There are generally two main types of tractors; those with wheels and others with crawler tracks. Wheeled models are all-purpose tractors designed especially for row crop use. Most are equipped with adjustable wheels to adapt to the size of the row and crop. Tracked models include heavy duty, high horsepower belted agricultural tractors. Tracked machines are also popular in the construction industry for earthmoving; these are commonly called crawler tractors or bulldozers.
Agricultural tractors can be categorized by size and use: there are smaller utility tractors; larger field tractors in either two-wheel, four-wheel drive or belted models, and orchard and vineyard tractors.
Utility tractors are generally of sizes up to 60 horsepower and designed to be used in smaller or medium-sized farms. They can be used for tillage, harvesting, haying, loading and a variety of other projects. Large two-wheel drive field tractors are classified as models ranging from 60 to 180 horsepower designed for heavy tillage, farmstead and other applications. Four-wheel drive large field tractors are models up to 400 horsepower or more, designed for large farm work. Orchard and vineyard tractors are designed for use in those specific markets. They are narrow models with a smooth and low profile to ensure they do not snag any branches or vines.
The name tractor is adapted from the Latin word trahere, or “to pull.”
 Steam- and Gas-powered Models
The first tractors were steam powered, but the exact date of their first appearance in farm work is up for debate. One source lists their introduction in the year 1868, while another claims “the first attempts at steam-powered plowing took place in the 1830s.” Either way, these first models were considered ingenious, but also impractically large and cumbersome. In fact, tractors did not become popular or reliable machines until after Nicolaus August Otto invented the first four-stroke gasoline engine in 1885. It made the engine lighter, more compact, and affordable.
However, the first gas-powered tractors, developed by John Charter and John Froelich, were just as big and awkward as their steam traction ancestors. Charter, of Sterling, Illinois, simply fixed his new gas-powered engine to a Rumley steam traction engine chassis in 1889, so it retained much of its previous weight. Froelich, of Northeast Iowa, attached his engine to a Robinson chassis, rigging his own gearing for propulsion. It was the first gasoline-powered traction engine capable of going forward and backwards.
According to Ralph W. Sanders’ book Vintage Farms Tractors, “the Froelich tractor, forerunner of the later Waterloo Boy tractor, is considered by many to be the first successful gasoline tractor known.”
A couple of other pioneers are notable. Charles W. Hart and Charles H. Parr were experimented with gas power during the 1890s. Together they formed the Hart-Parr Gasoline Engine Co. of Madison, Wisconsin. They created the first factory in the United States dedicated to manufacturing gas traction engines. They also reportedly coined the term “tractor” to replace vehicles previously called gas traction engines.
Small tractors, more accurately described as “motor plows,” began work on U.S. farms in 1910. They consisted of two wheels and an engine, to which horse-drawn implements would be attached. They were affordable, but not very powerful. Four-wheel models followed soon after. Wallis, International Harvester and Allis-Chalmers all concentrated on developing light four-wheel models during the early 1910s.
 Affordability and Standards
Henry Ford, who had been raised on a farm in Detroit, Michigan, understood the marketability of the tractor. However, he wanted to take affordability to the next level by making a tractor cheap enough that even the smallest farmer could afford. He began experimenting in 1907, and after 10 years of designing, developing, and testing, he introduced his Fordson Model F. The Model F ran on four cylinders and had unit construction. It was a full sized tractor cheaper than a motor plow. He minimized costs by utilizing mass production. Ford reduced the price of his tractor to $230. As a result, many companies were unable to compete, and went out of business.
However, there were many businessmen unwilling to admit defeat. In fact, they saw the burgeoning popularity of the tractor as a quick profitable investment or simply a way to take advantage of needy farmers. It created an American market full of “tricksters and charlatans, some of whom were tempting gullible investors with tractors that only existed on paper.” As a result, in 1920, the University of Nebraska developed a series of tractor tests that had to be completed before any new model could be sold in the state. The university’s tests developed a national, and eventually international, standard of quality.
Once tractors had become both reliable and affordable, it made financial sense for every farmer to purchase one, replacing his horses. Previously, farmers needed about five acres (2 ha) of land to grow the oats, hay, and fodder each workhorse required. With a tractor, that land could be turned into profit. It also saved a considerable amount of time. With five horses and a gang plow it would take about an hour and a half to till one acre (0.4 ha) of land. Whereas, a 27 horsepower tractor and a moldboard plow took 35 minutes to till the same acre, and only 15 minutes with a 35 horsepower tractor.
