A serpentine belt, also known as a multi-vee, poly-v, or multi-rib belt, is a single, continuous belt

Belt (mechanical)

A belt is a loop of flexible material used to link two or more rotating shafts mechanically. Belts may be used as a source of motion, to transmit power efficiently, or to track relative movement. Belts are looped over pulleys. In a two pulley system, the belt can either drive the pulleys in the...

 used to drive multiple peripheral devices in an automotive engine, such as an alternator

Alternator

An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...

, power steering

Power steering

Power steering helps drivers steer vehicles by augmenting steering effort of the steering wheel.Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver needs to provide only modest effort regardless of conditions. Power steering helps considerably when a...

 pump, water pump

Water Pump

Water Pump is one of the neighbourhoods of Gulberg Town in Karachi, Sindh, Pakistan. It is near main Water Pump that supplies fresh water to the city of Karachi....

, A/C

Air conditioning

An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

 compressor

Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

, air pump

Air pump

An air pump is a device for pushing air. Examples include a bicycle pump, pumps that are used to aerate an aquarium or a pond via an airstone; a gas compressor used to power a pneumatic tool, air horn or pipe organ; a bellows used to encourage a fire; and a vacuum pump.The first effective air pump...

, etc. The belt may also be guided by an idler pulley and/or a belt tensioner (which may be spring-loaded, hydraulic, or manual). The production serpentine belt was manufactured by Hutchinson and first used by Mercedes-Benz on the 1985 190 Series.

It is more efficient than the older multiple belt system and may consume less space in the engine compartment. By using a single, wider belt instead of multiple, thinner belts, the belt may be put under increased tension without stretching. Higher tension reduces slip, which increases belt life and mechanical efficiency

Mechanical efficiency

Mechanical efficiency measures the effectiveness of a machine in transforming the energy and power that is input to the device into an output force and movement...

. Reduced slip can allow the use of lower-ratio pulleys; this reduces the load on the engine, increasing fuel economy and available power. The tendency for V-belts to "flip over" in the pulley groove (at high RPM) is eliminated. A serpentine belt also is much easier to maintain and replace, since there is no need to remove multiple belts in order to replace one of them.

On some engine designs, the "back" (smooth side) of the belt may drive some accessories, this is typically limited to components requiring less torque or where a large angle of lap is present. Such accessories will counter-rotate vs. the "normal" pulleys.

The drawback of this single belt is that if the belt breaks, the vehicle loses all of its peripheral devices; however, the belt typically gives ample visual warning of impending failure, sometimes even totally shedding several grooves (ribs) while still continuing to function normally. Some vehicles use two serpentine belts for their system, such as the manual transaxle equipped Ford Taurus SHO

Ford Taurus SHO

The Ford Taurus SHO is a full-size performance sedan based on the Ford Taurus that was originally produced by the Ford Motor Company from 1989 until 1999. It returned in 2009 for the 2010 model year....

, 1995–1999 DOHC Nissan Maxima

Nissan Maxima

The first car to wear the Maxima name was introduced in 1981. It was essentially a Japanese-market Bluebird 910 with a longer nose. The car was offered as the 810 Deluxe or 810 Maxima that first year, and all 810s became Maximas for 1982...

, vehicles using the supercharged GM 3800

Buick V6 engine

The Buick V6, initially marketed as Fireball at its introduction in 1962, was a large V6 engine used by General Motors. The block is made of cast iron and all use two-valve-per-cylinder iron heads, actuated by pushrods....

engine, and many BMWs.