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Buyer's guide to e-bike systems

Everything you need to know about the major e-bike systems for road and gravel

Joseph Delves
11 May 2022

From being the new, slightly suspicious kid in town to taking a starring role in almost every bike brand’s catalogue, electric road and gravel bikes have hit the mainstream, and any cyclist looking for a little extra help is better served than ever. Today’s e-bikes are lighter, go further, feel more refined and often have systems so well integrated you’d be forgiven for thinking you were looking at a normal bike.

Broadly speaking there are two types of e-bike systems: those that supply pedalling assistance directly to the drivetrain, for example a motor turning the bottom bracket, and those that supply assistance via a hub motor. Bike frames are designed so batteries can be integrated into tubes or placed inside them, and wiring is hidden – hence e-bikes that look like conventional bikes.

Unsurprisingly, electrification arrives with a host of metrics to judge any system’s performance. There’s the power each can add to your pedalling, which is most usefully described in terms of Newton metres (Nm), a unit of torque. Then there’s battery capacity.

This is best evaluated in Watt-hours (Wh), the total number of watts that can be delivered for an hour at a specific voltage. Knowing this number might help you guess the system’s range, which is how far you can travel before recharging. However, given the difference in riding styles and some makers’ slightly generous estimates, you should treat these numbers with caution. Then there’s weight, which is simple enough, plus other considerations like charging time.

To make sense of all this new technology and what it means for riders, we sat down with the experts to explain the most popular e-bike motor systems on the market right now.

Mahle X35

As seen on Orbea, Colnago and Ribble bicycles, among others

Type: Rear hub motor
Torque: 40Nm
Total system weight (claimed): 3.5kg
Battery capacity: 248Wh
Range (claimed): 75km
Additional features: App connectivity and supplemental battery option mounted to water-bottle bosses

As one of the most minimalist systems, Mahle's X35 components (formerly known as Mahle Ebikemotion) are almost indistinguishable from non-electric alternatives.

The battery sits inside the frame; the motor inside an oversized rear hub, which can be totally obscured side-on with a 32-tooth cassette. And by placing the motor inside the rear hub rather than integrated into the bottom bracket, far less intervention is necessary when designing the frame.

‘One of the attractions of the system is the way it lets our e-bike range look like traditional bikes,’ says Jamie Burrow, ex-US Postal rider and head of product at Ribble Cycles. ‘The only major frame modifications required are a down tube wide enough to fit the battery and a chainstay port to feed the wiring loom to the rear hub motor.’

While the Mahle system has multiple external control options, the most common and neatest is a simple push-button that can be integrated into the top tube. This leaves handlebars pleasingly uncluttered by displays, and instead an illuminated, colour-changing ring around the switch provides information on the level of assistance, along with charge remaining.

There’s also the option to pair the system to your phone via Bluetooth to access more information and tuning options. The system is also extremely light, another advantage over most rivals.

‘Choosing the [Mahle] system allowed us to create the lightest e-road bike range and one of the lightest e-bikes in the world with our Endurance SL e Hero, which weighs 10.5kg,’ says Burrow.

This means bikes equipped with the system tend to feel less impeded by weight once above the motor’s 25kmh cut-off point, or in the event the battery goes flat. When in use, the relatively small amount of extra torque provided means the system feels quite natural. Burrow describes the sensation as ‘like you but on your best day ever’.

Yet the system isn’t without compromise. This emphasis on minimalism means some riders might find both pedalling assistance and battery a little underpowered – its effect is more like adding a brisk tailwind rather than a full-blown turbocharger.

Then there’s the fact that while the motor squirrels itself away quite well it still weighs 2.1kg, and this mass is concentrated at the rear wheel, which affects handling. Dropping the wheel out if you get a puncture is more of a pain, and because the battery is fixed it requires the whole bike to be brought to a power socket for charging.

The Mahle X20, a new system from the brand, goes lighter still with a claimed system weight of just 3.2kg.

    Bosch Performance Line CX

    As seen on Canyon and Cannondale bicycles, among others

    Type: Mid-drive motor
    Torque: 85Nm
    Total weight (claimed): 5.8kg
    Battery capacity: 400Wh-750Wh
    Range (claimed): 120km
    Additional features: The ‘smart’ version connects via Bluetooth

    Popular on gravel bikes such as Canyon’s Grail:ON range, Bosch’s Performance Line CX systems also feature on many mountain bikes and hybrids. Thus it’s little wonder that it boasts by far the most torque of the three systems shown here – a huge 85Nm.

