These images are a progression of refining my tyre shader that I'd been working on improving over each take on cars. I started with basic materials and slowly started to develop new ways to add finer details, such as adding CoronaRoundEdges and multiple glossiness layers. 

This was a material that I wanted to try really go far with.I created a 'sticky' look by adding a mask on top of the material that tried to give the appearance of debris and stones sticking to the tyres.