The motor fitted to an electric mountain bike can make a significant impact on how it rides and, with more motors and eMTBs available than ever in this burgeoning bike category, deciding on the best option can be bewildering.
In fact, ‘which electric mountain bike motor is best?’ is a question we get asked regularly at BikeRadar.
Of course, the answer isn’t clear-cut but, having headed up the new electric mountain bike category in our annual Bike of the Year test (dropping in May), I’ve been testing motors from all the leading brands.
This article will shed light on where each motor from the four main manufacturers (Bosch, Brose/Specialized, Shimano, Yamaha/Specialized) performs best – and where they falter.
There’s a lot to cover, so strap yourself in for the full deep-dive into electric mountain bike motors – or use the links below to skip to the sections you need. I’ve also included a glossary of the key eMTB motor terminology at the end of the article.
Electric mountain bike motors – what options are there?
Broadly speaking, there are currently two main categories of ebike motor.
Full-fat electric bikes typically use a high-power motor with between 70Nm and 100Nm of torque and are powered by high-capacity batteries with from 504Wh to 1,000Wh of energy.
I’ve focused my test on the four motor brands typically specced on most full-fat electric mountain bikes: Shimano, Bosch, Brose and Yamaha.
First is the Shimano EP8 motor, officially the DU-EP800, fitted to a host of bikes from brands including Santa Cruz, Yeti, Marin, YT Industries and Nukeproof.
Next is Bosch’s Performance Line CX, fitted to bikes from the likes of Mondraker, Trek, Whyte and Scott.
Then there’s Brose’s Drive S Mag, also known as Specialized’s Turbo Full Power System 2.2 Motor. This system is fitted to Specialized’s most powerful ebikes, as well as models from German brand Rotwild and Spanish brand BH Bikes.
Finally, we’ve got the Giant and Yamaha-developed SyncDrive Pro, also known as the PW-X3. Most commonly fitted to Giant bikes, it’s also available on some Haibike and Raymon models.
While I’ll focus on these models, this isn’t an exhaustive list of ebike motors.
A number of lightweight options exist, found on bikes where, unsurprisingly, there’s more focus on reducing weight, and less on all-out electric grunt.
Lightweight ebikes use smaller, less powerful motors delivering as little as 30Nm of torque but up to 60Nm. They’re usually fitted with lower-capacity batteries that are generally smaller than 500Wh. Bike weights are typically between 13.5kg and 20kg depending on exact specifications.
Here, Fazua’s modular Evation motor, fitted to bikes from Kinesis and Lapierre, goes head-to-head with Specialized’s Mahle-made SL motor, found on the American brand’s Turbo Kenevo SL and Turbo Levo SL bikes.
Canadian brand Rocky Mountain’s ebikes are fitted with a full-fat motor called the Dyname drive system, available exclusively on Rocky bikes.
Panasonic also makes motors, and there’s Shimano’s de-tuned EP8 RS found on the Orbea Rise to consider. There are a host of rear-hub motors, too, but these are less relevant for mountain bikes, and are more commonly found on electric road bikes or electric hybrid bikes.
Again, to avoid over complication, I’ve compared the four most common motors you’re most likely to encounter when considering an eMTB purchase.
Electric mountain bike motor specifications compared
Comparing the headline figures from each of the motors in this test is a good way to initially understand how they could feel out on the trail in any given scenario.
Torque, power and assistance
Higher torque and watt figures, or maximum support percentage, should equate to a more powerful-feeling motor, helping riders ascend quicker or with less effort.
Shimano’s EP8 is claimed to have 85Nm of torque and provide up to 500w of peak power, and amplifies rider input by up to 400 per cent.
Bosch’s Performance Line CX equals Shimano’s torque, also delivering 85Nm, but only offers 340 per cent support. Bosch wasn’t able to disclose the Performance Line CX’s peak power.
The Yamaha/Giant PW-X3/SyncDrive Pro also has 85Nm of torque, matching Shimano’s support ratio at 400 per cent. Continuous power is rated 250w – the maximum allowed under ebike laws – but Giant doesn’t quote peak power figures.
The Brose/Specialized Drive S Mag/Turbo Full Power System 2.2 Motor boasts 90Nm of torque, beating – on paper – the other motors on test. It’s also claimed to offer 410 per cent assistance and 565w of peak power.
