When you ride a bicycle, the front derailleur moves the chain between the higher and lower gears. If your derailleur is poorly adjusted, this can cause your chain to rub and the gears to shift and drop accidentally. If you are planning to ride your bike and go on a steep climb, you can avoid these problems by perfectly adjusting and tuning your derailleur. You simply need to set limit screws and adjust the cable tension on a Shimano 105 derailleur.
Set your limit screws using your Phillips head screwdriver to ensure that the derailleur does not move or shift the chain off its rings.
Shift your chain to the lowest gear. This is the smallest chain ring found in front of your bike, and the largest one at the back.
Set your L-limit screw or the one closest to your frame, using your Phillips head screwdriver so that your derailleur cage is placed closest to your bike. This will position it two millimetres away from your smallest chain ring.
Shift your highest gear with your largest chain ring in front of the bike, while you shift the smallest in the back.
Set your H-limit screw to ensure that the derailleur cage plate is placed farthest from the frame, and about two millimetres away from your bike's largest chain ring.
Use your pliers to pull the derailleur's cable away from your bike to eliminate slack, and tighten your cable bolt with your 5-millimeter Allen key. This is located on your cable pinch bolt, right above your front derailleur.
Shift between the two or three chain rings of your derailleur. Fine-tine your derailleur by increasing its tension with your shifter cable adjustment if the chain does not quickly shift or if it rubs.