I am afraid that the brake discs have a reputation for warping, even when not subjected to racing.
The problem is that most of us replace them with another new disc , which also does the same thing. Apparently once the discs have been through at least one heat cycle which causes warping , it is most unlikely that they will suffer the same fate again (ask a metallurgist, I am no expert)
The optimum path seems to be taking the discs to a machine shop where they can be surface ground, and to refit your "reconditioned" units.
There is an alternative which can be done with the discs still on the car , and that is to take them to Uncle Melvyn , who has a disc brake surfacing machine . This may not be as good as a surface grinding , but it does work. I had mine done in this way and have had no further issues (and I m not known for being light on my brakes!)
