Summer tyres can be used all year round if the weather or road surface conditions do not require the use of winter tyres.
The tread depth of the principal grooves of summer tyres must be at least 1.6 mm. In difficult conditions, in order to avoid aquaplaning, for example, the tread depth of summer tyres should be at least 4 mm.
Old winter tyres are not recommended to be used as summer tyres. You should bear in mind that winter tyres’ grip on wet or dry asphalt is usually significantly worse than that of summer tyres.