E-Bike Conversion Glossary: Terms Explained

In shops and manuals you meet terms you will rarely have used before. Here are the most important ones, short and without jargon, so that you read data sheets correctly and do not fall for advertising figures. Where a value is described as "usually", it is a rule of thumb.

Power and electricity

Rated continuous power: The power the motor may deliver continuously. It is what counts for legal approval, at most 250 W for pedelecs. Peak power may be higher for a short time. Many shops advertise the peak, so always look for the rated continuous power. For the legal side see pedelec law.

Voltage (V): The electrical voltage of the system. On 250 W kits, 36 V is standard, 48 V is more common on stronger kits. Battery, controller and display must have the same voltage.

Capacity (Wh): Watt-hours. Multiply volts by amp-hours: 36 V times 14 Ah gives 504 Wh. The figure says how much energy is in the battery and so determines range. More under battery.

Amp-hours (Ah): The charge the battery holds. On its own it says little; only with the voltage do you get the capacity in Wh.

Force

Torque (Nm): Newton metres, the turning force of the motor. Hub motors usually deliver 30 to 45 Nm, mid-drives 65 to 160 Nm. The higher, the stronger on hills. You can see the comparison of the types under mid-drive vs hub motor.

Torque arm: A part that stops the axle of a hub motor from turning in the dropout. More under torque arm.

Sensors

Cadence sensor (PAS): Measures only whether you pedal, not how hard. It is cheap but feels like being pushed. PAS stands for pedal assist sensor.

Torque sensor: Measures how hard you pedal and assists in proportion. That feels like a bought e-bike. It costs more.

Speed sensor: A spoke magnet or a sensor inside the motor. Without it the kit cannot keep to 25 km/h (GIGA).

Brake lever with cut-off: Switches the motor off immediately when you brake. With a cadence sensor this matters particularly, because otherwise the motor keeps running briefly. See brakes.

Electronics

Controller: The control unit. It regulates how much current the motor gets and knows limits such as 25 km/h. Bafang controllers can be configured with a programming cable and checked for 25 km/h (netzwelt). The Tongsheng TSDZ2 has free community firmware (OSF).

Display: Shows speed, assist level and battery state and is used to set up the system. It must match the voltage and the controller.

Higo and Julet: Two widespread connector styles on conversion kits. Higo is a waterproof round connector with an inline coupling, Julet a connector available with different pin counts. They are the most common source of faults: water, poor seating or kinked cables lead to dropouts. See common problems.

Legal

Pedelec: A bicycle that assists only while you pedal, with at most 250 W rated continuous power and a cut-off at 25 km/h.

Walking assist: Assistance without pedalling up to 6 km/h is allowed. A throttle that drives you beyond that is not (GIGA). Beyond that the bike is legally a motor vehicle.

Mechanics

Hub spacing: The distance between the dropouts into which the wheel is fitted. Usually 100 mm at the front, 130 to 148 mm at the rear. See hub spacing.

ETRTO: The standard for tyre and rim sizes. The second number on the tyre is the rim diameter in mm. See wheel sizes.

Hub motor: A motor in the hub of the front or rear wheel. With a mid-drive the motor sits at the bottom bracket. The types compared are under motor types.

Bottom bracket (BSA, Pressfit, BB30): The shell in which the crank axle runs. BSA is a threaded bracket (68 or 73 mm), Pressfit and BB30 are pressed in. See measure bottom bracket.

Friction roller: A drive that acts on the tyre with a roller. Light and removable, but with tyre wear and slip in the wet.

Seat-tube drive: A motor that sits in the seat tube of the frame. It requires a straight seat tube of 31.6 or 30.9 mm.

Anything missing?

If a term turns up in a shop or manual that is not here, ask. Honestly, a dealer who cannot or will not explain technical terms is rarely the best choice. What a kit costs overall is under costs.

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How reliable is this?

The speed sensor rule, the walking-assist limit and Bafang programming come from the linked sources. The value ranges for torque and voltage and the explanations of connectors and sensors are experience and assumptions that Fabio is still checking.