The “fat tire”; that is one having a cross-sectional diameter of 2″ or more, is what later fired the imagination of so many to how far a bicycle could go off road. It gave the mountain bike its extreme degree of ruggedness. Bicycle fat tires, also known as balloon tires, came into existence in the early 1930s, possibly late 1920s. Whether the first balloon-tire bike to be ridden off road was American or European (possibly German), I don’t know. Semperit had a 26 x 2″ tire in the early 1930s. Arnold, Schwinn & Co. of Chicago was introduced to such a tire in Germany in 1932 and popularized the size in America.