Kaged

Have taken my Z06 out for both AutoX and HDPE and have some questions on the operating limits of the Stability Control. Car is running on MPSS run flats and is in SPort 1 for these events.

After making rapid transitions (corners, tight chicanes) I occasionally feel the car "step out" by a few inches as the car enters the next straight and I roll on the throttle. Typically I maintain the throttle, let it settle down and roll it back on. Very rarely do I have the engine stutter to reduce power. When reviewing my PDR videos- I do not see any indication of engaging stability or traction control. Even when I have started to spin out the car, there are no TCS or SC indications on the videos.

So - a few questions:
1) When the car steps out slightly and then settles down - that is the StabilTrak system engaging - correct? Shouldn't there be an indication on the PDR video of that event?

2)For setting the best time (assuming line, etc are correct) and the steering is opening up as I enter the straight - should I keep rolling on the throttle and let the Stability control/Traction Control intervene?
As I have managed to yaw the car about 30 degrees in a couple of corners by being too rapid on the throttle, I don't quite have the trust factor that possibly I should. In both instances I recovered the car without any issue, but not something I want to make a habit of doing. These tires give essentially no warning (to me) before cutting loose.

Have looked through a lot of threads and haven't quite put it all together yet, hence the questions.

TIA,
Bill

Bill Dearborn

Stability Control is a function where the system can apply one brake at a time or reduce torque input to control yaw. All C7s have it and on Z51s, the GS and the Z06 it is available in all modes except Track Sport 2 and Track Race. Our cars also have Performance Traction Management (PTM) which is only available in Track Mode and all of its sub modes. When you are in any of the Sub modes of Track Mode the OM states you should go to full throttle as the car passes the apex of the turn. As you power away from the apex PTM will limit torque delivered to the rear wheels to the available traction and direct power flow to the rear wheel with the most grip. When PTM is active you will hear the exhaust blatting like a diesel powered truck using it's Jake Brake to slow down. If you don't hear that sound you haven't opened the throttle far enough. When you get that sound the rear may do a slide slip, however, you are still supposed to floor the throttle. That is opposite of everything you have been taught on how to use the throttle when exiting a turn.

It takes a lot of trust in the system to go wide open at that point and I haven't gotten there yet but it sounds like I have gone further than you. I am able to open the throttle to the point I can hear the exhaust blatting and I have felt the rear slide out and relaxed throttle just enough to reduce the slip while still keeping PTM active. It definitely helps you power out of a turn. I still haven't reached the point yet where I am ready to just push the throttle down and go for it.

However, there are some forum C7 owners who say they can do that and the car responds well when they do so. They say I should just go for it. I won't tell you to do that but I will suggest you try running in Track Wet Mode for a few laps and see how PTM works. I did that when I took my car to the track the first time and had to run in the rain. It is very aggressive in Wet Mode and intervenes a lot sooner than it would in Sport 1. Try Wet Mode on a Dry Track and just play with PTM so you can get a feel for it. Then move back to Sport 1 and try to activate it. To be on the safe side do it in a corner where the speed is slow enough and there is enough run off room that you have lots of room to correct the car if you get it wrong.

Bill

Larry M

How do we get into sub mode? Is there more than one sport mode? Can they be modified?

davepl

FWIW I "got used" to PTM by picking a corner with decent runoff and just incrementally overpowering the exit until I could hear the engine making a "different" sound, which is what it sounds like under PTM. It's quite distinctive.

I don't recall if I ever got to the "plant it and trust GM" point, but I was certainly able to get into PTM that way. It's impressive but unsettling. It does, however, work.

I like Bill's idea of running in PTM Wet to see if it intervenes earlier and makes it a little more "accessible" to play with.

Bill Dearborn

Weather, Eco, Tour and Sport Modes only have one setting. Track Mode has 5 sub modes that are reached by pushing the center button of the selector twice quickly once you have the selector in Track Mode. That opens up a selection the DIC that has Wet, Dry, Sport 1, Sport 2 and Race. Those two Sport sub modes have nothing to do with primary Sport Mode.

If you have the tools to access the program, know how to design/modify/write a program and have the separate engineering knowledge to determine what you want to do with the suspension and drive train to maximize performance then you can change the programming. Otherwise, it could be dangerous to your's and other people's health and well being.

