"why would they design two different types of valves? Thanks" There isn't a "they" involved here. Presta valves were standard in European countries while Schrader valves were standard in the US. I first saw them in the 1970s while working in a bike shop as we imported bicycles from Italy and France. They came with presta valves. Most of the racers I knew also used them on high pressure.narrow, sew-up tires. It was easier to pump them up with the frame pumps available at that time as you didn't have to also overcome the pressure required to open the spring loaded Schrader valve. I've used them exclusively since then and never broke a valve pumping up a tube that was on a rim drilled for the Schrader valve. I did install the "valve saver" spacer on some wheels and always carry a valve adapter.