4 Point 0

I was watching a vid on how PFC developed brakes and rotors for cup cars. They had to withstand 600 applications at a certain speed. They never knew everyone else failed this test. So Porsche laughed when they finally did it and gave them the contract. The follow up video discussed preemptive vs reactive ABS.

Motorsport ABS is just reactive. Perfect for tracking.
Street ABS also have preemptive ABS. This seems like it may be causing me some issues on the track.

Especially as i have changed tyre sizes.

Can someone smarter than me explain preemptive ABS and effect of changing diameter of tyres?


I may return to stock sizes next tyre refresh. This could be why Porsche say only run N-Spec tyres. As the crappy Ferrari K-Spec designed for 11 inch wheel 305 is perhaps different diameter and cause preemptive ABS interference? where as N-spec 305 designed for 12 inch wheel.

Only reason i occasionally have K-Spec is no stock of N-Spec Cup2-R. I also run RS spec front 265/35/20.

I run full traction control off, and coming onto the straight, I am getting what feels like some traction control interference. I think it may be preemptive ABS.

Nathan_

No expert on this but would anticipate that any preemptive ABS would rely on there being significant brake pressure and it wouldn’t cut the engine - it would cycle the ABS valves to prevent lock up.

If you are feeling a cut / retardation I would get some logging in place and determine what the engine is doing at that point.

4 Point 0

Apparently Porsche have made ABS part of the traction control system. It feels as if the car is braking when I’m on the gas. I’m no where near the brake pedal.

Its either the clutch is starting to slip, or the car is applying brake, in anticipation of the brakes about to be heavily used. The car also has a protective system that if you are heavily into ABS, it temporarily re-activates traction control.
But this isn’t my issue. I’m not on the brakes, I’m accelerating with a lot of g force on the car. The car is being held back until its straighter, and then full power comes on.

I really need to run “Dyno” mode which disabled all systems, including ABS. That would let me know for sure if its an ABS issue.

As I said, Motorsport ABS does not have these preemptive programming. Unless you are deep into the brake pedal, it’s doing nothing.

Ya know Nathan, if I had MoTeC, i wouldn’t be having any of these issues. 🤣. You can add motorsort ABS to MoTeC. Just saying 🤣

Nathan_

Have plenty of customers running Bosch M4 / M5 with it and yes, it is awesome.

just soooooooo busy right now!

I thought the integration was for using the brakes for yaw control at as part of the stability control which in fairness you could be feeling, might be one of those weird things where it says it is off but isn’t really.

I honestly don’t see why any braking aspect of ABS would come in to play with no brake pressure - you aren’t going to lock a wheel if you aren’t using the brakes.

4 Point 0

Actually, at one of our tracks, thats exactly what happens when you leave full traction control on!

I am pinning the accelerator flat to the floor, at 170km/hr and rising and the car would lock a rear brake and really unsettle the car. It was dangerous. Full traction off, and I am now doing 200 through there safely.

I also toasted a brand new set of OEM rear pads in 3 x 20 min sessions with traction on. Now i burn through 3 full front sets before the rears look worn.

fsmich

I add a similar issue when exiting a banked turn at Chuckwalla Raceway. Felt the rear brakes pulsing in the turn, then "bucking and grabbing"" on the exit and the straightaway under full power. I have about 15 days at this track and have never experienced this before.

The change to the car was new brakes, the AP competition kit. WRT (a local race shop) runs Ferodo 3.12 front pads, Dsuno rears when they install this kit on GT3's. "Because the 3.12's have too much bite in the rear and interfere with ABS".

I have 3.12's front and rear. Which worked with the oem calipers. But not the AP setup.

Emotion told me running 265 fronts with 305 rears WOULD cause stability issues. Your fronts at 265 have the same diameter as the rears, and stability is looking for fronts to be about 1/2" shorter rolling diameter. Maybe even in the underlying "off" mode.

I'm on my fourth set of rotors. I track a little

4 Point 0

Even though I had rake adjusted, I tend to think the 265’s up front are contributing to this issue.

I’ve only just replaced them as well. I may get my son to buy 245’s and swap him. See if that helps.

I mainly used to run Endless ME20, now i run Endless N35S, which has been the best pad so far. Zero fade at the track, almost no squeal on the street.

However I have been hearing great things about Race Technology RE10. I want to give those a go as soon as they are available in my size.

fsmich

I ran a set of RE-10's. They last forever, and are easy on the rotors. But they were noisy on the street. And you have to stand on the pedal in the big brake zones. I prefer the 3.12's that require a lot less pressure to get to threshold. I swap out to 2500's for street use.

4 Point 0

What size rotors? I’m running Brembo GTS BBK with 380 front and rear. The second set of calipers has changed to pink again. I’m looking into the forged GTR. Stiffer and nickel plated. Also running a 34 mm thick, deeper annulus rotor. I may need brake ducting as well. Is there anything for my GT3 front end?

fsmich

The Girodisc's were 350's. The AP's are 372/34 and 365/32. The kit is 15lb's lighter than the giro's and stock calipers. Only 4 track days on them, but the black anodized caliper finish is holding up.

Nathan_

@fsmich is right - if you have increased the diameter of the fronts relative to the rears the car will be more likely to think you have lost traction.

4 Point 0

Well it’s actually worse than that. Not only have i increased front by running N-Spec (Porsche) 265/35/20 front, I couldn’t get N-Spec rear. So I went K-Spec (Ferrari) 305/30/20 on rear. If you don’t know the difference between N-Spec and K-Soec, Porsche run 12 inch rim and Ferrari run 11 inch rim, and it shows. The K-spec look stretched.
So I have most likely decreased the rear and increased the front.

Mercedes Black Series have a 335/30/20.on a 12 and it looks flush. If I ran that, this time around, that would help?
It would be bigger than K-Spec anyway.

Yes its **** that you can get multiple 305’s all different sizes.

Since the K-spec is designed for an 11 it is most likely a 285 branded 305. Which means even if its a 30 it will have a smaller diameter than the N-spec one.

4 Point 0

N-Spec (Porsche)

K-Spec Ferrari


Does the K-Spec 305 look a little stretched to you? 🤣

thesaintusa

Do you think this variation in rolling diameter may be contributing to any of your issues?

No idea if it does, but now I am wondering.

And yes the K-Spec 305 looks quite a bit smaller than the N-spec.

enzotcat

Well, due to a complete lack of ability to get N-spec Cup 2s, Pirellis or Dunlops over here, I'm getting a set of K-spec's for my car - standard size 245/35ZR20 and 305/30ZR20. Hopefully this will not impact my handling too much. Kinda frustrating that we seem to be having persistent tire availability problems. Actually it was worse than that - I found a set, got them ordered, only for 1 of the rear tires to literally "go missing" - the shipper lost it irretrievably, so I wound up with 3 tires instead of 4, with no hope of getting the 2nd rear tire, at least in N-spec. So I took the conservative option - sent all 3 back, and am waiting for 4 K-spec tires to show up. At least they will be consistent in their stretchiness ...