distance range and battery life. It's not the most playful bike around, but it comes ready to rumble with a nice build, innovative features, a quiet motor, and a 650Wh battery that can take you where you want to go.
At a retail price of $5,399, the AM 4 is comparable in price to the other bikes in this review give or take a few hundred dollars. For that price you get roughly 20% more battery life and potential distance range, plus a well spec'd bike that doesn't need any upgrades to be a blast on the trail. Considering how well equipped and fun to ride it is, we feel it represents a pretty good value assuming you're looking for a fast and powerful electric mountain bike.
Testers were thoroughly impressed with the E-Stream EVO AM 4. This bike's combination of stability at speed, smooth power output, long battery life, and a nice build instantly made it a tester favorite. It's low-speed handling and heavier weight left a bit to be desired, and in the end, it was bested by the Specialized Turbo Levo Comp for the Editor's Choice Award. That said, we still think it is a great option, especially for the rider seeking more battery life and a greater distance range.
Other Versions and Accessories
Bulls makes a wide range of electric mountain bikes, both full suspension and hardtail models, in a variety of builds and price points. They make 2 versions of the E-Stream EVO AM including the AM 4 model reviewed here.
The E-Stream EVO AM 3 ($4,999) shares the same frame, battery, and drive unit as the AM 4. The component specification is quite similar although it has a RockShox Yari RC fork, a Shimano Deore drivetrain, and Nobby Nic tires front and rear.
Monkey link also makes a line of magnetic accessories that are compatible with the monkey link mounts integrated into the design of the AM 4. These include lights, watter bottles, and fenders. More information can be found on the Monkey Link website and accessories can be purchased from a number of online retailers.
— Jeremy Benson