If this were just a game of Top Trumps number crunching, the Brose would come out on top. But, as we’ll find out, it’s not as simple as comparing the numbers on a spec sheet.
What modes do each of the motors have?
Each of the motors have pre-programmed modes that the user can switch between when riding. The modes deliver different levels of assistance, usually from low to high.
Shimano’s EP8 has three riding modes: eco, trail and boost, plus a walk mode.
Bosch’s Performance Line CX motor has four stock modes, but depending on which control unit is fitted, the trail mode functions differently. For Purion-equipped bikes it has eco, trail, eMTB and turbo. Kiox 300 bikes have eco, trail+, eMTB and turbo.
Bosch’s eMTB and trail+ modes are reactive to rider input, where torque and power assistance levels are altered on the fly depending on how hard a rider is pedalling.
Specialized bikes have three stock modes – once again eco, trail and turbo – but if the bike is fitted with the MasterMind TCU control unit, it’s possible to change assistance levels in 10 per cent increments rather than switching between three predefined modes.
Finally, the Giant motor has five modes: eco, tour, active, sport and power. The active mode functions similarly to Bosch’s trail+ and eMTB modes, where increased rider input increases the amount of motor assistance.
Battery capacity and run times
Claimed run times can vary greatly and are dictated by a huge number of factors – not only which assistance level is selected or how much capacity a battery has.
Bike and rider weight, tyre compound and pressure, the weather conditions, trail type and smoothness, and how hard a rider is pedalling all influence how long an ebike’s battery can last.
That said, battery capacity is a good general indicator, where larger-capacity batteries will generally provide more range.
The Bosch motor is only compatible with Bosch batteries. The range starts with a 300Wh unit and increases to the headlining 1,250Wh battery. This makes it one of the biggest-capacity batteries.
Unlike Bosch, Shimano’s EP8 motor can be paired with third-party batteries. Shimano has its own 504Wh and 630Wh units, too. SL ebikes such as the Orbea Rise use a 360Wh unit, while Norco’s Range VLT with EP8 motor can be paired with a 900Wh battery capacity.
Meanwhile, Canyon has developed its own 720Wh and 900Wh batteries for use with the EP8 motor on the new Canyon Spectral:On.
Giant’s SyncDrive Pro motor features 625Wh and 750Wh battery capacities, but the Yamaha-branded version of the motor maxes out with a 600Wh capacity.
Specialized’s 2.2 motor is fitted with up to 700Wh capacity batteries, but the Brose version maxes out with a 630Wh unit.
The limiting factor for battery capacity is figuring out how to improve energy densities, where the aim is to fit the more potential energy into the same space without increasing battery size and weight.
Ever-advancing technology means ebike motors are decreasing in size and weight while offering more power and torque. This is a great thing for riders who are beginning to get the advantages of more power without significant weight penalties.
For our motors, the Shimano EP8 is the lightest, weighing a claimed 2,600g.
Next is the Giant/Yamaha motor, tipping the scales at a claimed 2,750g.
This is swiftly followed by the Specialized/Brose unit, weighing a claimed 2,900g.
Finally, Bosch’s Performance Line CX matches the Brose, also weighing a claimed 2,900g.
Given batteries can weigh from 3,150g (Shimano BT-E8035) up to 4,500g (Norco VLT 900Wh) depending on their capacity, the relatively small difference in weight between the Shimano and Bosch motors isn’t a particularly significant factor.
Displays and controllers
The Shimano EP8 and Bosch Performance Line CX motors both have bar-mounted displays, while the Giant and Specialized’s displays are built into the bike’s top tube.
The Shimano display has several variants, including ones with monochrome and full-colour displays. Shimano’s controller has two buttons and sits next to either the left-hand or right-hand grips.
Bosch produces a vast range of displays with varying functionality. The most basic is the Purion model, which even lacks smartphone connectivity. At the other end of the scale is the Nyon display that features touchscreen functionality. The model of display dictates which controller is installed.
Giant’s RideControl Go top tube display uses sequential LED lights to indicate remaining battery charge and which mode the bike is in. The redesigned RideControl Ergo 3 controller has three buttons and can be installed on either the left- or right-hand side of the bars, and button functionality is configurable using the app.
