[will.c]

For last weekend's event, I had:
- new OEM Z4 3.5is front rotors, new rear OEM rotors
- new Cool Carbon S/T pads all 4
- newly flushed to Superblue

Problem was when the brakes got really hot, a lot of steering wheel vibration came in. After 1 min cooling, everything became normal, so I went out for more. Another 3-4 laps in, problem repeated. Well, after asking around I found a solution: PFC01 pads. Now the question is:
Do I need all 4, or should I just get the front 2?

Premises:
CC pads for daily; PFC only for track; everything else is stock

Thanks in advance for your advises!

[ciomas]

had the same problem with CC after 2 laps at the ring. I would start with a proper track compound

[mid-corner fun]

I think you know my answer but here it is anyway, PFC01s or DTC70s. I'd love to try a slightly less harsh/longer lasting compound (PFC06s and DTC60s) but they're not available for OE M3/335 caliper size

[will.c]

Thanks for the responses. I'll def get the PFC01s without a doubt. But considering the rears do a lot less work, do I need to get the rears too? Can I just stick with CCs in the back and just get the front PFC01s? Or would this mess with the front-rear brake balance?

The reason for considering this is because:
- front and rear are almost same price at around 200-230/pair
- it'll take half the time to replace every time (I'll track often, every 2-4 weeks)

[RevC]

yes get rears as well, clamping force will be unevenly distributed imho. DTC's are way too agressive for those rotors imho, i've also not had good luck running pfcs on any of my cars they always leave uneven pad deposits and cause major judder (esp dtc70s). They also take tons of heat to work right and the noise..well. believe it or not i ran hawk +'s on my sti and they've outperformed or performed on par with almost ever other brake pad i've tried. the braking force is slightly decreased but if you want to learn and become a better driver you'll learn how to barely use your brakes. btw hope your going to njmp for your track days. cool carbons are not suitable for heavy track use, that's just my .02 though, i personally would recommend ferodo ds's pads per your application

[mid-corner fun]

No uneven pad deposits/zero judder with the DTC70s here. I even reuse the same rotors between my track and street pads, as long as you bed in and scrape out the track pad deposits this works well. Both the DTC70s and PFC01s will eat your rotors by the way. I find the DTCs to be more aggressive than the PFC01s.

As a sidenote, some people (including me) here and on m3post have reported clanking with the PFC01s. Some others have no issue with them whatsoever. In my setup, there's sufficient play space for the 01 pad ends to rotate up/down (not in/out) freely and start clanking at low speed, this does not affect braking, it's just annoying. PFC01s do not come with clips, FYI.

Also, unless something changed you cannot get DTC70s as rears, PFC01s make front and rear shapes for our calipers.

GL!

[will.c]

Great stuff guys! Damn.. this is not as easy as I thought. I'll do a little more research and shoot for proper race pads for all 4, whatever that brand may be, DTC70/PFC01/HP+/etc. Thanks for sharing your experiences!

[TC Kline Racing]

I would also recommend track pads on the front and rears as well. Depending on the corner you could get into a situation where the rear end will want to 'come around' alot easier if you don't have the same 'clamping force' in the rear as you do in the front.

I would also throw the HT-10's in for consideration. Intermediate to high torque with a smoother initial bite. Also has a consistent pedal feel.

[BMWsky]

I use the HT-10s as well and LOVE them. Granted, take them off when you leave the track as they make your car sound like a garbage truck that needs brakes, but they work so damn well. The hotter they get, the better they work (or so it seems to me).

[CJ421]

Good discussion. I was at the same event this past weekend and didn't have issues with my brakes. I have upgraded fluid + SS lines but stock brake pads. I noticed longer stopping distances toward the end of each session. But otherwise I had no problems.

I will be looking into pads before my next event.

[The HACK]

Originally Posted by wonho

Thanks for the responses. I'll def get the PFC01s without a doubt. But considering the rears do a lot less work, do I need to get the rears too? Can I just stick with CCs in the back and just get the front PFC01s? Or would this mess with the front-rear brake balance?

