My front rotors have lots and lots of heat cracks in them. No cracks are really open, and none reach the edge of the rotors. Rotors for this car are expensive, and I don't want to toss out rotors which still have a lot of life in them, but I would rather not crack a rotor braking at 120mph.

My rear rotors don't have heat cracks I can see, but they certainly are worn.

Similarly, my brake pads (full race pads) are more than half worn, but still have life in them. They may or may not last another track day. Should I just say "Oh, well" and toss them? I don't want to change pads at the track during the day, since it takes the brakes a long time to cool down enough to do that, and I really don't want to miss track time.

What criteria do people use for replacing wear items before they actually break?

 

It's unlikely (in my experience) that they'll actually fail on track. It's when they're cooling down in the pits that **TINK** one rotor face will go. I keep extra rotors on hand at the track to swap between sessions if needed. About 30 min. before your next session, take a look or a quick drive in the pits and it'll be obvious if the rotor's gone; then you'll have time to swap. Of course, YMMV.

 

I too carry used rotors as spares.

I just replace mine every spring and don't think about it. I know I'm throwing away rotors that have plenty of thickness but mine are usually very nasty after 10 track days.

I however think the OEM rotors for this car are cheap...

 

I change mine when the cracks start to show some gap, not when they are just faint hairlines. Some people wait till they hear a ticking sound on light braking, but I am more conservative. These rotors are cheap and less than pads. The pads you can let wear very low (like 1/16") as long as you check them regularly and they are not too cracked and crumbling. Changing pads is quick (15 min?) and can be done in between sessions with gloves easily if hot. Rear rotors wear very slowly and never heard of one cracking, and will outlast at least 5 or more sets of front rotors.