The Specialized MasterMind TCU, like the Giant’s display, is mounted to the bike’s top tube. The top-spec version features an in-built colour LCD display with customisable data fields.
The less sophisticated TCU uses LED lights to denote battery charge and selected mode, but both displays use the same four-button bar-mounted controller.
Apps and mode customisation
Each of these motor systems comes with its own smartphone app, connected via Bluetooth.
The functionality of the apps differs from brand to brand, with some offering only customisation of assistance levels, and others going deeper by providing detailed ride planning and tracking, with information on whether the bike’s battery has enough power to complete the ride in any given mode.
Shimano’s E-Tube Project app permits mode customisation and can turn your smartphone into a display screen for live ride data, if you’re using a bike phone mount.
Specialized’s Mission Control app can also be used to tune assistance levels, but goes deeper with ride recording and Smart Control, where the bike’s assistance is automatically tuned as you ride to ensure its battery won’t run flat.
Giant’s RideControl app can also be used to plan and record rides, and tune the motor’s power outputs.
The Bosch Flow app (which is one of multiple Bosch ebike apps, where each one is compatible with different head units and motor systems) can be used to tune motor outputs and plan and track rides.
Electric mountain bike motor ride impressions
All these specifications, statistics and details don’t mean much if they don’t translate to performance out on the trail.
I’ve ridden the four motor systems head to head on the same trails to find out how they feel in real-life scenarios, and give you the most accurate impression of their performance.
I’ve focused on their power delivery and how easy it is to control, and what that means when you’re tackling a technical ascent. I’ve also compared how powerful they ‘feel’, and when they ‘feel’ as though they’re giving you the most or least assistance.
How noisy they are can be a big issue for some riders, where quieter bikes are usually preferable, so that’s something I’ve also considered through testing.
Other factors, such as ease of use, mode selection and what it’s like living with each system are also key to ebike ownership.
Which ebike motor feels the most powerful?
Bosch’s Performance Line CX feels like the most powerful motor out on the trail, especially in its eMTB and turbo modes. The power it provides is addictive, constant and feels as though it matches and augments rider pedalling inputs with total cohesion.
The harder you pedal, the more the motor works. The support doesn’t tail off (if speeds remain below the power cut-off limit) with increases in cadence or power. You’re never left feeling that you want more assistance that the motor is refusing to provide.
Tackling ascents is a truly pleasurable experience, where a rider can either cruise at a lower speed and put in significantly less effort or pedal with vigour, expending more energy but getting to the top much, much quicker.
In contrast, the Shimano EP8 feels as if it has less power than the Bosch in its maximum boost mode. At times, it feels as if it throttles back on power, especially when you pedal harder on steeper or faster ascents. This can be a bit frustrating when you’re expecting its assistance to back up the effort you’re putting into the pedals.
That’s not to say the motor is slow or under-powered, but getting the most from it requires lower pedalling cadences compared to the Bosch motor.
At lower cadences, it has more power and assistance, but as a rider pedals faster or harder, it reduces its assistance on what feels like a sliding scale.
Arguably, the Specialized/Brose motor has a very distinct optimum support window, on either side of which power can feel a bit low.
In this window, it’s well matched to the Bosch in terms of power despite its headline figures being marginally higher. Each pedal stroke, especially at lower cadences, is harmonised with and augmented by the motor, where more rider input equates to a satisfying boost in assistance.
Unlike the Bosch, which keeps on providing assistance up to the limit, its power tapers down towards the very top end in a similar way to the Shimano EP8.
The Brose’s support window has been tuned to feel very natural, although a wider assistance window wouldn’t be a bad thing.
In terms of power, the Giant/Yamaha motor sits between the Shimano and Specialized/Brose, with plenty of support at lower cadences, and this remains constant as the rider pedals harder.
Compared to the Shimano EP8, it doesn’t run out of steam as quickly, but doesn’t quite match the continued assistance of the Bosch system.
On the trail, this makes the Giant motor feel feisty and raring to go, but this isn’t always a good thing where it can be very easy to spin the back wheel.
Which motor feels the easiest to control?
Starting from a standstill, the Giant/Yamaha motor can feel very binary in its power delivery, where it tends to want to take off quickly, providing full power.
