For men's international championship events, the downhill course is typically 2.4 to 5 km (1.5 to 3 mi) long, with a vertical descent of up to 1,000 m (3,281 ft) and terrain of a steepness and difficulty appropriate to the skill and endurance of the competitors. For women the course is 1.6 to 2.5 km (1 to 1.5 mi) long, with a maximum vertical drop of 700 m (2,297 ft). Courses are characterized not in terms of length but of time—e.g., a two-minute downhill. The average winning speed of downhill events is 64 to 80 km/hr (40 to 50 mph). Speeds over 200 km/hr (100 mph) are achieved on special short courses, but these events are not rated as official downhill races. (See speed skiing.) During straighter portions of a course, skiers go into a tuck position in order to be more aerodynamic and thus increase their speed. A unique, curved ski pole, which allows for a tighter tuck, is used in the downhill event. Since the turn of the 21st century, professional and recreational skiers alike have made ever greater use of parabolic skis, also called shaped skis, which have wider tips and tails and shorter lengths than conventional skis. The shorter length allows for better control and style on difficult terrain. Parabolic skis also provide greater stability during turns.