The Mountain Bike exists in the game as one of only three bicycles in GTA San Andreas, designed more for speed and power rather than nimbleness and ability to execute bicycle tricks. Indeed, the Mountain Bike is the most capable in hill climbing; even if an incline is significantly steep, due to the fact that it has multiple gears (while other bikes only have one). The player can tap the acceleration command while on a Mountain Bike can climb its slope with less effort than other bicycles. As mentioned, the Mountain Bike is less tailored for stunting, and only allows the player to execute moderately high bunny hops when the player can hop higher on a BMX.
Because of its implied off-road capabilities, the Mountain Bike is more commonly found ridden by leisure bikers in forested or hilly rural areas, including northern Whetstone (particularly around Mount Chiliad) and Missionary Hill.
The mountain bike returns its way into GTA V. It seems larger than GTA: San Andreas version. It's also featuring fenders now.
The Mountain Bike has a glitch that only works in the original PlayStation 2 version of Grand Theft Auto: San Andreas. While reversing, rapidly tap the accelerate button (normally X), and CJ's body will twist ridiculously out of proportion.