Originally Posted by
JimPz
The problem isn't that Ultegra rear has a 27 tooth limit & the cassette you will use, it's the 20 tooth difference on the fron chainrings. If you size a chain for the large front cog & large rear cog, in mana\y of the gears on the small ring the chain will sag a lot. If you size the chain to small cog/small chaing ring, you rip the derailleur off somewhere in the large chain ring. An ultegra rear der can't handle the chain wrap needed on a triple.
I have a pretty wide range front (52/42/24) and wide range rear (11-32 eight speed). I find that if I am on my smallest front chainring, I can't use my 11 or 12 tooth rear cogs on my cassette. But those gears are pretty cross chained, so I don't use them anyway. The issue is that the rear vintage XT derailleur (I think it is a M739?) won't take up all the slack.
Bottom line is that if you want every possible gear to be useable, then it matters. If you do not use the highly cross chained gears, you can run wider ranges than the derailleur can take up.
