powdrhound

Anyone have any issues with cracking of the Girodisc floating 350mm rotors? I'm wondering if this was a manufacturing defect in the steel as the other side did not crack even though it is worn to the point of the slots beginning to disappear.

http://www.flickr.com/photos/87731073@N06/8196475187/http://www.flickr.com/photos/87731073@N06/8196475187/ by http://www.flickr.com/people/87731073@N06/, on Flickr

crazyfrog

Looks like that disc got some serious heat through it !!! How many miles and how many trackdays you've done ?

powdrhound

6300 miles including 68 track session of about 20-25 min each.

crazyfrog

You just cooked them...You may be need to improve the cooling and make sure to do some cooling laps after any session on track. Make sure you are using the right pads too.

powdrhound

There's not much more cooling wise I can do. I'm using 6 piston brakes, 996 Cup car brake cooling ducts in the front with GT2 ducts in the rear, PFC 08/06 pads, and religiously do one full cool down lap after each session. After that, the rotors measure generally just shy of 400F both front and rear and calipers under 300F. Temp wise this is about 50-75F cooler than what my friend's 997GT3 ceramic rotors measure at. My rear rotors are in perfect shape, my right front is worn to the point of the slots being almost gone with just just tiny hairline cracks, but the left front is the one that cracked. Maybe after 68 track sessions there is enough heat cycles on the steel that it becomes more brittle and just gives... I've seen cross drilled rotors crack, just not slotted ones, that's why I thought maybe there was a material defect in the steel of the left front rotor and wanted to see if anyone else has come across this.

Below is a picture of the right front, just small surface cracks in that one and it's worn down even more.

http://www.flickr.com/photos/87731073@N06/8198930937/http://www.flickr.com/photos/87731073@N06/8198930937/ by http://www.flickr.com/people/87731073@N06/, on Flickr

crazyfrog

I have managed to kill a set of RS6Plus discs set ( 8 pots RS6 calipers) in one track day on an RS4....If outside temp is high and the track is small with no much long straight , brakes can't cool down. How do you brake ? I brake hard really late . 996 tt and 996gt2 are still on the heavy side and really pished hard the brake will take some hammering. Have you try Alcon rotors, many people use them on Gt3's and other models other here in europ, it seems really good for track use.

powdrhound

I brake late and very hard for a short duration of time. This heats up the brakes less than if you ride them. The track I run is a 15 turn 2.5mile circuit which is hard on the brakes especially at a 5200 ft elevation with summer track temps easily over 100F. Not much cooling air with such thin air.

Bob Rouleau

All rotors crack eventually.
Those with holes, sooner than slotted but slotted rotors will crack after enough hard use.

crazyfrog

100% agree with that . Try the Alcon to see what they are like. These cars are heavy and to be honest not for proper track use , if you plan to track it a fair bit you need to expect replacing rotors often I am afraid.
Try one cooling lap in the middle of a session it can help a little bit to extend their life....

powdrhound

I spoke with a number of race shops and it appears that I was getting pretty much to the minimum thickness on the rotors which obviously weakens them. A contact at Giro also mentioned that the likelihood of the crack is actually shock cooling due to the cool down lap at he end of the session. It appears that I may have actually over cooled the rotor too quickly by consistently doing a full cool down lap without hardly touching the brakes. The recommendation is to still use your brakes on the cool down lap but obviously with much lesser force and that will insure that the rotor material goes through a much slower cooling rate. This is why I was always seeing relatively low rotor temps when I measured them in the pits. Live and learn.

jcb-memphis

Thanks for sharing that....did not know you could "over cool" but it makes sense the way you explained it.

jb

powdrhound

Yeah, it makes perfect sense now especially considering that this past weekend temps at the track were pretty cool in the upper 50s so I was really pushing some very cool air over very hot rotors on my cool down laps. I see how that may have played a role in causing the crack.