The Dangerous First Mountain Bikes
The first "mountain bikers" were men on high wheelers (or penny farthings), that would ride them for adventure. Seeing how dangerous these vehicles were, the modern bike frame was invented. From here, the California cyclists that rode bikes for adventure kept iterating on which parts of the bike didn't work well for mountain biking. The final parts of the mountain bike were inspired by inventions from around the world.
from Fig. 1 by University of California
Key Facts In This Video
The pedals on high wheeler bicycles are directly connected to the front wheel. (0:13)
The modern bicycle style we know today was first called the safety bicycle. (0:37)
The Grateful Dead played at the Tour Del Mar bicycle race in the 1960s. (3:03)