Adjusting the gears on a bicycle keeps the shifts accurate. Adjust the gears while on the fly without tools. Modern bicycles use barrel adjusters on the shifter pods and derailleurs to provide a way of maintaining efficient shifts. Adjust your bicycle's gears after locating the barrel adjustment on the shifter pods found on the handlebar. A few quick turns of the barrel should get your gears shifting smooth and keep you on your way.
Sit on the bicycle and begin pedalling. While pedalling, turn the barrel adjustment of the shifter pod--found where the cable enters the shifter--one-quarter turn counter-clockwise. Shift through the gears and listen for sloppy shifts, and feel for missed shifts on the gears.
Continue pedalling and turn the barrel adjustment on the right hand shifter pod one-quarter turn clockwise to tighten the shifting. Make these micro-adjustments while shifting the gears. Stop the adjustments when your gears shift to your desired settings. A smooth shifting gear change is when the chain quickly engages the next cassette gear on the rear cluster.
Pedal further and turn the left hand shifter pod barrel one-quarter turn to the right and shift the left side shifter. Look down to the chain rings--the large toothed circles around the pedals--and check the chain is moving over the rings. Turn one-quarter increments until the chain ring shifting is smooth and all rings are covered.
Continue your ride with the adjusted gears. Shift the left-hand shifter again to watch the chain move up and over the chain rings. Smooth shifting on the front gears manifests in near effortless changes. Listen for metal crunching noises; this is an indicator you need to continue the barrel adjustments. A smooth shifting set of front gears is quiet, with little metal noise.