I'm not sure you understand. I recognize that their are 4 types of tyres and there have been 4 types for quite a while. But that is not my point.
A few races back +/- Pirelli announced that they were going to make their soft tyre even softer than it was all season long by changing the tyres compound. The compound is the chemicals that make up the tyre's tread.
540, Dirrezas (4) @ 275/35-18 ea, Eibach springs & bars, Bilstein Sports, Dinan Stage 2, slotted ATEs, Hi-Temp HTP pads, SS Lines, UUC-SS, White/Tan, Bling-free & Stealthy