What is Tractor Pulling?
Tractor Pulling is known as “the world’s heaviest motorsport.” The goal of tractor pulling is to determine the strongest machine and the best driver. Different to every other motorsport in the world, it is not about the speed, but distance pulled. The pulling track is a minimum of 30 feet wide by 320 feet long.
Tractor pulling is a competitive motor sport in which modified farm tractors, modified tractors or trucks drag a metal sled along a prescribed course. The sled contains a box filled with weight that is mechanically winched forward as the sled progresses along the course. Pulling this ever-increasing load eventually causes the vehicle to lose forward momentum and torque, although a rare few might indeed reach the end of the course, known as a “full pull.” The distance from start to finish is measured in thousandths of an inch and the tractor that pulls the sled the farthest distance is declared the winner. If more than one competitor reaches the full pull mark, a pull-off is held to determine a winner.
Competition-level tractors might look like standard-issue farm equipment, but the similarities stop at the basic body and tires. Tractor pulling is a sport based on horsepower and torque, which means that the engine must be modified to generate as much power as possible. Various classes have been developed for tractors based on limitations in the rules. Modified tractor limits are based mostly on weight. Engines include drag racing automotive type, jet turbines, aircraft and industrial engines in various configurations. Trucks come in two wheel drive, four wheel drive (naturally aspirated, blown, diesel) and semis.
History of Pulling
It is said that around the 1860s when farming machines were pulled by horse, farmers would boast about the strength of their horses. They would claim that their horse could tow large loads, such as a fully loaded hay cart or wagon. Farmers would challenge one another to contests to prove who had the strongest horse. A barn door was removed and laid flat on the ground, and the horse was then hitched to it, the farmer would then urge the horse to drag the barn door along the ground. One by one, people jumped on the door until the horse could no longer drag it; the horse pulling the most people the greatest distance was judged the strongest. This event, called horse pulling, is still carried out today with specially bred horses trained to have high strength and low stamina, rather than low strength and high stamina which is normally the case with racing horses. Instead of people, fixed weights on sleds are dragged as far as possible. While it is said that the term horsepower is derived from this event, in reality the term was coined by James Watt. It wasn’t until 1929 that motorized vehicles were put to use in the first events at Vaughansville, Missouri and Bowling Green, Ohio, the latter being where the current national championships are held. Although the sport was recognized then, it did not really become popular until the 50s and 60s. It was also realized, at that time, there were no uniform set of rules. The rules varied from state to state, county to county, and competitors never knew what standards to follow. This made the sport difficult for new entrants. SOURCE: wIkipedia.org
Modified Tractor– The class began as farm tractors with non-tractor engines and grew into fully custom machines with multiple engines and power plant types. All divisions of the Modified class use a maximum of a 20” drawbar and 30.5 x 32 tires.
Modified (RN)- 7,500 pounds, 3 blown automotive engines with 8-71 blowers, 2 blown automotive engines with 14-71 blowers, 1 or 2 Allison aircraft engines (based on blower type), 1 industrial or marine engine 12 cylinder limit, combination of NTPA recognized turbine engines not to exceed a maximum of 5050 total horsepower and other combinations.
Light Unlimited (GN)- 6,000 pounds, no turbines.
Modified (GN)- 7,500 pounds, 4 blown automotive engines with 8-71 blowers, 3 blown automotive engines with 14-71 blowers, 2 Allison aircraft engines, 2 industrial or marine engine 12 cylinder limit, combination of NTPA recognized turbine engines not to exceed a maximum of 5800 total horsepower and other combinations.
Unlimited (GN)- 8,000 pounds, any power plant making weight.
Super Stock Tractors– Diesel or alcohol powered, multiple turbo chargers. Heavy Super Stock tractors at Regional level will run 20” drawbar with the weight at 8000 for alcohol and 8300 for diesel. Light Super Stock Tractors at RN level only will run component tractors at 6200 lbs. and the agricultural rearend tractors at 6500 lbs. Grand National Open (Alcohol) and Diesel (Diesel fuel only) tractors run with a 20” drawbar and weigh 8000 pounds. The Grand National Light Super Stock class has a mixture of fuels, run at 6200 lbs. and put a a wild show due to the high horsepower to weight ratio.
Pro Stock Tractors– Single turbo charger diesel only tractor class. 10,000 pounds, 20” drawbar, 680 cubic inch displacement limit, 1 turbo charger, 24.5 x 32 tires, water injection and/or intercoolers allowed.
Light Pro Stock Tractors– All rules from Pro Stock class plus 540 cid limit, no component chassis, engine heads must be OEM agricultural-type for brand (no billet), no overhead cams, no inner/after coolers, “p” pump 3000 or 7100 series only (only one plunger per cylinder). 8500 pounds.
Limited Pro Stock Tractors– All rules from Pro Stock class plus 640 cid limit, no component chassis, engine heads must be OEM agricultural-type for brand (no billet), no overhead cams, no inner/after coolers, “p” pump 3000 or 7100 series only, maximum 2 valves per cylinder, turbo limit: 4.1 inlet smooth bore housing. 9500 pounds.
Super Farm Tractors– Limited single turbo charger diesel only tractor class. 9300 pounds, 20” drawbar, 640 cubic inch displacement limit, 1 turbo charger 3×3” (sealed after inspection), 24.5 x 32 tires, “p” pump, water injection allowed. No after/inter coolers or overhead cams.
Modified Mini Tractors– High power to weight ratio, offers exciting rides. Powered by automotive style or turbine engines. 2050 pounds, 18” drawbar, 18.4×16.1 tires. Turbines limited to NTPA 1800 horsepower rating, 575 cid blown or 650 cid naturally aspirated limits.