The reason for considering this is because:
- front and rear are almost same price at around 200-230/pair
- it'll take half the time to replace every time (I'll track often, every 2-4 weeks)

Here's a purely anecdotal evidence. I used to run Cobalt XR3s on my MZ4 Coupe, but for some reason the rears didn't fit so I'd always keep my Cool Carbon R/Ts in the rear and just swap out the front to the XR3s. Last year the XR3s wore out and I swapped over to DTC60s, and this time the front AND the back both fit so I bought an entire set.

While driving at California Speedway, we (BMW CCA) always put a set of chicane in on the front straight to keep the entry speed into turn 2 down and also prevent cars from destroying the engine from a very VERY long WOT. While braking for the chicane with the XR3 front and Cool Carbon R/T rear combo almost always leave the rear end wiggling from ~140mph indicated down to ~85mph in a very short span, that hasn't been the case with the DTC60 front and rear. Also, when coming in to measure my tire pressure, the front with the mixed compound would almost always be at least 2 psi higher than the rear, no matter what I do. And this is at multiple tracks.

Once switched over to same compound front and rear, the tire pressure almost always increase at the same rate, and if I set them to 29psi cold front and rear, I would come in 37psi hot, just in the ideal range for the tires front and back. While on mixed compounds I would always get the fronts 2-3 psi warmer, which would lead to either understeer or a weird "softness" sensation in the rear, like it was under inflated.

My theory is that the front brake pads are so much grippier, that it's doing a disturbingly MORE amount of work compared to the rear, therefore the front tire gets up to temp faster and holds higher pressure due to the front end doing so much more work while under braking. Result is unbalanced handling and poor balance once the tires are up to temp in a few laps.

Of course, this is all done with 3 different sets of pad compounds, so I can't tell you that it's the most scientific result. For all I know DTC60s are THAT much better than Cobalt XR3s (again, anecdotal evidence would suggest otherwise). So take it with a grain of salt.

Yes in a pinch, you can put the more grippy pads up front. But ideally, if you can get the same compound all around, the car will behave and handle better with that setup.

[TC Kline Racing]

Originally Posted by The HACK

Here's a purely anecdotal evidence. I used to run Cobalt XR3s on my MZ4 Coupe, but for some reason the rears didn't fit so I'd always keep my Cool Carbon R/Ts in the rear and just swap out the front to the XR3s. Last year the XR3s wore out and I swapped over to DTC60s, and this time the front AND the back both fit so I bought an entire set.

While driving at California Speedway, we (BMW CCA) always put a set of chicane in on the front straight to keep the entry speed into turn 2 down and also prevent cars from destroying the engine from a very VERY long WOT. While braking for the chicane with the XR3 front and Cool Carbon R/T rear combo almost always leave the rear end wiggling from ~140mph indicated down to ~85mph in a very short span, that hasn't been the case with the DTC60 front and rear. Also, when coming in to measure my tire pressure, the front with the mixed compound would almost always be at least 2 psi higher than the rear, no matter what I do. And this is at multiple tracks.

Once switched over to same compound front and rear, the tire pressure almost always increase at the same rate, and if I set them to 29psi cold front and rear, I would come in 37psi hot, just in the ideal range for the tires front and back. While on mixed compounds I would always get the fronts 2-3 psi warmer, which would lead to either understeer or a weird "softness" sensation in the rear, like it was under inflated.

My theory is that the front brake pads are so much grippier, that it's doing a disturbingly MORE amount of work compared to the rear, therefore the front tire gets up to temp faster and holds higher pressure due to the front end doing so much more work while under braking. Result is unbalanced handling and poor balance once the tires are up to temp in a few laps.

Of course, this is all done with 3 different sets of pad compounds, so I can't tell you that it's the most scientific result. For all I know DTC60s are THAT much better than Cobalt XR3s (again, anecdotal evidence would suggest otherwise). So take it with a grain of salt.

