Inordinate brake rotor wear

[marlinspike]

According to Advanced Autoparts' DIY section, scoring is caused by overheating. Perhaps try David Z's break in technique to start with a clean slate and see what happens from there?

[300CUL8R]

Took a look tonight and I think I'm in the same boat with 550 miles. What to we do besides the bedding technique? Is this a warranty item??

[tgt]

Originally Posted by 300CUL8R

Took a look tonight and I think I'm in the same boat with 550 miles. What to we do besides the bedding technique? Is this a warranty item??

There should be no question that this issue is a warranty item. Brake pads usually aren't warrantied, but early scoring like this isn't 'normal wear and tear'. Let us know how you make out with the dealer, I'll be eagerly waiting to see what they say.

-Travis

[DZeckhausen]

Sorry for coming in late to this discussion. I didn't notice it until someone posted a link back from the brakes forum.

Let me jump right to the heart of the matter. When StopTech had an SRT8 in for big brake kit measurements earlier this week, they also noticed this issue. The test car had very low mileage, yet the rotors were really chewed up and the front wheels were black with brake dust. The problem is not the rotors. It is the choice of friction by DC. The pads they picked are very abrasive when cold. In my opinion, they made an inappropriate pad selection and all SRT8 owners are going to experience this problem. Eventually, this is going to become a warranty issue and DC will have to issue updated pads to all SRT8 owners. That is assuming enough SRT8 owners bring the issue up to their dealers, get it documented, and insist that it's not due to "abuse" by the owner.

Now I would like to address some of the points raised by others in this thread. There is no such thing as "soft" rotors. With a few exotic exceptions, brake rotors are made of "gray iron" and the metallurgy of rotors from various manufacturers is virtually identical. There are an assortment of impurities that can be adjusted in the mix when casting the rotors. These impurities affect hardness, ability to be heat cycled without cracking, brittleness, and many other characteristics. You can make a rotor less prone to pad deposits, for example, by changing the amount of a particular impurity. However, there are side effects. By changing the amount of one impurity, you affect other characteristics of the rotor, such as it's resistance to cracking. That has to be compensated for by making the friction plates thicker and the air gap smaller (assuming the overall rotor thickness remains constant) and the rotor becomes heavier with less ability to flow air (smaller air gap) so the convective cooling falls off. My point is that rotor manufacturers have pretty much converged on the ideal mix of materials and there is not much variation between rotors produced by Brembo, StopTech, ATE, Zimmerman, Balo, Performance Friction, etc.

How did this rumor of "soft rotors" begin. I don't know for sure, but I can give you an educated guess. The metallurgy of a BMW rotor is virtually the same as that of a Mercedes rotor. Yet Mercedes rotors typically last 50% longer. When BMW customers complain to their dealer about needing to replace the rotors with every pad change, they are told that "BMW carefully designs the rotors and pads to wear at the same rate. BMW rotors are high performance and made of softer metal." That's nonsense! The truth is that BMW specifies only 1.6mm of allowable rotor wear before the rotors should be discarded. Mercedes specifies 2.4mm of allowable wear. There's your 50%! BMW tends to make design compromises aimed toward improving performance and handling. Thus, a 30mm thick BMW rotor has thinner friction plates and a larger air gap, providing less weight for better handling and improved airflow through the rotor for better convective cooling. Mercedes rotors are heavier, but they last 50% longer, extending the rotor service intervals and addressing the perceived needs of their customers.

Getting back to the SRT8 pad issue. There are two primary sources of friction between your rotors and your pads. One is called abrasive mode friction. You are all very familiar with that one. It's simply the collision and mechanical destruction of the peaks and valleys in the crystalline structure of your pads and rotors. Another less understood component is called "adherent mode" friction and only occurs if you have properly bedded your brakes. Bedding is the process of laying down a thin transfer layer of pad material on the swept surfaces of your rotors. See: http://www.zeckhausen.com/bedding_in_brakes.htm for instructions on how to do it. Assuming the brakes are properly bedded, when you romp on the brake pedal now, there are molecular bonds formed between the pads and the pad transfer layer on the rotors. As the rotors turn, these bonds are torn apart and reformed. It is the resistance of these bonds to being broken that gives you the adherent component to your friction. Adherent friction results in less rotor wear, quieter operation, less brake dust, and better pedal feel. Since you have a combination of abrasive and adherent friction working for you, you don't have to press on the brake pedal as hard to bring the car to a stop.

