By gearing down our vehicle, we could crawl up some pretty steep roads at speeds of less than 10 mph. While laboring uphill with about one hp of power at our disposal, we'd often envy the cars and trucks that passed us with seeming ease, their 200-plus hp internal combustion engines making the climb seem effortless. But as altitudes increased, we could sometimes hear how the passing vehicles seemed to be laboring harder to pull the grade. This wasn't our imagination; at 11,000 feet, near the top of our highest climb in Colorado, a gas or diesel-powered vehicle produces about a third less power than at sea level. We felt the physical effects of the thinner air as we attacked the pedals, but our electric motor churned out the exact same wattage as every other day.