Over the past 4/5 weeks I have noticed a huge difference in the way my 2003 BMW Z4 2.5 handles. The car sits on Bridgestone 255/40 R18 88W runflats on the front, set to 2.1 bar as instructed by BMW. With this sort of tyre and size of wheel, the car has always had a somewhat fidgety ride, often tramlining. However, it always handled well, especially on motorways etc. Having returned from a trip abroad, the car started to handle very badly, constantly pulling left and right, often wanting to dive from one side of the road to the other. The steering has also felt slightly vague. I took the car back to my local BMW dealer, who found no fault, other than the passenger tyre pressure was a bit low. After this was corrected the car drove better, but the problem soon reared is ugly head again. The tread on all tyres is an evenly worn with approx 6mm on the front pair. The dealer said I needed a KDF or S, at £250, which I understand is something to do with the geometry of the car, but tyre wear does not indicate a problem. A tyre company recommend I replace the tyres, as the underinflation may have caused a problem. I now am reluctant to drive the car, as it feels unsafe, and I am desperate to find a solution to this unexplained pulling to the left and right. The strength of the pulling varies from road to road depending on camber, but the car's characteristics have seriously changed. I would be very grateful for any advice or further investigations I could or should carry out.