I put a set of non runflat tires on my Z4 at delivery. I chose the new Yokohama ENVigor high performance all season tires, http://www.tirerack.com/tires/tires.jsp?tireMake=Yokohama&tireModel=AVID+ENVigor+%28W%29. They are available in a W speed rating and in the correct OEM staggered sizes. They are so new that TireRack had no reviews but based on previous experience with Yokohamas in the past I am confident that they will perform well. So far, I am very pleased. Ride is much improved and like you I am not an aggressive driver. I am looking for a good ride with decent handling and treadlife.