Originally Posted by
DougG
Well, this saves me from starting a thread. I'm also a Sequoia owner who's thinking of a new bike with a compact/triple option. I did upgrade my Sequoia a couple years ago, trashing the Sora pieces and going to a 105 triple with 12-27 cassette. So I know what that feels like.
The bike I've got my eye on is a Synapse Carbon 5 that is available with the same 105 setup that I'm now using, or with a compact 54/30 and 12-25 cassette. From reading the posts here, I'm now thinking of going with the double, but maybe installing an almost-new 105 12-27 cassette that I happen to have. I hope this can be done without derailleur or chain-length issues.
In any case, I've almost never been in the 30/27 gear combo on the steepest hills that I'm likely to encounter, so the 34/27 low gear should be sufficient. Thanks for the excellent discussion -- this section always has good info without some of the stuff that goes on elsewhere.
I just got a new bike with a 50/34 compact crank, that came with a 12-25 cassette (105). I had the shop change the cassette out for the 12-27, just to get a lower gear. The only issue is that a short-cage 105 RD will not support the total tooth-range of 16+15=31. So basically I need to stay away from the two extremes of the 50/27 and the 34/12, which don't make sense, anyway.
A long-cage 105 RD will of course handle all of the above gear combinations, but they are normally only used with triple cranks.
For what it's worth, the new 2010 Ultegra RD has a somewhat better total tooth-range (I can't recall the correct term to use for this, but it is the sum of the tooth differences of the chain-rings, plus the cassette.)
The 2010 Ultegra RD will support all gear combinations of a 50/34 compact crank, and the 11-28 Ultegra cassette (and therefore also works with the 12-27 105 cassette).