I do try to keep up, but I need advice on this one. I want to upgrade a bike from a single chainring to a double (or maybe triple). It has a 7-speed cassette, and I'm in no hurry to replace the rear hub, so it's likely to stay that way. My question is: should I look specifically for a 7 or 8-speed front derailleur on the grounds that a 10-speed one will have a narrow cage for narrow 10-speed chains? Or will an 8-speed chain run through it fine? Either way, reccommendations? The bike's running 105 and equivalentish components elsewhere, so that's the sort of level I'm afer.