The original runaway popularity of mountain bikes was mainly related to their greater comfort for casual cyclists, compared to the drop-handlebar, skinny-tire sport-touring bikes that had been the predominant adult style through the '70s and early '80s.
As mountain-bike racing became more organized, mountain bike designs started to morph into a more competition-oriented riding position, with longer top tubes, lower handlebars, narrower saddles, shorter wheelbases and more upright frame angles.
By the late '90s, this trend had gone so far that many casual cyclists were finding mountain bikes uncomfortable.
In response, the industry came up with comfort bikes. Typical comfort bikes resemble mountain bikes in wheel size, brake and gear equipment, but also differ in several ways:
- Shorter top tubes, for a more upright riding position
- Taller, often adjustable, handlebar stems, also for a more upright riding position
- Wider saddles with springs (and/or suspension seatposts)
- Smooth, wide tires for quiet and comfort on smooth surfaces
- Lower bottom brackets for easier mounting/dismounting
Comfort bikes are often seen as slower, stogier versions of hybrid bikes, and are targeted at pretty much the same market.
