That is a tough one. Some of it is time, some is conditions, some is miles. BB gets it about every two years (I have been doing 1000-1200 per year, but that is split between several bikes) it is miles and how much road grime....how often out in wet, gritty conditions? Cables....if they start getting excessive rust, fraying, or dragging...Bar Tape...when it needs it...Tires, when they wear too far or get cut...A FULL stripdown....I usually do that when I GET a bike (and who knows what service they had...some...NONE at ALL!)