With upright bikes, a race on flat terrain is much like a racing game with incredibly overly aggressive rubberband ai. If you're in the lead you have to work tw

With upright bikes, a race on flat terrain is much like a racing game with incredibly overly aggressive rubberband ai. If you're in the lead you have to work twice as hard as the person behind you, so you don't actually want to pull ahead until the very end. On hills this is much less true, as you're going slower and wind resistance is less of a factor. A recumbent bike greatly reduces wind resistance and makes it so that the person in second does 10% less work rather than 50% (numbers are made up). It's not that hills are easier, but that pulling ahead on flats would actually be viable.