    Based around a mid-drive design, the Bosch unit fits into a special bottom bracket shell and is a motor, transmission and bottom bracket in one, such that the bottom bracket’s axle is driven when the cranks are turned.

    Given this and the high power, the components are fairly burly, and Bosch-equipped bikes couldn’t pass as normal road or gravel bikes. Still, the system has shrunk in recent years and this fourth generation is now at least small and light enough to provide a viable option for road and gravel bikes.

    ‘In terms of weight and power density, a lot has happened in recent years,’ says one Bosch engineer. ‘For example, the size of our Performance Line CX motor has reduced by around half compared to the previous generation and we’ve also been able to reduce the weight by around 25% to 2.9kg.

    ‘Batteries have also developed in two directions. One: higher-capacity models containing more cells that are larger and heavier but offer increased range. Two: batteries with lower capacities that are lighter and more compact to better integrate into the frame. Both are suitable for e-road and e-gravel.’ Along with higher power, Bosch-equipped bikes are known for having good sensor technology.

    ‘Sensors measure the rider’s physical power input, cadence and speed and therefore are crucial in adjusting assistance accordingly. Torque, speed and acceleration are measured more than 1,000 times per second, which allows us to precisely determine how much support the rider needs in a respective situation.

    ‘Moreover, a gearshift detection system ensures smooth shifting and reduced chain wear. We believe this results in the rider benefiting from a particularly natural riding experience.’

    Given the vast amount of power on offer this is just as well, and in fact Bosch also offers more pared-back Performance Line products. However, we’ve yet to see anything other than the powerful Line CX featured on a drop-bar bicycle.

    It’s a relatively modular system, so be sure to check the size of the removable battery because these range from 400Wh (watt-hours) up to a hefty 750Wh. The size of the system’s various handlebar displays also varies drastically and, although some bikes will connect to a phone via Bluetooth for adjustment and monitoring, it’s worth noting this feature isn’t standard.

    Fazua Ride 50 Evation

    As seen on Pinarello, Pivot and Vitus bicycles, among others

    Type: Mid-drive motor
    Torque: 55Nm
    Weight (claimed): 4.6kg
    Battery capacity: 252Wh
    Range (estimated): up to 80km
    Additional features: Motor and battery contained within removable unit, battery separable; app connectivity

    The Fazua system is unique in incorporating both the battery and motor in a single removable unit. This assemblage then slots into the bike’s down tube to drive a differential-type unit that applies power directly to the cranks (much like the Bosch system). As such, although the battery is in the down tube, the Fazua is still considered a mid-drive unit.

    ‘This is a huge benefit because it lets us retain the characteristics of a road bike as you’re not loading the rear of the bike as you would with a hub motor,’ says Vitus’s road product manager, Jodie Shann. ‘Another big factor behind choosing Fazua was the torque.’

    Shann is alluding to the support the Fazua offers in terms of torque – high enough to assist at low cadence, yet not so high as to produce unnatural levels of thrust.

    ‘To get the most out of any system you need to be within a certain cadence range. When the rider drops the RPM, the system has to work harder and it becomes less efficient. So a higher-torque system gives you more efficient assistance at lower cadences,’ says Shann.

    Consider how your pedalling slows as you struggle uphill. For this reason, even fitter riders can benefit from a little extra torque in certain situations.

    ‘It’s also not just about power, it’s about how smoothly you can introduce that power,’ says Shann. ‘We think the Fazua helps retain that feeling of riding a road bike.’

    A further advantage with this system is that because the battery is removable from the overall drive unit, you can carry a spare battery with you, and it also doesn’t interfere with removing wheels – a benefit in the event of a puncture or the need to transport the bike.

    ‘Another consideration was people’s desire to upgrade or swap their wheels, which you lose out on with a hub-based system,’ adds Shann.

    Once integrated into an oversize down tube, Fazua components are moderately inconspicuous, while at the same time being removable, allowing the user to detach the battery and drive unit for charging.

    A tertiary benefit is that a Fazua equipped e-bike can also be ridden without the battery and motor attached, meaning they can be ridden in sportives or events restricted to conventional bikes.

    The ease with which the Fazua drive detaches also makes for easy servicing and, on the off-chance you do have a problem that requires serious maintenance, the system’s design means motor problems are unlikely to totally incapacitate your bike because the unit can often be sent off separately.

    All in all the Fazua seems to be the most popular system for mid to high-end gravel and road bikes and, as you might expect, it can also be controlled and tweaked using the companion app.

    Specialized SL 1.1

    As seen on Specialized bikes, duh. 