The lack of progressivity can make it feel clunky, where controlling wheelspins on steeper or more technical climbs is tricky. Being able to feed in the power more slowly or progressively is vital, and is something the Giant struggles with.
Power delivery from the Specialized/Brose unit is much smoother and more progressive on start-up. That means putting the motor’s assistance through the back wheel isn’t a balancing act, and harder, more positive pedal strokes can be made without wheelspin.
This gives the Brose motor a more natural feeling, where rider inputs are seamlessly matched, rather than turned into binary on or off motor outputs. But, as mentioned, it does make it feel a little down on power at very low or high cadences.
Shimano’s EP8 has a similarly natural feeling when you’re already riding, mostly because of its throttled top-end support.
Setting off in turbo mode on steeper or gnarlier ascents can be trickier, with the motor trying to provide a lot of assistance very quickly. If you’re not careful with how hard you pedal, or if you’re not ready for the assistance to start, it’s possible to wheelspin, making controlling the bike more difficult.
Impressively, the Bosch’s power delivery is progressive despite it feeling like the most powerful motor out on the trails. The power increase tapers up, and is matched to how hard a rider pedals regardless of mode. This makes hard starts on steep or technical sections relatively easy.
Massive amounts of low-cadence, easy-to-control grunt augments this further. The Bosch doesn’t need hard pedal strokes to provide assistance, where light pushes of the pedals turn the back wheel slowly but with plenty of torque. It behaves in the same way a low-range gearbox does on an off-road vehicle, improving traction and control massively.
All four of the motors feature overrun, where the motor assistance continues for a short period after a rider has stopped pedalling, but the amount and duration they provide differs.
The Yamaha – true to its binary feel – is the quickest to cut off on the climbs. This can make tackling tricky uphill sections harder than systems with a longer overrun because there’s more reliance on human power to keep the bike moving.
Specialized’s cut-off is the most gradual in terms of feel, tapering down the power rather than stopping it abruptly. This makes it easy to predict and control.
The Bosch motor also tapers down its power rather than stopping it instantly. This makes it much easier to adjust pedal timing in rocky sections or briefly hop up a step without being left with no assistance.
The Shimano EP8 is quick to cut power at the end of its overrun period, rather than tapering. Depending on the circumstances, though, the length of its overrun is usually enough to maintain motor assistance when it’s needed. Push it too far, however, and you’ll be left without any assistance at all.
Which motor is the most efficient?
A wide range of factors affect how efficiently a motor uses its battery power, including bike and rider weight, tyre compound and carcass thickness (thicker carcasses or stickier compounds require more power to overcome rolling resistance), trail conditions, the temperature and weather, and how well maintained the bike is.
It’s worth noting I tested the different motor systems on different bikes from different brands, all with varying specs and components, frame and suspension designs and weights. While this reduces the scientific element of the testing, general efficiency trends have appeared.
Shimano’s EP8 appears to be the most efficient motor where bike weights, tyre compounds and trail or weather conditions had the least effect on battery range.
Although merely an indication of what’s possible, an EP8 motor with a 630Wh battery can deliver over 2,000m of climbing on a single charge in eco.
Specialized’s Brose motor with a bigger 700Wh battery, although slightly less efficient than the EP8, is still impressive. Like the Shimano, at lower assistance levels in excess of 2,000m of ascending is more than feasible.
The Bosch’s battery life was affected by multiple factors. On a Purion-equipped bike with DoubleDown casing, MaxxGrip Maxxis tyres in eco mode, more than 2,000m of climbing was regularly achievable, even in terrible weather conditions.
However, on a Kiox 300 Smart System bike with a larger 750Wh battery, on a bike fitted with DH casing MaxxGrip Maxxis tyres, only 1,700m of ascending was just about attainable.
Although this is an unscientific comparison, it highlights how different factors alter battery life.
Finally, based on my testing, the Giant’s motor isn’t particularly efficient compared to the other three. It was possible to crack only 1,500m of climbing on a single charge in the lower assistance modes despite its battery being almost identical in size to both the Shimano and Bosch bikes in this test.
Clearly, its eagerness to assist at low cadences is affecting the battery’s range.
How noisy are the motors?
Factors such as frame material and design, and motor and battery location play a part in how noisy ebike motors are. Whether that noise is generated by the motor working, or by hitting bumps or coasting is another factor.
