Shimano RD-TY30 is a rear derailleur designed for 7-speed SIS systems. It has a total capacity of 34T, which means it can handle a wide range of gear combinations. The RD-TY30 is compatible with sprockets ranging from 14T to 28T, making it suitable for a variety of riding styles. It features a GS cage design, which provides increased chain wrap and stability, making it ideal for use with mountain bikes or other applications where chain retention is important. The RD-TY30 is also compatible with Shimano's SIS index shifting system, which provides precise and reliable shifting performance.