Shape is wide open. Streamlining behind the rider is wide open until you hit the rear axle. You can do anything you want as long as no part is more than 40" above the ground, can't be more than 8" past the tire, the section past the axle can't be below the top of the rim of the rear tire, (violated by many) and 180 degrees of wheel must show. Since streamlining is defined as forward of the rider, this works for open class also.
