This is probably one of the most important visual representations of the “mathmagical” concept of energy conservation in trail building with bikes in mind that I have made. It’s not as much about the graph as it is about the concept of the conservation of energy and how we can use it to enhance rider experiences using gravity to control speeds as we wish. It’s not magic, but a depiction of, as my “trailscendentalist” friend’s email handle read “mathmagical” reality.
Consider the graph above and the grade and erosion graph at the grades page. Also consider that water will probably move slower, I haven’t figured out just how much slower as fluid dynamics is no joke very complicated, but suffice to say, water is very powerful and will carry trails away fast. It doesn’t take much. The point here though is that we can use grades to control speeds, and lift people off the ground too if we want. Also note that this is coasting, with pedaling riders can go faster. Take home message: we don’t need much grade to go fast, or too fast without user conflict, so why not keep them “mellow” for climbing sake, not to mention erosion, and user conflict and safety sake?
I’ll follow up with more later, but this is what I will share for now. Note that the graph does not account for wind drag, but depending on the density of the air and the speed of the wind, the drag forces are typically negligible at most bike speeds experienced on trails. Direct headwinds and tailwinds are likely to have the most significant impact on final velocities. Also see: 26 vs 27.5 vs 29 down hills