Another Gearing Question: Old vs New

[Triskeliongirl]

My understanding is that a long cage ROAD derailleur (i.e. ultegra) will accomodate up to a 27 top gear, but not a 32. I have read you can sometimes stretch it to 28 with judicious shifting. To use with a 32 or 34, you need a long cage mountain derailleur (i.e. XT). I will say I find my bike is SLOWER even in the higher gears with the 11-34 than 12-27 casette, due to the large gaps between the gears. So, unless you really NEED a cog larger than 27, I would avoid the 11-34/11-32, etc. One option is to get the mountain derailleur, and BOTH cog sets to swap out as the terrain demands (that is what I did on one of my bikes). But, for this to work, you need to first set it up to work on the 11-32 or 34, since you have to be sure there is enough chain, and then you can swap casettes without issues. The shifiting will be not quite as crisp with the mountain vs road derailleur, and there is a small weight penalty, but my bike set up this way shifts fine. If I were gonna do this though, I'd get the 11-34 rather than the 11-32. If you want a really low gear, why not go all the way to 34?