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[ANSWERED] "Ice mode" in PTM driving modes

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[ANSWERED] "Ice mode" in PTM driving modes

 
Old 07-17-2018, 02:41 PM
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jvp
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Default [ANSWERED] "Ice mode" in PTM driving modes

The original question is here.

village idiot asked:
A number of us were wondering why the hard brake pedal mode ("ice mode" as its been called ) is active in PTM, especially sport 2 and race. It seems like it activates when a wheel is suddenly or quickly locked, like it would on ice or other low friction surface. Unfortunately, a wheel locking quickly happens a lot on the track because, generally, one or more tires are unloaded at any given time, plus things like bumps and curbing unload them.

A combination of being unloaded with big brakes and track brake pads seems to engage this "ice mode" on the track, where it's difficult to see the benefit of it. So what is this "ice mode" and why is active in PTM? It seems very dangerous.
Tadge answered:
The key to understanding this phenomenon is that a true ‘ice mode’ where specific calibrations are changed due to distinct surface detection doesn’t exist in any way in the ABS control algorithm. We understand the behavior you are describing but it is not a mode detection that can be turned on or off. The calibrations that can cause this long recovery of deceleration are part of the fundamental ABS wheel control calibration. These calibrations are remarkably complex and significantly beneficial in many situations both on and off track and can’t just be shut off in PTM, they are part of the core wheel control function within ABS. If we did not have variable rates of decel recovery the common race track situations you describe such as curb strikes and spike brake applies while cornering would be very poorly controlled.

To achieve the level of performance expected of Corvette the calibrations are quite sensitive. Further, the control is being done based entirely on four wheel speed sensors which are measuring wheels in extremely dynamic situations. Very rarely is any one wheel traveling at the true speed of the car when ABS is needed. Certain very aggressive driving behaviors can cause any number of calibrations that are critical to overall track performance to produce a lag in decel development, eliminating these situations as much as possible is one of the main tasks that require our extensive engineering effort throughout years of vehicle development work.

Given the significant effort put into optimizing these calibrations we have found that in almost all of the cases where this behavior is noticeable to the driver there have been modifications made to the vehicle that effect the ABS calibration. Different tires, brake pads, and suspension components are examples of modifications which can influence this behavior. We try to predict some common changes that an owner might make to a vehicle but we have no way to test every tire on the market or every brake pad and hardware combination. Further, the more we accommodate race tires or brakes the less robust we are to all season tires or lower dust street pads and vice-versa. You would not expect your engine controller to accommodate a new cam shaft or headers without calibration changes so the same logic applies here.

However, if you have changed any of these components you may find that modifying your brake pedal apply to a softer engagement (even very slight changes) can help the system work with your new components. We have many drivers on the team who have never once experienced this situation and turn in exactly the same lap times as those of us who do occasionally find it.

It’s also important to note that this characteristic of ABS control is not unique to Corvette. It can be found in the ABS systems of many suppliers and across most performance oriented cars, particularly those that have had any kind of modifications made to their brakes or suspension systems.

Having watched these discussions for as long as we have been doing chassis controls, we anticipate many great theories on new, easier ways to do this better… but please keep in mind that any new control idea must be able to work in real time. I.e. with no benefit of analysis after the event or knowledge of the next event (event meaning a 20 millisecond departure of a wheel towards lock or similar situation). It also must work with only 4 wheel speeds and none of those speeds will be a perfectly accurate measure of real vehicle speed. It’s a tough task since there are a near infinite number of variables affecting performance and if we optimize around a rare circumstance we will very likely compromise a commonplace event.
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Old 07-17-2018, 07:58 PM
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I will say that ABS is one of the things C7s have done right. The C7 Z breaking calibration is astonishing, and I've used it all the time in HPDE to brake late and a catch up on many pure race cars. In autocross you can linger on the brake while turning and make for killer turn in.

Used in track mode with TC and AH completely off.

