Are you new to the exciting world of electric mountain bikes but baffled by the extra jargon, parts and components?
Learning and understanding the parts of a mountain bike can be tricky enough, and that’s without the extra complications of motors, batteries, assistance modes and watt-hours thrown in.
In this guide, we’ll be cutting through all the marketing hype to explore all the key parts and components that make up an electric mountain bike, as well as busting the jargon and equipping you with the knowledge you need to navigate the ever-growing ebikes market.
Parts of an electric mountain bike
Battery
Often removable for charging or travel, the battery is integrated into the down tube on most eMTBs and connected to the motor using wiring with a waterproof connection. Power is provided by a bank of lithium-ion (Li-ion) cells. Some brands offer ‘range extenders’ – additional batteries that can be attached for longer rides.
Controller
Frequently mounted on the handlebar near the left-hand grip, this can be used to toggle between motor modes and to cycle through different screens on the bike’s display unit.
Display unit
Sometimes, this is mounted on the bar or stem, but it can also be integrated into the bike’s top tube or elsewhere. It shows useful information, including battery charge, current mode, speed, predicted range and cadence.
Motor
eMTB motors are also known as the drive unit. eMTBs generally use a ‘mid-drive’ system, where the motor is mounted at the junction of the down tube and seat tube. This lowers the bike's centre of gravity, to improve handling and performance.
eMTB jargon explained
Modes
Most motors feature selectable, often user-programmable and sometimes automatically controlled, support levels. These change the amount of power and torque supplied. ‘Eco’ mode generally provides the least support, while the ‘Boost’ or ‘Turbo’ setting unleashes full power.
Overrun
Motor assistance usually continues for a short period after the rider stops pedalling. This is called overrun and can be useful on technical climbs, where you need to change your pedal-stroke timing to avoid ground strikes.
Peak power
UK and EU law limits e-bike motors to 250W of continuous, standard power. Many manufacturers claim peak power higher than this, but this output is only in certain circumstances and for short periods. If a motor doesn’t deliver as much power as expected, it may be because it has reached a 250W continuous peak and is ‘throttling back’ to avoid exceeding the limit.
Pedal-assist/Pedalec
These are terms that describe ebikes with motors that only provide assistance when the rider is pedalling – the only type of eMTB that can be legally used on UK trails.
Support percentage
How much the motor augments a rider’s pedalling inputs. A drive unit with 100 per cent support will essentially double the rider’s power – so if they put out 50W, the motor will also provide 50W, amounting to an overall system power of 100W. Support percentages are directly related to motor peak power, and usually in the region of 300 to 400 per cent.
Torque
The amount of twisting or rotational force the motor provides. A higher torque value, given in Newton metres (Nm), will make the motor feel more powerful.
Walk assist
A feature most ebikes have, where they’re able to propel themselves at low speed without the rider pedalling, making it easier to push them up steep sections.
Watts (W)
The measurement of motor power.
Watt hours (Wh)
A standard measure of electricity, equivalent to the power consumption of one watt for one hour. Ebike battery capacity varies from 320Wh to 900Wh, and as technology improves, so does energy density, where more power can be contained within the same space.
Electric mountain bike basics
How does an eMTB work?
A ‘mid-drive’ motor connected to the cranks senses when you begin pedalling and kicks in to supplement your output.
Power comes from a battery hidden in the down tube, and you can control the amount of assistance using a display and/or buttons mounted on the handlebar or integrated into the top tube.
Under UK law, ebikes must have a maximum continuous (averaged out over time) output of 250W and the assistance must cut out at 15.5mph. This ensures there’s a clear delineation between eMTBs, which can legally be ridden anywhere a regular ‘pedal bike’ can, and electric motorbikes.
What different types are there?
Like mountain bikes in general, eMTBs differ in terms of geometry, suspension travel, wheel size and parts fitted, with something to suit every riding style and most budgets. However, they can be divided into two main groups – ‘full-power’ and ‘SL’ (aka ‘lightweight’).
As the name suggests, full-power electric mountain bikes supply maximum assistance to support your pedalling, courtesy of a motor with a peak output of 500W+ and at least 85Nm of torque. Many also come with a higher-capacity battery (600Wh+) to ensure a decent range. All this grunt has its drawbacks, though, in the form of extra weight.
SL ebikes have less torque (50-60Nm) and, in many cases, a lighter, less powerful motor, combined with a smaller-capacity battery (320-500Wh). The idea is this gives a more natural ride feel and makes the bike easier to chuck around on the trail, especially when combined with lighter components. Many are compatible with optional range extenders in case you want to do the odd longer ride.
What are the advantages over a regular MTB?
Pedalling assistance can help riders with injuries, disabilities or health problems get out on the trails, or less fit riders keep up with sportier friends/partners.
Because they’re quicker up the climbs, eMTBs also enable you to cover more ground in less time, which is great for getting in quick laps, notching up plenty of descending or finishing long routes before darkness falls. They’re also a lot of fun to ride and bring a whole new dimension to technical climbs.
What are the disadvantages?
The initial cost is high, and there are more things to go wrong down the line, from motor issues to battery degradation. They’re also heavy – with full-power bikes often weighing upwards of 25kg and even top-end SL bikes starting from around 16kg.
If the motor and battery weight is low down and central in the frame, this doesn’t have too much of an effect on the handling, and can even aid grip and stability on descents. However, the extra heft is noticeable on flatter trails, when pushing uphill and when loading an ebike into a vehicle – or if you crash and it lands on top of you.
