Floridamark

Gyrodisc on the way. Hope these will last Saturday at Sebring.

village idiot

Those rotors should be good for another day or two. I wouldn't push much harder than that though. Measure the thickness with some calipers

The HACK

Those rotors are FINE. Cracks come from rapid heating and cooling typically seen on track. Until the cracks reach the edge of the rotor there's nothing to be alarmed for IMO.

Floridamark

Great to hear. I hope the new XP20 dont fry them in one day. Should I stop using cooling fans after a session on my brakes?

https://www.homedepot.com/p/VP-20-1-...0-BL/303793378

lobsterroboto

lol I ran OEM rotors for 2 years that looked a lot worse than that.

Floridamark

Great to hear. Will shoot pics after this weekend.

village idiot

yes. You want them to cool down as slow as humanly possible. 30 minutes between sessions is PLENTY of time to cool a rotor. It also only blows air on one side of the rotor, which creates more thermal stresses.

I run Hawk DTC70 and mine are fine after 6 or 7 days. I wouldn't worry. What tires are you running?

Floridamark

Hooiser R7

The HACK

Sometimes it doesn't really matter, because MOST of the rapid cooling and heating occurs on track. Especially tracks with long straights followed by heavy braking zones then followed by more straights. West coast tracks like Laguna Seca, Auto Club Speedway, these two tracks are brutal on brakes, but they also have straights following nearly every single heavy braking zone.

The end result is high heat build-up, then immediately followed by some rapid cooling. Conditions like this causes the exterior surface of the brake rotor to cool while the interior remain hot, causing the surface to "stress" and fracture. Small cracks like this is normal. It's when these small cracks start to extend, connect, and reach to the edge of the rotor surface is when you should start thinking of replacing them, because once it reaches the edge, the crack will grow rapidly as the heat and cooling expansion/contraction cycles now can come into full effect.

It's sort of like tempered glass, where the surface tension is high because the pressure caused by rapid cooling of the molten glass creates incredible tension inside the glass, thus making them incredibly strong...But a small crack will shatter the glass. On rotors with high carbon count, imagine the edge of the rotor as the glass surface. Once the cracks reach the edge of the rotor the cracking will accelerate rapidly. But as long as the cracks aren't connecting and aren't reaching the far outside edge, they're as strong as bull.

Typically low carbon cast iron don't suffer from this because they're more "pliable" than high carbon iron. However, high carbon iron is desirable for rotor applications because they're stronger and last longer. Also, heat treated rotors tend to suffer LESS from micro cracks like this too, at least that's been my experience from a few decades ago. Applying cooling fan to hot brakes in paddock will exacerbate this. I wouldn't do the cooling fan deal unless you're suffering from serious fluid fade issues.

village idiot