E-Bike Motor and Drive System Guide: Battery, Controller, Sensors and Display

An e-bike drive system is more than a motor and a battery. It is a control system that turns rider input, terrain data and stored energy into assistance in real time.

The motor provides torque. The battery supplies energy. Sensors measure what the rider and the bike are doing, while the controller coordinates the response and the display gives the rider a way to see and adjust it. When those components are developed and calibrated as one system, engineers can tune not only output, but also traction, efficiency, noise and ride feel.

What an e-bike drive system is

Motor: converts electrical energy into mechanical torque. Its specification usually lists rated power in watts, peak power in watts, torque in newton meters, and weight in kilograms.

Battery: stores energy and supplies current on demand. Its specification usually lists energy in watt-hours, capacity in amp-hours, nominal voltage, weight, and energy density in Wh/kg. Controller: interprets sensor data and sets motor output. This is rarely published separately, since it sits inside the drive unit on integrated systems.

Sensors: measure rider input and bike state, covering inputs such as pedaling torque, cadence, wheel speed, gear position and bike attitude.

Display and app: show data, change settings and report faults. Their specification usually covers screen size and brightness, connectivity, and adjustable parameters.

Motor output shapes acceleration and climbing. Battery capacity affects how long that performance is available, while controller tuning has a major influence on how smoothly assistance responds to the rider.

On a conversion kit these parts are sourced separately and matched by the builder. On a factory-fitted bike they are developed and calibrated together, which allows functions such as torque delivery, hill start assistance and shifting to be coordinated at system level.

How the five parts work together on a ride


Push down on a pedal and a torque sensor registers the force, a cadence sensor registers how fast the cranks are turning, and a wheel speed sensor registers how fast the bike is moving. The controller reads those inputs continuously, compares them against the selected assist mode, and meters current from the battery to the motor. The display shows the result.

On a climb the same inputs change together. Cadence drops, pedal torque rises and wheel speed falls, and a system that reads gradient and resistance raises the assistance ratio within the range the rider has set. Two motors with similar torque figures can therefore feel quite different to ride, depending on how their control software interprets those signals.

How an e-bike motor works

An electric bike motor converts battery current into torque by turning a rotor against a stator, then gears the result down to a useful speed. The two families differ in where that torque reaches the bike.

Mid-drive motors
Hub motors
A mid-drive motor sits at the bottom bracket and applies torque to the chainring, so its output passes through the bike's gears before reaching the rear wheel. Selecting a lower gear multiplies the motor's torque as it multiplies the rider's, which helps on steep and technical ground and keeps efficiency reasonable at low speed. The central, low position also keeps mass near the bottom bracket, which riders generally read as balanced handling.

Because that torque passes through the chain and cassette, drivetrain wear becomes a larger consideration than on a hub system. Mid-drives are also more complex to integrate, and are most often found on dealer-supported bikes. Avinox drive units are mid-drive units.
A mid-drive motor sits at the bottom bracket and applies torque to the chainring, so its output passes through the bike's gears before reaching the rear wheel. Selecting a lower gear multiplies the motor's torque as it multiplies the rider's, which helps on steep and technical ground and keeps efficiency reasonable at low speed. The central, low position also keeps mass near the bottom bracket, which riders generally read as balanced handling.

Because that torque passes through the chain and cassette, drivetrain wear becomes a larger consideration than on a hub system. Mid-drives are also more complex to integrate, and are most often found on dealer-supported bikes. Avinox drive units are mid-drive units.
A mid-drive motor sits at the bottom bracket and applies torque to the chainring, so its output passes through the bike's gears before reaching the rear wheel. Selecting a lower gear multiplies the motor's torque as it multiplies the rider's, which helps on steep and technical ground and keeps efficiency reasonable at low speed. The central, low position also keeps mass near the bottom bracket, which riders generally read as balanced handling.

Because that torque passes through the chain and cassette, drivetrain wear becomes a larger consideration than on a hub system. Mid-drives are also more complex to integrate, and are most often found on dealer-supported bikes. Avinox drive units are mid-drive units.
A hub motor sits in the front or rear wheel and drives the wheel directly, independent of the gears. Because it bypasses the drivetrain it adds no chain wear and needs no bottom bracket compatibility check. Geared hub motors use internal reduction gearing and produce more torque for their size. Direct-drive hub motors have no gears, run quietly and can support regenerative braking, at the cost of weight and drag when unpowered.

