It is mandatory to put on the winter tires from 1st Nov. in Austria.
In the Grossglockner road, one section is a viaduct which is sometimes frozen. Be careful even if you have put on the winter tires.
I went to Col de l'Iseran in the biginning of October to find out that although it is still open, it is not possible to drive with summer tires. My 1M was summer tire so I was not able to climb to the top. The temperature was minus 5.5 degrees C.
This web might be handy to know which pass is open.
http://www.alpen-journal.de/alpenpaesse.html
