Supermoto is a cross-over or evolution of motocross and road racing. Races are commonly held on road racing or medium sized go-kart tracks with an off-road section in the infield. Most supermoto race tracks are typically configured with approximately 70% tarmac and 30% dirt with small jumps but a dirt section is not required. The motorcycles used are frequently custom-created combinations of off-road motorcycles and road-racing rims/tires, known as 'supermotard' bikes. Riders also wear a combination of road race and offroad equipment, normally leathers and a motocross helmet and boots. Unlike normal motorcycle racing, the emphasis lies on slower speeds—typically less than 100 mph (160 km/h)—short and twisty tracks, where rider skill matters far more than outright machine performance.