The front derailleur and rear derailleur serve as the transmission on a bike. These two components, controlled by the shifters, move the chain into different gears on the cassette and chain-rings/crank . Derailleurs and shifters are critical components that should be checked for wear and serviced regularly. If a cable adjustment doesn’t solve shifting problems, worn driveline components such as the chain, derailleur, and cassette may be the cause.  Make sure the derailleur and shifters you purchase have the same speed cassette or amount of gears as your exsisting bike. It is also a good rule of thumb to use shifters and derailleurs by the same manufacturer (Shimano shifters with shimano derailleurs) to avoid any compatability issues. Unsure of what your bike needs? Contact our experts to make sure you purchase the right parts.