In order to take advantage of adherent friction, there needs to be some heat in the system. Most street pads are designed to work in adherent mode when the brakes are only slightly warm. So after the first touch of the brakes, adherent friction kicks in. Most street pads tend to work well up to about 800 or 900 degrees, at which point the friction level falls off. Race pads can work up to 2,000 degrees, but they may not kick into adherent mode until about 400 degrees. That's why race pads need to be warmed up during the first lap before they really start working. And it also explains why race pads, driven on the street, are incredibly abrasive to rotors and produce lots of dust. They aren't getting hot enough to get into their adherent mode. All you have working for you is abrasive friction. For racers, who switch back and forth between street and track pads, this can even be useful. See: http://www.zeckhausen.com/avoiding_brake_judder.htm

From the results reported by StopTech and by the members of this forum, the SRT8 pads seem to have the characteristics of a race pad when driven on the street. It's worth experimenting a bit and seeing if proper bedding can help. But I think the root cause of this problem is that the stock pads have a prodominantly abrasive mode of operation under street conditions. Unfortunatly, the pad shape is a new one and not yet documented by FMSI. Until that happens, we're at the mercy of DC to come out with a more appropriate street pad.

[Rebel78]

Damn, I've got 550 miles on mine, I haven't even thought about checking my rotors, I'll take a look next time I'm out. It does make a ton of brake dust though. This pretty much sucks if rotors are gonna give out after 30K.

[Johnny Vig]

I am in the same boat as everyone else. We all should send a letter to dcx or document with our dealer so we can hopefully get new pads before the rotors are ruined.

DZeckhausen, thanx for all the great info. I am also wondering in the meantime if there will be some different pads in the aftermarket that we can get so we could reduce the brake dust. It is annoying beyond belief. Thx.

[jconnolly1119]

Originally Posted by DZeckhausen

Sorry for coming in late to this discussion. I didn't notice it until someone posted a link back from the brakes forum.

Let me jump right to the heart of the matter. When StopTech had an SRT8 in for big brake kit measurements earlier this week, they also noticed this issue. The test car had very low mileage, yet the rotors were really chewed up and the front wheels were black with brake dust. The problem is not the rotors. It is the choice of friction by DC. The pads they picked are very abrasive when cold. In my opinion, they made an inappropriate pad selection and all SRT8 owners are going to experience this problem. Eventually, this is going to become a warranty issue and DC will have to issue updated pads to all SRT8 owners. That is assuming enough SRT8 owners bring the issue up to their dealers, get it documented, and insist that it's not due to "abuse" by the owner.

Now I would like to address some of the points raised by others in this thread. There is no such thing as "soft" rotors. With a few exotic exceptions, brake rotors are made of "gray iron" and the metallurgy of rotors from various manufacturers is virtually identical. There are an assortment of impurities that can be adjusted in the mix when casting the rotors. These impurities affect hardness, ability to be heat cycled without cracking, brittleness, and many other characteristics. You can make a rotor less prone to pad deposits, for example, by changing the amount of a particular impurity. However, there are side effects. By changing the amount of one impurity, you affect other characteristics of the rotor, such as it's resistance to cracking. That has to be compensated for by making the friction plates thicker and the air gap smaller (assuming the overall rotor thickness remains constant) and the rotor becomes heavier with less ability to flow air (smaller air gap) so the convective cooling falls off. My point is that rotor manufacturers have pretty much converged on the ideal mix of materials and there is not much variation between rotors produced by Brembo, StopTech, ATE, Zimmerman, Balo, Performance Friction, etc.

How did this rumor of "soft rotors" begin. I don't know for sure, but I can give you an educated guess. The metallurgy of a BMW rotor is virtually the same as that of a Mercedes rotor. Yet Mercedes rotors typically last 50% longer. When BMW customers complain to their dealer about needing to replace the rotors with every pad change, they are told that "BMW carefully designs the rotors and pads to wear at the same rate. BMW rotors are high performance and made of softer metal." That's nonsense! The truth is that BMW specifies only 1.6mm of allowable rotor wear before the rotors should be discarded. Mercedes specifies 2.4mm of allowable wear. There's your 50%! BMW tends to make design compromises aimed toward improving performance and handling. Thus, a 30mm thick BMW rotor has thinner friction plates and a larger air gap, providing less weight for better handling and improved airflow through the rotor for better convective cooling. Mercedes rotors are heavier, but they last 50% longer, extending the rotor service intervals and addressing the perceived needs of their customers.

