[Swift016]

Guys,
I need help/feedback...
I have a 2019 XLE A10. ...only mods are Goodrich stainless brake lines and Motul 600 brake fluid.. Michelin Ps4s at 34psi hot.

Yesterday at Barber I ran in Track with nannies on, and Sport Competitive...I had bad fishtailing under moderate braking from higher speed... the car was unstable and felt like way too much rear bias to a race car... the rears would chirp and feel like locking up... I never felt the anti-skid cycle , but was too busy to look at the dash..

Is the anti skid part of the ESC ? How does yaw control activate and when ? I assume that is with differential braking through ESC...
The car never felt like it was braking at a normal rate, and I had to use brake markers much earlier than usual..

I know the Mich are not track tires, but I don’t believe that is the issue... my mech says my stock brake pads were good, but have not rechecked them today, I’ll also check rotors for any issues.. track camber and toe are spot on.

Anyone else have an experience like this ? I can’t risk another track day until I find the cause... bummer !

Thanks,
Bill
Newnan, Ga

[cdb95z28]

Like you mentioned, your tires are not track tires. Not even close to it. The tires are the biggest factor in traction. Change out your tires and see how it drives.

And yes, you would have to brake earlier, and you won't be able to be as aggressive with the Michelins compared to the OE 3Rs.

If you have alot of front negative camber that can cause instability under heavy braking. The rears chirping are saying they are loosing traction, hence the ABS engagement.

[CW3SF]

The tires are the likely issue. IMHO.

[Swift016]

Originally Posted by cdb95z28

Like you mentioned, your tires are not track tires. Not even close to it. The tires are the biggest factor in traction. Change out your tires and see how it drives.

And yes, you would have to brake earlier, and you won't be able to be as aggressive with the Michelins compared to the OE 3Rs.

If you have alot of front negative camber that can cause instability under heavy braking. The rears chirping are saying they are loosing traction, hence the ABS engagement.

I have run these tires on track before, without these issues.. I understand the increased braking distance due to less traction... the rears were locking up without ABS activating... rear end was fishtailing ... again, it felt the same as way too much rear bias... front tires never lost traction.. I believe the street tires would have less grip at all corners..

This was like an extreme brake bias issue, and I don’t know how ESC, yaw control and ABS factor in this problem..

Thanks guys,
Bill

[cdb95z28]

I talked to a GM Gen6 brake engineer concerning a braking issue I had 2 years ago on my Gen5 1LE. The only thing that was different for me in that instance was a tire change. That was the obvious part of course. He agreed and stated the ABS cal is sometimes not very forgiving. They are calibrated to alot of factors, similar to an engine cal. Since the tires are at the heart of the ABS, and ESC, a big change from the OE cal (3R) is not going to yield a good result.

Did you run those same exact tires, the same set, before on track? If so, since they are a street tire, they are already heat cycled out. The fronts didn't lose traction because of the weight transfer. I bet those tires would have a softer sidewall compared to the 3R, possibly the ESC would pick up on that. Did the car feel like it had more dive under braking?

[cdb95z28]

Ironically those tires in my instance were Michelin Pilot Sport Cup 2. With those tires my car would put the power down better than with the 3R, but the cornering grip and braking grip were reduced. My ABS was calibrated for 285/35-20 Goodyear G:2 and 4 piston Brembos. I moved up to the 6 piston Brembos and 305/30-19 3Rs with Raybestos ST43 pads. A big change.

[Swift016]

Originally Posted by cdb95z28

I talked to a GM Gen6 brake engineer concerning a braking issue I had 2 years ago on my Gen5 1LE. The only thing that was different for me in that instance was a tire change. That was the obvious part of course. He agreed and stated the ABS cal is sometimes not very forgiving. They are calibrated to alot of factors, similar to an engine cal. Since the tires are at the heart of the ABS, and ESC, a big change from the OE cal (3R) is not going to yield a good result.

Did you run those same exact tires, the same set, before on track? If so, since they are a street tire, they are already heat cycled out. The fronts didn't lose traction because of the weight transfer. I bet those tires would have a softer sidewall compared to the 3R, possibly the ESC would pick up on that. Did the car feel like it had more dive under braking?

Good info, thanks...

These were the same tires... I never thought a street tire would heat cycle out like a race tire..

I felt little to no dive under braking.. it felt like most of the braking was on the rear... interestingly, cornering and acceleration grip did not seem to be reduced at all.... my only issue was in straight line moderate braking... I believe threshold braking would have resulted in an uncontrollable car.
I believe the Mich’s are a great street tire, and acceptable for occasional track days, as long as you don’t expect 3r performance... this was a bigger issue than 4 corner loss of grip..

I’m tying to find something else... I’ll get the car on a lift and check for dramatically worn front pads.., I thought the ABS would account for that ???

Thanks again,
Bill

[TrackClub]

Originally Posted by Swift016

Guys,
I need help/feedback...
I have a 2019 XLE A10. ...only mods are Goodrich stainless brake lines and Motul 600 brake fluid.. Michelin Ps4s at 34psi hot.

Yesterday at Barber I ran in Track with nannies on, and Sport Competitive...I had bad fishtailing under moderate braking from higher speed... the car was unstable and felt like way too much rear bias to a race car... the rears would chirp and feel like locking up... I never felt the anti-skid cycle , but was too busy to look at the dash..

