they are solid. they don't dissipate heat as well as the vented fronts. mostly a problem with turbo cars.

I don't think its necessarily only rears though.

The one I cracked was a front, I just don't have a picture of it.

--Ian

It may also be people leaving their handbrake on after a track session.

or they use severely undersized rear brakes that heat up and don't do diddly squat...

A little from column A and a little from column B.

We see the same issues on other marque cars with cross drilled rotors - they aren't worth the ago.

Note to self, carry spare rear rotor blanks.

Think the bigger issue is them cracking during a race. More important to do pre-emptive measures.