Caterpillar track
Continuous tracks or caterpillar tracks are a system of vehicle propulsion
Vehicle propulsion
Vehicle propulsion refers to the act of moving an artificial carrier of people or goods over any distance. The power plant used to drive the vehicles can vary widely. Originally, humans or animals would have provided the propulsion system, later being supplemented by wind power...

 in which modular metal plates linked into a continuous band are driven by two or more wheels. The large surface area of the tracks distributes the weight of the vehicle better than steel or rubber tires on an equivalent vehicle, enabling a continuous tracked vehicle to traverse soft ground with less likelihood of becoming stuck due to sinking. The prominent treads of the metal plates are both hard-wearing and damage resistant, especially in comparison to rubber tires. The aggressive treads of the tracks provide good traction in soft surfaces but can damage paved surfaces. Special tracks that incorporate rubber pads can be installed for use on paved surfaces to prevent the damage that can be caused by all metal tracks.

Continuous tracks can be traced back as far as 1770 and today are commonly used on a variety of vehicles including bulldozers, excavators and tanks, but can be found on any vehicle used in an application that can benefit from the added traction, low ground pressure and durability inherent in continuous track propulsion systems.


Perhaps the oldest implementation of something resembling continuous tracks is to be found in theories of prehistoric erection of large stone monuments, when megalith
A megalith is a large stone that has been used to construct a structure or monument, either alone or together with other stones. Megalithic describes structures made of such large stones, utilizing an interlocking system without the use of mortar or cement.The word 'megalith' comes from the Ancient...

s may have been slid atop rounded wooden logs. The logs were grooved near their ends to be held in alignment and rotation by belts out past the edge of the megalith and lubricated by some means, probably organic. The logs are carried from the back of the procession to the front in an endless chain, like continuous track. The system is a precursor to development of the axle, which keeps a rotating cylinder fixed relative to its cargo.

In modern times, continuous track propulsion systems can be traced back to a crude continuous track system designed in the 1770s by Richard Lovell Edgeworth
Richard Lovell Edgeworth
Richard Lovell Edgeworth was an Anglo-Irish politician, writer and inventor.-Biography:Edgeworth was born in Pierrepont Street, Bath, England, grandson of Sir Salathiel Lovell through his daughter, Jane Lovell....

. Polish mathematician and inventor Józef Maria Hoene-Wroński
Józef Maria Hoene-Wronski
Józef Maria Hoene-Wroński was a Polish Messianist philosopher who worked in many fields of knowledge, not only as philosopher but also as mathematician, physicist, inventor, lawyer, and economist. He was born Hoene but changed his name in 1815.-Life:...

 conceived of the idea in the 1830s. The British polymath
A polymath is a person whose expertise spans a significant number of different subject areas. In less formal terms, a polymath may simply be someone who is very knowledgeable...

 Sir George Cayley
George Cayley
Sir George Cayley, 6th Baronet was a prolific English engineer and one of the most important people in the history of aeronautics. Many consider him the first true scientific aerial investigator and the first person to understand the underlying principles and forces of flight...

 patented a continuous track, which he called a "universal railway" (The Mechanics' Magazine, 28 January 1826). In 1837, a Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n inventor Dmitry Zagryazhsky designed a "carriage with mobile tracks" which he patented the same year, but due to a lack of funds he was unable to build a working prototype, and his patent was voided in 1839. Steam powered tractors
Traction engine
A traction engine is a self-propelled steam engine used to move heavy loads on roads, plough ground or to provide power at a chosen location. The name derives from the Latin tractus, meaning 'drawn', since the prime function of any traction engine is to draw a load behind it...

 using a form of continuous track were reported in use with the Western Alliance during the Crimean War
Crimean War
The Crimean War was a conflict fought between the Russian Empire and an alliance of the French Empire, the British Empire, the Ottoman Empire, and the Kingdom of Sardinia. The war was part of a long-running contest between the major European powers for influence over territories of the declining...

 in the 1850s. An "endless railway wheel" had been patented by the British engineer James Boydell
James Boydell
James Boydell was a British inventor of steam traction engines. His most significant invention was the first practical track-laying vehicle, for which he received British patents in August 1846 and February 1854....


