Editing Continuous track (section)

== Engineering ==
<gallery heights="150px" mode="packed">
File:Tracks (diagram).png|Diagram of tracked suspension: (1=rear drive wheel (rear wheel drive), 2=track, 3=return rollers, 4=front drive wheel (front wheel drive), 5=road wheels, 6=idler)
File:Leclerc p1040882.jpg|A [[sprocket]] wheel on a [[tank]]
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=== Construction and operation ===
Modern tracks are built from modular chain links which together compose a closed chain. The links are jointed by a hinge, which allows the track to be flexible and wrap around a set of wheels to make an endless loop. The chain links are often broad, and can be made of manganese alloy steel for high strength, hardness, and abrasion resistance.<ref>{{cite web |url=http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=69 |title=Austenitic Manganese Steels |access-date=2011-08-24 |url-status=live |archive-url=https://web.archive.org/web/20120308160132/http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=69 |archive-date=2012-03-08 }}</ref>

Track construction and assembly is dictated by the application. Military vehicles use a track shoe that is integral to the structure of the chain in order to reduce track weight. Reduced weight allows the vehicle to move faster and decreases overall vehicle weight to ease transportation. Since track weight is completely [[Unsprung mass|unsprung]], reducing it improves suspension performance at speeds where the track's momentum is significant. In contrast, agricultural and construction vehicles opt for a track with shoes that attach to the chain with bolts and do not form part of the chain's structure. This allows track shoes to break without compromising the ability of the vehicle to move and decrease productivity but increases the overall weight of the track and vehicle.

The vehicle's weight is transferred to the bottom length of track by a number of road wheels, or sets of wheels called [[bogie]]s. While tracked construction equipment typically lacks suspension due to the vehicle only moving at low speeds, in military vehicles road wheels are typically mounted on some form of suspension to cushion the ride over rough ground. Suspension design in military vehicles is a major area of development; the very early designs were often completely unsprung. Later-developed road wheel suspension offered only a few inches of travel using springs, whereas modern hydro-pneumatic systems allow several feet of travel and include [[shock absorber]]s. [[Torsion-bar suspension]] has become the most common type of military vehicle suspension. Construction vehicles have smaller road wheels that are designed primarily to prevent track derailment and they are normally contained in a single bogie that includes the [[idler-wheel]] and sometimes the sprocket.

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File:Bundesarchiv Bild 101I-635-3965-28, Panzerfabrik in Deutschland.jpg|Overlapped and interleaved road wheels of a German [[Tiger I]] heavy tank
File:Bundesarchiv Bild 101I-750-0001A-05A, Bau von Zugkraftwagen 3t (Sd.Kfz. 11).jpg|upright|An [[Sd.Kfz. 11]]'s half-track units, showing the rims of its six ''Schachtellaufwerk'' overlapped/interleaved roadwheel sets for each track unit per side
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==== Overlapping road wheels ====
Many World War II German military vehicles, initially (starting in the late 1930s) including all vehicles originally designed to be half-tracks and all later tank designs (after the [[Panzer IV]]), had slack-track systems, usually driven by a front-located drive sprocket, the track returning along the tops of a design of overlapping and sometimes interleaved large diameter road wheels, as on the suspension systems of the [[Tiger I]] and [[Panther tank|Panther]] tanks, generically known by the term ''Schachtellaufwerk'' (interleaved or overlapping running gear) in German, for both half-track and fully tracked vehicles. There were suspensions with single or sometimes doubled wheels per axle, alternately supporting the inner and outer side of the track, and interleaved suspensions with two or three road wheels per axle, distributing the load over the track.<ref>Peter Chamberlain and Hilary Doyle, ''Encyclopedia of German Tanks of World War II'', 1999</ref>

The choice of overlapping/interleaved road wheels allowed the use of slightly more transverse-orientation [[torsion bar]] suspension members, allowing any German tracked military vehicle with such a setup to have a noticeably smoother ride over challenging terrain, leading to reduced wear, ensuring greater traction and more accurate fire. However, on the Russian front, mud and snow would become lodged between the overlapping wheels, freeze, and immobilize the vehicle. As a tracked vehicle moves, the load of each wheel moves over the track, pushing down and forward that part of the earth or snow underneath it, similarly to a wheeled vehicle but to a lesser extent because the tread helps distribute the load. On some surfaces, this can consume enough energy to slow the vehicle down significantly. Overlapped and interleaved wheels improve performance (including fuel consumption) by loading the track more evenly. It also must have extended the life of the tracks and possibly of the wheels.{{Citation needed|date=December 2016}} The wheels also better protect the vehicle from enemy fire, and mobility is improved when some wheels are missing.

