Shimano's Tiagra Rear Derailleur provides precise gear changes. Everything you need in a derailleur is here: smooth 11-tooth pulleys, a light-action spring and a wide outer-pivot design that 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.
Largest cog this derailleur can handle: 27 tooth
The Shimano Tiagra Rear Derailleur is compatible with 7, 8, and 9 speed cassettes.