Another inconsistence response:
My road bike runs a compact crank (Shimano Ultegra triple 30/42/48 ). The bike was bought 2nd hand & originally was set up for cyclocross ( example of Cyclocross : http://www.cyclingnews.com/cross.php?id ... ry-petange
) which is why it runs such small cogs (lowish, close ratio) up front.
As I was looking at mostly road work involving generally higher speeds I did the ring at various LBS for a larger chainwheel upfront, from 48t to 50t (or maybe 53t). I was told that simply going to a larger chainwheel I may have to look at getting a new front derailleur to accommodate the new larger chainwheel diameter & ensure smoother, effective changing.
But I’m not convinced.
I haven’t changed the cogs yet as there is still more kays left in the drivetrain and the current gearing isn’t too bad (spinning is good isn’t it?), so I’ll make the ratio change when the whole drivetrain comes up for renewal. As it’s Ultegra throughout it’s not going to be cheap.
If I then try it & the existing front derailleur does work well with the new cogs, then I’ll change.
Sometimes you have take a punt & be your own expert, by making your own mistakes.
FYI, a pic of my roadbike, just after I bought it. The green tyres Michelin Cyclocross Sprint 700x30C were replaced with Vittoria Rubinos 700x23.