Here's a description from Wikipedia:
Truck and Tractor pulling, also known as power pulling, is a motorsport competition, popular in United States, Europe (especially in the Netherlands, Denmark and Germany), Australia and Brazil, and New Zealand which requires modified tractors to pull a heavy sled along a 35 foot wide, 330 foot long track, with the winner being the tractor that pulls the sled the farthest. The sport is known as the world's most powerful motorsport, due to the multi-engined modified tractor pullers.
All tractors in their respective classes pull a set weight in the sled. When a tractor gets to the end of the 100 metre track, this is known as a "full pull". When more than one tractor completes the course, more weight is added to the sled, and those competitors that moved past 300 feet will compete in a pull-off; the winner is the one who can pull the sled the farthest.
The sled is known as a weight transfer sled. This means that as it is pulled down the track, the weight is transferred (linked with gears to the sled’s wheels) from over the rear axles and towards the front of the sled. In front of the rear wheels, there is a "pan". This is essentially a metal plate and as the weight moves over this the resistance builds. The farther the tractor pulls the sled, the more difficult it gets.
The most powerful tractors, such as those in the 4.5 modified class in Europe, can produce over 10,000 horsepower.
This is the sled they have to pull.
Something went wrong, maybe the wheel.
This tractor was driven by a woman with a pink helmet.
Finally a short video:
I'm not sure if I'll go again but at least I've seen something new.