I had this problem - down to 2mm on inner edge of tyres after 6000 miles. Told by one service centre - all X5s do it as they have large negative camber. I did not believe this. Spent some time investigating on the Internet and have seen most of the comments posted on here somewhere or another - many are misleading or incorrect. I did discover a youtube video showing replacement of the balljoint at the end of the lower suspension swingbar. This is not a true 'ball joint' but is a cylindrical bearing with some rubber inserts forming part of it. The only way that wear in this can be detected is by taking the tension out of the rear suspension (joint) by compressing appropriately (possibly depressurising a rear air suspension) - just jacking up the car will NOT allow the wear to be spotted.

I searched around for a repair shop with a reputation for BMW servicing/repair - pretty much a backstreet operation but busy. The mechanic confirmed (without prompting) precisely what I discovered. The swing arm bushes were replaced together with the control arms which possess two joints themselves. To date the excessive wear seems to have stopped.

Common sense tells you that if the 'ball joint' on the swivel arm is worn, then from the mechanical arrangement it will not just affect the camber of the wheel but will also affect the tracking dramatically. The problem is that the wear in this joint will not be spotted unless the maechnic is specifically looking for it and knows what he is doing. Provided that the control arm ball joints are OK, wear in the swing arm joint (unless extremely excessive) will not show up when checking tracking as there is no twisting torque from load on the wheel to throw the tracking out - unlike when driving.

Apparently the X5 wears out these joints in about 60K miles. My cost for the job - about £500

How this helps !!!