This
is a picture of a typical Mountain Bike. These bikes are made for
the biker who likes to ride off-road with their bikes.
You may notice from the picture that the tires are fat and knobby. This provides the traction needed when riding in unfavorable conditions. One draw back to these tires is that on pavement, they produce a lot of drag, slowing down and producing more work for the rider.
The position of the handlebars also tend to put the weight of the rider more forward , relying less on the comfort of the seat. The seat, in fact, is rather small, being utilized more as a support than a comfort feature.
These bikes also usually some with full suspension systems. This helps provide riders with a smoother ride for their adventures.
Summary- Mountain Bikes are designed
for biking on rough terrains. They are not designed for long
distance riding of any kind. I am not saying you can not ride
distances on them, they are just not designed to provide comfort for
that. If you desire to ride dirt trails, then this is the type of
bike you would want to purchase.