Lower tread depth causes a decline of the braking performance on ice or snow-covered roads. Therefore, it is advisable to keep track of your tyre profile. Legal requirements vary strongly from one country to another. You must absolutely replace tyres when the tread depth falls below 1.6 mm – this is not only unsafe but also illegal. Some countries do request even higher standards though – e.g. Finland and Norway: 3 mm, Romania: 2 mm, Serbia or Austria: 4 mm.
We recommend consulting local laws and considering the regional weather conditions before taking a trip abroad in winter. For your own security please consider that tyre performances decrease with the tread depth.