Hairline Cracking In Rotors?
 

Anyone think this is any cause for concern? I'm swapping them out soon anyway, but I thought i'd get some opinions. The cracks appear to be on the surface, but running my finger along them, it appears to be smooth. The car is tracked hard, but i've never seen hairline fractures like this in solid vented rotors, typically only in x-drilled rotors.

Front Rotors:

Attachment 173026

Attachment 173027

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By comparision my rear rotors are completely smooth, with no visible cracking

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looks like the pad isn't the right shape. The center where it is cracking is going through more rigorous heat up/cool down cycles because of the pad (my best guess).

That looks like standard heat checking to me, I don't think it's cause for concern. Here is a pic of the rotor I had to throw away last year, the crack was big enough to get my fingernail into.

Jasonhttps://www.northamericanmotoring.co...orIBX_0026.JPG

They're Mintex xTreme pads specifically made for the MCS. Only thing I can think of is that a rock or something got stuck in between the pad and rotor and somehow caused more heat buildup. I'll have to take a look at the other side, that's the passenger side rotor.

Something like that. I don't doubt that they're the right pads for the car just that maybe there was a manufacturing defect that may have caused them to wear the rotors unevenly.

It's entirely possible. Either way i'll have new front Calipers, Pads, and Rotors on in the next few weeks, so it's all incidental :thumbsup:.

I just swapped rotor & pads out on my car too. Those rotors look exactly like my front ones. My rears were also free of cracks. I'd say for driving on the street it's not a big deal. On track use wouldn't be advisable.

Those aren't wear cracks they're heat cracks.

This is actually a good rule of thumb to follow. My rotors look similar to the ones first pictured by the OP and I'm not stressing. With the amount of heat that builds, espespecially with HP aftermarket pads, there's more than likely going to be some very (and I mean very) minor cracking. You more than likely won't see this with a less hard OE pad.

The consequences of a failed rotor on the race track make me say if you track a car with cracks like the op's you are taking a large risk. My call was to replace them.

Normal wear and tear for an oem rotor enduring high temp use. The added Cf of a good pad elevated the work of the front rotor to the point it is now operating at the limits of its capacity and stress cracking would be considered normal.

Not a lot you can do about it. Buy replacements of low cost knowing you'll replace them often or consider a BBK for the added mass. Air ducting to help cool the oem part may by you some time too.

The rears are along for the ride regardless.

But you also watch and be sure that the pads reach proper operating temperature and stay there. Pad efficiency will be reduced if they are run too cool. A drop in temperature is good to an extent but is brake duct cooling really required on a street only car?

Wouldn't this be a case of the pad material on the rotor showing some cracking and not the rotor?

So then would the recommendation be to NOT run these rotors on the track? I had considered getting new brakes for the track day on the 18th, but I wanted to let these run their course first. I'm likely stepping up to a BBK soon anyway.

cracking up?
 

toddtce is correct- that is perfectly normal and nothing to be worried about. I'm more concerned about the fact that you paid money for vented rotors that aren't venting anything. Did anyone notice that the vent does not extend to the end of the rotor? Where is the gas supposed to go? I would call up your manufacturer and ask what the deal is?
Unless your doing some serious racing, a BBK is a waste of money (check out mc2 March edition). And if you are going to race, most of the race series out there (SCCA & NASA) require stock OEM rotors anyway. The only series that would allow for a BBK would be the Koni Mini Challenge. I believe that it only runs in teh UK and Australia. Testing has shown that OEM rotors perform at the same levels as non-OEM's in stopping distance. All you need is a good brake pad. (check out www.autoxcooper.com-those guys have it together.):mad::mad::mad:

