A retarder is a driver-activated auxiliary braking system which operates independently of the service brakes, engine and gearbox. It applies a retarding force through the driving wheels and is rated for continuous use, without loss of efficiency. In most European countries, retarders are mandatory fitment for buses, coaches and some heavy transport vehicles because they significantly improve the safety of these vehicles.


A TELMA Electro-magnetic Retarder is an assembly of electromagnetic coils, which when activated by an electrical current, creates eddy (Foucault) currents between two rotors and a stator and retards the movement of the rotor. Fitted into the driveline of a vehicle the Telma retarder acts directly on the driven wheels and reduces the speed of a vehicle. The energy created in the operation of a Telma retarder is converted into heat. Correctly applied, however, this temperature build up will be dissipated through efficient heat sinks on the retarder and no loss of efficiency will occur.

The retarder can be activated by switches fitted to the accelerator and the clutch and by a hand-operated lever mounted to the steering column or the dashboard. Telma retarders are frictionless and virtually maintenance free.



The electromagnetic technology guarantees unequalled instantaneous availability and full braking power provided by the Telma retarder, regardless of the vehicle’s speed. Telma retarders remain effective even after the engine stops, or when the gearbox is in neutral.

As they dissipate the energy generated during braking directly into the atmosphere without using the engine’s liquid cooling system, Telma retarders are effective in all situations, thereby ensuring that a vehicle always remains at the driver’s desired speed.

Risks associated with service braking system overheating are therefore avoided and the system remains fully operational in case of emergency.


The complete lack of friction makes Telma retarders totally silent in all conditions of use. The electromagnetic technology guarantees Telma retarders’ instant response to driver solicitations, thus allowing for an unprecedented driving experience. The ease of use, flexibility and progressive character of Telma retarders guarantees exceptional comfort for the driver and its passengers.


The exceptional reactivity of Telma retarders prevents excessive fuel consumption during fast switches between deceleration and acceleration phases. Telma retarders never go against the engine: they can instantly stop producing braking torque upon driver’s request.

The recognised quality, reliability and durability of Telma retarders make them a profitable investment that quickly pays for itself and, by extending the vehicle’s braking ability, they increase the average operational speed.

Environmentally Friendly

Telma retarders comply with the European ROHS directive (2002/95/CE) restricting the use of certain hazardous substances in the construction of electrical equipment.

The total lack of friction makes Telma retarders fully silent under all conditions of use, as well as guaranteeing the absence of particle emissions or any other pollutant release into the environment. The contribution of Telma retarders to the reduction of the equipped vehicles’ energy consumption actively contributes to the reduction of greenhouse gas emissions.

As they comply with the European directive 2004/108/EC on electromagnetic compatibility (EMC), Telma retarders present no electromagnetic incompatibility with the environment. Telma retarders are maintenance-free and do not require any fluid change or wearing parts replacement.


Telma Retarders are commonly used in the following vehicle types:

Garbage trucks
Mining vehicles
Heavy haulage
Crane trucks
Coaches and buses
Petrol tankers
Cement trucks
Cattle haulers
Cash transportation
Freight trucks