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What Causes Rotors To Crack?

Abo Bob
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Roy Grand Master

Roy

Posted
Posted

Its a simple answer really. Just get the plain rotors, non slotted. And once you have them in your hot little hand go and get them slotted however you like.

But thats assumign the slots are the problem...reality is its probably only part of the problem.

scathing Grand Master

scathing

Posted
Posted
I don't see how you can blame the pads.

Firstly, the metal in the rotor will be massively more conductive than the pad material (Any pad material).

I don't see the pads as to blame. But if you've got a pad that can handle higher temps, your rotors will hit higher temps if you start braking to use that extra capacity.

In the OEM setup, the pads can act like a thermal cutout. You can't get too much heat into your rotors because your pads will overheat and pack it in well before that will happen. But go to a pad and fluid that doesn't mind a bit of work, and all of a sudden your rotors are achieving temperatures they didn't used to. And you'll start seeing heat problems you wouldn't otherwise achieve with lesser pads.

As an analogy, we all know about the WRX's driveline. The clutch is intentionally weak, so if the tool behind the wheel decides to keep doing redline clutch dumps the clutch lets go. But when those owners decide to upgrade the clutch....since the clutch can now transfer more torque.....the gearbox then takes the load and starts disintegrating.

(This is all speculation on my part, but what I'm saying is that while the pad isn't guilty of extra heat its also not irrelevant to why the rotors are heating up more.)

djr81 Grand Master

djr81

Posted
Posted

Scathing what you are saying is fine, but remember it is the rear rotors we are talking about. They don't get any where near as much heat loading as the fronts. Yet they still crack.

A second point to remember is that, however good your brake ducting is, for the time you are braking you are not getting any cooling effect relative to the heat input. So losing a few tenths of your brake pad coefficient, whilst it makes the braking zone longer has very little effect on the peak temperatures the rotors reach. In saying that there will obviously be a difference on the rotor face immediately beneath the pad. The crucial point as far as this post is concerned is that the cracks do not form or propogate from this region - they are edge cracks.

In trying to pick something to fix the problem I would suggest:

Remove the stone shields. The fit closely to the inside of the rotor & may well promote a differential in the cooling of the rotor which in turn will induce stress & promote fatigue.

Try some one elses rotors. I have pretty much lost faith in DBA. certainly I can't see the value in the 4000 series. Maybe try RDA, project mu or even something fancy like AP Racing.

I dont see the problem being from the slots in the rotor. Almost all race rotors have slots of some description. But perhaps worth noting is that other than DBA, no one seems to run the slots to the outside edge of the rotor.

GTRgeoff Grand Master

GTRgeoff

Posted
Posted

Easy answer, the DBA engineering and metallurgy is crap. Don't buy their product while they persist with their novelty bs of k-paw and stupid slot design. They have had cracking and wear problems for years.

Thermal management after lapping is important for homogeneous cooling and grain structure development, and for preventing pad material migrating through the disc causing localised material changes but won't make the buggers crack.

RDA have not let me down and I'm considering buying a set for the GTR and flogging the DBA's it came with.

T04GTR Grand Master

T04GTR

Posted
Posted

poor metal in the rotors. thats just metal fatigue. from overheating and cooling to rapidly.

dba isnt to bad but there not cast using diferant metal from run of th muck taxi spec 35dolar rotors.

there :motorsport: range use diferant material im prety sure.

this is why im curiouse about whats gonna happen to the rotors used in those g4 8 pot kits...

not to worry adam. jjust stick the stockes on there and theyle be fine. and last longer to :)

tacker Mentor

tacker

Posted
Posted

Well my G 4 discs are working ok and i think the material in the disc must be ok as i washed the car and most times i used to get rust form on the old discs but not any more for some reason. So i would say they are made of a better material than the older discs, or the heat treatment is better. Still have another 300kms to go for bedding in and then we will see how they stand up on a track day.

PMATT Explorer

PMATT

Posted
Posted

For anyone who is interested about rotors why don't you come down to DBA this saturday the 4th of November between 12.30 and 4.00pm Race Brakes Sydney have organised some tours during the afternoon of the DBA factory so you can see and ask questions about your problems.NO kids under 16 sorry and covered toe footwear has to be worn.You do not have to book just turn up and wait for the next tour to start also RBS will have some specials for the day(just a plug).

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