I've got a 4 year old 2005 2.5i Z4 that is primarily a garage queen and has under 18K miles. During a special free BMW post-warranty inspection, it was pointed out to me that the rear tires (RFTs)were getting unsafe, particularly the right rear one. A couple of reasons for this (even though I would check tire pressure every month and adjust accordingly-however the tires were wearing evenly and showing no signs of inflation or alignment problems). First, on inital starting, the right rear tire does more work than the left one. And, of course, the rear tires, in general will wear out before the fronts (present tread depth is 6/32) rear drive cars. And another important contributor to excessive rear tire wear is that I didn't rotate the tires.

So, aside from keeping tires properly inflated, I strongly suggest that if you want to keep your tires as long as possible, rotate them. Now, there is another consideration: Could it be that I disliked these RFTs so much that I unconsciously let them wear out sooner than they should have??? Could be, could be.

2002 TiSil/Blk 325i SP
2005 Merlot/Tan Z4 2.5L