In 1877, a Russian, Fyodor Blinov
Fyodor Blinov
Fyodor Abramovich Blinov was Russian inventor who introduced one of the first tracked vehicles in 1877 , and then developed his idea and built the first steam-powered continuous track tractor for farm usage...

, created a tracked vehicle called "wagon
A wagon is a heavy four-wheeled vehicle pulled by draught animals; it was formerly often called a wain, and if low and sideless may be called a dray, trolley or float....

 moved on endless rails" (caterpillars). It lacked self-propulsion—it was pulled by horses, instead. Blinov got a patent for his "wagon" the next year. Later, in 1881-1888 he created a steam-powered caterpillar-tractor. This self-propelled crawler was successfully tested and showed at a farmer's exhibition in 1896.

A little known American inventor, Henery T. Stith, developed a continuous track prototype, which was, in multiple forms, patented in 1873, 1880, and 1900. The last, was for the application of the track to a proto-type off road bicycle built for his son. The 1900 proto-type is retained by his surviving family.

An effective continuous track was invented and implemented by Alvin Lombard for the Lombard Steam Log Hauler
Lombard Steam Log Hauler
The Lombard Steam Log Hauler, patented 29 May 1901, was the first successful commercial application of a continuous track for vehicle propulsion. The concept was later used for military tanks during World War I and for agricultural tractors and construction equipment following the...

. He was granted a patent in 1901. He built the first steam-powered log hauler at the Waterville Iron Works in Waterville, Maine, the same year. In all, 83 Lombard steam log haulers are known to have been built up to 1917, when production switched entirely to internal combustion engine powered machines, ending with a Fairbanks diesel powered unit in 1934. Undoubtedly, Alvin Lombard was the first commercial manufacturer of the tractor crawler. At least one of Lombard's steam-powered machines apparently remains in working order. A gasoline powered Lombard hauler is on display at the Maine State Museum in Augusta.

In addition, there may have been up to twice as many Phoenix Centipeed versions of the steam log hauler built under license from Lombard, with vertical instead of horizontal cylinders. In 1903, the founder of Holt Manufacturing, Benjamin Holt
Benjamin Holt
Benjamin Leroy Holt was an American inventor who was the first to patent and manufacture a first practical crawler-type tread tractor. The continuous-type track is used for heavy agricultural and engineering vehicles to spread the weight over a large area to prevent the vehicle from sinking into...

, paid Lombard $60,000 for the right to produce vehicles under his patent. There seems to have been an agreement made after Lombard moved to California, but some discrepancy exists as to how this matter was resolved when previous track patents were studied.

At about the same time a British agricultural company, Hornsby
Richard Hornsby & Sons
Richard Hornsby & Sons was an engine and machinery manufacturer in Lincolnshire, England from 1828 until 1918. The company was a pioneer in the manufacture of the oil engine developed by Herbert Akroyd Stuart and marketed under the Hornsby-Akroyd name. The company developed an early track system...

 in Grantham
Grantham is a market town within the South Kesteven district of Lincolnshire, England. It bestrides the East Coast Main Line railway , the historic A1 main north-south road, and the River Witham. Grantham is located approximately south of the city of Lincoln, and approximately east of Nottingham...

, developed a continuous track which was patented in 1905. The design differed from modern tracks in that it flexed in only one direction with the effect that the links locked together to form a solid rail on which the road wheels ran. Hornsby's tracked vehicles were given trials as artillery tractor
Artillery tractor
Artillery tractor is a kind of tractor, also referred to as a gun tractor, a vehicle used to tow artillery pieces of varying weights.-Traction:...

s by the British Army
British Army
The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...

 on several occasions between 1905 and 1910, but not adopted. The patent was purchased by Holt. The Hornsby tractors featured the track-steer clutch arrangement, which is the basis of the modern crawler operation, and some say an observing British soldier quipped that it crawled like a caterpillar. The word was shrewdly trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...

ed and defended by Holt.

American James B. Hill
James B. Hill
James B. Hill was an American inventor.Hill worked as a drainage tiler in northwestern Ohio in the 1870s and 1880s, during which time he devised a machine that he later named the Buckeye Traction Ditcher...

, working in Bowling Green, Wood County, Ohio, patented what he termed "apron traction" on September 24, 1907.

