The distance needed for a cycling event to be considered ultra-distance cycling or an endurance race is far more vague than in ultra running (any race longer than a marathon) or in ultra-triathlon (any race longer than an Ironman Triathlon). Any bike race longer than a century ride, which is , is sometimes considered to be ultra-distance cycling; however, such events are relatively common, so using a longer distance to define the category is more useful, such as any race that is longer than , or even a double century, .