Most drivers wait to buy new tires and
rims until their tire tread falls below 2/32 of an inch. (The tread on new tires is generally 10/32 of an inch). Most people use the old penny test to measure their tread, unless their car has a built in wear indicator. Others will do a manual measurement and begin to think about replacing their tires when the tread falls below that depth. However, some studies have shown that worn tread can become dangerous much sooner. Some tests suggest that once tires lose half their tread they begin to create problems.
Driving on car tires with low tread can affect how the vehicle performs in already hazardous conditions. For example:
On wet roads, low tread can have a significant impact on brake times. Cars can take as much as three to six feet longer to stop in wet conditions. This is very similar to what happens when you are cycling on a wet road.
Cars will hydroplane sooner if the tread is less than 4/32 of an an inch.
Tires will loose their ability to grip on snow or icy roads as the tread wears off. This can result in the tires taking longer to accelerate and can reduce the tire’s traction by nearly 15 percent if a tire has even half of the tread gone. Bald tires perform at even worse levels.