Is the anti skid part of the ESC ? How does yaw control activate and when ? I assume that is with differential braking through ESC...
The car never felt like it was braking at a normal rate, and I had to use brake markers much earlier than usual..

I know the Mich are not track tires, but I don’t believe that is the issue... my mech says my stock brake pads were good, but have not rechecked them today, I’ll also check rotors for any issues.. track camber and toe are spot on.

Anyone else have an experience like this ? I can’t risk another track day until I find the cause... bummer !

Thanks,
Bill
Newnan, Ga

Hi Bill, I would say this is a very unusual behavior. Firstly, a few questions:

1. Have you run the car as is, on track before with no issues? Or was it the first time?
2. Are the tires stick sizes?
3. What Track Mode were you in? There is no such thing as "Sport Competitive". So, were you in Competitive Mode, or PTM Sport 1 or 2?
4. What is your front toe alignment?
5. What phase of the corner did you experience the rear instability? Straight line braking before turn in? During turn in while trail braking?
6. Do you have Rev Match on, or blip yourself? Is the instability while downshifting, or before?
7. How many track days/cycles on the tires?

Some musings ahead of your answers:

As long as tires are stock sizes, they should not provoke any ill behavior from ABS or ESC. S4s are not G3Rs, but many use them for track duty and they should behave well, even though not offering as much grip. Lots of uber cars come with them as OEM rubber, including C8 and Euro cars. Conversely, many run slicks on their cars and have no ABS issues. So, my guess is it is not the tires. Even if they were completely cycled out, loss of grip should be fairly equal F vs R and not provoke rear stepping out per se. My friend once raced a borrowed Nascar stock car on old tires used for winter storage. Sure, the car had reduced grip everywhere, but would slide equally F and R, as one would expect. He had little grip, but still a well balanced car.
(I don't recommend such practice, unless one is truly proficient in car control lol!).

Rear getting lose under braking can be caused by too much toe out in the front, too much rake (as in too tall tires in the rear), brake bias issues due to master cylinder malfunction, loss of braking power in the front vs rear (such as no pads left in the front, which would increase rear bias mechanically). Possibly brake line issues, causing more rear vs front bias. Basically something that will either decrease F bias, or increase R bias, or impact same, regarding F to R bias.
EDIT: also caused by not blipping throttle sufficiently when downshifting. Or, perhaps, thinking Rev Match is on, while it is not...

ABS engaging would elongate the braking zone, but i have never heard of it unsettling the rear (that would clearly and completely negate its positive role as a key safety function and make folks spin out instead).

I don't think it is an ESC issue, as it engages when direction of car travel vs steering input yaw is excessive (by applying brakes to a given wheel to counter act the yaw and prevent a potential spin). Clearly, this would not apply under straight line braking as there would be no yaw to manage (assuming the system is not malfunctioning).

Over to you sir regarding more details per my questions please.
Cheers!

PS My worst spin ever, was on entry to a mid speed corner at about 80mph, when i didn't blip the throttle sufficiently during downshift and that caused the rears to lock up. It was instant, violent and scary as hell. Thankfully, nothing bad happened, but i could have easily rolled the car as i shot off track sideways (this was in my old C5Z btw).

[collinms]

Why not use PTM? One of the best features of the car...

[kropscamaro16]

i had ps4s on my car switched over to supercar3 dropped 6 seconds at fontana and then 5 seconds at big willow...great street/auto x tire horrible on track

[TrackClub]

Originally Posted by collinms

Why not use PTM? One of the best features of the car...

Agree, the PTM is an excellent system. Yet, I don't think it would play a role here. Competitive Mode (if this is what Bill ran) should have given him the same benefit of ESC as PTM Sport 1, while possibly making the car much looser on exits due to lack of TC. But, not under braking.

But, a good point overall and i also consider the PTM an absolute cat's meow

[TrackClub]

Originally Posted by kropscamaro16

i had ps4s on my car switched over to supercar3 dropped 6 seconds at fontana and then 5 seconds at big willow...great street/auto x tire horrible on track

You must have been napping, or maybe having sex or something to drop 6 seconds solely due to tires
Not suggesting S4s are as fast as G3s, but sure as heck they are not 5 secs off on a buck 30 lap (assuming they are not completely cycled out).

Auto Club Speedway - Fontana, CA
1. 1:49.88 - birdmanf16 in '18 SS 1LE, OE Goodyear's, e85 tuned with CAI, Video
2. 1:50.60 - Tim202 in '18 ZL1 1LE, OE 3R tires, all stock see post #314
3. 1:51.91 - Destroyer_1LE in '17 SS 1LE on 5/20/18, PS4 Tires, Spoiler extension, see post #220
4. 1:57.066 - Rootsie in '18 V6 1LE on 10/7/18, Nexen NFERA tires see post #246
5. 2:00.18 - Rootsie in '18 V6 1LE on 5/4/19, P-Zero All seasons, stock

PS I recall we had this conversation before, but i cannot recall what exactly you fessed up to lol

PSS This is all in good humor, that's all. Cheers!

[kropscamaro16]

1:53 at fontana last time and 1:35 at big willow yesterday...not sure wtf im doing but ill take it haha

[TrackClub]

Originally Posted by kropscamaro16

1:53 at fontana last time and 1:35 at big willow yesterday...not sure wtf im doing but ill take it haha

Lol!