Hello! I changed to winter tires today, because it has become quite frosty and the snow used. I bought the tires last year only new. It is Continental TS850. Over the summer they were in the garage all the time. When I wanted to put them on today, one tire was almost completely flat and the other three clearly below 1.5bar. I still had this with no car. I also find it interesting that all 4 air was lost. On what could ma n to bring it back? Perhaps a mounting error or rims or valves in the bucket?