Altus is a Shimano brand bicycle component group, designed for use with urban sport and youth bikes. The group includes a pair of shifters, one mounted on either end of the handlebar, which allow the cyclist to change gears with the mere flick of a lever. The shifter on the right of the handlebar will change gears at the rear of the bike, while the shifter on the left will change those at the front. The two sets can be used in conjunction to create an array of gear combinations.
Use your thumb to push the lever atop the shifter forward, to shift from a smaller to a larger sprocket. While the sprocket may be larger, this will in fact result in an “lower” gear. Pedalling will be noticeably easier, although the bike will travel less distance per pedal stroke.
Squeeze the small lever beneath the shifter in toward the bike, by using your index finger, to shift from a larger to a smaller sprocket. Pedalling resistance will increase, as will the amount of distance the bike travels per pedal stroke.
Practice using both shift levers. Generally, an ideal gear is whatever feels right at the time. If pedalling is difficult, shift to an easier gear (top lever). If pedalling feels too easy, shift to a harder gear (bottom lever).
Push the lever atop the shifter forward, with your thumb, to shift from a small chain ring to a larger one. Moving the chain to a larger chain ring increases the gear ratio, therefore increasing both pedalling resistance and the amount of distance travelled per pedal stroke.
Shift from a larger chain ring to a smaller one, by using your index finger to squeeze the small lever beneath the shifter in toward the bike. Pedalling resistance will decrease, as will the amount of distance travelled per pedal stroke.
Use the front gears to make dramatic changes in pedalling resistance. While the rear gears are used to fine-tune pedalling resistance, front gear pedalling resistance differs greatly from one gear to another. Generally, use your easier front gear for hills and strong headwinds, and the larger gears for level terrain and tailwinds.
When first learning to shift gears, ride in a safe, traffic free area. This will allow you to focus a certain amount of attention on learning the gears without putting yourself in harm's way.