Efficiency becomes a consideration at low road speed. Without access to the bike's gears, a hub motor turning slowly operates further from its efficient range, and riders climbing steep off-road gradients at walking pace report both reduced efficiency and heat build-up. On flat commuting routes, where wheel speed stays high, that rarely appears.

E-bike motor power, torque and speed limits

Rated power, peak power and assist speed describe different things, and specification sheets often list them side by side.

Rated power and peak power


Rated power is the continuous output a motor is certified to sustain. In the EU, the UK and Australia it is the figure that determines whether a bike is classified as a pedal-assisted bicycle, with 250 W as the threshold.

Peak power is the maximum the system produces for a short period, during acceleration or a steep climb, and it can be several times the rated figure. Every Avinox drive unit is rated at 250 W, with peak output running from 1000 W on the M1 to 1500 W on the M2S. A large gap between the two allows a system to stay within pedal-assist regulation while holding reserve for short, high-demand moments.

Confusing the two figures leads to errors in both directions. A rider in the United States may read a 1500 W peak system as exceeding the federal 750 W limit, when the rated output is 250 W. A rider in the UK may read the same system as not road legal, when it is certified at 250 W rated.

What a torque figure tells you


Torque, in newton meters, describes turning force. Higher torque allows harder acceleration from low speed and lets a rider hold a climb at a lower cadence. It does not affect top speed, which is set by regulation.

Torque figures are also not directly comparable across motor types. A mid-drive's torque is measured at the chainring and is then multiplied by the selected gear before it reaches the ground. A hub motor's torque is applied at the wheel with no such multiplication, so a 100 N·m hub motor and a 100 N·m mid-drive put different force through the contact patch.

Torque density, torque divided by motor weight, is more useful when comparing systems, because motor weight is also weight the rider carries uphill.

On a steep technical climb, usable torque depends on more than the maximum the motor can produce. The system also has to respond to cadence, gear selection and changes in traction. The Avinox M2S drive unit delivers up to 130 N·m across its four regular assist modes, with Boost available for up to 60 seconds when more torque is useful. In Boost it produces up to 150 N·m from a 2.59 kg unit, which Avinox states as a torque density of about 57.9 N·m/kg.

Assist limits in the UK, EU, US and Australia

Assist speed is set by regulation rather than by motor output. Once the bike reaches the limit for its market, assistance is progressively reduced and the rider supplies everything above it.

In the European Union, the rated power limit is 250 W and the assist cut-off is 25 km/h (15.5 mph), under Regulation (EU) No 168/2013.

In the United Kingdom, the rated power limit is 250 W and the assist cut-off is 25 km/h (15.5 mph), per GOV.UK, electric bike rules.

In the United States, the rated power limit is 750 W and the assist cut-off is 32 km/h (20 mph), per 15 U.S.C. § 2085.

In Australia, the rated power limit is 250 W and the assist cut-off is 25 km/h (15.5 mph), per Transport for NSW.

How the battery affects range and weight

The battery is usually the heaviest single component in the drive system and the one that sets the practical limit on a ride.

Watt-hours, energy density and weight

Watt-hours describe how much energy a battery holds. Amp-hours alone do not, because a 20 Ah pack at 36 V and a 20 Ah pack at 48 V hold different amounts of energy. Multiply amp-hours by nominal voltage and compare that figure.

Energy density, in watt-hours per kilogram, becomes important once capacity is set, because every watt-hour added is also mass the motor has to move. The integrated Avinox FP700 battery carries 700 Wh at about 3.18 kg, roughly 220 Wh/kg, which keeps a large capacity within a weight range closer to that of smaller packs.

Range depends on rider weight, temperature, terrain, cadence and assist mode, so any single figure needs its conditions attached. Avinox measured approximately 60 km of mountain biking, or around 1,440 m of climbing, with a 75 kg rider on an eMTB fitted with the FS800 battery in Auto mode.

Integrated batteries, removable batteries and second batteries

Integrated packs sit inside the down tube. They give a cleaner frame, keep mass low and central, and charge on the bike.

Removable packs come out for charging, which matters when the bike lives in a garage and the outlet is indoors, or when the bike is stored somewhere cold. They add mounting hardware and a lock interface, and are usually a little heavier for the same energy.

