[Cloud9blue]

Been running slotted ECS front rotors (http://www.ecstuning.com/BMW-E92-335...ors/ES2190266/) for over a year now. And after nearly a dozen events, they have started to crack pretty badly, so I replaced them with a new set just last week.

At less than $100 a pair, I figured a gave Meyle rotors a try (http://www.ecstuning.com/BMW-E92-335...ors/ES2612423/).

The same thing is that they don't bite nearly as hard as my old beat up slotted rotors, even after they got an nice even pad transfer layer on them... I have to brake 10-15 yards earlier and apply more pressure on the pedal than I used to.

The datalog reflects the same thing: the maximum decel. g-force went from -0.8g with the old rotors to -0.6g with the new blank rotors. I haven't touched anything else in the brake system, same PFC08 pads, and same ATE brake fluid...

Always though the slotted, drilled rotors are more of a gimmick with modern brake pads compounds. But my experience says otherwise. Just wondering if anyone else experiences the same thing with blank to slotted rotors. Or perhaps there is something else going on here (brake booster vacuum leak???)

[The HACK]

Does the data log brake pressure (I doubt it, but have to ask)? If it does you can compare the brake pressure vs. actual decel graph to rule out other possibilities.

The OTHER possibility, although it's just a wild-@ss guess from me, is that the pads have developed either a lip, a groove, or TAPER that matched the slotted rotors. The end result is either the new rotor is slightly larger, or smaller in diameter (few tenth of a mm) resulting in the pads not making a perfect and ideal mating surface to the new rotor. You can sort of test this by wetting down the rotors, let a thin layer of rust develop, then go out and brake lightly to see if the pads sweep the rust off the entire surface of the rotor. If you don't see the entire rotor clean of rust within the first light braking application, then the pads are either tapered or grooved. Or if there are significant streaks of rust that remains, then there are grooves in the pad that isn't making contact with the rotor.

Usually this will go away within some miles, like about 500 miles of regular driving. Unfortunately, for track pads they won't mate for a couple of sessions. But if the results you're seeing is consistent and overtime that these new rotors are not nearly as effective as the old, then other possibilities exist (like air trapped in the system when you pushed the pads back in that got moved around).

[Cloud9blue]

Originally Posted by The HACK

Does the data log brake pressure (I doubt it, but have to ask)? If it does you can compare the brake pressure vs. actual decel graph to rule out other possibilities.

The OTHER possibility, although it's just a wild-@ss guess from me, is that the pads have developed either a lip, a groove, or TAPER that matched the slotted rotors. The end result is either the new rotor is slightly larger, or smaller in diameter (few tenth of a mm) resulting in the pads not making a perfect and ideal mating surface to the new rotor. You can sort of test this by wetting down the rotors, let a thin layer of rust develop, then go out and brake lightly to see if the pads sweep the rust off the entire surface of the rotor. If you don't see the entire rotor clean of rust within the first light braking application, then the pads are either tapered or grooved. Or if there are significant streaks of rust that remains, then there are grooves in the pad that isn't making contact with the rotor.

Usually this will go away within some miles, like about 500 miles of regular driving. Unfortunately, for track pads they won't mate for a couple of sessions. But if the results you're seeing is consistent and overtime that these new rotors are not nearly as effective as the old, then other possibilities exist (like air trapped in the system when you pushed the pads back in that got moved around).

I don't have datalog for the brake pressure sadly (JB4 prevents any sort of canbus logger on the OBD port), but the pedals require significantly more pressure than I have before. But the issue is pretty evident from the g-force log which I attached below. The red dots are from yesterday and the grey ones are from last year. All were done using the PFC08 compounds and Hankook RS-3 tires.

I thought it was the wear matching between the old pads (1/2 worn at the beginning of yesterday's session) and the new rotors. But the rotors already have 500 miles on them since I put them on a week ago. Between the nice transfer layer on the rotor surface after each session and I burn through pads pretty quickly (used another 1/5 of the original thickness in just 3 sessions), I would imagine the pads are well matched to the new rotor surface by now.

Super confused by this point, but if this doesn't get any better after the next track events, I might just use these blank rotors for street use and get a new set of ECS slotted rotors.

[The HACK]

Usually the tires dictate how much deceleration G force you can generate though, so I don't quite know how to interpret this data. If you have brake pressure data, which you don't, it would then indicate to you that the pressure is the same but it's generating less G force, hence pointing squarely in the brake system.

So you're getting consistent brake pressure? No soft pedal?