The type of noise will affect different people in different ways. Some motors whine, some squeak, while others whirr. When freewheeling downhill, they can thud, rattle and tap.
Arguably, when under load, ebike motors sound like a rafter of turkeys gobbling, and once you’ve made that audible association, it’s hard to unhear it.
When climbing, the Shimano EP8 and Yamaha motors have the most obvious whines – or turkey gobble sound – that fluctuates with pedalling inputs. The sound they make isn’t particularly loud but the variation in pitch, or turkey gobble, can make both these motors sound louder than they are.
The Bosch makes a more constant whining sound with a higher pitch than the EP8 and Yamaha motors. This sound makes it easier to tune out compared to the Giant and Shimano motors, but it’s arguably marginally louder.
The Specialized/Brose motor has a lower-pitched whine that, like the Bosch, is constant. It’s also quite loud, but because of the more constant pitch, it’s much easier to ignore than the EP8 or Yamaha.
On the descents, the Specialized is the quietest motor. No rattles, knocks or dull thuds – as the internal freewheel engages or disengages – were emitted.
The Bosch motor has a dull, defined clunk when freewheeling downhill over rough terrain and is arguably louder than the Brose.
The Yamaha/Giant unit has a tapping, higher-pitch knock. This is more noticeable than the Bosch – mostly thanks to its pitch – but can also be felt through the pedals.
Shimano’s EP8 is the loudest and most rattly. This noise is generated from the motor’s own freewheel engaging and disengaging, and can be replicated off the bike by moving the cranks back and forth quickly. The noise can be felt through the bike’s pedals, but once you’ve got used to it, it’s possible to tune out relatively easily.
What’s it like living with each motor?
Day-to-day usage and life with each of the motors is similar. Care and maintenance instructions – such as avoiding submersion in water or cleaning with a pressure washer – are universally shared, and are good practices to follow with any mountain bike regardless of how it’s powered.
Battery removal after washing to let components dry out depends on each frame’s design, rather than being related to any motor system specifically, where some batteries are easier to remove than others.
Care and maintenance aside, one of the most frustrating things about living with certain ebikes is the lack of an accurate battery percentage display. The on-bike Bosch Purion and Shimano EP8 displays, and the Giant and Specialized’s basic TCU LED indicators, all show battery charge in 20 per cent increments.
This makes judging exactly how much battery life you have left trickier than an accurate percentage figure.
Bosch’s Kiox 300 and the Specialized MasterMind TCU display show accurate battery life percentages. This feature is a great addition, and for bikes with smart LCD displays (such as the EP8), maybe a future software update could include this functionality.
Which is the best electric mountain bike motor?
A vast number of variables and a rider’s individual requirements will influence the answer to this question.
For me, it’s a close call between the Shimano EP8 and Bosch Performance Line CX systems because both motors offer plenty of power and good battery life. You’ll also have the greatest choice of bikes, given Shimano and Bosch motors are most commonly specced.
Although an ebike’s motor and battery are key components, and seriously influence how a bike rides, its suspension design, frame geometry, and the parts fitted to it are also important considerations.
You might have the most powerful, efficient and progressive-feeling ebike motor in the world, but that’s useless if it’s fitted to a bike that’s compromised in other areas.
By saying that, I’m not suggesting Giant and Specialized bikes are bad. In fact, quite the opposite is true, and I declared the S-Works Turbo Levo the best bike I’ve ever ridden, but as a consumer if you want a Brose or Yamaha motor, you’re limited to a smaller number of bikes that may or may not suit your needs compared to their Shimano or Bosch counterparts.
In a perfect world, I’d meld together the natural-feeling assistance of the Brose, the battery life of the Shimano and the outright power of the Bosch, coupled with Specialized’s discreet MasterMind TCU and Giant’s RideControl Ergo 3 control buttons.
Of course, none of that is possible, and as it currently stands I would personally be looking to buy bikes fitted with Shimano’s EP8.
Electric mountain bike explainers and terminology
What are the terms associated with ebikes, and what do they mean? Adding a motor and battery to a bike introduces layers of complication, where additional understanding can be key to getting the right motor for your needs.
Where are ebike motors fitted?
Electric mountain bike motors are usually fitted to the bike’s main frame at the down-tube and seat-tube junction, replacing the bottom bracket. The motors attach to the frame with large, weight-supporting bolts that mean they can be removed for servicing or repair.