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Old 07-18-2018, 11:44 AM
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ponderingtom
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This is so disappointing. I accept the explanation in the answer, but I don't accept that I don't have a way to turn it off. I bought this car to drive on road courses. I'm in Alaska, so I haven't hit a road course yet, but I attended a few time trials on a large, rough, airport with max 130mph speeds. The brakes felt different in every turn and didn't work in one of them. Consistently. I've done several autocrosses, and at one of them, I almost blew through the finish cones because I had no brakes at the end.

Side note: one of those time trials was completely stock everything. Tires, wheels, pads, rotors. Still had the issue. It was actually worse though with different wheels/tires.

Bottom line: For Sale: 2017 Corvette 3LZ Z07. I guess I'm headed back to Mustang world. SMH
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Old 07-18-2018, 02:40 PM
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I guess I didn't realize it was this complex. I would've just asked, "hey why can't you just make ABS less aggressive when PTM is turned on." Clearly it's not as simple as that.
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Old 07-18-2018, 08:59 PM
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Originally Posted by dparm View Post
I guess I didn't realize it was this complex. I would've just asked, "hey why can't you just make ABS less aggressive when PTM is turned on." Clearly it's not as simple as that.
It isn't about aggressive. Think about the variation in road conditions you can have at each wheel. One wheel on gravel, one on pavement and two on snow. I have had Ice Mode occur a couple of times on my C6Z. That was the only Corvette that happened on. However, I have benefited from having ABS on my cars. The best example I have of that is 1997 when I had my first C5 I was giving a ride to an instructor at the Glen when we came downhill through the Carousel turn following a Mustang. As you track out to go down the chute the hill has a slight crest so you can't initially see the pavement in the chute. As I came over that crest there was power steering fluid all over the track and the Mustang driver was suddenly trying to collect his car before it spun. Even though he was on oil he was still slowing rapidly as the car was sideways to me and I was doing right around 105 mph so we had a rapid closing scenario. I was in the fluid before I could even flinch. I had to slow down and steer around him so tapped the brake and all 4 wheels started doing their ABS thing. The car lurched a little but I was able to steer past the Mustang and out of the oil onto good pavement and get around the next turn at the bottom of the chute. That is what ABS does for you on and off the race track. Saying you want to turn it off is ludicrous. I more than likely would have T Boned that Mustang without it. The power steering fluid came from the Camaro that was in front of the Mustang. It dumped everything it had in one quick shot due to a hose breakage. I got an AttaBoy from the Instructor that day. He thought we were goners. The car really impressed him.

Bill
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Old 07-18-2018, 10:13 PM
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A few things:
1. I've never experienced this issue with limited track day experience (6 days)
2. It appears the OP and GM agree this tends to happen on modified cars.
3. I do follow the logic of modifying the engine leading to a tune requirement being similar to tuning ABS when it comes to brakes and suspension changes. It does seem like it would be a very sensitive system.
4. Have others experienced this issue in other cars as it is stated to be a common challenge?
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Old 07-18-2018, 11:31 PM
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I would be more accepting of the answer if we, like was described, had the ability to just tune our ABS system as we do with a modified engine. I am only aware of very few people who are capable of messing with this stock configuration. Everyone else must strip the factory ABS and install an aftermarket setup. We can’t just modify this feature to fit our car, which leaves us vulnerable and dangerous if we change anything from factory specs.