Shortly after Ford released its Model F, John Deere Co. entered the tractor market. In 1918, it acquired tractor pioneer the Waterloo Co., who was now outdated and struggling. John Deere released a two-cylinder Model D in 1923, which was so popular it remained in production for a further 40 years. They eventually replaced it in the 1960s with four and six-cylinder models.
Meanwhile, International Harvester was having success with its Farmall tractor model, which combined the powerful, lumbering qualities of a pulling thresher with the nimble, lightweight features of a row crop tractor.
 Rubber Wheels
By the 1930s, modern tractors were simple, cheap, and reliable. However, there was still a lot of room for improvement. The tractors ran on large bare steel wheels equipped with large protruding spade lugs to help traverse through sticky surfaces. This meant they were difficult to drive on the road; even with bolted bands on the lugs they did not travel above a walking pace. Recognizing this problem, Allis-Chalmers released a tractor model with pneumatic tires in 1932. They cost an additional $150, “but the benefits were so overwhelming that within a few years most new tractors followed suit.” These new tires made the tractor easier to steer and capable of traveling at much higher speeds.
 Hitching Systemstow-hitch system currently being used created a lot of drag, which, when working in heavy soil, would bog down the tractor enough to cause it to stall or even flip over. It was also quite arduous and time consuming to hitch and unhitch attachments. So, an Irish tractor salesman named Harry Ferguson, with a talent for engineering, began developing a new system. He invented the three-point hitch, which some argue, “Was the single, most significant advance in tractor technology, bar none.”
The three-point hitch transferred the weight of attachments to the tractor’s rear wheels, improving traction. The new hitch also included “draft control;” a process that automatically lifted the attachment while working in tough or sticky soil to reduce drag until the spot was passed. Hitching and unhitching was now completely hydraulically controlled, making the process much quicker and less painstaking.
Ferguson followed up by producing a specially designed tractor for his attachment system. Henry Ford took the opportunity to manufacture Ferguson’s tractor. The Ford 9N was released in 1939. It was a small, lightweight tractor with a hitch capable of doing the work of a much larger machine.
 Diesel Power
In 1926 International Harvester engineers traveled through Europe studying and experimenting with diesel technology. Two years later they were field testing their first diesel tractor in Arizona. By 1933 IH had produced its first diesel engine, a PD-40 four-cylinder power unit designed for use in farm tractors.
John Deere released its first diesel-powered tractor in 1949, the Model R. It had a diesel version of a twin-cylinder engine, but larger at 416 cubic inches (6,818 cc). It produced 51 horsepower at the power take-off (PTO) and set a new record in fuel economy at the University of Nebraska tractor tests. In three years, 20,000 Model Rs were sold. Numerous other U.S. manufacturers jumped on the success of diesel, manufacturing their own diesel-powered engines. However, gasoline and liquefied petroleum gas remained optional fuel sources until the early 1970s.
Allis-Chalmers followed the diesel innovation with Power Shift and two-clutch Power Control technology with its WD45 model in 1953. Power Shift enabled the adjustment of the rear wheel tread using engine power. The two-clutch Power Control produced continuous power take-off, meaning the PTO would not stop to declutch.
 Transmissions and Four-wheel Drive
By the 1950s, manufacturers began experimenting with more range and stability in their engines’ transmission. At this time they were simple, single range gearboxes with three, four, or five speeds. In order to change gears or speeds one had to stop the machine, change the gear and restart it, which was difficult, especially when the tractor was stuck in deep soil with a heavy plow attached.
The first transmission breakthrough was achieved with International Harvester’s torque amplifier: adding a two-cylinder epicycle gearbox to the original model, doubling the number of available ratios and allowing for gear shifting on the move. Similar models were manufactured by Allis-Chalmers, Minneapolis-Moline, and Case.
Transmission development led to the increase in both tractor power and speed. Although 40 horsepower was top class for a tractor engine before World War II, manufacturers did not see fit to focus on power and speed until the late 1950s and early 1960s. Allis-Chalmers released its D19 model in 1961. Its engine, the first turbo-diesel engine in a tractor, increased power by 25 percent. The company followed the D19 with the D21, which increased power again to 103 horsepower. John Deere, Case, and International were not far behind with their own 100 horsepower tractors. However, these companies soon discovered that two-wheel drive tractors were only capable of producing so much speed.
