Brake Pads: PFC 08's are high adventure...anyone tried 331 332?

[elbert]

I'm relatively new to HPDE; driving at an intermediate level. My car has Michelin PS4S, track-capable suspension and alignment, and I use PFC08 with Motul 600/660.

Reeling in the speed from 110+ to 40 mph is high adventure - there is a bit of a vague feeling for the first second or two. Even after 5 or more laps, if the situation involves a braking zone after a long straight there is a period of time...maybe 1 or 1.5 seconds where these pads are heating up and the friction is increasing. In the process, at least initially they don't really seem to bite like I would expect. ]

tl;dr version
Your pads need more heat

long version
I had the same experience as you with my 08 pads. I fixed it by gaining speed.
I took a 10 year break from track events (work, family), and started back up in 2018. When I started up again, I was very rusty, maybe intermediate level at best.
For the first few events, I would experience the split second lag before having any bite. I was unfamiliar with the pads at the time, so I thought that was how they worked.
However, now that I'm getting back up to speed (heh), I don't have the lag anymore.

As a side note: you really need to turn off your DSC.
- It is detrimental to your development as a driver
- It can overheat your rear pads
- It will literally slow you down

[OldRanger]

Are you running brake ducting?

I am not running brake ducting. I (still) have the removable plastic covers in the wheel arch trim that block that opening. But, I'm fairly certain my brakes aren't over-heating.

Thanks for your perspective on the PFC 331, 332 combo!

[OldRanger]

...the Back Straight has a dip just before the braking zone. That can cause a tire grip/suspension rebound issue, depending upon how the car is set up I always like to clearly understand whether a "felt" issue is grip or braking. I assume stock calipers? Slider pins clean and straight? You are using anti-rattle clips? No pad knockback? Pad wear even and rotor sweep looks right?

PFC-08s should be solid, repeatable and need no heat beyond the first lap. Do you have a high, solid brake pedal with no signs of air in the lines? Which fluid?

Thanks for the questions, I understand.

Regarding dips in the track and possible rebound/grip issue: I have Ohlins R&T w 400/700 springs with dampers set to 6 and 4 from hard front/rear respectively. The ABS gets involved, but not dramatically. I had DSC on the whole time, my car is a 2005/MK60 - it was interveneing predictably and still allowing good speed. I believe there is fairly good traction for PS4S, but I'm keeping my eye on those damper settings. I made a change before this HPDE - increased/firmed up the dampers 10% (2 cllicks) from my last track day after adding a GC Front Sway set soft and the 700# rear springs. My concern, like yours would be that the rebound damping is too firm. Related: the chassis behaved well on the ski jump at speeds around 100mph.

I use stock calipers that I rebuilt after my son drove/HPDE in May. Slider pins are clean/straight, I'm using anti-rattle clips, the pad wear is even and the rotor sweep looks right. I have a solid brake pedal with no signs of air in the lines (no fading, no need to pump the brakes). I use a pressure bleeder, but I would be too bold to say things are 100%. Since the pedal doesn't fade nor require any pumping, I don't think I have an issue with air or knockback.

More on knockback: it is possible, but minor. I occasionally get a minor pull to the left (from the front) that I noticed more on my other track day in August. If there is/was any, it would be reasonable based on the conditions of the front wheel bearings that I just changed this week. I presume originals with 166K miles. The right one came off with finger-only pressure turning the 3-jaw puller and was rather noisy. They were in need of replacement for track duty.

[Estoril]

I think you spend time here: Summit Point, Shenandoah Back Straight into the Loop. Most noticeable there vs the bridge straight. My instructor didn’t notice it or have any concerns. His response while on Shenandoah was along the lines of “it’s good you’re learning how they work”. He encouraged me to brake where comfortable. In the case of the Loop, he wanted me to start braking where the curbing started.

FWIW, I have no plans to change pads - I’m just in learning mode making sure I understand the dynamics and pad design.

Another possible explanation is: that this is simply what it feels like for the first 1-2 seconds of braking from 110+ mph. The conclusion I came to was that the friction was increasing into braking but that could be a misperception. I’m a relative newbie (on 4 wheels at these speeds).

I was on Shenandoah this past weekend with SCCA, instructing in the Nov group. I'll note that the Back Straight has a dip just before the braking zone. That can cause a tire grip/suspension rebound issue, depending upon how the car is set up I always like to clearly understand whether a "felt" issue is grip or braking. I assume stock calipers? Slider pins clean and straight? You are using anti-rattle clips? No pad knockback? Pad wear even and rotor sweep looks right?

PFC-08s should be solid, repeatable and need no heat beyond the first lap. Do you have a high, solid brake pedal with no signs of air in the lines? Which fluid?

[OldRanger]

Before I comment - what has your Instructor said about this issue? He is in the car has a firsthand perspective. Which track's long straight?

I think you spend time here: Summit Point, Shenandoah Back Straight into the Loop. Most noticeable there vs the bridge straight. My instructor didn’t notice it or have any concerns. His response while on Shenandoah was along the lines of “it’s good you’re learning how they work”. He encouraged me to brake where comfortable. In the case of the Loop, he wanted me to start braking where the curbing started.

FWIW, I have no plans to change pads - I’m just in learning mode making sure I understand the dynamics and pad design.

Another possible explanation is: that this is simply what it feels like for the first 1-2 seconds of braking from 110+ mph. The conclusion I came to was that the friction was increasing into braking but that could be a misperception. I’m a relative newbie (on 4 wheels at these speeds).

[Estoril]

Before I comment - what has your Instructor said about this issue? He is in the car has a firsthand perspective. Which track's long straight?

[eacmen]

PFC08 have plenty of initial bite IMO. Haven't tried the other pad compounds you mentioned. But usually with higher cold bite you may end up wearing the rotors more. PFC08 seem to be a good trade off on performance vs wear.

[r4dr]

Are you running brake ducting?

08s are inherently low bite, but they should be pretty consistent unless they're cooling off (as evidenced in that graph as well). The 33X compounds are quite excellent, and the 332/331 combo might work pretty well for your car. The digressive rear lets the friction fall off as the rear gets light under brake dive, reducing the chance of ABS intervention due to the rear locking up.

[OldRanger]

I'm relatively new to HPDE; driving at an intermediate level. My car has Michelin PS4S, track-capable suspension and alignment, and I use PFC08 with Motul 600/660.

Reeling in the speed from 110+ to 40 mph is high adventure - there is a bit of a vague feeling for the first second or two. Even after 5 or more laps, if the situation involves a braking zone after a long straight there is a period of time...maybe 1 or 1.5 seconds where these pads are heating up and the friction is increasing. In the process, at least initially they don't really seem to bite like I would expect. At 100 mph, you are traveling about 150 feet per second, so this is relevant for when to start braking. The other consideration at the end of the brake zone: if the pads are increasing friction as temperature rises...that makes modulating the brakes for trail braking becomes a challenge.

Now, all of this might simply be a learning curve I need to work through. I can adapt to this...especially given that it's consistent behavior. But...has anyone tried the PFC 331 (Front) and 332 (Rear) setup that is digressive? They have\\\ a substantially higher amount of friction at lower temps and a lower friction on the rear pads? That seems to make a bunch of sense for HPDE sessions on a car like the M3 with ABS.