Everyday driving I run 32
At the strip I have tried 32 and then 27, 27 hooked up better.
First time at the autocross I tried 40 and it was too much, it would not hook up.
The second time at the autocross I set it at 30 and it was a lot better.
There are triangles near the edge of the tire that are wear references. Under heavy side loads the tire will roll under, you will see scuffing start to approach the triangles, if the scuffing starts to wear away the triangles you need to add more pressure.