While I appreciat Mike's vote of confidence on the rotor above, I'll have to respectfully disagree with his postion on the value of the BBK. The reasson we see the thermal cracks above is that it's operating beyond its capable duty cycle. While there remains little stopping distance improvement in the BBK as pointed out, the value of the BBK is not about stopping the shortest, it's about stopping the same over and over. By increasing rotor diameter the effectiveness and efficiency is improved. Thus the duty cycle is lower. Where this rotor is operating at or near peak duty cycle the larger rotor can achieve the same stopping effectiveness over and over and for a longer time as it only requires 85% duty cycle to ahcieve the same result. As rotor size (both OD and width) increase this value continues to improve. Clearly there are some benefits to a 13 x 1.25" 15lb rotor for the most sever duty use! Finding the balance of how much is enough vs how much is too much varies by the designer, the user and the intended application. A giant masive rotor for street use and Autocross is of little value. A larger and meatier rotor for track day use and greater heat saturation is a winner. One might trade some other value such as rotational mass and acceleration for; not better braking...but sustained braking. Mike's comments on the venting mirrors my own any longer. I'm slowly moving (back) to a fully vented- to the edge gas vent pattern as new rotors replace old. Like other suppliers I opted to do the same "start/stop" pattern that is the norm. The problem is that they don't really vent anything. And they seem more prone to pulsation than those of old. I've been doing this since 1993 and have yet to have a rotor crack at the gas vent solely due to the vent running to the edge. Drilled; yes, lile all the others.... As for continued use of the rotors in question, I'd keep an eye on them and if the cracks become larger (which they will) I would pull them. Addiing some better pads will help with the bite on the rotor also however if you try to elevate this too much you'll be back in the duty cycle problems all over again do to over taxing this casting even further.

Todd,

You don't think this is just the pad material "cracking and flaking"? From the discoloration it would seem to be pad material not rotor.

i just went out and checked my rotors! they look nothing like the OP's. i have todd's 13" X .81 front rotors. i will soon be purchasing my third set of front rotors and the second set for the rear. no cracking, just getting skinny. i know that todd routinely says that BBK's don't decrease stopping distance and just resist fade better. i will tell you that on my car, the stopping distance is sick short! while still driving w/ instructors at DE's, my last instructor described my car as a set of brakes w/ a car attatched. he could not believe how deep i could (and would) go. i've gone with progressively higher torque pads as i have gone with stickier tires. stopping (slowing) distances have become a function of balls, not brakes. OP, i highly recommend a BBK from TCE (and dedicated track pads).

Pads and tires have more to do with stopping distances than rotors do. :thumbsup:

I still read this as thermal stress cracks or "heat checking" as it's often called. In short; an over stressed rotor operating at the peak of its duty cycle.

I'll toss out some thoughts on the dark band; pad smear from the pads chunking in the middle (need pad pic), stress cracks providing air flow to that portion of the rotor changing pad to rotor contact, or iron particulates tearing from the rotor surface and cracks smearing on the friction surface.

"What is pad smear for 200 please."

:thumbsup:

I was in the process of acquiring a BBK before I even noticed this, as of now, I'm not sure which one, but I'll likely have one before my next track day.

I'm not sure why the gas slots don't go all the way to the rotors edge, the general consensus with slotting appears to be that they're much better at wiping the pads clean than actually helping with pad outgassing.

http://www.tirerack.com/brakes/brake...0+Series+Rotor

Those are the rotors I have. They've definitely been up there in the temperature range, Last track day I hit them with an IR thermometer and they were over 1100 degrees.

I've already spoken to Autoxcooper and we're working something out for new pads once I get the front brakes sorted out :thumbsup:.

BTW;

So why the small band of dark material (pad material) only in one area???

Pull the pads out and put a straight edge on the back side. I have $20 says the backing plate looks like a banana. All the work is being done at the center of the pad due to the pad deflection under the required high pressure being exerted upon it. As it gets hot it begins to deform which only goes to make the center portion run hotter and hotter...a slippery slope that does not get better.

I agree, which is why I'm trying to pass up all these deals on R56 and JCW Brakes so I can get a nice 4 piston caliper to spread that piston load out :thumbsup:.

Do you know off the top of your head whether Carbotech makes pads that will fit the Wilwood kits you sell?

I'm definitely going to shoot some photos of the pads when they come out.

Now, this situation would be a good cause to invest in something like the caliper stiffening bushings, correct? That's if the OP wasn't going balls to the wall to a BBK.

I do have the Tyrolsport stiffening bushings. That helps to some degree, unfortunately an inherent design flaw in any single piston caliper is that all the piston pressure is on the center of the pad.

At high temperatures the pad deforms and bows out in an arc (See Banana Comment). This concentrates all the heat and pressure on a single point on the rotor rather than across the entire pad swept surface.

Todd can likely explain it better than I can, but it's not something that a stiffening kit will solve. Unfortunately if you're going to be tracking your car on a track with intensive braking points, you need a BBK, or at the very least you need to expect to change your rotors out every 8-10k miles.