About six months ago I bought my first road bike, an old Peugeot Nice 12 speed. I got hooked an have already bought a second, a 2009 Bianchi Via Nirone 7 (18 speed).
Anyway, I'm looking to upgrade some parts on the Bianchi, mainly the crankset, and I have a few questions. I'm looking at parts on ebay and see that they are designated as 9 speed, 10 speed, etc. Is there really a need to stick with the correct speed for the cassette I have? If so, why? I'd think that a 9 speed chrankset's cogs would be the same as a 10 speed's, no? I see a ton of 10 speed stuff listed, not so much for the 9 speed that I have.
for the most part you can get away with using a 10speed crankset with an othewise 9 speed drive train. There is a difference in the gap between chainrings on 9 and 10 speed systems...the gap is narrower on 10speed system to accommodate the narrower chain...the chain is narrower to accommodate the increase number of cogs on the rear hub.
Between 9 and 10 speed drivetrains the gap is not normally significant enough to cause a problem with front shifting. If you were using a 7 speed crankset with a 10 speed chain you might find the chain falls and jams between the chainrings. This can happen with mixing 8 and 10 speed components and "could" potentially happen when mixing 9 and 10 speed components as well but you more than likely will not have any problems.