My impression following bryan sheddon (the guy 1 second slower) is that he uses very little brakes at all. But hey Ive only done it once.

Dann

 

I've spoken with Bryan (driver of aforementioned stock car), and he has given me much advice about what lines to take at Wakefield circuit. So much so, that I am following the same lines, and using the same braking points as him.

 

That wear is called "radial taper", and like everyone said, it is very common on the stock Miata rotor/caliper setup. The OEM solid disc rotor and single piston floating caliper are prone to pad radial taper in high-heat (track) use. Google it. Stop Tech has a few good articles about brake tech, including different types of pad wear.

I don't know if it is just the pad thickness or if the pads eventually overheat, but the problem definitely gets worse as the pads wear. Once you get to the 1/2 way point, and the pads look a bit white/charred, things start to go downhill fast. If you could, it might be helpful to install a couple of shims (titanium backing plates) to help keep the piston inside the caliper body. This is an option for some aftermarket calipers but I'm not sure there is room for them on the stock calipers.

With the stock setup, I was at the point where I was chucking pads at the 50-40% mark. :(