Last edited by fleming23; 07-18-2018 at 11:31 PM.
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Old 07-19-2018, 01:55 AM
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Originally Posted by fleming23 View Post
I would be more accepting of the answer if we, like was described, had the ability to just tune our ABS system as we do with a modified engine. I am only aware of very few people who are capable of messing with this stock configuration. Everyone else must strip the factory ABS and install an aftermarket setup. We can’t just modify this feature to fit our car, which leaves us vulnerable and dangerous if we change anything from factory specs.
I understand the desire, but I think modifying an ABS system is far different from changing engine, aero, or suspension bits. Based on the vast amount of control logic that I assume goes into a system, my belief is we (customers/tuners/shops) would make the factory system much worse before we made it "better: which in turn would push many either back to stock or to a dedicated race setup which is ideal.
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Old 07-19-2018, 08:52 AM
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Originally Posted by truth.b View Post
I understand the desire, but I think modifying an ABS system is far different from changing engine, aero, or suspension bits. Based on the vast amount of control logic that I assume goes into a system, my belief is we (customers/tuners/shops) would make the factory system much worse before we made it "better: which in turn would push many either back to stock or to a dedicated race setup which is ideal.
I don't disagree, but eventually someone will figure it out and give us the ability to "tune" it correctly. The same could be said for tuning a GM ECM. There are so many tables that if you go in and start screwing with them, you can destroy an engine in a hurry, but if you know what you are doing you can make proper adjustments. Again, this is all based on modifying a car, which isn't what Tadge, or GM, is concerned with, but many of us have and are as this impacts our ability to drive our car, and our personal safety.
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Old 07-19-2018, 11:29 AM
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Originally Posted by fleming23 View Post
I don't disagree, but eventually someone will figure it out and give us the ability to "tune" it correctly. The same could be said for tuning a GM ECM. There are so many tables that if you go in and start screwing with them, you can destroy an engine in a hurry, but if you know what you are doing you can make proper adjustments. Again, this is all based on modifying a car, which isn't what Tadge, or GM, is concerned with, but many of us have and are as this impacts our ability to drive our car, and our personal safety.
Yep, But just think how long it took for a company (DSC) to come out with a controller for the mag ride and unfortunately its not backwards compatible with the 2nd or 1st gen setups and even as good as it is they've had hiccups between C7 model years. My personal belief is that engine tuning is "easier" than ABS tuning because the control logic for a engine is more confined than that of very dynamic braking system.

Last edited by truth.b; 07-19-2018 at 11:30 AM.
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Old 07-19-2018, 12:47 PM
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Originally Posted by fleming23 View Post
I would be more accepting of the answer if we, like was described, had the ability to just tune our ABS system as we do with a modified engine. I am only aware of very few people who are capable of messing with this stock configuration. Everyone else must strip the factory ABS and install an aftermarket setup. We can’t just modify this feature to fit our car, which leaves us vulnerable and dangerous if we change anything from factory specs.
I agree they should address something. i think the point that Tadge brought up regarding all season tires and low dust pads was the most enlightening. Clearly there is a “lowering” of the limits of this system to due accommodating “crap” like this. Most of us will never put super sports or weak low dust pads on our cars and many like you are going even more aggressive than cup2’s and stock brakes. There obviously needs to be a “track cal” for the ABS if it can’t accomodate these two extremes. Should just be a menu option on the settings screen.
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Old 07-19-2018, 06:12 PM
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Originally Posted by Bill Dearborn View Post
It isn't about aggressive. Think about the variation in road conditions you can have at each wheel. One wheel on gravel, one on pavement and two on snow. I have had Ice Mode occur a couple of times on my C6Z. That was the only Corvette that happened on. However, I have benefited from having ABS on my cars. The best example I have of that is 1997 when I had my first C5 I was giving a ride to an instructor at the Glen when we came downhill through the Carousel turn following a Mustang. As you track out to go down the chute the hill has a slight crest so you can't initially see the pavement in the chute. As I came over that crest there was power steering fluid all over the track and the Mustang driver was suddenly trying to collect his car before it spun. Even though he was on oil he was still slowing rapidly as the car was sideways to me and I was doing right around 105 mph so we had a rapid closing scenario. I was in the fluid before I could even flinch. I had to slow down and steer around him so tapped the brake and all 4 wheels started doing their ABS thing. The car lurched a little but I was able to steer past the Mustang and out of the oil onto good pavement and get around the next turn at the bottom of the chute. That is what ABS does for you on and off the race track. Saying you want to turn it off is ludicrous. I more than likely would have T Boned that Mustang without it. The power steering fluid came from the Camaro that was in front of the Mustang. It dumped everything it had in one quick shot due to a hose breakage. I got an AttaBoy from the Instructor that day. He thought we were goners. The car really impressed him.

