Rotor replacement due on PFC Z54 BBK?

[rsyring]

Anyone have a recommendation for determining when to replace rotors? I have a PFC Z54 front big brake kit on a 2011 BMW M3 and the rotors are showing spider web cracks. I have a new spare set I could put on, but don't want to needlessly do it.

From my reading online, minor webbing is ok as long as there are not cracks connecting between cross-drilled holes. But these rotors don't have holes, so I'm not sure how to evaluate. I don't have a full history on the rotors because I purchased it last year. I also have been unable to find out the minimum rotor width or acceptable wear amount (which I could compare to the new set) online.

If it matters, I'm an intermediate driver, will be at a couple tracks that are harder on brakes (e.g. Mid-ohio & pitt race), and am transitioning from summer tires to a stickier lower tread wear tire (but not a slick).

Pic: https://photos.app.goo.gl/7PSLQy6fJMXjp5mb9

[danvitmon]

Cracks are ok so long as they don't go to the edge of the rotor. Make sure you check the inside side of the rotor as well. Rotor explosions on track are rare but are incredibly scary and can cause serious damage to you and the car.

Also these rotor rings are harder to get nowadays. I think Bimmerworld stocks a few but I believe PFC rarely makes them, if at all.

[derbo]

If you can catch your fingernail on the cracks, its time to replace.

This is a good article on inspection/maintenance
https://paragonbrakes.com/rotor-insp...d-maintenance/

[Davisca455]

This pic shows the “cracking” after Motorsport use that Derbo’s document describes.
I replaced these (kept them as spares) because I was headed to Sears Point.