[Cloud9blue]

Originally Posted by The HACK

Usually the tires dictate how much deceleration G force you can generate though, so I don't quite know how to interpret this data. If you have brake pressure data, which you don't, it would then indicate to you that the pressure is the same but it's generating less G force, hence pointing squarely in the brake system.

So you're getting consistent brake pressure? No soft pedal?

Brake pedal pressure has been very consistent, it is just that more is required than usual. That said, the brake fluid (ATE) is a little old after 3 months and 5 DEs.

I am dumbfounded by the data as well. Given that I am running brand new rubbers, I should be able to brake at least as well as before. Not sure what's going on...

[Knonsense]

at less than 50% cost of the ECS rotors, it would stand to reason that they would perform ~1/2 as well.

moving from -0.8g to -0.6g is a -25% delta in maximal g force.

methinks you're getting exacted what you purchased.

what's the kinetic friction coefficient for the ECS and the Meyle metals?
how does the slot in the ECS rotor vs the solid Meyle rotor affect thermal energy transfer and dissipation?

if all you changed was the rotors, you should look at the rotors for the answer.

[Cloud9blue]

Originally Posted by Knonsense

at less than 50% cost of the ECS rotors, it would stand to reason that they would perform ~1/2 as well.

moving from -0.8g to -0.6g is a -25% delta in maximal g force.

methinks you're getting exacted what you purchased.

what's the kinetic friction coefficient for the ECS and the Meyle metals?
how does the slot in the ECS rotor vs the solid Meyle rotor affect thermal energy transfer and dissipation?

if all you changed was the rotors, you should look at the rotors for the answer.

Cast iron is cast iron. So you are saying the friction coefficient of the meyle rotors are 25% less than the ECS ones, despite the increase in the surface area??? I find that hard to believe.

There is very little difference in their friction coefficient unless it is entirely different material or if the iron has underwent a phase transformation at higher temperature (formation of cementite due to heat spots that occur from bad rotor run outs and excessive brake pad deposit, which I see no evidence of such).

From what I can see, the two rotors are identical, with the same thickness and vane counts. Of course, the metal composition in the Meyle rotors could be significantly different from that of the ECS. But both are reputable brands with being an actual OE supplier, neither of which just some random ebay parts with no quality control, and the raw material costs of cast iron is very low anyway, so there isn't much you can cut corners on that...

My guess is that slotted rotors allow for a more even pad transfer layer with these PFC 08 pads, as the slots would clean away the particles that would cause grooving and uneven wear that tends to happen more with blank rotors. A more consistent transfer layer would result in better bite between the pads and rotors, as I would imagine.

I will update this when I collect more track data in the coming weeks. And perhaps test out the hardness of these rotors, which would indicate if there is any significant materials difference between the two.

[feuer]

Originally Posted by Cloud9blue

Cast iron is cast iron. So you are saying the friction coefficient of the meyle rotors are 25% less than the ECS ones, despite the increase in the surface area??? I find that hard to believe.

There is very little difference in their friction coefficient unless it is entirely different material or if the iron has underwent a phase transformation at higher temperature (formation of cementite due to heat spots that occur from bad rotor run outs and excessive brake pad deposit, which I see no evidence of such

There is no increase in the surface area since the rotors are the same size dispite the new rotor being little thicker. The area that the pad is using is identical. True, cast iron is cast iron but the properties might be different resulting in different friction coefficient. Also how it was cast. I suspect of this just as the poster above.
http://www.calmet.com/different_types_of_cast_iron.html

[Cloud9blue]

Btw, I have been getting vibration on the highway ever since I installed these rotors, particularly noticeable when I apply brakes at 80-90mph. Thought it was just some rust build up on the hub surface preventing the rotors from sitting true, but the problem never went away despite having me cleaning the hub surface twice...

Got tired of the problem, so I spent the time to put the old ECS rotors back on. Guess what, the vibration was completely gone. The only downside is that the slotted rotors are a bit noisier on the highway than the blank ones.

I have to say I am going to recommend against these Meyle rotors in the future. It is one thing to use inferior metals that doesn't bite nearly as well as the ECS ones, which most people will never notice with stock type street pads, but having a brand new rotor out of true is completely unacceptable from a quality control point of view...

[chris82]

This may help your cause:

https://racetechnologies.wordpress.c...cs-face-types/

Slotted rotors are absolutely not a gimmick, race teams use them all the time depending on the track and length of the race

[Kgolf31]

I use OEM Blanks and HP+ Pads and have data showing of 1.01 Gs in braking at complete threshold.

I'm with Hack on his analysis.