In mountain biking, friction is encountered on the bike in a few very important areas. These are the wheel bearings, drivetrain, and brakes. The wheel bearings, if properly maintained, should produce a very inefficient amount of friction and it usually goes unnoticed. The drivetrain on a mountain bike consists of the chain, gears, and shifting mechanisms, and it produces about an 1.5% energy efficiency drop. This performance from the drivetrain can only be achieved if the proper care is given to the different parts involved, and it is regularly is lubricated. Finally we come to the biggest area of friction found on the mountain bike, the brakes. In the case of brakes, friction is our friend, and actually prevents accidents and deaths when riding in the mountains. There are several types of brakes on the market for mountain bikes, but they all have one purpose, and that is to slow the bike down using friction.