Caterpillar Tractor Company began in 1925 from a forced reorganization of the Holt Manufacturing Company
Holt Manufacturing Company
The Holt Manufacturing Company traces its roots to the 1883 establishment of Stockton Wheel Service in Stockton, California, United States. Benjamin Holt, who was later credited with patenting the first workable crawler tractor design, incorporated the Holt Manufacturing Company in 1892...

; an early successful manufacturer of crawler tractors. Caterpillar brand continuous tracks have since revolutionized construction vehicles and land warfare. Track systems have been developed and improved during their use on fighting vehicles. During World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 Holt tractors were used to tow heavy artillery by the British and Austro-Hungarian armies, and stimulated the development of tanks in several countries. The first tanks to go into action, built by Great Britain, were designed from scratch and inspired by but not directly based on the Holt, but the slightly later French and German tanks were built on modified Holt running gear.

A concept vehicle called the Hyanide
The Hyanide is a hybrid motorbike vehicle designed and created by German designers Tilmann Schlootz and Oliver Keller. The motorbike is a combination of dirt bike-snowmobile-four-wheel vehicle concepts which was first showcased at the 2006 Michelin Challenge Design competition. It can move through...

 proposes a continuous track drive motorcycle. It involves a steerable continuous track to enable the vehicle to corner.

Construction and Operation

Modern tracks are built from modular chain links which compose together a closed chain. These chain links are often broad and made of manganese alloy steel for high strength, hardness, and abrasion resistance. The links are jointed by a hinge. This allows the track to be flexible and wrap around the set of wheels to make the endless loop.

Track construction and assembly is dictated by 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. 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. Extra weight is an advantage when optimizing for traction and power over speed and mobility.

The vehicle's weight is transferred to the bottom length of track by a number of road wheels, or sets of wheels called bogie
A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...

s. 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
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...

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.

Transfer of power to the track is accomplished by a drive wheel
Drive wheel
A drive wheel is a roadwheel in an automotive vehicle that receives torque from the powertrain, and provides the final driving force for a vehicle. A two-wheel drive vehicle has two driven wheels, and a four-wheel drive has four, and so-on....

, or drive sprocket
A sprocket or sprocket-wheel is a profiled wheel with teeth, cogs, or even sprockets that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which are radial projections that engage a chain passing over it...

, 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 - 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 in 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
Christie suspension
The Christie suspension is a suspension system developed by American engineer Walter Christie for his tank designs. It allowed considerably longer movement than conventional leaf spring systems then in common use, which allowed his tanks to have considerably greater cross-country speed and a lower...

, leading to occasional misidentification of other slack track-equipped vehicles. Many WW II German military vehicles, including all half-track and all later tank designs (after the Panzer IV
Panzer IV
The Panzerkampfwagen IV , commonly known as the Panzer IV, was a medium tank developed in Nazi Germany in the late 1930s and used extensively during the Second World War. Its ordnance inventory designation was Sd.Kfz...

), had slack-track systems, usually driven by a front-located drive sprocket, running along the tops of the often overlapping, and sometimes interleaved large diameter doubled road wheels, as on the Tiger I
Tiger I
Tiger I is the common name of a German heavy tank developed in 1942 and used in World War II. The final official German designation was Panzerkampfwagen Tiger Ausf. E, often shortened to Tiger. It was an answer to the unexpectedly formidable Soviet armour encountered in the initial months of...

 and Panther
Panther tank
Panther is the common name of a medium tank fielded by Nazi Germany in World War II that served from mid-1943 to the end of the European war in 1945. It was intended as a counter to the T-34, and to replace the Panzer III and Panzer IV; while never replacing the latter, it served alongside it as...

, in their suspension systems. The choice of overlapping/interleaved road wheels allowed the use of slightly more torsion bar suspension members, allowing any German tracked military vehicle with such a setup to have a noticeably smoother ride over challenging terrain, but at the expense of mud and ice collecting between the overlapping areas of the road wheels, and freezing solid in cold weather conditions, often immobilizing the vehicle so equipped.


Tracked vehicles have better mobility than pneumatic tyres over rough terrain. They smooth out the bumps, glide over small obstacles and they are capable of crossing trenches or breaks in the terrain. Riding in a fast tracked vehicle feels like riding in a boat over heavy swells. Tracks are tougher than tyres since they cannot be punctured or torn. Tracks are much less likely to get stuck in soft ground, mud, or snow since they distribute the weight of the vehicle over a larger contact area, decreasing its ground pressure
Ground pressure
Ground pressure is the pressure exerted on the ground by the tires or tracks of a motorized vehicle, and is one measure of its potential mobility, especially over soft ground. Ground pressure is measured in pascals which corresponds to the EES unit of pounds per square inch...

