The legal minimum tread depth for car tyres is 1.6mm across 75% of the tyres width and all around its circumference. However, it is important to note that safe driving in wet and snowy weather conditions is affected by the tread depth, the pattern design, and the rubber compound of the tread of your tyres. The optimal tyre performance in the wet is achieved when your tyres have at least 3mm tread across 85% of the tyres width. While there is no national law governing minimum tread depth in the US, 42 states consider 2/32 inch (approximately 1.6 mm) the minimum legal tread depth, while California and Idaho consider 1/32 the minimum. In Canada, the minimum tread depth of 2/32 inch for cars/light trucks is a federal standard, enforced by local police under the authority of the Motor Vehicle Safety Act. It is important to note that tires with tread depth below 4/32 inch can significantly increase braking distances in wet weather. Therefore, it is recommended to check your tyre tread depth regularly and replace your tyres in good time to ensure safe driving.