Yes in a pinch, you can put the more grippy pads up front. But ideally, if you can get the same compound all around, the car will behave and handle better with that setup.

Very well said. This is a great explanation.

[turugara]

So many NJ guys who go to NJMP. This is awesome!

I run pfc01's on both the front and the rear for the track. I have had no rotor problems but the brakes themselves do squeal like pigs and clank quite a lot. Otherwise I run them for most of the months when I do hpde's either every or alternating weekends.

I have driven with them on the street but I wouldn't recommend it. The initial cold bite is nearly nonexistent and is very dangerous. Plus switching out pads gets easier as you it more often. First time it took me two hours for the first pad, an hour for the second caliper, and half an hour for the rest. Now it takes less than an hour for all four.

[will.c]

Mmm very interesting stuff here... I'll def get the same race compounds for all four per your advises.

Now, I'm still waiting for a few more quotes, but so far I noticed how some pads are not available for the rears, i.e. Ferodo DS, DTC-70, HT-10, etc. (or at least through Raceshopper.com) Is this true? If not where did you get em?

At this point, I'm leaning towards Carbotech XP12s or XP10s because they come with clips, avail both F&R, and good with high temps.. unless any opposition from you guys.

[mid-corner fun]

some race pads are indeed for front-fitments only (such as DTC70s), you can go down to the next available level of the same brand for rears. bimmerworld and tirerack, among other vendors, have charts with available part #s for each pad vendor/car type combination.

[TC Kline Racing]

Originally Posted by wonho

Mmm very interesting stuff here... I'll def get the same race compounds for all four per your advises.

Now, I'm still waiting for a few more quotes, but so far I noticed how some pads are not available for the rears, i.e. Ferodo DS, DTC-70, HT-10, etc. (or at least through Raceshopper.com) Is this true? If not where did you get em?

At this point, I'm leaning towards Carbotech XP12s or XP10s because they come with clips, avail both F&R, and good with high temps.. unless any opposition from you guys.

[vwong]

Originally Posted by wonho

At this point, I'm leaning towards Carbotech XP12s or XP10s because they come with clips, avail both F&R, and good with high temps.. unless any opposition from you guys.

My vote goes to Carbotech. I'm using XP12 front and XP10 rear, and I'm very happy with them.

[will.c]

I'm bringing this thread back for some more enlightenment from you guys. I appreciate your time in advance.

This past track weekend, my brake issue came back - Steering jutter while braking when brakes are hot.

Brake specs:
Z4 3.5is front (2 piece?) rotors, OEM sport rear rotors
Carbotech XP12 pads front, XP10 rear
Brand new flush to Superblue
(All of these components are not worn much at all.)

Symptoms:
First 4-5 laps, no problem; smooth & solid feel.
When heated up, steering jutter happens while braking, slowly getting worse.
Within next 2 laps, jutter becomes pretty ridiculous so I have to pit in.
2 minute rest and back out, brakes become smoother again.

I guess I'm getting a bit better at this particular track, but this lack of confidence of braking hard & consistently is getting to be really disappointing. I thought, maybe I'm dragging the brakes too much, thus heating them up necessarily. However, after trying different combinations of pedal force and duration at each corner, I've come to conclusion that jutter happens regardless, that is, if I'm pushing the car hard. (When I took it easy, I didn't get the jutter as much.)

What do you think?

[The HACK]

Problem is either insufficient brake cooling, or improper bed-in.

[will.c]

Originally Posted by The HACK

Problem is either insufficient brake cooling, or improper bed-in.

Quick and painless answer. I will address those items for my next event and report. Thanks.

[The HACK]

Well, my answers are typically short and to the point, or they're War and Peace type dissertations...

If my initial hunch about insufficient cooling or improper bed-in is correct, there's no need to read further. But if you want one of those dissertations I'm FAMOUS for...

There are a thousand factors that can contribute to vibration under braking. And they all have one common cause. Heat in the brake system. The symptoms will vary, and the component that suffers, or the remedy will vary too.

