You should change tires when you look at the grooves and they are ground pretty smooth. You want grooves in your tire so that it has good traction. If you put a nickel in-between your grooves and it doesn't stick out, then your tires are still good.
To increase friction
So the water you drive through will be channelled through the grooves to prevent aquaplaning.
Tire grooves channel and disperse the water on wet roads. If it weren't for grooves, your tires would be 'aquaplaning' on every patch of water, and not gripping the surface.
The grooves or "tining" placed on concrete bridge decks (surfaces) are created for for automobile tire traction when it rains and to help direct the water runoff. Typically the grooves are created in the transverse direction across the direction of automobile travel. More recently longitudinal grooves have gained favor because there is less noise generated when tires follow longitudinal grooves when compared to more noise generated when tires cross transverse grooves.
The differences are the size and the purpose. Regular tires are made to grip the asphalt, and also fitted with grooves to push water away, keeping it from hydroplaning. The off road tires are thicker, and the grooves are much deeper, giving it the ability to have good traction in the dirt and rocks.
Frank Seiberling
Depends on the track mainly but cutting proper grooves in your tires is a good start
get a penny, and place it upside down (with Lincoln's head facing down) in one of the grooves. if you can see the top of the head its time to get new tires.
Tyres have treads to give better grip on the road, especially on a wet road.
Kenda kenetica tires are all weather tires with center grooves that increase water dispersion. The random variable pitch tread reduces road noise. These tires are made for riding comfort. Kenda kenetica tires are a reliable tire.
Deeper grooves improve traction for off road use but are noisy when on road use.