In Austria it is highly recommended to have winter tires on your car between November 1st and April 15th. Driving in good weather with summer tires is still allowed but driving in wintery road conditions without winter tyres or snow chains can incur a fine of € 35. If other road users are endangered as a result, fines of up to € 5,000 may be imposed and you could be held responsible for any accidents if thought that winter tires could have prevented them. So best to switch them over!
In the warmer months most people switch back to summer tires. All weather tires are also allowed if you don’t want to switch twice a year, although the winter ones are safer on the roads. Storing and carrying them to your car each time can also be a hassle but many garages will store your spare tires for you for around €40.
According to the law, only tires which bear the following letters are regarded as winter tires: “M+S”, “M.S.” or “M&S” or with an additional or an exclusive snowflake sign. All-season tires may only be used as winter tyres if they have such an inscription.
Special use tires are only regarded as winter tire if they bear the following letters: “ET”, “ML” or “MPT”.
Official information in English here on the requirements for winter tires in Austria. Plus a useful article from the Local.