Pit bikes are frequently heavily customized with decorative add-ons and performance-enhancing parts. Many riders and mechanics bore-out or replace engines in order to increase displacement and therefore power output. Motocross be strong be brave be humble be badass posterHeavy duty suspension systems, are often a necessary addition, since the stock mini-bike suspension was designed for a small child. Wheel, brake, and tire upgrades are sometimes performed to improve handling. Pit bikes also have their own separate competitions held with classes generally corresponding to wheel size. This is a notable difference from Motocross and Supercross competition, where classes are separated by engine displacement. Pit bike racing is a relatively new niche of motocross, and as such, there is no official governing body similar to the AMA.