Overly-sensitive ABS at the track?

[dparm]

This is not necessarily an M3-specific question, but rather, a general question.

On the track, I find it difficult to use the full brake pedal travel every time. In some corners, and sometimes unexpectedly, the ABS engages and I have to back off slightly. I can definitely see it in the Corvette because the PDR shows the brake application at way less than 100%, but it did happen to me in the M3 even with AD08R tires (though a bit less often).

Is this a symptom of too much brake and not enough tire?

[tdott]

What brake setup?

[dparm]

Originally Posted by tdott

What brake setup?

My M3 had a slotted StopTech ST40 with Ferodo DS2500 pads & Castrol SRF fluid. Tires were Yokohama AD08R (255/275 sizing on ZCP wheels).

The Corvette has the "hook" 370mm iron front rotors with 6-pot Brembos up front, and 365mm and 4-piston Brembos in the back. OEM pads and OEM fluid. Tires are Michelin PSS ZP (285/335).

[///Mobbin]

I experienced this before with "not enough tire" or rather brake pads that were fresher and a grade above the tires I was running. Turning traction control off lessened the effect fwiw (and I haven't turned it back on since).

[tdott]

Were you running stock rear pads? Perhaps a more aggressive rear pad is needed to even things out.

I haven't had a problem with stock brakes at the track, when I first bed in my DTC-70s in the front it was super easy to trigger the abs on the street, but at the track they were great.

Can you feel or tell with wheel is locking up first?

[dparm]

So I just ordered new pads and talked to Dave Zeckhausen of Zeckhausen Racing. It sounds like my understanding of ABS behavior at the track was incorrect and might have led to me overusing the brakes (e.g. not braking hard enough -- a rookie mistake).

Up until now, I was operating on the assumption that ABS at the track is a bad thing -- it equates to hot pads being hammered repeatedly onto hot rotors. As such, anytime I felt the ABS engaging, I would slightly back off the brake pedal to be right at the threshold.

Dave corrected me and said this is not how a modern ABS system works. The pulsating in the pedal is because the wheel speed sensor is seeing a difference in deceleration rates and is telling the ABS controller to open the check valve and adjust the fluid pressure slightly. It does NOT mean your pads are being pulsated onto the rotor.

His advice was to just keep pressing harder if you feel the pedal pulsating.

[Richbot]

It's a symptom of Corvettes gonna Corvette, they seem to engage ABS early and often across the front wheels IMO

but C7GS Corvette ABS is one of the best-optimized for track in the world, use it

Also not sure how the data system in GM is set up but 100% on the brakes probably just means the max of the range the brake pressure sensor is expecting to see, not whether you're at threshold or not or braking as hard as possible right?

[dparm]

Originally Posted by Richbot

It's a symptom of Corvettes gonna Corvette, they seem to engage ABS early and often across the front wheels IMO

but C7GS Corvette ABS is one of the best-optimized for track in the world, use it

Also not sure how the data system in GM is set up but 100% on the brakes probably just means the max of the range the brake pressure sensor is expecting to see, not whether you're at threshold or not or braking as hard as possible right?

The PDR data shows you exactly how hard you were braking. I don't know how it derives that, but the point remains that if you look at the output, I wasn't using the full braking potential because I [mistakenly] thought the ABS was going to damage the rotors.

[Z K]

The only time I've engaged ABS on track is when I am on the brakes hard in the rain or other low traction situations.

I've found that the wheel will usually lock and skip slightly before ABS engages. That's how I know I've reached the limit of tire grip under braking. I am also running more aggressive brake pads so that may be why my wheel locks before ABS engages.

[ThunderMoose]

I personally think ABS is a good think. Here's what can happen when you're expecting it and it doesn't work. The E46 M3 is me.

[Candide13]

Originally Posted by dparm

So I just ordered new pads and talked to Dave Zeckhausen of Zeckhausen Racing. It sounds like my understanding of ABS behavior at the track was incorrect and might have led to me overusing the brakes (e.g. not braking hard enough -- a rookie mistake).

Up until now, I was operating on the assumption that ABS at the track is a bad thing -- it equates to hot pads being hammered repeatedly onto hot rotors. As such, anytime I felt the ABS engaging, I would slightly back off the brake pedal to be right at the threshold.

Dave corrected me and said this is not how a modern ABS system works. The pulsating in the pedal is because the wheel speed sensor is seeing a difference in deceleration rates and is telling the ABS controller to open the check valve and adjust the fluid pressure slightly. It does NOT mean your pads are being pulsated onto the rotor.

His advice was to just keep pressing harder if you feel the pedal pulsating.

It's an interesting idea, but I don't think using ABS on track routinely is the right thing to do. Maximal breaking, threshold breaking, occurs just below the ABS kicking in, so when it kicks in reducing brake pedal pressure is the right thing to do, normally. Now, in a true emergency situation ABS allows you to simply floor the brake pedal whilst still being able to steer around obstacles on the road, but that is not the usual situation on a track.

But even if your tech is right, and using ABS is safe and fast, I would still not want to do it. After all, how do you win at HPDE? By enjoying to drive your car at the limit of traction, without computers changing the definition of "limit" here. That's why traction control goes off for advanced HPDE driving (at least in the dry, ask me how I know) etc.. ABS falls in the same category for me, but I am glad it remains there for true emergency braking, so I don't need to switch it off, but I try not to use it.

