If you've ever ridden or heard a single cylinder motorcycle, you understand why they are called "thumpers". That big piston doesn't love high rpms. Rather, it prefers to push out tons of torque at the bottom end of the tachometer. This BMW was one of many of the single cylinder choices available in the 50's.
"They were pinkish things about five feet long; with crustaceous bodies bearing vast pairs of dorsal fins or membraneous wings and several sets of articulated limbs, and with a sort of convoluted ellipsoid, covered with multitudes of very short antennae, where a head would ordinarily be." -- H. P. Lovecraft, "The Whisperer in Darkness"