This relatively complicated approach has not been used since World War II ended. This may be related more to maintenance than to original cost. The torsion bars and bearings may stay dry and clean, but the wheels and tread work in mud, sand, rocks, snow, and other surfaces. In addition, the outer wheels (up to nine of them, some double) had to be removed to access the inner ones. In WWII, vehicles typically had to be maintained for a few months before being destroyed or captured{{Citation needed|date=December 2016}}, but in peacetime, vehicles must train several crews over a period of decades.

==== Drive train ====
Transfer of power to the track is accomplished by a [[drive wheel]], or ''drive [[sprocket]]'', driven by the motor and engaging with holes in the track links or with pegs on them to drive the track. In military vehicles, the drive wheel is typically mounted well above the contact area on the ground, allowing it to be fixed in position. In agricultural crawlers it is normally incorporated as part of the bogie. Placing suspension on the sprocket is possible, but is mechanically more complicated. A non-powered wheel, an ''idler'', is placed at the opposite end of the track, primarily to tension the track, since loose track could be easily thrown (slipped) off the wheels. To prevent throwing, the inner surface of the track links usually have vertical guide horns engaging grooves, or gaps between the doubled road and idler/sprocket wheels. In military vehicles with a rear sprocket, the idler wheel is placed higher than the road wheels to allow it to climb over obstacles. Some track arrangements use return rollers to keep the top of the track running straight between the drive sprocket and idler. Others, called ''slack track'', allow the track to droop and run along the tops of large road wheels. This was a feature of the [[Christie suspension]], leading to occasional misidentification of other slack track-equipped vehicles.

==== Steering ====
Continuous track vehicles [[steering|steer]] by applying more or less drive torque to one side of the vehicle than the other, and this can be implemented in a variety of ways.
{{Main|Differential steering}}

=== "Live" and "dead" track ===
Tracks may be broadly categorized as ''live'' or ''dead'' track. ''Dead'' track is a simple design in which each track plate is connected to the rest with hinge-type pins. These dead tracks will lie flat if placed on the ground; the drive sprocket pulls the track around the wheels with no assistance from the track itself. ''Live'' track is slightly more complex, with each link connected to the next by a bushing which causes the track to bend slightly inward. A length of live track left on the ground will curl upward slightly at each end. Although the drive sprocket must still pull the track around the wheels, the track itself tends to bend inward, slightly assisting the sprocket and somewhat conforming to the wheels.

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=== Rubber track pads ===
Tracks are often equipped with rubber pads to improve travel on paved surfaces more quickly, smoothly and quietly. While these pads slightly reduce a vehicle's cross-country traction, they prevent damage to any pavement. Some pad systems are designed to remove easily for cross-country [[military combat]].
<gallery heights="150px" mode="packed">
File:Caterpillar Tracks On Seal Machine.jpg|Small tracks on a roadworks machine. Note the rubber pads to reduce wear on the carriageway.
File:USMC-12197.jpg|Worn and new track pads on an M1 Abrams main battle tank
File:CASE_IH_8240_Raupenantrieb.JPG|[[Rubber tracks]] (''[[Case IH]] 8240'')
File:Armored vehicle on trailer p1040729.jpg|Tracked vehicles long-distance hauling on equipment trailers
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=== Rubber tracks ===
Starting from late 1980s, many manufacturers provide rubber tracks instead of steel, especially for agricultural applications. Rather than a track made of linked steel plates, a reinforced rubber belt with [[wikt:chevron|chevron]] treads is used.