    Type: Mid-drive motor
    Torque: 45Nm
    Weight (approx): 3.8kg
    Battery capacity: 320 Wh (+160 Wh extender)
    Range (claimed): up to 130km (+65km)
    Additional features: Launch Control App

    Putting its resources to good use, Specialized brought its motor production in-house several years ago. Now its e-bike facility in Switzerland develops and builds the motors for its enormous range of electric road, mountain, and hybrid bikes.

    One obvious upshot of this is that they and the firm’s batteries are stunningly well integrated into the bikes. Another has been a relentless focus on decreasing overall system weight while maintaining range. 

    Take the firm’s top-end S-Works Turbo Creo SL, which weighs a claimed 11.9kg. With its SL 1.1 motor apparently accounting for just 1.95kg, its 320Wh battery should provide 130km of assistance.

    The firm’s bikes also benefit from a range extender option. This bottle-shaped additional battery fits into the cage on the seat tube. Plugging straight into a dedicated frame port, it’s a clean-looking way to add around another 65km of juice. 

    All considered, it’s a slimline looking system. Yet, despite this, it can add as much as 240 watts of assistance, quite a lot for a road bike. Still less potent than the motors used on its mountain bikes, Specialized describes the effect of the engine as being 2x you. Like your legs, the system is most effective when supported by a cadence of between 60 and 100 RPM.  

    Currently, Specialized makes a single e-road bike platform, the versatile Creo. However, starting with the aluminium framed Turbo Creo SL Comp E5 at £4,000 before eventually rising to the all-carbon S-Works Turbo Creo SL wonder bike at £12,000, there are still many different options.

    Pleasingly for those that find the larger prices a tad hard to swallow, each uses the same motor and battery system. All also benefit from the firm’s mission control app. 

    This smartphone program gives you easy access to all your motor tuning options and a nifty integrated power meter to gauge how much effort you’re contributing. With sliders to customise elements like peak power, support level, and acceleration, you can design and save custom profiles that will dictate how the motor responds when riding.

    Along with tracking your movements, the app allows you to change the setup depending on the scope of your planned adventure. This will then adjust the motor and battery output based on how far or how long you want to ride.

    Generally receiving favourable reviews, you’d be forgiven for wondering about the long-term serviceability of a proprietary motor. However, since Specialized has been rolling since 1974 and now turns over an estimated $500,000 a year, we wouldn’t worry excessively. Anyway, as it stands, you get a five-year warranty, which is one of the most generous around.

    Shimano Steps

    As seen on Giant bikes

    Type: Mid-drive motor
    Torque: 40-85Nm
    Total weight (claimed): various
    Battery capacity: 418 Wh-630Wh
    Range (claimed): up to 185km

    Despite its domination of the cycling industry, it’s rare to see Shimano’s Steps electronic drive parts on a road bike. It’s not that they couldn’t work. It’s just that the component giant has decided to focus on the hybrid and mountain bike segments.

    With both genres well served by the company’s systems, it doesn’t seem in a hurry to make develop the smaller and lower-powered systems more suited to road bikes.

    Given Shimano’s proven reliability and dealer network, this is a shame. However, if you’re after a practical system for a hybrid or off-road bike and aren’t bothered about size, there’s a lot to recommend the brand’s Steps range.

    This expansive collection of components offers many variations, each based around a central mid-motor. Currently, the main difference is between the powerful EP8, E8000, and E7000 lines, which are designed principally for mountain bikes, and the more touring-focused E6100, E6000, and E5000 products.

    While explaining the benefits of each system would require several pages, one thing that stands out is that Shimano has relatively few in-tube battery options. This means that while there’s a large selection of different capacity power packs, most will bolt relatively clunkily to the frame.

    While this makes for easy removal and interchanging, it can leave bikes equipped with Steps looking a bit unwieldy. In fact, it’s only the latest EP8 system that offers a dedicated integrated battery option. It’s partly the reason why the brand’s penetration into the road market has been minimal.

    Wireless adjustment via a companion app is also mixed. It depends on the components being compatible with Shimano’s E-Tube system. If they are, you’ll get excellent live tracking, mapping, and range estimation.

    If they’re not, you’ll be left with a slightly more old-school feeling display unit. Currently, it’s just E5000, E6100, E7000 and EP8 that are compatible, leaving E6000 or E8000 users out in the cold.

    That said, smartphone-connected or not, all the various iterations of the system we’ve tried have been highly competent and easy to use. With basics like motor performance down, if some more basic versions have been a little less sleek and digitally integrated than some, on paper Shimano’s newer systems look much improved.

