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Eight-wheel drive

From Wikipedia, in a visual modern way
Chassis of an 8×8 vehicle
Chassis of an 8×8 vehicle

Eight-wheel drive, often notated as 8WD or 8×8, is a drivetrain configuration that allows all eight wheels of an eight-wheeled vehicle to be drive wheels (that is, to receive power from the engine) simultaneously. Unlike four-wheel drive drivetrains, the configuration is largely confined to heavy-duty off-road and military vehicles, such as armored vehicles, tractor units or all-terrain vehicles such as the Argo Avenger.

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Drivetrain

Drivetrain

A drivetrain is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the drivetrain is the components of a motor vehicle that deliver power to the drive wheels. This excludes the engine or motor that generates the power. In marine applications, the drive shaft will drive a propeller, thruster, or waterjet rather than a drive axle, while the actual engine might be similar to an automotive engine. Other machinery, equipment and vehicles may also use a drivetrain to deliver power from the engine(s) to the driven components.

Drive wheel

Drive wheel

A drive wheel is a wheel of a motor vehicle that transmits force, transforming torque into tractive force from the tires to the road, causing the vehicle to move. The powertrain delivers enough torque to the wheel to overcome stationary forces, resulting in the vehicle moving forwards or backwards.

Four-wheel drive

Four-wheel drive

Four-wheel drive, also called 4×4 or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case providing an additional output drive shaft and, in many instances, additional gear ranges.

Tractor unit

Tractor unit

A tractor unit is a characteristically heavy-duty towing engine that provides motive power for hauling a towed or trailered load. These fall into two categories: heavy- and medium-duty military and commercial rear-wheel-drive semi-tractors used for hauling semi-trailers, and very heavy-duty typically off-road-capable, often 6×6, military and commercial tractor units, including ballast tractors.

All-terrain vehicle

All-terrain vehicle

An all-terrain vehicle (ATV), also known as a light utility vehicle (LUV), a quad bike, or simply a quad, as defined by the American National Standards Institute (ANSI), is a vehicle that travels on low-pressure tires, has a seat that is straddled by the operator, and has handlebars. As the name implies, it is designed to handle a wider variety of terrain than most other vehicles. Although it is a street-legal vehicle in some countries, it is not street-legal within most states, territories and provinces of Australia, the United States or Canada.

Argo Avenger

Argo Avenger

The Argo Avenger is an eight-wheeled all terrain vehicle built by Argo. On land the vehicle is steered turning the wheels on the two sides of the vehicle at different speeds. On water the vehicle can be propelled either by the treads on the tires, or by an outboard motor. Optionally, on very loose or swampy land a pair of large band tracks can be strung over the vehicles' wheels.

Operation

When such a vehicle only has eight wheels by definition all are driven. When it has twelve – with two pairs of ganged "dual" wheels on each rear axle – all are also driven but the 8×8 designation remains. Very occasionally, on the Sterling T26 for example, the two front axles can be fitted with ganged "dual" wheels.[1] For most military applications where traction/mobility are considered more important than payload capability, single wheels on each axle (often referred to as super singles) are the norm. On some vehicles, usually recovery trucks or heavy tractor units, the rear two axles will have wider single tires than the front two axles.[2]

Heavy hauler and ballast tractor 8×8s have had a long history as prime movers both in the military (as tank transports and artillery tractors), and commercially in logging and heavy equipment hauling both on- and off-road. Most eight-wheel drive trucks have two forward axles and two at the rear, with only the front pair steering. Occasionally a single front axle and three rear (tridem) are seen, an example being the Oshkosh M1070 tank transporter. In such configurations, the front and rear axle usually steer.[3] Other set ups include that of the ZIL-135.

Many wheeled armored vehicles have an 8x8 driveline, and on these the axles (which usually have independent suspension) are more evenly spaced. Latest generation 8x8 wheeled armored vehicles have steering on the rearmost (fourth) axle to improve mobility in urban and confined situations.[4]

In the case of both truck and armored vehicle applications, drive may be limited to the rear two axles for on-road use, this reducing driveline stress and tire wear, and increasing fuel efficiency.

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Axle

Axle

An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type of axle is referred to as a spindle.

Tow truck

Tow truck

A tow truck is a truck used to move disabled, improperly parked, impounded, or otherwise indisposed motor vehicles. This may involve recovering a vehicle damaged in an accident, returning one to a drivable surface in a mishap or inclement weather, or towing or transporting one via flatbed to a repair shop or other location.

Tank transporter

Tank transporter

A tank transporter is a combination of a heavy tractor unit and a mating full trailer or semi-trailer, used for transporting tanks and other armoured fighting vehicles. Some also function as tank recovery vehicles, the tractors of which may be armoured for protection in combat conditions.

Heavy hauler

Heavy hauler

A heavy hauler is a very large transporter for moving oversize loads too large for road travel without an escort and special permit.