A second battery on the down tube extends range for long days without carrying that weight permanently. On the Avinox system the RS600 or RS480 serves as the secondary pack alongside a main battery, with additional mounting and connection accessories.

Charging and long-term battery health

Charging speed is set by the charger rather than the pack. The 508 W Avinox charger takes the FP700 from 0 to 80 percent in about 1 hour 16 minutes, where the 168 W charger takes roughly 3 hours 54 minutes for the same pack.

Cycle life is the figure that becomes relevant over years of use. Avinox rates its packs at up to 80 percent of initial capacity after 500 full charge cycles, measured in a 25°C laboratory using the official charger, and that figure covers cyclical rather than calendar aging. Storage state of charge also influences aging, which is why Avinox batteries can be set in the app to stop charging at 95, 80 or 70 percent when a bike is stored between rides.

What the controller does

The controller continuously interprets sensor data and adjusts motor output. That calibration influences how quickly assistance arrives, how smoothly it builds and how predictable the bike feels when traction changes.

Control strategy varies between systems. Speed-regulated control delivers a preset level of assistance once pedaling is detected. Current-regulated control varies output in proportion to rider effort, which allows assistance to follow changes in pedal pressure more closely.

Sustained output also depends on thermal management. As motor temperature rises, the controller reduces output to protect the hardware, which riders notice as assistance easing off late in a long climb. The M2S uses a temperature sensor together with cooling fins and flat wire windings to improve heat dissipation and energy conversion efficiency, which extends how long higher output can be held.

On integrated systems the controller itself is sealed, so what the rider influences is its tuning. The Avinox Ride app exposes assistance level and range, maximum torque, maximum power, maximum acceleration, assisted start, continued assist, motor overrun and Boost duration. Assistance range is useful to understand first. It sets a minimum ratio for flat ground and a maximum for steep ground, and the system moves between them based on gradient and resistance. Setting both values the same holds assistance constant regardless of terrain.

How sensors influence assistance

Torque, cadence and speed sensors give the controller a real-time picture of rider input and bike movement. The more accurately those signals are interpreted, the more naturally assistance can follow changes in effort and terrain.

Torque sensors and cadence sensors

A cadence sensor detects whether the cranks are turning and how fast. Assistance arrives at a preset level for the chosen mode, independent of how hard the rider pushes. It is inexpensive and predictable, and riders commonly report a short delay before assistance appears and a more uniform character on varied ground.

A torque sensor measures the force applied to the pedals and scales assistance in proportion. Assistance follows effort, which riders generally describe as a more natural feel, and because output tracks input rather than running at a fixed level, it also tends to use less battery over the same distance.

Most current mid-drive systems use both, with the torque signal setting the level and the cadence signal shaping how power is delivered.

Speed sensors and the assist cut-off

A wheel speed sensor reads a magnet or a toothed ring, usually mounted to the rear brake rotor, and reports road speed to the controller. It supplies the speed shown on the display and enforces the legal assist limit by reducing assistance as the bike approaches the cut-off for its market.

It is also the sensor most affected by workshop time. When a rotor or a wheel is changed, the sensor ring has to be refitted in the correct position, or the system may misread speed and either reduce assistance early or report a fault.

What gear position and bike attitude add

The Avinox Drive System reads five inputs: pedaling cadence, pedaling torque, riding speed, gear position, and bike attitude through an inertial measurement unit.

Gear position tells the system how its torque will be multiplied before it reaches the ground, so output can be matched to the ratio actually selected. Bike attitude read alongside wheel speed allows the system to detect a rear wheel beginning to spin or a front wheel beginning to lift and trim output automatically. In practice this is most noticeable on loose, steep climbs, where traction changes faster than a rider can respond. The same inputs support hill start assist when pulling away on a slope and walk assist when pushing the bike up ground too steep to ride.

What the display and app add

Ride data and navigation

Legibility in direct sunlight determines how much of a display is usable on a ride. Avinox control displays use a 2-inch OLED panel with peak brightness of 800 nits and an IP56 rating, and record more than 40 types of sensor data with a layout the rider configures in the app.

Navigation is where a display can replace a second device. Routes imported from Komoot can be sent to the screen with turn-by-turn directions and off-course alerts, and several display models deliver up to 65 W of USB-C power to a phone or a light.