Four-wheel drive models did not hit the mainstream until the 1970s, but some companies were already creating “giant tractors” for niche markets. The Steiger brothers from Minnesota built four-wheel drive tractors with articulated steering equipped with a large diesel engine. Other companies also began to manufacture these mammoth machines. The tractors produced by Steiger, Versatile, Big Bud, and Wagner were ideal for harvesting large wheat fields in the Midwest. Some of these vehicles were powered by 300 horsepower engines and weighed more than 15 tons.
 Safety and Comfort
By the late 1960s, tractor power and versatility had increased exponentially, but little innovation had been made in the area of safety and comfort of the operator. Tractor operators were subject to the elements and required to maneuver heavy and awkward instrumentation and controls. John Deere introduced ROPS (rollover protection system) in 1966. Deere followed this development with the Sound Guard cab, which provided a much quieter cab, increased visibility, as well as a radio/cassette player. Other companies followed these advancements with their own in an effort to provide a safer and ultimately more attractive machine for their customers.
 Further Advancements: Transmission Size, Crawler Tracks, and Electronics
With increased power came an increase in transmission size. Some transmissions were available with as many as 20 different speeds with full power shifting, enabling all gears to be reached without stopping the machine. Hydrostatic transmissions also became available in the 1970s. The hydraulic drive, capable of infinite variations in speed within a fixed range, replaced the conventional gearbox.
During the 1980s some companies instituted rubber crawler tracks for certain models of tractors. They were capable of reaching higher speeds and could be extremely useful in certain jobs, but wheels were still preferred for row crop use. Case-International developed a unique track system called Quadrac that replaced the four wheels with four individual rubber tracks.
The last truly significant advancement in the tractor manufacturing industry was the development of electronics. The invention of the microchip revolutionized all sizes, models, and makes of the tractor. It provided precise control of fuel injection benefiting power, torque, and emissions. It allowed transmissions to choose the perfect ratio, even overriding the operators’ control. Also, tractors with electronics kept an accurate list of all variables to inform the operator of any and all concerns.
 Features/How it Works
Generally a tractor’s main purpose is to pull and/or power various types of agricultural attachments, equipment, or even hydraulic pull scrapers. It is powered by either a diesel engine or gasoline engine and is available in belted, mechanical front wheel, two wheel, or four-wheel drive models.
 Common Manufacturers
- Buhler Versatile
- Case IH
- John Deere
- LS Tractor
- Mahindra & Mahindra Ltd.
- Massey Ferguson
- New Holland
- Tong Yang Moolsan
- White Motor Co.
 Ritchie Bros. Marketplace
- Tractors for sale
- Mechanical Front Wheel Drive (MFWD) Tractors
- 4WD Tractors
- 2WD Tractors
- Utility Tractors
- Track Tractors
 Additional Photos
 Used & Unused Tractors for Sale
Search for unused and used tractors being sold at Ritchie Bros. unreserved public auctions.
- ↑ Tractors. About.com. 2008-09-24.
- ↑ Origins of Agriculture. Britannica. 2008-09-24.
- ↑ Sanders, Ralph W. Vintage Farm Tractors: The Ultimate Tribute to Classic Tractors. Voyeur Press: 2004.
- ↑ Tractors. About.com. 2008-09-24.
- ↑ Glastonbury, Jim. The Ultimate Guide to Tractors. Chartwell Books: 2006. 8.
- ↑ Glastonbury, Jim. The Ultimate Guide to Tractors. Chartwell Books: 2006. 9.
- ↑ Machines. Living History Farm. 2008-09-24.
- ↑ Glastonbury, Jim. The Ultimate Guide to Tractors. Chartwell Books: 2006. 10.
- ↑ Glastonbury, Jim. The Ultimate Guide to Tractors. Chartwell Press: 2006. 12.
- ↑ About Us. MaxxForce, 2008-12-05.
- ↑ Glastonbury, Jim. The Ultimate Guide to Tractors. Chartwell Press: 2006. 13.
- ↑ Glastonbury, Jim. The Ultimate Guide to Tractors. Chartwell Press: 2006. 13.
- ↑ Glastonbury, Jim. The Ultimate Guide to Tractors. Chartwell Press: 2006. 16.