But the most basic, most simple answer to ANY brake problem...99.9% of it is lack of sufficient cooling or improper bed-in.

Now. I'm going to jump around a little bit. My brain just doesn't work in a linear sense (I'm a creative type...Marketing guy. So bear with me). Symptoms of improperly bedded pads will most of the time feel like "warped rotors," or vibration under braking. Now, the symptoms will be almost identical to what you describe, and this is what's going on. There are certain spots on the rotor that has more pad deposit than other spots due to improper bed-in. As rotor and pad heats up, the "high-spots" become more pronounced and therefore front end starts shaking like an epileptic (sorry if I offend any seizure sufferers, it's the first analogy that came to mind) after about 4-5 laps of hard driving under braking. SOME cooling off will alleviate the problem, but problem will come right back as soon as the pads and rotors are heated up again. This is actually more common on drilled or slotted rotors vs. OEM blanks for some reason I can't fully explain.

Typically, though, improperly bedded pads will have far more consistent symptoms, like almost always vibration when braking, the only difference is as the brake system gets hotter and as you brake harder, the vibration gets more severe since MORE deposit will be placed on the high spots. You can almost always see bad bed-in by shining a bright light on the rotor, there will be spots on the rotor, like dark patches, that indicate more pad material has been deposited.

Another thing I've noticed though, and this is a little harder to visualize, is that certain vented rotors have a tendency, once it's heated up to a point, to develop uneven expansion rates. I've seen this on factory rotors on heavier class race cars driven by VERY fast guys, where you can clearly see a pattern on the rotor, where there's no opening of the vanes there's typically more deposit than vented area of the rotor. I suspect, on heavier cars (this was on a 3,600 lbs race car using stock rotors) the rotors just can't dissipate heat fast enough and the end result is uneven surface temperature leading to weird pad deposit patterns on the rotor. I remember viewing the video once, and noticed that the car vibrates like crazy under braking. Driver's response? "Because race car." This car would have benefitted tremendously from more cooling because of the weight of the car and the stock rotor. I believe eventually the rotor CRACKED and they moved on to an aftermarket fixed caliper system with larger rotors to accommodate after the first season.

One other thing I noticed, is that certain pads are more susceptible to creating this weird "vibration" problem than others, and certain part of a pad's life is far more susceptible to this problem. For example, my Cobalt XR3s started having this issue with the pads dropping weird deposits on the rotor despite proper bed-in, as soon as the pads wore down to ~50% original pad thickness. Never had the problem before until the pads are slightly less than 50%, then it got progressively worse. Part of the problem may be that the rotors got used to seeing a Hawk street compound during the normal driving conditions, and as the pads wore down, they heat up quicker and the same deposit routine during my orientation laps are leaving uneven deposits. I don't know. I've also noticed that the problems are more pronounced on days that are REALLY cold by California standards, like starting the day in the high 40s. So far, the Hawk DTC-60s I'm using does not seem to have the same characteristics. I also noticed the Carbotech XP-8 I used to use on my E46 to show similar wear pattern...As soon as it starts to go down below 50%, weird deposit problems starts to show up.

Granted, the Hawk DTC-60s still have about 60% pad thickness left to it, so I'll see soon enough if the same problem will rear its ugly head once the DTC-60s wear down. In the mean time, if your pad has less than 50% material left on them, I'd seriously consider altering the bed-in routines in the morning, or sacrifice the first session and slowly bring the brake temps up, and let it cool-down almost like a brand new bed-in process before hammering the brakes.

[will.c]

Originally Posted by The HACK

Hack, I find your dissertations very reasonable, enlightening, and even enjoyable to read. And this one has given me an emphasis on the importance of PROPER break-in. I didn't know the brakes were such delicate machines btw.. I do daily-drive these pads, so weird deposits are most likely inevitable. And this past time, I didn't break them in properly; I just used the first a few laps as warm up and break-in.

Again, thanks a lot for your time on this, and I will definitely try a few solid sessions of break-in prior to my next event, as well as exploiting some venting options, and report back with results!