Getting back to the SRT8 pad issue. There are two primary sources of friction between your rotors and your pads. One is called abrasive mode friction. You are all very familiar with that one. It's simply the collision and mechanical destruction of the peaks and valleys in the crystalline structure of your pads and rotors. Another less understood component is called "adherent mode" friction and only occurs if you have properly bedded your brakes. Bedding is the process of laying down a thin transfer layer of pad material on the swept surfaces of your rotors. See: http://www.zeckhausen.com/bedding_in_brakes.htm for instructions on how to do it. Assuming the brakes are properly bedded, when you romp on the brake pedal now, there are molecular bonds formed between the pads and the pad transfer layer on the rotors. As the rotors turn, these bonds are torn apart and reformed. It is the resistance of these bonds to being broken that gives you the adherent component to your friction. Adherent friction results in less rotor wear, quieter operation, less brake dust, and better pedal feel. Since you have a combination of abrasive and adherent friction working for you, you don't have to press on the brake pedal as hard to bring the car to a stop.

In order to take advantage of adherent friction, there needs to be some heat in the system. Most street pads are designed to work in adherent mode when the brakes are only slightly warm. So after the first touch of the brakes, adherent friction kicks in. Most street pads tend to work well up to about 800 or 900 degrees, at which point the friction level falls off. Race pads can work up to 2,000 degrees, but they may not kick into adherent mode until about 400 degrees. That's why race pads need to be warmed up during the first lap before they really start working. And it also explains why race pads, driven on the street, are incredibly abrasive to rotors and produce lots of dust. They aren't getting hot enough to get into their adherent mode. All you have working for you is abrasive friction. For racers, who switch back and forth between street and track pads, this can even be useful. See: http://www.zeckhausen.com/avoiding_brake_judder.htm

From the results reported by StopTech and by the members of this forum, the SRT8 pads seem to have the characteristics of a race pad when driven on the street. It's worth experimenting a bit and seeing if proper bedding can help. But I think the root cause of this problem is that the stock pads have a prodominantly abrasive mode of operation under street conditions. Unfortunatly, the pad shape is a new one and not yet documented by FMSI. Until that happens, we're at the mercy of DC to come out with a more appropriate street pad.

Thanks for all the info Dave. I do have one question about the bedding process though. If I bed the brakes and then take the car up to the dealership to document the problem for a warranty issue, are they going to look at the amount of pad material on the rotors ( due to the bedding process ) and claim that this IS abuse by the owner. I know alot of dealerships really don't know much more than we do about these cars and DC has never had a car come with a brake system like this ( or at least that I'm aware of). I'm just afraid I'll bed the brakes and some yahoo at the dealership will look at the rotors and go "what the hell have you been doing to this car?"

I guess what I really need to know is "what should we do first?" By the way, my car has 530 miles on it right now.

Thanks Dave

[DZeckhausen]

Originally Posted by jconnolly1119

Thanks for all the info Dave. I do have one question about the bedding process though. If I bed the brakes and then take the car up to the dealership to document the problem for a warranty issue, are they going to look at the amount of pad material on the rotors ( due to the bedding process ) and claim that this IS abuse by the owner. I know alot of dealerships really don't know much more than we do about these cars and DC has never had a car come with a brake system like this ( or at least that I'm aware of). I'm just afraid I'll bed the brakes and some yahoo at the dealership will look at the rotors and go "what the hell have you been doing to this car?"

I guess what I really need to know is "what should we do first?" By the way, my car has 530 miles on it right now.

Thanks Dave

The bedding process puts a very light gray haze on the rotors. It's what all rotors are supposed to look like. Unfortunately, most people don't know to do this, so they end up with uneven transfer or no transfer at all. Often they end up with a judder problem as a result and they end up thinking their rotors are "warped." Replacing the rotors does make the problem go away, but unfortunatly also reinforces their faulty mental model of what really happened. For those who want to read more, check out: http://www.stoptech.com/whitepapers/...otors_myth.htm

To answer your question, I would say go ahead and try the bedding process. The transfer layer is subtle and the dealers are unfamilier enough with this car that they won't have a clue. They aren't sophisticated enough to look for it and it they were, they would also know that it's a good thing. Whatever you do, don't bring up the bedding process to an uneducated service advisor, since they are going to be looking for any way to not have to deal with this. I could just see one of those guys latching on to this and using it against you.

One more thing. I expect these pads are so abrasive when cold that they will chew away any transfer layer put down by the bedding process. These things seem to behave like track pads rather than street pads.

[Northern Rider]

Originally Posted by Northern Rider

I think there is something else going on here. The pads and rotors on the 300C are standing up very well. DCX are using ceramic pads in that application.

Without a close look, it's hard to tell, but the problem might lie in the pad compound rather than the rotors themselves.

Dave Z, a sponsor and resident brake expert, hopefully will see this thread and join in.

Thanks for the explanation, Dave. It confirmed my suspicions about the aggressive pad compund.

[jconnolly1119]

Thanks so much for your time Dave.. LET THE BEDDING PROCESS BEGIN!!!!