Winter tyre tread depth does not create one simple safety cliff. In 2026, ADAC reported a study that tested five 185/65 R15 winter tyres and compared about 8 mm of new tread with 4 mm and 2 mm. At 4 mm, the average wet-braking result was essentially unchanged, but water clearance, wet handling and snow performance had already deteriorated. At 2 mm, the losses were broader, with average cornering-aquaplaning resistance 52.2% lower than the new-tyre reference.

For a driver, 4 mm is therefore a useful replacement-planning point under ADAC's safety recommendation. This technical guide does not provide a legal minimum: check the current official requirements wherever the car is driven. Measure each tyre in the relevant tread grooves, plan ahead as it approaches 5 mm, and act on ADAC's 4 mm replacement recommendation. This guide explains all eight disciplines, separates the two published measures of wet handling, shows the available model-level comparison, and turns a tread measurement into a practical replacement decision.