Ski conversion apparatus for converting a cross-country ski to a downhill contoured ski. A tip shape modifier is attached to the tip section of the ski by expandable wedge assemblies and mating dovetails. A tail shape modifier is attached to the tail section of the ski by longitudinal dovetails and a detachable connection. The tip shape and tail shape modifiers are carried by the cross-country skier and attached to the cross-country skis when necessary to ski downhill in deep snow.