Four Wheel Drive Trucks– Stock appearing 4×4 truck, 6200 pound, 650 cid limited naturally aspirated engine, 112 inch circumference and 20 inch wide rim tire limit, 26” drawbar.
Super Modified Four Wheel Drive Trucks– Stock appearing 4×4 truck, 6200 pound, 500 cid limited supercharged or turbocharged engine, 112 inch circumference, 20 inch wide rim tire limit, 26” drawbar.
Diesel Pro Stock Four Wheel Drive Trucks– Stock appearing 4×4 truck (most street-like class), 8000 pound, diesel fuel only, 460 cid limit with a maximum 3.0” turbocharger, “p” pump, DOT tires (35” maximum), and 26” drawbar.
Super Stock Diesel Four Wheel Drive Trucks– Stock appearing 4×4 truck, 7500 pound, diesel fuel only, 460 cid limit, limited to 2 stage configuration of turbochargers, water injection allowed, “p” pump, maximum tire 35” tall with tread not to exceed 18”, and 26” drawbar.
Two Wheel Drive Trucks– Truck body, 6200 pound, 575 cid limit, turbocharged or supercharged engines, alcohol fuel, 18.4 x 16.1 tire, 30” drawbar.
Super Semi– Stock appearing semi with single or multiple turbochargers. 20,000 pounds, 16” drawbar, diesel fuel only, DOT approved tires. Engine must be from a production-available commercial truck with minimum of 500 units produced. Up to two stages of pressure allowed in turbocharger system.
Pro Stock Semi– Stock appearing semi with single turbocharger. 20,000 pounds, 16” drawbar, diesel fuel only, DOT approved tires. Engine must be from a production-available commercial truck with minimum of 500 units produced. One turbocharger, any size.
The Pulling Sled
In the early days, either a dead weight of fixed mass was dragged, or the step-on method was used, which people stood at fixed positions and stepped aboard as the sled passed. Today’s sleds use a complex system of gears to move weights up to 65,000 pounds. Upon starting, all the weights are over the sled’s rear axles to give an effective weight of the sled plus zero. As the tractor travels the course, the weights are pushed ahead of the sled’s axles, pushing the front of the sled into the ground, synthetically creating a gain in weight until the tractor is no longer able to overcome the force of friction.
The sled can be adjusted in many ways to create a desired pull. Weight can be added or removed from the box. Adding weight on the pan can give more starting weight to the pan of the sled. The box gearing can be changed to move faster or slower, and the starting position of the box can be moved among a two feet area, affecting the distance of travel. The final adjustment is the placement of the trip, which applies the push down system to expend the full weight of the sled on to the pulling vehicle.
- Box– Contains the weight used to stop the vehicle and moves up the length of the sled rails progressively during the pull, driven off the front set of sled wheels.
- Weight Block– Most sleds use a “full block” that weighs 2,000 pounds and a “half block” weighs 1,000 pounds.
- Pan– Applies the force of the weight to the ground creating needed friction. The sled starts with only the front of the pan touching the ground. Bars attached to the bottom of the pan help make added friction at the end of the pull to stop pulling vehicle.
- Trip– Sits between the frame rails of the sled. As the box moves up the rails the trip is hit and starts the push-down system. The trip is adjustable.
- Push-Down System– Uses hydraulic cylinders to lift the back half of the sled in the air, allowing 100 percent of the sled’s weight on the pan.
- Kill Switch and Hook– The kill switch is always hooked first, allowing the sled operator to stop the engine of the attached vehicle in the event of an emergency or if the vehicle breaks free of the sled. The hook is used to connect the sled to the pulling vehicle and extends the weight of the sled to the vehicle’s hitch.
- Sled Operator– The driver of the sled. Has the responsibility of maintaining a controlled pull at all times. May pull kill switch if they feel something is out of control.
Levels of Competition
NTPA competition takes place on four levels: Super National, Grand National, Regional and State.
State Level– The grass roots of organized pulling, the first stepping stone to the other levels. Competition vehicles may be as powerful as higher levels. Some classes are not available at this level, while some are only available at this level.
Grand National– Considered to have the “best of the best” in pulling competition. Home to some of the top competitors and shows in the sport.
Regional Level– The beginning of the “National” pulling level. Many of the competitors and their vehicles are Grand and Super National in ability, but focus on this level due to the time commitment at the higher levels.
Super National– Highest level of competion and reserved for the very best events. Grand National competitors also follow this level of competition. 2019 NTPA Super National events: Budweiser Dairyland Super Nationals Tomah, Wisconsin; Lions Super Pull of the South Chapel Hill, Tennessee; and The National Tractor Pulling Champions Bowling Green
AC: An Allis Chalmers Tractor.
Allison: World War II vintage v-12 aircraft engine.1710 cu. In., approximately 2000 horsepower.
Arias: Racing engine brand common in Minis and TWD trucks.
Binder: International Tractor.
Boost: Air pressure generally by turbos or superchargers.
Bore & Stroke: Diameter of the cylinders and the distance the piston moves up and down the cylinder.
Box: Part of a weight transfer machine that carries and transfers the weight.
Brush Pull: Non-sanctioned pull.
Cam: The camshaft, a revolving engine part that moves the valves up and down.
Carb: The carburetor.
Chevy: A Chevrolet style engine. Also referring to the Chevrolet brand of cars and trucks.
Chevy Hemi: An engine that uses a Chevrolet style block with Hemi style heads. Arias is a common brand of this style engine.
Class: Type of vehicle and rules used to define that type of vehicle(s). Modified, Super Stock (Open or Diesel), Two Wheel Drive Truck, Mini Modified, Semi, Pro Stock, etc.
Clay: The most desirable track surface.
Cleats: The tread on a tractor tire.
Cubes: Cubic inch displacement of an engine.
Cut Tires: Trim the tire bar to a preferred angle for maximum bite.