Editing Tractor (section)

== Design, power and transmission ==

=== Configuration ===
Tractors can be generally classified by number of axles or wheels, with main categories of [[two-wheel tractor]]s (single-axle tractors) and four-wheel tractors (two-axle tractors); more axles are possible but uncommon. Among four-wheel tractors (two-axle tractors), most are [[two-wheel drive]] (usually [[rear wheel drive|at the rear]]); but many are two-wheel drive with front wheel assist, [[four-wheel drive]] (often with articulated steering), or [[continuous track|track]] crawler (with steel or rubber tracks).
[[File:Farmall Regular. 1930 (8167774826).jpg|thumb|The Farmall introduced the row crop configuration, which utilized a narrow frontend wheel arrangement]]
[[File:Zetor 25 - Ystad-2022.jpg|thumb|The diesel powered [[Zetor]] 25, was the first model from the [[Czech Republic|Czech]] manufacturer [[Zetor]] in 1946.]]
[[File:Volvo T 25.1.jpg|thumb|Volvo T25, 1956, gasoline tractor]]
The classic farm tractor is a simple open [[vehicle]], with two very large driving wheels on an axle below a single seat (the seat and [[steering]] wheel consequently are in the center), and the engine in front of the driver, with two steerable wheels below the engine compartment. This basic design has remained unchanged for a number of years after being pioneered by Wallis, but enclosed cabs are fitted on almost all modern models, for operator safety and comfort.

In some localities with heavy or wet soils, notably in the Central Valley of California, the [[Caterpillar, Inc.|"Caterpillar"]] or [[crawler tractor|"crawler"]] type of tracked tractor became popular due to superior traction and flotation. These were usually maneuvered through the use of turning brake pedals and separate track clutches operated by levers rather than a steering wheel.
[[File:John Deere track tractor 8330T.jpg|thumb|170px|center|John Deere tracked tractor 8330T]]

[[File:Modern-tractor.jpg|thumb|A modern front wheel assist [[farm]] tractor in [[Netherlands|the Netherlands]] ]]
Four-wheel drive tractors began to appear in the 1960s. Some four-wheel drive tractors have the standard "two large, two small" configuration typical of smaller tractors, while some have four large, powered wheels. The larger tractors are typically an articulated, center-hinged design steered by hydraulic cylinders that move the forward power unit while the trailing unit is not steered separately.

[[File:Wheat Planting Rig May 2007.jpg|thumb|A modern 4wd articulated crawler power unit planting wheat in North Dakota]]
In the early 21st century, articulated or non-articulated, steerable multitrack tractors have largely supplanted the Caterpillar type for farm use. Larger types of modern farm tractors include articulated four-wheel or eight-wheel drive units with one or two power units which are hinged in the middle and steered by hydraulic clutches or pumps. A relatively recent development is the replacement of wheels or steel crawler-type tracks with flexible, steel-reinforced rubber tracks, usually powered by hydrostatic or completely hydraulic driving mechanisms. The configuration of these tractors bears little resemblance to the classic farm tractor design.

=== Engine and fuels ===
The predecessors of modern tractors, traction engines, used [[steam engine]]s for power.

==== Gasoline and kerosene ====
Since the turn of the 20th century, [[internal combustion engine]]s have been the power source of choice. Between 1900 and 1960, [[gasoline]] was the predominant fuel, with [[kerosene]] (the [[Rumely Oil Pull]] was the most notable of this kind)being a common alternative. Generally, one engine could burn any of those, although cold starting was easiest on gasoline. Often, a small auxiliary fuel tank was available to hold gasoline for cold starting and warm-up, while the main fuel tank held whatever fuel was most convenient or least expensive for the particular farmer. In the United Kingdom, a gasoline-kerosene engine is known as a [[petrol-paraffin engine]].

==== Diesel ====
[[Dieselisation]] gained momentum starting in the 1960s, and modern farm tractors usually employ [[diesel engine]]s, which range in power output from 18 to 575 [[horsepower]] (15 to 480&nbsp;kW). Size and output are dependent on application, with smaller tractors used for [[lawn mower|lawn mowing]], landscaping, orchard work, and [[truck farming]], and larger tractors for vast fields of wheat, corn, soy, and other bulk crops.

==== Liquefied petroleum gas ====
[[Liquefied petroleum gas]] (LPG) or [[propane]] also have been used as tractor fuels, but require special pressurized fuel tanks and filling equipment and produced less power, so are less prevalent in most markets. Most are confined for inside work due to their clean burning.

