Why does my bicycle chain fall off?

Author Name Answered by: Mark, An Expert in the Bike Maintenance Facts Category

One of the biggest frustrations of cycling is when your chain falls off the bike. This can really throw a hitch in your plans and deflate the true joy found in cycling. The chain never falls off at a convenient point in your trip. This guide will teach you how to take care of the situation to get you up and riding again as soon as possible. Furthermore, it will teach you how to take preventative maintenance measures to ensure your chain doesn't fall off any more.

The chain falls off a bicycle for any number of reasons. The chain tension could be too loose. The bike could be in an inefficient gear. Or, there could be something at fault in the derailleurs or the chain. When your chain falls off there are quick fixes to get you back and riding, and then there are some deeper diagnostics to keep you riding fast.

When your chain falls off: a quick fix.

The first thing to do when your chain falls off is to immediately stop pedaling. If you keep pedaling, you could jam the chain in between the wheel and your bike frame and even cause permanent damage. Once you have stopped pedaling, stop the bike. Put down your kickstand or lean your bike against a wall, post or tree. Now you are prepared to put your chain back on the bike. If your chain has fallen off, it is likely it will be difficult to move the chain without decreasing the tension on the rear derailleur.

You will want to use your left hand to push the rear derailleur cage (the long part with two wheels the chain winds between at the rear of your bike) forward to slacken the tension in the chain. This will allow you to use your right hand to place the chain back onto the correct sprocket or chain ring. Now, lift up your rear wheel from the ground and turn the pedal with your hand to ensure that the chain is back on and powering the rear wheel. If the rear wheel is moving, congratulations! You have successfully put your chain back on.

Now it is not always reasonable to investigate the in-depth reason for why your chain fell off. So it make sense to continue on your way until you find yourself with an hour or two to really diagnose the problem behind why the chain falls off your bike. Only continue reading this repair guide for when your chain falls off, if you your chain falls off repeatedly during a short ride.

To diagnose the ongoing problem you will need to put your bike in a stand, in a tree, tie it so it hangs in your garage, or worst case place it upside down. This permits you to access the drivetrain system (shifters, gears, cranks, pedals, chain, and derailleurs) without having to move the bike. The first thing you want to do is to chain through all the gears of your bike while listening for any clicking or abnormal noises that might indicate if there is a loose or damaged link in the chain. If you do not notice any irregularities in the chain, then shift the bike into the lowest possible gears.

Move behind the rear wheel follow the chain line as it moves from the rear sprocket through the derailleur and up through the front derailleur and around the crank. If in this lowest gear the rear derailleur is not in alignment (ie the chain is being pushed left or right so it is not nice straight line) this is why your chain falls off? You will want to adjust the rear derailleur screws (one may be labeled H or L for high or low) to bring the chain into alignment with the lowest gear. Now shift to the highest gear and continue the same steps. If in any gear, your derailleurs are rubbing or pulling your chain out of alignment from that gear, that is why your chain falls off! You can fix that by adjusting the control screws on the rear and front derailleurs so your chain falls off no more!

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