This " adaptor claw" is held on mainly by the rear axle nut, or the quick-release skewer. (Note on many older or less expensive bicycles, the hanger is not part of the frame, but is a separate part, which comes with the derailer. This is because the part of the derailer that usually gets bumped is the strongest part, the parallelogram linkage that moves the cage back and forth. When the derailer gets biffed, it is not usually the derailer itself that bends, but rather the hanger, the tab of the frame dropout that the derailer attaches to. In some cases, this can render a frame a total loss. If you are truly unfortunate, the pull of the spokes on the derailer can tug it backwards so forcefully that the dropout (the frame part that the rear axle and derailer attach to) will be bent very sharply backward, or even broken. If you are less lucky, it takes a few spokes with it, and can easily ruin your rear wheel. In some cases, it will actually go into the spokes of the rear wheel while it is turning. When a rear derailer gets whacked, it bends inward, toward the spokes. The rear derailer is the most fragile and exposed part of a bicycle, and they are always getting bonked. Rear Derailer Adjustment Before You Try To Adjust A Rear Derailer, Make Sure It Isn't Bent!īefore you try to adjust your rear derailer, you should really make sure it isn't bent. It has very little to do with the quality of the derailer. This is the major reason that modern derailer gear systems work better than older ones. Newer sprockets usually have specially shaped teeth, and ramps on their sides to make shifting smoother without the protruding rivet pins.
These chains fit the 3.5mm space between the sprockets of 5-and 6-speed freewheels. Up through the 1970s, chains had protruding rivet pins that snagged on the sides of the teeth. Eventually, it gets snagged on the sides of the teeth of the larger sprocket, and yanked up and away. The chain is forced to rub against the side of the larger sprocket next to the one it is riding on. When the chain is being shifted from a smaller sprocket to a larger one, it is slightly different. It then falls off of the sprocket and lands on the next one in line. When the angle becomes sharp enough, the chain can no longer mesh with the sprocket. The rear derailer looks more complicated, but the only additional complication is that the rear derailer also contains the arm with the spring-loaded pulleys, that takes up the slack as the chain goes to smaller sprockets.īoth derailers work by pushing the chain sideways, so that it runs at an angle onto the sprocket, instead of straight. As it does, it pushes the chain sideways until it can't run on the chainwheel it has been riding on, then the chain falls off and lands on the chainwheel closest to its new location. The front derailer simply consists of a cage made of sheet metal that can move back and forth from side to side. Gear shifting is accomplished by leading the chain from one sprocket to another.ĭerailers look complicated, but they are actually very simple, brute-force devices. Most manufacturers recommend you replace your chain once the gap between the rollers has grown (due to wear) by 0.75%.įollow our guide to see whether your chain is still in fighting shape.Most modern bicycles use derailer (or dérailleur, if you prefer the French spelling) gearing systems. However, change it before its too degraded and you’ll prolonge the life of the other bits of your drivetrain. Let your chain get too worn and your shifting will suffer, along with the state of your chainrings, cassette and jockey wheels.