Diagnostics, security and firmware

Integrated diagnostics can identify faults on the display or in the app, helping riders determine whether an issue can be resolved directly or requires dealer support. The Avinox health management system checks the drive system at power-on, alerts on the display with an audible warning if it finds a fault, and shows fault detail with self-diagnostic suggestions in the app. Security runs through the same channel, with abnormal movement alerts, password authentication that disables assistance, and a remote beep for locating the bike.

Feature availability varies by display model. The DP100 and DP100-F support 4G, which enables remote alerts when the bike is out of Bluetooth range, and require a Nano SIM fitted behind the screen. The DPC100 supports Apple Find My and does not support 4G. It is worth confirming which display a bike carries before assuming a security feature is present.

Drive system maintenance and common faults

How motor torque affects chain and cassette wear

The drivetrain is not part of the drive system, but on a mid-drive it carries everything the drive system produces. Motor torque and rider torque pass through the same chain and cassette, so a bike producing well over 100 N·m at the chainring loads those parts beyond what legs alone would.

Drivetrain wear depends on several factors, but shifting under high load is especially hard on chains and cassette teeth. Moving the chain from one cog to another while full torque is applied loads the shift ramps and tooth profiles, and the effect concentrates on the smallest cogs, which have the fewest teeth sharing it. Riders who stay in a high gear and a high assist mode on climbs tend to see wear appear soonest.

Technique reduces it: easing off pedal pressure for the moment of the shift, shifting before the gradient forces it, and shifting one gear at a time. Avinox also handles part of this in the system. Smooth shift lets the drive unit rotate the cassette to complete a gear change when one is detected, so the shift is completed without the rider having to time a break in torque. It runs on bikes with a SRAM Eagle Transmission groupset powered by the SRAM AXS cable, on firmware V00.11.03.04 or later, with the feature enabled on the control display.

What motor noise usually means

A low, even hum under load is normal for a geared mid-drive and comes from the reduction gears. Changes in that sound are worth attention.

A rhythmic click following crank rotation usually points to the chainring interface or the crank fitting rather than the motor. A grinding sound that rises with load points at the reduction gearing. A rattle when coasting over rough ground, often called pedal kickback noise, comes from backlash in the gear train, which the M2S reduces with a dual-meshing gear design. A new noise accompanied by reduced power is worth having diagnosed rather than monitored.

When an e-bike motor needs repair or replacement

Sealed drive units are not rebuilt outside a service center. Bearings, seals and speed sensor rings are serviceable items, while the motor is treated as a replaceable assembly, so warranty terms and dealer coverage are worth reviewing alongside torque figures.

Two conditions can resemble motor failure. A battery that has lost capacity produces weak assistance that fades under load, and a speed sensor reading incorrectly produces assistance that cuts out at the wrong moment. Both are worth checking before assuming the drive unit is at fault.

How to choose an e-bike drive system

Terrain is a practical starting point. Steep, technical or loaded riding suits a mid-drive with meaningful torque, while flat commuting on predictable surfaces is well served by a hub motor at lower cost and with less drivetrain maintenance.

From there, a few questions change the answer. What is the rated power, and is it legal where you ride. What is the battery capacity in watt-hours, and under what conditions was its range measured. Does the system use a torque sensor, and can you ride one before buying. What can be adjusted after purchase, since tunable assistance can be moderated while a fixed system cannot be sharpened. What is covered by warranty, for how long, and who does the work.

One consideration is less visible on a specification sheet. Drive system selection happens early in a bike's development, influencing down tube volume, the bottom bracket area, cable routing and weight distribution, so the system is chosen before the frame design is fixed and is not something an owner can change later. Continued access to firmware, batteries, displays and compatible components therefore forms part of the purchase rather than a later concern.

Avinox supplies drive units, integrated and removable batteries, control displays, wireless controllers, the Avinox Ride app and the charging hardware as one family, developed and updated together. Canyon, Commencal, Forbidden, Megamo and Atherton build bikes around it alongside Amflow, and the system holds the Design and Innovation Award 2025, the iF Design Award 2025, and a Best in Test award from E-MOUNTAINBIKE Magazine. Software updates can add or refine functions without new hardware, and smooth shift reached bikes already in use through an app update.

When comparing systems, consider purchase price alongside battery capacity, drivetrain wear, software support, service coverage and long-term parts availability. The Avinox drive unit pages list rated and peak power, torque, weight and battery pairing conditions for each unit.

Frequently asked questions