In general, all vehicles are required to have tires in proper and safe condition with a minimum tread depth of 2/32 of an inch.
This is the law in most states.
To indicate that tires have reached that point, tires sold in North America are required to have wear bars. The bars are located at the bottom of the tread grooves in several locations around the tire. They are designed to warn you when your tires no longer meet minimum tread depth requirements.
Another popular way of checking your tire tread depth is the penny test. Simply insert a penny into your tire’s tread groove with Lincoln’s head down. If you can see all of Lincoln’s head, your tread depth is less than 2/32 of an inch and it is time to replace your tires.
With 2/32″ of remaining tread depth performance on wet highways and at high speeds has been significantly reduced. Water cannot be compressed and you need more tread depth to allow rain to escape through the tire’s grooves.
To perform well on wet roads, you should consider replacing your tires when they reach approximately 4/32 of an inch.
In snow, traction has been virtually eliminated if your tires have 2/32″ of remaining tread depth. To maintain good mobility you need approximately a tread depth of 6/32 of an inch.
Because tread depth is so important element for traction, winter tires usually start with noticeably deeper tread depths.
42 states consider 2/32 inch the minimum legal tread depth. California and Idaho consider 1/32 the minimum, and Arkansas, Montana, New Mexico, North Dakota, South Carolina and West Virginia have no standards on tread depth.