A good test is to take a penny and place it in the tread grove with the head of Lincoln facing down. If you can see the top of Lincoln's head you need new tires. If the tread is worn more on the inside or outside you need a front end alignment. If the tread is worn on the outer edges you are running the tires with too low air pressure. Worn in the center, too much air pressure. Of course dry rotted and cracked tires need replacing no matter the tread depth.
If the tire you are replacing is still in relatively good condition, it can be used for a spare. Look for area's of tread that are worn down to the metal. If you see these, don't keep the tire.
Tires need replacing. 2/32nds is the minimum tread depth for a tire to be safely used. In most statesin the USA it is a law, can get ticketed. Tire tread that low compromises braking handling in wet and snowy conditions.
It is an indicator of tire tread wear.
Tire impact damage road damage includes puntures cuts tears and other physical tire injuries. Bulges on the tire indicating the carcass is separating from the plies. Uneven tire wear. Cupping indicates bad shocks or struts. Tires wearing on the middle of the tread indicates too much air pressure. Wearing on the both outside edges of the tread indicates too little air pressure. Wear on one side of the tread indicates front end out of alignment. Scuffing also indicates alignment problems. Cracks in the tire indicates the tires are dry rotted and need replacing no matter how much tread they have left.
A typical automotive vehicle legal tread depth is 2/32", which isn't much.
When you are traveling along and the tires are unable to move the water on the road through the tread and dissipate it the tire will lift off the road. This is hydroplaning. Normally this is caused by tires that are worn out and need replacing. But if the water on the road is deep enough a new tire will hydroplane.
If you mean tire tread depth, the minimum is 1.6mm.
Increases grip if there is water on the roadway the water can enter the holes in the tread and not interfere as much with the rubber contact with the road.
Minimum LEGAL tire tread depth is 2/32nds of an inch.
Tire spec in PA is 2/32 of an inch of minimum tread
That's a rating for how well the tire tread wears - the higher the rating the more miles you can put on the tire before it needs to be replaced
There should be at least 2 mm.