==== Wood ====
During the Second World War, petroleum-based fuel was scarce in Europe, so European vehicles including tractors were commonly converted to use a [[wood gas generator]] or "gasifier."<ref>{{Cite web|title=Wood gas vehicles: Firewood in the fuel tank|url=https://www.lowtechmagazine.com/2010/01/wood-gas-cars.html|
archive-url=https://web.archive.org/web/20220221205156/https://www.lowtechmagazine.com/2010/01/wood-gas-cars.html|archive-date=2022-02-21|access-date=2025-03-08|website=Low-Tech Magazine |date=18 January 2010 }}</ref>

==== Biodiesel ====
In some countries such as Germany, [[biodiesel]] is often used.<ref>{{Cite web|url=https://www.inforse.org/europe/dieret/altfuels/biodiesel.htm|title=BIODIESEL|website=www.inforse.org}}</ref><ref>[https://web.archive.org/web/20120320080038/http://www.bebioenergy.com/documents/BallaratUniversity.pdf BE energy promoting biodiesel for use in tractors]. Department of the Environment and Heritage, Australila</ref> Some other biofuels such as straight vegetable oil are also being used by some farmers.<ref>[https://web.archive.org/web/20101113115326/http://articles.cnn.com/2008-08-08/living/farmer.fuel_1_jatropha-diesel-fuel-biodiesel?_s=PM:LIVING Jatropha being used to run a tractor]. ''CNN'' (2008-08-08)</ref><ref>{{Cite web|url=https://extension.psu.edu/forage-and-food-crops|title=Forage and Food Crops|website=Penn State Extension}}</ref>

==== Electric powered ====
Prototype battery powered [[electric tractor]]s are being developed by a German company, [[Fendt]], and by two US companies, [[Solectrac]] and Monarch Tractor.<ref name="Gaines"/><ref name="Weisbrod"/> [[John Deere]]'s protoype electric tractor is a plug-in, powered by an electrical cable.<ref name="hobby20020723"/> [[Kubota]] is prototyping an autonomous electric tractor.<ref name="Szymkowski"/>

=== Transmission ===
Most older farm tractors use a [[manual transmission]] with several [[gear]] [[ratio]]s, typically three to six, sometimes multiplied into two or three ranges. This arrangement provides a set of discrete ratios that, combined with the varying of the throttle, allow final-drive speeds from less than one up to about 25 miles per hour (40&nbsp;km/h), with the lower speeds used for working the land and the highest speed used on the road.

Slow, controllable speeds are necessary for most of the operations performed with a tractor. They help give the farmer a larger degree of control in certain situations, such as field work. When travelling on public roads, the [[slow moving vehicle|slow operating speeds]] can cause problems, such as long queues or tailbacks, which can delay or annoy motorists in cars and trucks. These motorists are responsible for being duly careful around farm tractors and sharing the road with them, but many shirk this responsibility, so various ways to minimize the interaction or minimize the speed differential are employed where feasible. Some countries (for example the [[Netherlands]]) employ a [[road sign]] on some roads that means "no farm tractors". Some modern tractors, such as the [[J. C. Bamford|JCB]] Fastrac, are now capable of much higher road speeds of around 50&nbsp;mph (80&nbsp;km/h).

[[File:OlderModelTractor.JPG|thumb|left|An older model European farm tractor, of the type still common in Eastern Europe]]
Older tractors usually have [[Manual transmission#Unsynchronized transmission|unsynchronized]] transmission designs, which often require the operator to engage the clutch to shift between gears. This mode of use is inherently unsuited to some of the work tractors do, and has been circumvented in various ways over the years. For existing unsynchronized tractors, the methods of circumvention are [[Double clutch (technique)|double clutching]] or power-shifting, both of which require the operator to rely on skill to speed-match the gears while shifting, and are undesirable from a risk-mitigation standpoint because of what can go wrong if the operator makes a mistake – transmission damage is possible, and loss of vehicle control can occur if the tractor is towing a heavy load either uphill or downhill – something that tractors often do. Therefore, operator's manuals for most of these tractors state one must always stop the tractor before shifting.

[[File:John Deere 3350 tractor cut.JPG|thumb|Cutaway of a John Deere tractor]]

In newer designs, unsynchronized transmission designs were replaced with [[Manual transmission#Synchronized transmission|synchronization]] or with [[continuously variable transmission]]s (CVTs). Either a synchronized manual transmission with enough available gear ratios (often achieved with dual ranges, high and low) or a CVT allow the engine speed to be matched to the desired final-drive speed, while keeping engine speed within the appropriate speed (as measured in rotations per minute or rpm) range for power generation (the working range) (whereas throttling back to achieve the desired final-drive speed is a trade-off that leaves the working range). The problems, solutions, and developments described here also describe the history of transmission evolution in [[semi-trailer truck]]s. The biggest difference is fleet turnover; whereas most of the old [[Tractor unit|road tractor]]s have long since been scrapped, many of the old farm tractors are still in use. Therefore, old transmission design and operation is primarily just of historical interest in trucking, whereas in farming it still often affects daily life.