Bill
Bill, I experienced a similar situation (without the lack of visibility you had) at Sebring a few years back. Approaching the braking zone for turn 3 encountered coolant on the track, two cars ahead of me, one went left the other right,
I went through the coolant while braking for the turn and ABS saved the day.
ABS,don't leave home without it!

Last edited by speedwaywhite; 07-20-2018 at 12:36 PM.
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Old 07-19-2018, 07:12 PM
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Originally Posted by speedwaywhite View Post
Bill, I experienced a similar situation (without the lack of visibility you had) at Sebring a few years back. Approaching the braking zone for turn 3 encountered coolant on the track two cars ahead of me, one went left the other right,
I went through the coolant while braking for the turn and ABS saved the day.
ABS,don't leave home without it!
Or, in the case of this "icemode" issue: ABS, crash into a wall with it!

You all may think it's ludicrous to turn off ABS. I, and many that have experienced this issue (I assume), would rather have it off than on. My chances of coming over a hill and needing ABS because of something slick on the track is far less than my chances of going off track because of my car deciding I don't need all the braking power available to me. It has happened to me too often to think otherwise.
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Old 07-21-2018, 11:22 AM
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Kind of aggravating that we have multiple modes for traction control and active handling, even in my 2002, but we don't have a track setting for ABS even in newer cars.

I agree about the desire to tune ABS. When I and my collaborators get our open-source ’0411 PCM tuning finished I'll look into ABS next. I can't promise anything of course, but it's worth investigating.

Engine tuning was hard in the beginning, ABS tuning will be too, but it's all just software, sensors, and actuators.

Last edited by NSFW; 07-21-2018 at 11:22 AM.
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Old 07-21-2018, 01:07 PM
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Originally Posted by ponderingtom View Post
Or, in the case of this "icemode" issue: ABS, crash into a wall with it!

You all may think it's ludicrous to turn off ABS. I, and many that have experienced this issue (I assume), would rather have it off than on. My chances of coming over a hill and needing ABS because of something slick on the track is far less than my chances of going off track because of my car deciding I don't need all the braking power available to me. It has happened to me too often to think otherwise.
Good point.
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Old 07-21-2018, 04:27 PM
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I'm new to Corvettes, but I've experienced situations (in other track cars, as well as racing in dedicated race cars) where I've had to 'lock up' to avoid hitting the wall,or going off...hence the old driver training adage "when in a spin, both feet in".
Whether this happened from driver error, or having encountered spilled fluids, or being bumped, is not the point. Locking up the best way of scrubbing off speed once all else has failed and you're already sideways
This is the scariest element of ABS, that you can't intentionally save the car this way...not so much the 'ice mode' scenario.

But, I've also encountered situations of cars ahead suddenly vomiting fluid, where ABS would have been VERY welcome vs trying to finesse through a mess 'manually'.

Having said all that, while I do find it a performance advantage on track, in a dumbing-down kind of way, I think it also makes it a bit more difficult to tune for optimal brake bias (ie pad selection, etc) because ABS can mask which end would lock up first.
So, I'm not sure if anything is being given up in that respect, especially once we've strayed from OE. In fact, now I'm even questioning why I, and others, often select somewhat milder pad compounds for the rear. Isn't stock the same compound front and rear? Rear brakes are already smaller, so why do we feel we have too much rear bias and need milder pads? Has anyone actually experimented without ABS to establish this as the best thing?

Anyway, I've digressed, but I consider ABS a wonderful, essential safety device for street, but one which I wouldn't mind at least having the option of disabling on track, like the other dynamic driving aids...but really, no biggie...I'd rather have it and live with it, than not.

