Tread Depth - Slick, Semi-Slick and Normal

A tire's tread exists principally to expel water from the contact surface of the tire as it rolls along the ground. With a good tread design a tire is able to maintain a safe grip on the ground in wet conditions. The neccesity of a tire being able to have reasonable handling in the variety of conditions found in real world driving has led to there being government regulations in regards to this.

Tire tread comes at a disadvantage however as the air pockets created by tread neccessarily reduces the amount of rubber hitting the road. This means that in dry conditions there is less rubber and therefore less traction available in specifically dry scenarios. There are three broad categories of tires used for the different conditions with slick, semi-slick and normal treads.

Semi-slick tires are an attempt to make a road legal tire that has some of the characteristics of a slick tire. They have a limited tread pattern to render them road legal but are designed specifically for road conditions. The primrary use case is for people that want to race their vehicle but need to drive it to the race track on public roads and do not want to change tires upon getting there. The semi-slick tire offers improved dry performance at the cost of degraded but still legal wet weather performance. They also tend to have a significantly reduced life span as the rubber composition is such that it provides a sticky grip but tends to quickly degrade. They are also far louder than many normal road tires as the lack of tread tends to increase noise.

Slick tires are almost always illegal to use on the road but offer the ultimate in dry weather performance. Having no tread at all they are in danger of aquaplaning in even the slightest wet conditions. The increased amount of rubber touching the ground at any one time offers substantial improvements in dry cornering over a regular road tire. Almost all slick tires are additionally designed with an rubber composition that becomes sticky with heat and this enables increased traction. Unfortunately this also means they are vulnerable to heat cycling which is a process where rubber changes its characteristics based on the heating and cooling process. This heat cycling leads to an extremely short lifespan compared to any other tire. These tires are also dramatically louder than any other tire design.