Just my two cents..

[roastbeef]

is the abs triggering when you are starting to put in steering input, like with trail braking?

[dparm]

Originally Posted by roastbeef

is the abs triggering when you are starting to put in steering input, like with trail braking?

No. Straight-line braking.

[ayao]

Originally Posted by Candide13

It's an interesting idea, but I don't think using ABS on track routinely is the right thing to do. Maximal breaking, threshold breaking, occurs just below the ABS kicking in, so when it kicks in reducing brake pedal pressure is the right thing to do, normally. Now, in a true emergency situation ABS allows you to simply floor the brake pedal whilst still being able to steer around obstacles on the road, but that is not the usual situation on a track.

But even if your tech is right, and using ABS is safe and fast, I would still not want to do it. After all, how do you win at HPDE? By enjoying to drive your car at the limit of traction, without computers changing the definition of "limit" here. That's why traction control goes off for advanced HPDE driving (at least in the dry, ask me how I know) etc.. ABS falls in the same category for me, but I am glad it remains there for true emergency braking, so I don't need to switch it off, but I try not to use it.

Just my two cents..

Several years back there was a thread by a guy who had cracked some PFC DD rotors -- and IIRC after the rotors were sent back to PFC for analysis there was a lot of discussion about ABS activation causing a hammering effect on hot rotors that lead to the failure.

[SYT_Shadow]

Originally Posted by Candide13

After all, how do you win at HPDE? .

By crushing your enemies, seeing them driven before you and hearing the lamentations of their women

[Candide13]

Originally Posted by SYT_Shadow

By crushing your enemies, seeing them driven before you and hearing the lamentations of their women

Nemesis video, that's all I say.

[SYT_Shadow]

Guys

I'm at WGI for the IMSA event

As my brother and I are in the Glen Club 'VIP', pro drivers come in to talk.

Last year we met Danika when we came for Nascar. I asked her if she missed tracks that turned both ways. She didn't seem amused and replied that she left IndyCar for Nascar because she preferred ovals. Oops.


Aaaaanyway. This year we got Oswaldo and Katherine from the Acura NSX GT3 team.

In the Q&A, Oswaldo was asked about his biggest challenge coming from the Prototype cars to the GTs.

He said ABS. That in the prototype cars 'my foot is the abs' because there isn't any. [This reminds me of a GT3 991 driver asking the friend who uses my 6mt E92 at the track how he can keep up with a manual, to which my friend answered 'my arm is my dct'. ]
Anyway, he said the prototype could take as much brake as you could muster due to the aero and you never had an issue.
He went on to say the GT cars all have abs, and the idea is to brake right before abs intervenes. Also, when abs intervenes the car no longer brakes as well so he has a hard time lifting the pedal just enough to remove abs intervention


So
A pro driver just confirmed the same thing we have all heard. Abs intervention is bad (i.e. slower) and should not be used by design

[roastbeef]

Makes sense. Think of it like this, and intervenes at the threshold of a lockup. Which is, by definition, a loss of traction. Not full loss, but loss as in- less. So it intervenes to get it back. There is time lost there.

Op, maybe practice lifting off the brake at lower speeds as you decelerate and see if you can still maintain the same braking force. 90% pedal pressure may not be necessary once you decelerate and only 70% is necessary to achieve the same stopping power, but it prevents abs. I don't know for sure, I'm only throwing a thought out there.

[bigjae1976]

The point of ABS is to allow you to steer the car during max braking. ABS also extends your braking distances. So using ABS under threshold braking is just making you threshold brake for longer.

DSC is for the gas pedal. Think of ABS as the DSC for the brakes.

Does DSC make you faster?

[dparm]

Originally Posted by Candide13

Nemesis video, that's all I say.

I will never get tired of that video.

[SYT_Shadow]

If I posted any of my track videos they'd go viral, just like this one.

Unfortunately I cannot and try to maintain a low profile. All in car screaming, yelling and gesturing stays in the car

[Mvez]

Let's not forget that how you get on the pedal also affects the ABS intervention rate.

If you want good tech info on how OEM and Race ABS works, watch the many videos online of Darrick Dong from PFC giving his tech talks. They are extremely informative, and give the novice, experts, and racers info all to chew on, regardless of what kind of car you drive.

Almost all brake systems work the same in which they give all 4 wheels brake force, but the ABS bleeds pressure off the unloaded tires (the rear typically in a straight line brake), which is also caused by how aggressive the initial brake application is. It's to create stability. Most track cars want to try and add more rear bias to increase OVERALL braking ability. However, to achieve this, the application of the brake must be so that you don't have the system dump all the rear brake and go to full front bias, hence ABS doing its thing.

They key is to get pressure on brake, then progressively but quickly get to max pressure, then trail off. This way you get as much brake ability from all 4 wheels, without dumping the all rear bias and sending it into full front bias. The goal is to maximize that time when you have as much rear brake bias as possible, and slow the dump of rear brake. This is why I don't like pads with lots of initial bite, they immediately make it harder for you to avoid ABS dump.

My car, on Trofeo-R and Ferodo DS1.11 (which I think have too much initial bite) seem to be a decent match, and I honestly don't have much to complain about the BMW ABS. I just avoid the late brake hero stuff, and the car does pretty much what it's told.

13 minutes starts his ABS discussion. He has some older ones from 2014 as well.