E-Bike Conversion Kit Product

Overview

An e-bike conversion kit retrofits electric assist onto an existing bicycle. The standard recipe replaces one wheel with a Hub Motor Wheel, hangs a Battery Pack on the downtube or rack, mounts a Motor Controller between them, and adds a Display Unit and Sensor Set so the system knows when the rider is pedaling. A competent installation takes two to three hours with ordinary bike tools and adds 6–9 kg. The kit market exists because the conversion delivers most of a factory e-bike's function at a quarter to half the price, on a frame the owner already has.

The hub motor

Kit motors are almost all hub motors, because a hub is the one place on a bicycle where a motor can be added without touching the drivetrain. Inside the Motor Housing, a Stator Assembly of laminated steel teeth and copper windings is fixed to the Motor Axle, while a Rotor Assembly ring of neodymium magnets spins with the shell. Geared hubs — the dominant kit type — interpose a Planetary Reduction of roughly 5:1 so the motor itself spins around 1500 rpm where it is efficient, while the wheel turns at 200. Nylon planet gears keep it quiet and serve as the designed wear item. A one-way Freewheel Clutch lets the wheel overrun the motor, so an unpowered geared hub adds no pedaling drag; the trade is that it cannot regenerate on braking, a feature only heavier direct-drive hubs offer.

Torque reaction is the installation's one safety-critical detail. The axle's flats transmit 30–45 N·m into the dropout slots, and aluminum dropouts — especially suspension fork ends — can spread and release the axle. The Torque Arms in the Installation Kit clamp the flats to the frame and are considered mandatory for front-hub installs. Three Hall Sensor elements in the stator report rotor position to the controller, their wires sharing the slotted axle bore with the Phase Cable.

Controller and battery

The Motor Controller is a three-phase inverter: six Power MOSFET switches chop battery DC into phase currents at 15–20 kHz, commutated from the Hall signals, with an Current Shunt closing the torque loop and enforcing the 15–25 A battery limit. The DC-Link Capacitors smooths PWM ripple — its electrolytics are the classic failure point in cheap units — and the extruded Controller Case sinks roughly 10 W of switching loss.

The Battery Pack is the kit's costliest component. A typical 48 V pack wires 52 cells as 13s4p Li-ion Cell, 18650 in molded Cell Holders with spot-welded nickel strip, giving 480–630 Wh and 40–80 km of assisted range. The BMS Board supervises every series group for over/under-voltage, balances during charge, and disconnects on fault, backed by a one-shot Thermal Fuse. The pack rides in a keyed Battery Case on a rail mount whose Discharge Connector blades engage as it slides home; charging is through a separate Charge Port at 2–4 A, taking four to six hours. Battery certification (UL 2849, EN 50604) is the sharpest quality divide in the kit market — uncertified packs are the source of the e-bike fire statistics.

Sensors and the law

What separates a legal pedelec from an electric motorcycle is the gating logic, and that lives in the Sensor Set. The basic PAS Sensor is a 12-magnet ring on the crank spindle: it proves the rider is pedaling within half a crank revolution, which is all EN 15194 requires, but the resulting assist is on/off and surges. The upgrade is a strain-gauged Torque Sensor in the bottom bracket that measures actual pedal force so the motor mirrors the rider's effort — the single largest ride-quality difference between cheap and good kits, and the architecture every factory mid-drive uses. Brake Cut-Offs on both levers kill power the instant braking begins. The Thumb Throttle is jurisdiction-dependent: a full power lever in US Class 2, limited to 6 km/h walk-assist in the EU. A spoke-mounted Speed Magnet gives true wheel speed for the 25 km/h (EU) or 32 km/h (US) cutoff, since motor RPM is ambiguous behind the freewheel clutch.

The Display Unit on the bars sets assist level through its Button Pod, shows speed and charge on the LCD Panel, and holds the configuration menu where wheel size and speed limit are set — also where kits are commonly and illegally derestricted, which voids the bicycle's legal status as a pedelec.

Installation realities

The Wiring Harness ties everything together with color-keyed waterproof Higo-style Connector junctions, dressed along the frame with Cable Guides. Mechanical fit is the usual obstacle: the motor wheel must match dropout spacing (100 mm front, 135 mm rear are the kit standards), rim size must match the controller's speed calculation, and disc rotors and freewheels thread onto the hub's provided interfaces. The Rim & Spoke Set build uses short, steep spokes around the oversized hub, a stiffer and less forgiving wheel than stock.

Front-hub kits are the simplest install and keep the drivetrain untouched; rear hubs put traction and weight where it belongs; mid-drive kits (a separate class) replace the bottom bracket and drive through the gears, winning on hills at the cost of chain wear and installation depth. For a commuter on mostly flat ground, the geared rear hub with torque-arm insurance remains the default answer.