(Photo: AP) After World War II, motorcycle racers began seeking new thrills by adding right- and left-hand curves and bumps to the standard oval track. Today, this all-terrain thriller is the only event that is held at both the summer and winter X Games. Size Of Sport: Data not available Most Excellent: At the 2002 Gravity Games in Cleveland, Travis Pastrana and Mike Metzger became the first riders ever to land a backflip, widely considered the sport's coolest and most dangerous trick. Talk And Tricks: Bar Hop: When the rider shoots his legs through his arms, which are holding onto the handlebars Cliffhanger: When a rider hooks his feet and rides no-handed Saran Wrap: Taking one hand off the bars while passing one foot up and over Sources: Sporting Goods Manufacturers Association, EXPN.com