How does wear affect grip? Wet grip in particular gets worse as the tread on your tyres wears. This is more marked as the tyre wears below 3mm of tread and approaches the legal limit. Check your tyre’s tread depth more often once it gets down to 3mm and aim to replace tyres before the tread wears below 2mm. This is more important as autumn and winter approach – better new tyres now than struggle through the cold and wet with tyres approaching the legal minimum tread depth.