Ballast tractor

Ballast tractor

A ballast tractor is a specially weighted tractor unit of a heavy hauler combination. It is designed to utilize a drawbar to pull or push heavy or exceptionally large trailer loads which are loaded in a hydraulic modular trailer. When feasible, lowboy-style semi-trailers are used to minimize a load's center of gravity. Typical drivetrains are 6×4 and 6×6 but also available in 8×6 and 8×8. Typical ballast tractor loads include oil rig modules, bridge sections, buildings, ship sections, and industrial machinery such as generators and turbines.

Artillery tractor

Artillery tractor

An artillery tractor, also referred to as a gun tractor, is a specialized heavy-duty form of tractor unit used to tow artillery pieces of varying weights and calibres. It may be wheeled, tracked, or half-tracked.

Logging

Logging

Logging is the process of cutting, processing, and moving trees to a location for transport. It may include skidding, on-site processing, and loading of trees or logs onto trucks or skeleton cars. In forestry, the term logging is sometimes used narrowly to describe the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard. In common usage, however, the term may cover a range of forestry or silviculture activities.

Steering

Steering

Steering is a system of components, linkages, and other parts that allows a driver to control the direction of the vehicle.

Oshkosh M1070

Oshkosh M1070

The Oshkosh M1070 is a U.S. Army tank transporter tractor unit. The primary purpose of this combination for the U.S. Army is the transport of the M1 Abrams tank.

ZIL-135

ZIL-135

The ZIL-135 is a large, eight-wheeled military transport and self-propelled artillery truck produced during the Cold War by the Soviet Union starting in 1959. Its purpose was to carry and launch an artillery missile, specifically a FROG-7, from surface-to-surface. The ZIL-135 was widely exported to other communist countries, most notably North Korea, where it is a common sight in films and military marches. It also served as the TEL for the BM-27 Uragan artillery rocket system.

Fuel efficiency

Fuel efficiency

Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is often illustrated as a continuous energy profile. Non-transportation applications, such as industry, benefit from increased fuel efficiency, especially fossil fuel power plants or industries dealing with combustion, such as ammonia production during the Haber process.

Gallery

  • Eliica, the eight-wheeled electric car of Hiroshi Shimizu.

    Eliica, the eight-wheeled electric car of Hiroshi Shimizu.

  • Kynos Aljaba 8x8 tank transporter tractor with wide-footprint tyres

    Kynos Aljaba 8x8 tank transporter tractor with wide-footprint tyres

  • Boxer APC; note the single tyres and near-equal spacing of the front and rear wheel pairs

    Boxer APC; note the single tyres and near-equal spacing of the front and rear wheel pairs

  • The Oshkosh M1070 HET is unusual in that while an 8x8 it has a single driven front axle, and a driven rear tridem

    The Oshkosh M1070 HET is unusual in that while an 8x8 it has a single driven front axle, and a driven rear tridem

  • This TATRA T 815 recovery truck has dual rear wheels (12 wheels in all) but is still categorized as an 8x8

    This TATRA T 815 recovery truck has dual rear wheels (12 wheels in all) but is still categorized as an 8x8

  • This 8x8 fire truck is unusual in that it steers by frame articulation

    This 8x8 fire truck is unusual in that it steers by frame articulation

  • On most wheeled armoured 8x8s the front two axles steer, although on current generation offerings it is becoming more common for the rear axle to contra-steer, this improving maneuverability in confined spaces

    On most wheeled armoured 8x8s the front two axles steer, although on current generation offerings it is becoming more common for the rear axle to contra-steer, this improving maneuverability in confined spaces

  • It is not unusual for longer wheelbase trucks with four axles to have greater spacing between the front axle pair (the steering axles), as this helps reduce turning circle

    It is not unusual for longer wheelbase trucks with four axles to have greater spacing between the front axle pair (the steering axles), as this helps reduce turning circle

  • The DAF YP 408 APC may appear to be an 8x8 but in fact the second axle is not driven, making the configuration 8x6

    The DAF YP 408 APC may appear to be an 8x8 but in fact the second axle is not driven, making the configuration 8x6

Source: "Eight-wheel drive", Wikipedia, Wikimedia Foundation, (2023, January 13th), https://en.wikipedia.org/wiki/Eight-wheel_drive.

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Further Reading

Heavy Expanded Mobility Tactical Truck

Four-wheel drive

Front-engine, front-wheel-drive layout

Rear-engine, rear-wheel-drive layout

Half-track

Transfer case

Locking differential

Dump truck

Portal axle

Medium Tactical Vehicle Replacement

Drive wheel

Six-wheel drive

Tractor unit

M520 Goer

Tank transporter

H-drive

All-wheel drive

Oshkosh M1070
See also
References
  1. ^ "US Army Sterling T26 8 x 8 12-ton Heavy Truck". milweb.net. Retrieved 2016-02-11.
  2. ^ "Tatra 816-6VWN9T 43 610 8x8.1RTruck". Retrieved 2016-02-11.
  3. ^ "Oshkosh M1070A1". Archived from the original on 2015-10-11. Retrieved 2016-02-11.
  4. ^ "Piranha 5". army-technology.com. Retrieved 2016-02-11.
External links
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