    Steps now also offers a phenomenal range of different options that bike makers can mix and match to achieve their aims, along with specialist parts like those for cargo bikes.

    Despite Shimano not offering many road-specific options, Giant is one of a few high-profile firms that use the firm’s parts to power its drop handlebar bikes. The 2022 Revolt E+ bike makes use of its powerful E8 mountain bike system to provide an enormous 85Nm and up to 400% assistance and is aimed at gravel-style riding.

    Yamaha PW Series ST

    Seen on Yamaha road bikes and many hybrids and mountain bikes

    Type: Mid-drive motor
    Torque: 70Nm
    Total weight (approx): 6.4kg
    Battery capacity: 500 Wh
    Range (claimed): N/A

    Yamaha has also become a significant player in the electric pedal bike market. Creating motors for many manufacturers’ bikes and a small range of own-brand bicycles, its most road-suitable motor is the PW Series ST.

    Included on the recently released Yamaha Wabash RT, it’s now backed up by a broader range of in-tube type batteries, which means that both elements can now be more neatly integrated into the frame. As such, the Wabash RT smuggles a 500Wh battery into its down tube to produce a chunky 70Nm of extra assistance.

    It may be on the heavier end of the scale for a dedicated road system, but Yamaha’s products offer serious power both in terms of immediate assistance and battery life. There isn’t currently an app-based control system, so you’ll be left to select from one of four modes via a handlebar-mounted remote. These are complemented by an automatic mode that adjusts assistance based on riding style, terrain, gradient, or prevailing conditions.

    Featuring Yamaha’s Quad Sensor System to help optimised support across a wide range of uses, the motor is particularly designed to accommodate the kind of high-cadence pedalling associated with road usage. Generally arriving with a standard motor tune, the PW Series ST motor is intended for both on and off-road use and can be found on a wide range of bikes. 

    E-bike conversion

    Turn your current bike into an electric bike

    As an alternative to shelling out for a new e-bike, it’s possible to convert an existing bike by adding a motor and battery. These conversion systems tend to be based either around a replacement wheel whose hub contains the motor, or a unit that fits below the bottom bracket and adds power via the drivetrain. The battery is fastened elsewhere, often on the handlebar or down tube.

    One company making wheel-based electrification systems is London firm Swytch. Its Universal eBike Kit (£999-£1,249) uses a front hub motor and is available to suit several wheel sizes, meaning it will work with everything from Brompton folding bikes up to full-size road racers. Replacing the bike’s front wheel, Swytch’s 40Nm hub motor adds around 1.5kg to the bike’s weight.

    The unit is connected to a battery pack on the handlebars, which looks much like a regular – albeit boxy – bar bag. This can be removed for convenient charging or security when locking the bike outside. Combined with the motor, total system weight is around 3.5kg and range is up to 50km (claimed).

    A second option is a mid-drive system, such as Bafang’s M315 kit (from around £500). Slotting in place of your bottom bracket, the Bafang motor sits beneath the frame and directly drives the included chainset.

    Providing up to 100Nm of torque, the motor can be combined with multiple frame-mounted batteries depending on your range requirements, and the total system will add around 4.3kg.

    E-bikes and the law

    Stay on the right side of the tracks

    While the press might get in a tizz about hooligans racing about on electric bikes, anyone who’s tried one will understand why this is an unlikely scenario. Electric bicycles in the UK must meet specific criteria, and key among these is a limit on speed and motor power – 250W max power and a hardly hair-raising top speed of 15.5mph (25kmh).

    Above this cut-off point you’ll get no motor assistance whatsoever and will be back to relying solely on your legs for propulsion. Any legal e-bike must also be activated via its pedals and not via a throttle.

    Stick to these rules and your bike will be considered an electrically assisted pedal cycle or EAPC, and anyone over the age of 14 can legally ride one without insurance or the need to wear a helmet. Yet given all this, how come you occasionally see riders whizzing past without turning a pedal?

    The most likely explanation is that they’re riding an illegally modified bicycle equipped with an overpowered motor and throttle-style acceleration. Such kits are readily available over the internet.

    A second option is that the rider has de-restricted a bike that otherwise met UK EAPC criteria. This dark art involves tinkering with the electronics that control the motor to override its normal operation.

    Doing this will almost certainly void your warranty and your bicycle will now be a motorcycle, so will need to be registered and taxed. Anyone caught riding such a bike without a licence could be in severe trouble, especially if involved in an accident.

    Up to speed on motor technology? Find out more about the different styles of bikes they power with our guide: types of electric bikes compared

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