Shimano 105 represents Shimano's entry-level bicycle racing components. Each cassette is composed of a cluster of different sized sprockets (the newest cassettes will have as many as 10) with each sprocket providing a unique gear ratio. Over time, due to friction from the chain, the individual teeth on these sprockets grow dull and may cause the chain to skip. The removal of Shimano cassettes, including Shimano 105, requires a specially designed lockring removal tool.
Remove the wheel from the bicycle. For rear wheels, first shift the gears to the smallest rear sprocket and largest from chainring. This makes freeing the wheel from the drive chain easier.
Place the wheel between your legs with the cassette facing away from you.
Insert the Shimano lockring tool into the centre of the Shimano 105 cassette. Attach an adjustable wrench to the flats of the lockring tool. Hold the handle of the wrench with your right hand at approximately the 9 o'clock position.
Attach the chain portion of a chain whip to one of the cassette sprockets. Hold the handle of the chain whip in your left hand at approximately the 3 o'clock position.
Push the handles of the two tools together toward the ground. This will loosen the cassette lockring.
Unscrew the lockring fully and remove the cassette from the wheel.
Align the spline pattern on the interior of the new Shimano 105 cassette with the spline pattern on the freehub. The freehub is the rotating mechanism that held your old cassette. The two spline patterns must match, otherwise the cassette will not fit onto the freehub.
Use your fingers to screw the cassette lockring in place on the face of the cassette. Using your fingers initially will ensure that you don't cross-thread the lockring.
Insert the lockring tool into the centre of the cassette and once again attach your adjustable wrench to the flats of the lockring tool.
Turn the wrench and lockring tool clockwise to fully tighten the Shimano 105 cassette in place.
Place the wheel back on the bicycle. For rear wheels, first press the back of the smallest sprocket against the inside of the chain and then push the wheel in place inside the frame.