Early mountain bike were relatively a limited evolution of touring and cyclo-cross bikes of the same era with few modifications mainly:
26” wheels with bigger knobby tires
Cantilever brakes adopted from cyclo-cross and touring bikes
Triple cranksets with granny gear imported from touring bikes
The frames were an evolution from touring frames with relaxed angles and significantly longer wheel base
Only in the late 1990’s the MTB geometry evolved with significantly increasing front fork travel, then rear suspensions and disk brakes, and during the 2000’s the bigger wheels (650B – renamed 27.5 and 700C renamed 29”) were introduced. When mountain bikes, especially enduro and downhill models started more and more to look like motorcycles without an engine to address more and more extreme terrain, a gap was created for people that enjoy riding off road but whose focus is more on covering large distances on non-paved roads and wide trails.
That gap was filled by gravel bikes, but when looking at it closer and ignoring for a second the high tech of carbon frames and hydraulic disk brakes, aren’t gravel bike more or less a re-incarnation of the early Mountain Bikes?
Based on that question, and upon a request from a client, I embarked on turning a 1995 Specialized RockHopper into a gravel bike.
Original 1995 Specialized RockHopper (Google Images)