In this tutorial, we learn how to adjust a rear derailleur on a mountain bike. First, get on the bike and start to ride it like normal, except have it mounted into one place. Then, shift the front derailleur into middle gear and the rear derailleur to the smallest gear. After this, shift back gear up one gear while pedaling. If it hesitates going up to the next gear turn the barrel adjuster counterclockwise until it moves smoothly into gears. Do this again through each step until it shifts smoothly through all the gears. When finished, you will be ready to ride your bike out and enjoy it!