Thanks to its main frame location, the motor forms a part of the bike’s suspended mass and lowers the centre of gravity, which can help improve handling and suspension. It means it doesn’t rely on long cables that could get damaged to connect to its battery.
Motors that are integral with the rear-wheel hub (and sometimes front-wheel hub) are less common on mountain bikes, but are frequently found on cheaper hybrid or commuter models.
What types of ebike are there?
Currently, there are two categories of ebike.
Full-fat ebikes typically use a high-power motor with between 70Nm and 100Nm of torque and are powered by high-capacity batteries with from 504Wh to 1,000Wh of energy.
Generally, bikes of this nature weigh between 23kg and 28kg, depending on frame size, components fitted and battery capacity.
Full-fat ebike motors include Giant’s SyncDrive Pro, Shimano’s EP8, Bosch’s Performance Line CX and Brose’s Drive S Mag.
SL or super-light ebikes use smaller, lower-powered motors and batteries delivering as little as 30Nm of torque but up to 60Nm. They’re usually fitted with lower-capacity batteries that are generally smaller than 500Wh. Bike weights are usually between 13.5kg and 20kg depending on exact specifications.
There are fewer SL ebike motors compared to full-fat ones, but examples include the Mahle-made Specialized SL motor, Fazua’s Evation, and the Shimano EP8 RS.
Below are explanations of some key terms associated with ebikes.
Pedal assist motor / Pedal electric cycle (Pedelec)
The name given to ebike motors that only provide assistance when a rider is pedalling. As soon as a rider stops pedalling, the motor’s power cuts off. In the European Union, the UK and Australia, pedal assist is available up to 25 km/h (15.5mph). In the USA, it has a higher threshold of 20mph (32km/h).
The term given to the electric system that provides power. It can also be called the drive unit or engine.
Normally removable, the battery can be integrated into the bike’s down tube or sit on top of it. It’s usually connected to the motor using wiring with a waterproof connection.
Frequently mounted to the handlebars near the grips, the controller’s buttons change between each of the bike’s modes and can cycle the display, if one is fitted.
Sometimes this is fitted to the handlebars or stem, but it can also be integrated into the bike’s top tube or elsewhere. It can display multiple bits of useful information, including battery charge and current selected mode, along with speed, range and cadence.
Most motors feature user-programmable or selectable support levels. The mode types change the amount of power and torque assistance a motor will provide. For example, Shimano’s lowest-power mode is called ‘eco’, while Bosch and Specialized’s highest setting is called ‘turbo’.
A feature most ebikes have, where they’re able to propel themselves at low speed without the rider pedalling. This helps riders push the bikes up technical or steep sections they’re unable to ride.
The measurement of ebike motor power. Watts are universally used to measure power from electricity and gas, through to engines, motors and human power.
The law states ebike pedal assist motors must not provide more than 250W of continuous, standard power. As motors reach their top speed, they must reduce assistance gradually and finally cut off.
Manufacturers claim peak power outputs higher than the 250W limit for a lot of their motors, but this output is only in certain circumstances and only for a short period of time. When averaged out over time, the motor shouldn’t exceed the 250W continuous or standard power rating. Motors can sometimes feel as though they’re not delivering as much power as a rider is expecting, usually because they’ve reached a 250W continuous peak and are ‘throttling back’ to avoid exceeding the limit.
This refers to how much the motor augments a rider’s pedalling inputs and is given as a percentage. Motors with 100 per cent support will essentially double the rider’s power, so if a rider puts out 50w of power the motor will also provide 50w, amounting to an overall system power of 100w. Support percentages are directly related to motor peak power (above), and are usually in the region of 300 to 400 per cent.
Newton Metres (Nm) are used to measure torque. Torque is the amount of twisting or rotational force the motor provides to assist the rider. Higher torque values will make the motor feel more powerful.
Watt hours (Wh)
This is a standard measure of electricity equivalent to the power consumption of one watt for one hour. Electric bike battery capacity varies greatly, and as technology improves so does energy density, where more power can be manufactured into the same space.
Motor assistance usually continues for a short period after a rider has stopped pedalling. This is called overrun and can be useful in technical climbing sections, where pedal timing needs to be changed to avoid ground strikes.