Originally Posted by
ramuji
If I go with Ultegra 6600 crankset/rear hub/rear derailleur, are 8-9-10 speed cassettes from the past 20 years backwards compatible with 6600 or do I need to look specifically for a 6600 cassette?
The FH-6600 has a steel freehub with standard splines and will accept most common Shimano compatible cassettes. Use a spacer behind the cassette for those that calls for it.
Even the 7800 cassettes will fit on the FH-6600.
It just doesn't work the other way around. The FH-7800 uses an alloy freehub body with taller splines, so the CS-7800 is required.
Correction, the 6600 cassette in most combos with a 11t or 12t smallest sprocket should work with FH-7800. Also the 5600 cassettes should work.