The Pro Stock Semi (PSS) division are the heavyweights of tractor pulling! Weighing in at 18,500 lbs, these behemoths overshadow everything else on the pulling track and for that matter, anything else in motorsports! When they come thundering down the track, the heavier the load gets, the harder they pull. Sometimes you wonder if they’ll ever stop. With many competitors running multiple turbochargers, the PSS class has become known for its power and thrilling performances by each competitor.