I just got a 06' 325i sedan last week. It's the best car I've ever owned. I wanted to do some work on it for more power and more of a sport ride. I was told that if I put anything in it I would have to change something else just to balance things out (for ex. If I change the tires and rims to racing ones I would have to adjust the suspension or change it) but they could be wrong. I'm looking at cold air intakes and exhaust systems but I want to start small for now to get my feet wet. BMW parts aren't cheap so any help would be great. I know a little about cars but I want to know more before I get started. I would like to work on it on my own rather than take it to some mechanic and pay an arm and a leg. I have access to a car lift and garage so I can get pretty deep into things. Any input would be great thank you!!