Do summer tyres whose tread depth has been worn down to 3-4 millimetres work about as well as new summer tyres?

New summer tyres have a tread depth of 7-8 millimetres. When the tread depth has been worn down to 3-4 millimetres grip in wet conditions starts to deteriorate and the risk of aquaplaning increases. For this reason you should replace summer tyres that have worn down to 3 millimetres. You must, however, replace tyres that have worn down to 1.6 millimetres.