This basic mod adds a more realistic tyre tread pattern for Tarmac stages and is used on the rallycross class cars in the game. The bottom of the tyre has been modified to be darker than the sidewalls as it is in real life and now reflects light when the sun shines on it, especially in wet conditions (comparison example below)
This all comes down to personal preference of course. Installation is very simple but remember!
*Be sure to backup your original files first if you decide you want to change back!
Some comparison pics below (you'll have to look closely at the tread/color difference)
*Credit to the livery creators