Colorado Springs Auto Repair Shop
According to traditional advice, if your tire tread has worn to 2/32 inches (which is the tire tread depth law in certain states), or if the tread wear indicator bar is visible, it's time for new tires.
Drivers will notice a decrease in safe traction and braking power in snow and rain with many tires. Tires wear slowly and many car owners don't check the tread depth of their tires regularly. The loss of traction can be difficult to see until the vehicle stops on its own.
When new tires are installed, they typically have a 10/32 inch to 11/32 inch tire tread depth. To ensure adequate grip, the deep tread and grooves and slits in the tread allow water and snow to escape. As the tread wears, the grooves and openings in the tread become smaller, more moisture is trapped underneath the tire. The tire rides on a slippery surface made of water ("hydroplaning") and snow, instead of "biting" pavement.
This results in longer stopping distances and more wheel spinning at acceleration. It also means less grip in turns.
The severity of the slipping and sliding and when it starts will depend on the tire design. It could be long before you notice that your tires are bald and need to get replaced. Some tires could experience safety problems when there are less than 5/32 inches of tread left. This would make it difficult to buy new tires. However, some tires simply have better snow and wet-pavement traction and can maintain it for longer distances.
Tire mechanics can check for excessive or unusual wear and measure the tread depth using a gauge to advise on how long you have left. Parts stores have depth gauges that can be used to check worn tires. You can also do the penny test by inserting a Lincoln-head penny (top should go headfirst) into a groove in the tread; if Honest Abe is visible, then you will need new tires.
For more on the proper tire maintenance, check out Colorado Springs Auto Repair Shop.