Eric Ondoy

Hey Guys-When is it time to replace rotors? When the heat cracks are longer
(like 7mm's) and the cracks reach the end of the rotor? I know it is good to replace them in the beginning of each track season-supposing there is enough track hrs. on them.

Thanks for the replys in advance fellow rennlisters!!!

guykoken

As I recall it, it's time to replace if there are three or more cracks from hole to hole or if any crack goes to the edge. Anyone else who knows or thinks he does, please chime in.
Richard Bain

LVDell

Here is the "official" PCNA answer......

enthusiast

Similar guidance from a previous Porsche model.

Guidance from Porsche AG on 964 Cup Car Cast Iron Disks.
"Ventilated discs will develop small heat cracks with race use. These cracks will have no effect on braking. Discs must be replace (sic) when three or more adjacent radial holes are connected by cracks or the outside edge of the disc is cracked."


I have been following these "crack" replacement criteria for years with no disc failures. The holes are weak points in the disk. The heat and stress cause the cracks. Air cooling fixes will help, but they won't eliminate the cracking. Also note that the inside of the disk has less cracks than the outside because the air flow enters there. The maximum cooling takes place while the vehicle is moving.

Bob Rouleau

I found two things which made my GT3 rotors last longer.
1) Pagid RS 19 or 29 pads in front and RS 14 in the rear. Not only does it improve brake balance by making the rear rotors work more, it saves the front ones.

2) Cup brake ducts. These replace the black plastic ducts under the car. The Cup version is larger and direct more coolng air the the rotor.

Best,

rabjohns

I have seen some Steel GT3 rotors with grooves vs holes. Does anybody have experience with these. DO they cool just as well?

Ed Newman

Bob has it right, but if your drive hard at the track, they don't last long. I got 5 days out of my last set of fronts. I recently switched to the Brembo GT3R 2 pc set. They are slotted not drilled. So far only two days, I am doing a 5 day stint at the Glen in a few weeks, I hope they will make it through that and a few more days.

boqueron

Ed,

When you say that your rotors last 5 days, could you please comment on what is an average day ,what type of track and pads ? I have done aproximately 10 track days added to other events, and my rotors are not finished yet ..(!?). I am not the slowest of my group...

( I am begining to get woried.. It could be that I am fast in a bunch of slow GT3 drivers... )

Ed Newman

My car is actually a 996 C2 X51 so I weigh a little less and have less horsepower. The average day is 4-5 sessions in DE or 2 practice, a qualifying and a sprint race. I have been runnign RS19 pads, just switched to 29's. I have cup brake ducts as well. I drive the car VERY hard, its the only way I can keep up with those DAMN GT3's. I've heard some of the cup cars guys complaining that thye only get 3-4 days out of a set (and they weigh 500 lbs less!). Its all a matter of how hard you push the car.

boqueron

Well.... I drive with RS19's and now with RS29's. One Track day is about six 30 minute sessions. I probably drive 3 of them ( 90 minutes aprox ) "100%" which means 2 seconds slower than a professional driver with the same exact car on a 1'51" track...

And I use the same original rotors for the last 1 track events .(!!)

PS.- It seems that the longevity consensus is more on your side than on mine..

boqueron

I meant..10 track events..

rabjohns

What is your setup? Cup ducts? Etc.

boqueron

Nothing special... Only Pagids..

BTW.- It could depend on the type of track, driving style,etc...

Ed Newman

One point of difference may be the rotors. I was running cup rotors which I believe are a little thinner and lighter than the GT3 rotors. Also worth discussing is tires. I run Hoosier R6s (245/315). More grip could translate to more heat on braking and faster cracking.

boqueron

I agree with you on the tyres . Slicks allows a shorter and stronger braking ? A friend of mine drove my GT3 ( Toyos R888's) and got out of the track ( just reaching the threshold the car continued on a straight line ) after trying to brake at the same reference - he claims - than he was braking 15 minutes before with his GT3 on slicks...