I paid 40 bucks total for nitrogen fill, which is good for life of the tires (I can some added anytime by my dealer for no additional cost). 41/42 PSI is the recommended X6 air pressure for driving over 100 mph or "in a sporting manner", according to BMW. Otherwise, it is usually set at 33/36. My technician, Todd Thomas, at SunMotorCars BMW who has won several awards and is one of the top ten BMW master mechanics in the USA also recommended the 41/42. Another reason for such a high pressure is that run flats tend to wear on the outside edge in BMW X vehicles with minimum pressure. The higher setting will prevent that and will give better fuel mileage, longer tire wear, and much better handling. BTW, the active steering in combination with the 41/42 PSI in my X6 provides amazing directional accuracy at all speeds.