Tires: tire problem, negative camber, rotating tires

Question
I have a BMW 325I year 2006.  I bought the car in May 2006 (New car).  I used this car for going to work only, the car now is around 20,000 miles.  About 2 months ago I realize the car make noise but thought that is normal because it's a sport car.  Recently I took the car to dealer for oil change and also have them check out.  They said the tires (all 4 tires) were evenly cupping and need to change new tires.  I asked the dealer to check on the car ofcourse they said "there is nothing wrong with the car". My questions are:
1. Is this normal?
2. Is there any way to prevent it from happening again?
3. If this is normal that mean every year I have to change tires?
Can you help?  Thanks!
Melanie

Answer
Melanie,

First let's start with the basics:

Cupping - more properly termed "irregular wear" - is caused by misalignment and aggravated by insufficient rotation and insufficient inflation pressure maintenance.

So "nothing wrong" is ....ah....wrong!

BMW's use a lot of negative camber in order to get the handling they are noted for.  Guess what this causes - right! - irregular wear.  And since BMW doesn't recommend tire rotation - in order to preserve the handling (rotating tires causes a short term loss in handling) - the net effect is that all the tires are destined to get irregular wear eventually.

BMW seems to think this is OK.

So the first thing would be to replace the tires and get an alignment.  The alignment shouldn't be "close enough is good enough" - it should be "as near to nominal as possible".