Originally Posted by
xwhaloo
Thanks - What is the biggest cassette that will work with a standard Shimano Dura-Ace rear derailleur (7800)? If I can fit a 30 on the back, I wouldn't need to convert my other bike (the trek 2300) to a compact for this ride. To fit the 13-34 cassette (do you have one in a 10 speed that would work with Dura Ace??) do I just need to get a long cage derailleur?
I can speak a little to using 9-speed (DA and Ultegra) rear derailleurs with big cogs. For a ride with long uphill sections (Virginia's Skyline Drive), I replaced my Ultegra 12-27 with a SRAM 12-32 cassette. Derailluer is a short cage DA 9 speed and I used the same chain. The derailleur was able to shift into the big cog from the small chainring (39x32). This gave me about 10rpm/mph, which worked out really well for the long uphill grades and is almost as low a gear as a road triple (30x27). I also used it for a hilly (~6,000 ft climbing) century.
You have to remember to AVOID cross-chaining, especially the big-big combination (52x32). While I could shift into big-big on the workstand, the derailleur was out of capacity and I risked damaging the drive train if it was under load. While I have not tried it, I suspect a long-cage (U9 triple) derailleur and a longer chain would work. I've read other posts on bikeforums (check the touring and roadie sections) where people have used MTB rear derailleurs that have no problem with an 11-32 or 11-34 cog set.