In comparison to steel tracks, rubber tracks are lighter, waste less power on internal friction, make less noise and do not damage paved roads. However, they impose ''more'' [[ground pressure]] below the wheels, as&nbsp;they are not able to equalize pressure as well as the stiff mechanism of track plates, especially the spring loaded ''live'' tracks. Another disadvantage is that they are not disassemblable into tracks and therefore cannot be repaired, having to be discarded as whole if once damaged.

Previous belt-like systems, such as those used for [[half-track]]s in World War II, were not as strong, and during military actions were easily damaged. The first rubber track was invented and constructed by [[Adolphe Kégresse]] and patented in 1913; in historic context rubber tracks are often called [[Kégresse track]]s. First rubber-tracked agricultural tractor was the [[Oliver Farm Equipment]] HGR from 1945-1948, which was ahead of its time and only saw small-scale production.

=== Advantages ===
* Tracked vehicles are much less likely than wheeled vehicles to get stuck in soft ground, mud or snow, since the tracks distribute the weight of the vehicle over a larger contact area, decreasing its [[ground pressure]]. The seventy-ton [[M1 Abrams]] tank has an average ground pressure of just over {{convert|15|psi|kPa|abbr=on|lk=on}}. Since tyre air pressure is approximately equal to average ground pressure, a typical car will have an average ground pressure of {{convert|28|psi|kPa|abbr=on|lk=on}} to {{convert|33|psi|kPa|abbr=on|lk=on}}.
* Tracked vehicles have better mobility over rough terrain than those with wheels: they smooth out the bumps, glide over small obstacles and are capable of crossing trenches or breaks in the terrain. Riding in a fast tracked-vehicle feels just like riding in a boat over heavy swells.
* The larger contact area, coupled with the cleats, or [[grouser]]s, on the track shoes, allows vastly superior traction that results in a much better ability to push or pull large loads where wheeled vehicles would dig in. [[Bulldozer]]s, which are most often tracked, use this attribute to rescue other vehicles (such as [[wheel loader]]s) which have become stuck in, or sunk into, the ground.
* Tracks cannot be punctured or torn and are more resilient in [[military combat]]. Should a track be broken, it often can be repaired immediately using special tools and spare parts, without the need for special facilities; this may be crucial in combat situations.

=== Disadvantages ===
[[File:JGSDF type10 Tank higashi fuji Firing Space accident.JPG|thumb|A [[JSDF]] [[Type 10]] with a thrown track]]
The disadvantages of tracks are lower top speed, much greater mechanical complexity, shorter life and the damage that their all-steel versions cause to the surface on which they pass: They often cause damage to less firm terrain such as lawns, gravel roads, and farm fields, as the sharp edges of the track easily rout the turf. Accordingly, vehicle laws and local ordinances often require rubberised tracks or track pads. A compromise between all-steel and all-rubber tracks exists: attaching rubber pads to individual track links ensures that continuous track vehicles can travel more smoothly, quickly, and quietly on paved surfaces. While these pads slightly reduce a vehicle's cross-country traction, in theory they prevent damage to any pavement.

Additionally, the loss of a single segment in a track immobilizes the entire vehicle, which can be a disadvantage in situations where high reliability is important. Tracks can also ride off their guide wheels, idlers or sprockets, which can cause them to jam or to come completely off the guide system (this is called a "thrown" track). Jammed tracks may become so tight that the track may need to be broken before a repair is possible, which requires either explosives or special tools. Multi-wheeled vehicles, for example, [[8 X 8]] military vehicles, may often continue driving even after the loss of one or more non-sequential wheels, depending on the base wheel pattern and drive train.

Prolonged use places enormous strain on the drive [[Transmission (mechanics)|transmission]] and the mechanics of the tracks, which must be overhauled or replaced regularly. It is common to see tracked vehicles such as bulldozers or tanks transported long distances by a wheeled carrier such as a [[tank transporter]] or [[train]], though technological advances have made this practice less common among tracked military vehicles than it once was{{Citation needed|date=December 2016}}.

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