Last edited by tommyc6z06; 07-21-2018 at 04:29 PM.
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Old 07-22-2018, 08:47 PM
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Originally Posted by tommyc6z06 View Post
I'm new to Corvettes, but I've experienced situations (in other track cars, as well as racing in dedicated race cars) where I've had to 'lock up' to avoid hitting the wall,or going off...hence the old driver training adage "when in a spin, both feet in".
Whether this happened from driver error, or having encountered spilled fluids, or being bumped, is not the point. Locking up the best way of scrubbing off speed once all else has failed and you're already sideways
This is the scariest element of ABS, that you can't intentionally save the car this way...not so much the 'ice mode' scenario.

But, I've also encountered situations of cars ahead suddenly vomiting fluid, where ABS would have been VERY welcome vs trying to finesse through a mess 'manually'.

Having said all that, while I do find it a performance advantage on track, in a dumbing-down kind of way, I think it also makes it a bit more difficult to tune for optimal brake bias (ie pad selection, etc) because ABS can mask which end would lock up first.
So, I'm not sure if anything is being given up in that respect, especially once we've strayed from OE. In fact, now I'm even questioning why I, and others, often select somewhat milder pad compounds for the rear. Isn't stock the same compound front and rear? Rear brakes are already smaller, so why do we feel we have too much rear bias and need milder pads? Has anyone actually experimented without ABS to establish this as the best thing?

Anyway, I've digressed, but I consider ABS a wonderful, essential safety device for street, but one which I wouldn't mind at least having the option of disabling on track, like the other dynamic driving aids...but really, no biggie...I'd rather have it and live with it, than not.
I attended a seminar at the SEMA show by the head of motorsports from Pagid. One of the things he spoke about was his amazement at the fact that people use different compounds front and rear. He said that was a bad idea as the different compounds react differently as they heat up in terms of firction coefficients and friction linearity versus temperature and that it make braking on track un-predictable. He said it was much better to use similar compounds front and rear with similar temperature characteristics and then to tune the brake balance by hydraulic means such as brake balance controllers typically used in race cars. That caries the force applied to the pistons in the front versus rear calipers.
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Old 07-23-2018, 12:23 AM
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Thanks. That makes total sense and confirms my own thoughts and experiences.
Using different compounds on the back end not only strays from the factory’s ‘tested’ setup, but also ‘gives up’ some potential braking from the rear and therefore must add additional heat into the already over-taxed fronts that everyone complains about.
And less than optimal bias will be masked by the ABS.

I wish I had gone with my gut instincts, but being new to a car, one tries to listen to the sages in the brake business.
Next time....
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Old 07-23-2018, 05:35 AM
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Originally Posted by descartesfool View Post
I attended a seminar at the SEMA show by the head of motorsports from Pagid. One of the things he spoke about was his amazement at the fact that people use different compounds front and rear. He said that was a bad idea as the different compounds react differently as they heat up in terms of firction coefficients and friction linearity versus temperature and that it make braking on track un-predictable. He said it was much better to use similar compounds front and rear with similar temperature characteristics and then to tune the brake balance by hydraulic means such as brake balance controllers typically used in race cars. That caries the force applied to the pistons in the front versus rear calipers.
How common is it to have similar rotor temps front and rear? I've only tracked 3 cars but all of them were hotter up front. Running the same compound in different heat ranges front vs rear doesn't sound like a recipe for increased predictability, but I'll admit I haven't tried it.

Last edited by NSFW; 07-23-2018 at 05:41 AM.
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Old 07-24-2018, 07:04 AM
  #20  
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Ducati and Aprillia have had adjustable ABS on their bikes now for a couple of years. Its not that hard you have four settings. Off 1,2,3 each has its own characteristics. If they can offer it so can GM, it is just a matter of cost and effort to develop the algorithms.
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