Originally Posted by
Barrettscv
Shifters and derailleurs are the first items people look for when determining group. Crankset and cassette are considered next. Brakes, hubs, bottom bracket and headset are usually independent of the other components, but sometimes are the same make and model.
Components don't need to match. 10 speed Shimano are compatible regardless of Dura Ace, Ultegra, 105 or Tiagra brand. Sram and Shimano can be mixed to some extent. Cranksets can be mixed and matched.
I would add a some caveats. Shimano Dynasys shifters and derailers (mountain bike components) will only work within the Dynasys system. A Dynasys derailer will not work with Shimano STI road components. Shimano road front derailers will work with STI road shifters and Shimano mountain bike front derailers (old stock before 2012) will work with Shimano mountain bike shifters but Shimano road front derailers may not work with Shimano mountain shifters. Sometimes they can be made to work together but it's hit or miss. Dynasys doesn't work outside the platform.
Sram X shifters and rear derailers will work together but won't work with other shifters. Sram front derailers will work with Shimano mountain bike shifters.
Finally, Shimano has changed the pull ratio on their road brakes. 2013 STI may not work with other brakes or with older Shimano components.
You have to be careful what you try and mix and match now. Stupid Shimano!