The tires are per owner manual's size 225 40 18 and 255 35 19 tires are new. After reading Hawk's experience with Goodyear sounds it doesn't sound like a rim problem. Rear one's really only drop suffiecient pessure in winter and here zero degrees is not uncommon. I put one of those valve stem pressure monitors on the stem for a while...NEVER DO THAT...they are plastic and when they snap off they are pains to remove. Those showed a constant pressure drop and before and after the monitors same prob.

The Goodyear manager said that the rims were made in India and the enamel wasn't right so they were leaking and being silently recalled. He stated all the Chyrs 300 rimes were being recalled and other rims made in Europe had the zinc left out of the manufacturing process. This was on saturday so I haven't had a chance to confirm it...although it is looking doubtful after reading your posts.