. In addition the larger contact area, coupled with the cleats, or grouser
A grouser or cleat is a protrusion on the surface of a wheel or continuous track segment, intended to increase traction in soil, snow, or other loose material, in the same manner as cleated shoes provide traction to athletes. Track segments which incorporate grouser bars are known as 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
A bulldozer is a crawler equipped with a substantial metal plate used to push large quantities of soil, sand, rubble, etc., during construction work and typically equipped at the rear with a claw-like device to loosen densely-compacted materials.Bulldozers can be found on a wide range of sites,...

s, which are most often tracked, use this attribute to rescue other vehicles, (such as wheel loaders), which have become stuck in, or sunk into, the ground. Tracks can also give higher maneuverability, as some tracked vehicle can turn in place with no forward or backward movement by driving the tracks in opposite directions. In addition, should a track be broken, assuming the correct tools are available, it can be repaired without the need for special facilities; something which is crucial in a combat situation.

The seventy-ton M1 Abrams
M1 Abrams
The M1 Abrams is a third-generation main battle tank produced in the United States. It is named after General Creighton Abrams, former Army Chief of Staff and Commander of US military forces in Vietnam from 1968 to 1972. The M1 is a well armed, heavily armored, and highly mobile tank designed for...

 tank has an average ground pressure of just over 15 psi (103.4 kPa). Since tire air pressure is approximately equal to average ground pressure, a typical car will have an average ground pressure of 28 psi (193.1 kPa) to 33 psi (227.5 kPa).


The disadvantages of tracks are lower top speed, much greater mechanical complexity, and the damage that their all-steel versions cause to what passes beneath them: they are perceived/misconceived to severely damage hard terrain like asphalt pavement, but in actuality, often have significantly lower ground pressures than equivalent or lighter wheeled vehicles, but often cause damage to less firm terrains such as lawns, gravel roads, and farm fields, as the sharp edges of the track easily routs the turf. Vehicle laws and local ordinaces often require rubberised tracks or track pads due to this ideal. However, a compromise between all-steel and all-rubber tracks exists. Attaching rubber pads to individual track links ensures continuous tracked vehicles can travel more smoothly, quickly, and quietly on paved surfaces. While these pads slightly reduce a vehicle's cross-country traction, they keep it from (in theory) damaging 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 in an overly tight position or to come completely off of 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 upon the base wheel pattern and drivetrain.

Recently many manufacturers have used rubber tracks instead of steel, especially for agricultural use. Rather than a track made of linked steel plates, a reinforced rubber belt with chevron treads is used. In comparison to steel tracks, rubber tracks are lighter, make less noise, create less maximal ground pressure
Ground pressure
Ground pressure is the pressure exerted on the ground by the tires or tracks of a motorized vehicle, and is one measure of its potential mobility, especially over soft ground. Ground pressure is measured in pascals which corresponds to the EES unit of pounds per square inch...

 and don't damage paved roads. The disadvantage is that they are not as solid as steel tracks. Previous belt-like systems, such as used for half-track
A half-track is a civilian or military vehicle with regular wheels on the front for steering, and caterpillar tracks on the back to propel the vehicle and carry most of the load. The purpose of this combination is to produce a vehicle with the cross-country capabilities of a tank and the handling...

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
Adolphe Kégresse
Adolphe Kégresse was a French military engineer, inventor of the half-track and dual clutch transmission....

 was patented in 1913; rubber tracks are often called Kégresse tracks.

Prolonged use places enormous strain on the drive transmission
Transmission (mechanics)
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...

 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
Tank transporter
A tank transporter is a specialized road vehicle for the transport of tanks, to and from the battlefield or during peacetime. They are necessary to limit the mileage of the tracked vehicles and also to reduce wear on road surfaces which can easily be damaged by such heavy vehicles...

 or train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...

, though technological advances have made this practice less common among tracked military vehicles than it once was.

"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 with a bushing that 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 conforming to the wheels somewhat.

External links

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