I am receiving a trek 7200 from my credit card points and need to decide on a frame size. Been to a few bike shops around town and have test rode a 17" that seemed to fit and ride okay, but felt a little cramped when standing to pedal. I don't really know what to look for. Someone told me today that a 20" is probably better because I have a long torso, even though my legs and arms are short, and I sat on one that felt okay, but I never rode it. I see that most of the parts are adjustable, but what are the main tradeoffs for getting a bike too big/small. I seem to be right in the middle. I'm 5'9". Are there any surefire signs that the bike I'm getting is too big/small?
If you want something close to "accurate", a shop will have to measure your arm length, torso length, and inseam and then you'll get a bike size that will fit "90% of the population" with your measurements.
Once you have the correct frame size, most people say that adjustments in the seat and stem length should get you comfortable.
Most shops charge a small fee for such a fitting, and I'm sure it's negotiable too.