Shimano Ultegra RD-6500 Derailleur

The Shimano Ultegra RD-6500 Short Cage (SS) is a classic 9-speed rear derailleur. When building or maintaining a bike with this component, here are the top 5 compatibility points you need to consider:

1. Number of Speeds (Shifters): The RD-6500 is designed explicitly for 9-speed drivetrains. You must use it with 9-speed shifters (e.g., Shimano ST-6500, ST-5500, or any other Shimano 9-speed road shifter). Using it with shifters for a different number of speeds will not work correctly, as the cable pull ratio is designed for a 9-speed cassette.
2. Cassette Tooth Range (Largest Cog): The official maximum largest cog size for the RD-6500 Short Cage is 27 teeth (27T). Some users have reported successfully running a 28T cassette with careful B-screw adjustment, but going beyond that is not recommended. It may result in poor shifting, especially on the larger cogs.
3. Total Drivetrain Capacity (Chain Wrap): This is a critical point. The short-cage RD-6500 has a total capacity of 29 teeth (29T). This number is calculated by adding the difference in teeth between your largest and smallest front chainrings and the difference in teeth between your most significant and smallest cassette cogs.
   • Calculation: (Largest Chainring – Smallest Chainring) + (Largest Cog – Smallest Cog) $\le$ 29T.
   • Exceeding this capacity will lead to a slack chain in the small-small gear combination and a potentially stretched-out or broken derailleur in the large-large combination.
4. Chain Compatibility: The RD-6500 is designed to work with a 9-speed super-narrow chain, such as a Shimano CN-HG92, CN-HG73, Connex, KMC, or SRAM 9-Speed. While some older 8-speed chains might fit, the shifting performance will be compromised. A 10-speed or 11-speed chain is too narrow and is not compatible.
5. Front Derailleur Compatibility: For optimal performance, the RD-6500 is best paired with a Shimano 9-speed road front derailleur (like the Ultegra FD-6500). While most Shimano road front derailleurs from that era will work together, using a front derailleur from a different brand or a different number of speeds may lead to a mismatched pull ratio, affecting shift quality.