Sled pulling is considered one of the world's most powerful motorsports due to the use of extremely high performance engines and, in some cases, use of multiple engines staged in a single vehicle. It is not unusual for a Modified (class) tractor to run multiple 1000+ hp engines, and a competition truck to run a 2,000+ hp diesel powerplant. Anyone with a truck may participate in sled pulling, as there is a tiered class system that accommodates various applications and performance levels.
In many organized pulls, classes are categorized by the maximum turbocharger size allowed for that class. For example, the 2.6" class is restricted to trucks with a maximum 2.6 inch turbocharger inducer. There are classes for stock/street legal trucks, heavily modified trucks, and many classes between. 4 wheel drive trucks generally hang removable weights on the front of the vehicle to improve traction of the front tires.
How Sled Pulling Works
Trucks are hitched to a dynamic weight transfer vehicle called a sledge. Participants generally spool their turbos before being signaled to start their pull. The sled has wheels in the rear and a sliding weight that initially rests over these wheels. As the sled travels forward, the transfer weight travels toward the front of the sled, increasing the friction force of the sled onto the track and making it more difficult for trucks to overcome the frictional force between the sled and the track. Trucks pull until they can no longer overcome the increasing force of the sled and are abruptly stopped. The 300 foot mark is typically considered a "full pull", although track distances are often considerably longer.
Sled Pulling Techniques
While each driver has their own unique approach to sled pulling, there are 2 major techniques. One technique is to leave the starting line hard and accelerate as quickly as possible before the weight of the sled starts overpowering the vehicle. The principle here is that the momentum of a fast moving truck will keep the sled moving longer. The second technique is the slow and steady approach. Leave the line strong, but conservatively in order to maintain traction, and relying on torque and traction to keep the sled moving as the force is increased. One might argue that the best sled pulling technique is a combination of both principles and depends on a variety of variables.