Shimano 105 Rear Derailleur (Short Cage)
Details
Shimano's 105 Rear Derailleur is a sweet upgrade. Shifting is almost effortless thanks to its light-action spring and the top pulley stays a uniform distance from each sprocket so shifts resonate with the plunk of exact gear engagement. And, the wide outer-pivot design increases rigidity for precision shifts every time.
An important part of a rear derailleur's job is keeping the chain taut as you change gears. Chain-wrap capacity is a number that tells whether or not a derailleur will be able to do this on the drivetrain you plan to use it on. Calculate chain-wrap capacity with this formula: Chain-wrap capacity = (large chainring - small chainring) + (large rear cog - small rear cog). Example: 53/42 chainrings and a 12-23 cassette: (53 - 42 = 11) + (23 - 12 = 11) = 22-tooth chain-wrap capacity.