Just bought Michelin X-Ice2 for my HCH. Tires centre was suppsed to balance and check inflation. Checked tire pressures when I got home and found that all the tires are between 25-28.5 psi (yikes...I hope my tire guage is just wrong). They are inflated with nitrogen. Any one know whether nitrogen is available at gas stations, or is that only available at the tire centres? Also, can I add regular air to my tires, if there is nitrogen in them right now?