The hub is a Sachs Torpedo 2 speed automatic. This design is different from a kickback hub. It quietly slips into high gear around a certain cadence and pedaling pressure. It actually works pretty well, at least this one which is only getting light duty use. They were introduced in 1973 and are sometimes seen on old Schwinns.

---

When 26" bikes upgraded in the late 70s to alloy rims and Snakebelly tires, they shed many pounds over the old combination of chrome steel rims and Uniroyal tires. When you consider how much better the alloy brake surfaces worked, and the improved grip of the tires, this may arguably have been the biggest upgrade ever on mountain bikes.