monroepaul

Going to HPDE tomorrow. Putting in race seats, harness bar, wheels, and stuff and noticed on the right front rotor I am just starting to get a couple of hairline cracks where the cross drilling is. Will I be okay for the day tomorrow and order new rotors on Monday or is this something that needs to be addressed immediately

gkmccready

Is it a crack, or heat checking? Have a picture? A bunch of folks will ask if you can catch a fingernail on it, if you can it's time to chuck the rotor...

73-84 IMSA Widebody

Moral of the story..don't use cross drilled rotors.

Lan.Jet

As long as the crack does not connect two holes or to the outside edge of the rotor they are ok.

Gray Ghost GS

I experienced first hand and have seen too many failures at the track with guys that tried the drilled rotors - the blank rotors are the best and safest "bang for the buck". Slotted rotors are fine if you want to spend the extra dollars - I just don't think they're worth it. One event at VIR there was a stack of cracked drilled rotors almost as tall as their plastic garbage cans. They simply don't last on the track - don't let anyone else tell you otherwise.

monroepaul

They just started to crack they don't connect to other holes yet and you can't feel them to the touch. I am going to get rid of them after tomorrow and I am bringing the stock rotors to the track tomorrow just in case. Thanks for all of the helpful info so quickly as least I'll have piece of mind at the track tomorrow.

tmak26b

A few cracks? Mine has hairline cracks from each hole! As long as they are not deep and connected, you are okay

AU N EGL

Keep a close eye on them.
When those rotors look like this, they are shot

rbl

Disagree ... but then I guess you could go for the "big" crack with the plain rotors
Cross drilled rotors hold up as well as any other if they are treated the same.

73-84 IMSA Widebody

Hey I'm not an engineer...I just stayed at a Holiday Inn Express.
Search for a few of the older threads for cross drilled rotor discussions, my understanding is that the reason for using cross drilled rotors, release of pad gases, is no longer an issue with new pad materials and that the cross drilling creates weak points where heat builds up and promotes cracking. As most look at rotors as disposables standard rotors are the easiest to get, least expensive and most durable.
Your results may differ and the opinions expressed do not necessarily represent anyone who knows what they are talking about.

ghoffman

Well, I am an engineer with 20+ years doing structural analysis for aerospace systems (TRW, Lockheed Martin. Northrop Grumman). I am constantly amazed by this discussion. I just did some case studies and I will start another thread on this. In summary I will not use, or sell any slotted or holey rotors.

rbl

I don't disagree with that; however, I do disagree with a "general" statement that cross drilled rotors are a POS ... they are not, and I have litterally hundreds of track miles on them to prove it in my case.

Treated equally, that is the operative term here, and I think they do seem to hold up as well as any other IMO. Just because they are drilled does not automatically mean they are bad which is what was implied and what you are implying Gary. I don't think you can come up with objective data to support that, and I have never seen any yet. Lots of discussion and theory but no real data. I see c5 rotors all over that have cracked but very few (maybe never) Z51 rotors that have cracked.

Put a set of drilled rotors on car X and use them. Then repeat that exactly with only a change to a standard rotor of equal inherent quality. What does that data say?

C5 rotor v. Z51 drilled rotor is a good example. That is also the only rotor I am personally familiar with.

gkmccready

Will a C6 Z06 rotor do for an example?



Like how it's cracked all the way through the hat portion? Thought you might... this was a friend of a friend in his brand new C6Z with track pads, first event with the car, very familiar on track.

rbl

Thats a dandy for sure ... so your conclusion is this happened because of the holes right?

gkmccready

My conclusion is that the cracks run straight through all the holes where the stress risers were. Could this have happened with a solid rotor? Sure. As quickly? Beats me. But the holes certainly give a good place for the cracks to start and grow, eh?

rbl

So do you think it started in the drilled hole in the pad area?

I wonder if it started in the "big hole" in the center??? If it did, then logically it would go to one of the drilled holes and then massive failure is imminent.

I don't think the drilled holes are the reason for that failure ... do you? I doubt they had anything to do with the failure.

gkmccready

Yes.

Material thickness is much greater there, and the heat is much less.

Yes, I do believe they were a significant contributor to the failure. You don't? Here you have a material that's much hotter in certain areas than others, expanding at different rates in a confined system. It's just looking for some place to put that energy... and then it finds a stress riser... I also believe this is why good 2pc rotors have a better chance of survival with the friction ring free to expand and contract separate from the hat.

GettReal

The last comment is whats making me post. I have almost 10 events on my current cross drilled rotors and I check them religously for cracks, so far, nada. Since I have been tracking my car (only the last couple years seriously) I have used 2 piece rotors. My first set was a set of 2 piece Wilwoods and now I'm using 2 piece Baers Eradispeeds. Can anyone tell me if it changes their opinion of slotted and cross drilled rotors if they are 2 piece??

rbl

I don't think the drilled holes are the cause of the failure. However, I can't say what was the cause either. My argument is that treated the same I believe you would have seen the same failure.

I admittedly do not drive the car as hard as others. However, it does see almost 140 and gets into the ABS routinely on every lap with good tires. I use PFC Z pads and they actually work as well as my Carbotech XP10's. I use them hard and I wear them out .... the car seems to stop just fine. There is a lot of hype about these brakes as you know.

I got a phenomenal 28 track days out of these front Z51 rotors and they still could be used. I guess If I went to a real aggressive pad, don't cool them down and just run the crap out of them I could destroy them sooner. I can guarantee you that the C5 rotors would be broken long ago on this car.

Why this is I have no real explanation other than the quality of the rotor ... but, as you can see, the holes have done no damage. This is my data and your may vary. I will add that I have had the same result on the last 3 cars too (Z51’s). I have never broken a rotor on any of the C6's ... yet ...LOL.

AU N EGL

and here is ONE 20 min race on a OEM C6Z06 rotors




Braking style has a lot to do with how quickly rotors crack too.

PPL that are easy on their brakes the rotors will last longer. PPL that are very hard late brakers will eat rotors for lunch