The most rugged bicycles are mountain bikes. They are meant to be ridden on dirt tracks, on steep and pebbled inclines and across hairpin bends. Very rarely the cyclists drive on paved mountain roads. Most cyclists love to use their mountain bike on narrow, unpaved trails. This results in greater wear and tear, forcing the cycle manufacturers to come up with sturdier bikes.
The mountain bikes therefore have fatter and bigger tires made of stronger rubber. This gives the cyclist better traction, and also allows the bicycle to run freely on pebbled tracks or to roll smoothly over obstacles.
Another important feature of mountain bikes is the suspension. All mountain bikes come with strong suspension. Some recent bikes have both front and rear suspensions to help the cyclist withstand heavier thuds.
Based on the kind of suspension they have, mountain bikes are classified as hard tails, soft tails, fully rigid and dual suspension bikes. The hard tails have a front suspension fork, the rigid types have a rigid fork; soft tails have rear suspension that rests on the frame than pivots; and dual or full suspension bikes have a front suspension fork and rear suspension. They also have a rear shock absorber as well as a linkage.
Cross-country mountain bikes are generally made of resilient and light weight material. They can weigh as less as 20 pounds; the heaviest being around 40 pounds. Enduro or all-mountain bikes are generally heavier than cross country bikes. Their weights range from 30-35 pounds. They have better suspensions that work well while climbing uphill or steering over hairpin bends.
The free ride mountain bikes are built of stronger and heavier materials. They are designed for easier pedaling than any other downhill bike. They can be easily maneuvered around dangerous obstacles and steep turns. However, they are not as efficient as cross country bikes due to their weight. They weigh between 40-50 pounds.
The Downhill Mountain bikes are not as strong as free ride bikes but they are most suitable for riding on downhill tracks and race courses. They have better traction than most mountain bikes.
The trial bikes don’t have suspension and are usually meant for short distances. They lack a proper seat or a vestigial pad and are lighter than most bikes -- weighing around 15-20 pounds.
Dirt Jumping, Urban and Street Mountain Bikes fall in between the trial bikes and mountain bikes. They are very strong and have one to nine gears with a chain guide for both front and rear gears.