I've been commuting on a mountain bike these past 3 years. Now I want to get into road bike racing. Is it worth saving up money over a few months for a carbon fibre bike? Or should I just go and buy a good quality aluminum bike tomorrow?
There are two answers to this question:
- (Money no object)
Go out and buy yourself a carbon frame with all the trimmings. If you want to race, there is no better hardware option.
- (Money important)
you say you haven't even begun to race yet. How do you know you'll like it? How do you know you'll be any good? If you go down a carbon route, you're talking about a serious investment which could possibly end up gathering dust in your garage. Frankly, you should consider a steel bike at this stage. When you're losing races because of the weight of the bike, then it's time to upgrade.
Be careful with something like bike racing, it will eat up your every last penny if you're not careful.
A good rule of thumb is: if you spend less than $2000 get aluminium instead of carbon as you'll get more bang for your buck. A good quality aluminium frame with some nicer wheels will generally give a better/faster ride than an entry-level carbon bike (bought just for the sake of having carbon!).
The slight performance/comfort benefits of a more expensive carbon bike are of no concern to an entry-level racer. The most gains for you will simply come from more regular and longer rides.
For a novice racer, frame material doesn't matter. As for the groupset, Tiagra's fine. The differences in Shimano's groupsets is mainly weight, plus so durability. I'm speaking from experience here- I would swear that my Tiagra equipped cross bike shifts better than my Dura-Ace road bike!