Keep your bike's gears shifting smoothly by learning how to adjust a rear derailleur. The rear derailleur guides the bike's chain from one sprocket on the back freewheel to the next. The smaller the sprocket, the higher the gear and the faster your bike will go. When you adjust your rear derailleur, there are a few things to look out for.
To adjust a rear derailleur, you will need:
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Your bicycle
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Phillips head screwdriver
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Check to make sure the derailleur is not bent. The rear derailleur is a fragile piece of equipment and is also one of the most exposed elements on your bike. You can bend the derailleur by laying the bike down on its right side or by wacking it against a pole or fence when you lock the bike. If the derailleur is bent, your best bet is to take it your local bike mechanic, who will have a special tool used to unbend it. Trying to unbend it with your bare hands may cause further damage.
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Tighten the high gear screw. Once you've determined that your derailleur is not bent, adjust the high gear screw, usually marked with an "H." Turn the screw until it is so tight that you cannot shift into high gear.
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Loosen the high gear screw, one half turn at a time. Slowly loosen the screw until you can shift into high gear.
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Tighten the low gear screw, which is usually marked with an "L," until you cannot shift into the lowest gear. Remember, the lowest gear is the largest spocket on the freewheel and the highest gear is the smallest.
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One half turn at a time, loosen the low gear screw until you are once again able to shift to the lowest gear.
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If you bike is still unable to shift properly after you've adjusted the derailleur, it may be time for a new freewheel. Inspect the teeth of the sprockets. If they are worn down, head to your bike shop and pick up a new freewheel for the back. You should also invest in a new chain at the same time.
