I currently have a bike with full Tiagra groupset with a compact 34/50 at the front and 12-28 on the back.
Next year I will be using the bike for racing and I was looking at changing either the chain ring from the 34 to 39, and maybe even the 50 to 53. Or else I have the other option of changing the 12-28 to maybe 11-25 or 11-23.
Which would you recommend me doing? The races wouldn't feature huge hills, many of them will probably be flat circuits in suburbs of a city.
Changing the rear cassette would give me the option of being able to change it to the 12-28 if it was a real hilly race, but I would like to leave it alone once I make the initial change if I can.
Would I need to make any adjustments to the bike as it is - standard from shop- if I change the chainrings, or if I change the rear cassette?