Bill

Kaged

Biill,et all,
Thanks for your input on this. I have had the PTM activate a few times and almost always lift the throttle when it starts to happen. Will try using the "Wet" setting during an upcoming AutoX and see if I can get more use to it (i.e keep my foot on the gas).
Below is a short clip where I yawed/drifted the car about 30 degrees on a turn at the track this week. Probably rolled on the gas a bit too fast for the corner. Lifted the throttle and corrected the steering when it started to go. The thunk you hear as the car straightens out is my helmet hitting the side pillar! I do not hear the engine cut out or see any indication on the video that TC or SC activated. Shouldn't I be seeing some indication of the TC or SC activation on the PDR video?
Youtube link - TIA,
Bill

Bill Dearborn

Bill,
I don't think PTM cut in during your slip. I do think you may have gotten on the throttle a little too soon with the front wheels turned to much but it is hard to say for sure. Try loading your mp4 file into Cosworth Tool Box and use it to study the sequence of events and what you may have done.

Here is a video of an autocross I ran last year. If you listen at the 50+ second point and then right after at the 1 minute + mark as I am exiting corners you can hear the exhaust noise change to a blatting sound. That is when PTM cut in.


It cut in at other times as well but those two times were particularly noticeable.

Bill

rikhek

Here's a video showing trust/usage of PTM "most" of the time. Listen while you watch my throttle position and you'll get the idea. You hear the car blat-blatting as the PTM system does it's job. Once in a while my mind takes over and I feather the throttle.

Once you get used to it and trust it it's amazing....

djnice

When you are in PTM modes the TC and SC do not light up even though they maybe active. As I recall, Sport1 only has SC active, no TC. You still need to be smooth on the throttle to keep the car straight. When lifting the throttle too quickly the computer cannot do as much to solve the problem. Your slide looks like too much throttle, then you lifted completely before the computer had a chance to intervene, then the lift contributed to more slide. It does actually look like SC straightened you out.

You could also try the wet mode in an empty parking lot just to make sure the car is working correctly. As I recall, the TC or SC will light the dash indicator, but not on PDR when in PTM. It will display on the PDR if you are in sport mode.

Also, PTM adds the ability to reduce engine power when the computer sense spin. Someone correct me, but I think it just retards timing. So in wet through sport 1 you get both SC and power management. In sport 2 and race you only get power management. I could be off slightly, but its the general concept I am trying to relay.

Bill Dearborn

Not sure what it does when it detects tire slip but in my autocross video posted above you can hear it working at the launch. I let out the clutch and push down on the gas pedal and you hear a blat, blat, blat and then the engine slows and takes off.

Bill

spearfish25

I don’t think Stabilitrak flashes any lights when engaged in a PTM mode. I’ve only seen it in the non-PTM modes. A friend spun in Sport 1 and there was nothing in the PDR footage to show stability control intervention. The times I’ve had the car get ‘out of shape’ and felt stabilitrak in Sport 1 have been rare but I don’t recall dash lights either.

BEZ06

Below is a picture of the PDR showing a "skidding car" icon in the upper right. I think it means the StabiliTrak/Active Handling is active, but it could mean the ABS was in action:



You can see above the RPM display it shows I was in Sport 1, and AH is still active in Sport 1.

This was at Daytona running the Rolex 24 roadcourse as I was braking down on the tri-oval preparing for turn into T1 into the infield. The tri-oval is still banked in this area, and you can see the slight left steering angle, and in the bottom left you can see the forward G from fairly hard braking and a slight right lateral G from the slight left turn.

So....whether this was AH or ABS, I dunno!?!?

Butt....something definitely causes a "skidding car" icon to appear on the PDR. I've never noticed it when driving, but I've seen it a number of times when reviewing PDR videos.

.

Questar

Tadge did a good job a while back explaining PTM modes and how they affect traction control, stability control, etc...

Tadge answered:
Although we have talked publicly many times and published quite a bit of documentation about PTM (and other chassis controls), there continues to be additional questions. Assuming this section of the forum attracts a very tech-savvy audience, we are going to give a more technical description than our usual public statements. At the risk of helping our competitors, I have asked Alex Macdonald, our lead Corvette development engineer and expert in chassis controls to provide the definitive treatise on PTM. So, thanks for asking….

Performance Traction Management was first brought to the market on C6 with the 2010 ZR1 and was available on C6 Z06’s with MR from 2011-2013. It has evolved with each new model of Corvette since then but still retains the same functions and philosophy as when it was introduced. All of this discussion applies to any Corvette with PTM, not just the C7. For C7 any Z51 with MR dampers and all Z06’s are equipped with PTM.

The first important part of PTM is the traction control function. This is the core of PTM. Later I will describe the other adjustments it makes to the chassis but the fundamental change in each mode is the logic and calibration of the traction control.

It will help to understand how the standard TCS system works when not in PTM. See Fig 1 for an example of a C7 Z06 turning left at 25mph and approximately 0.8G lateral acceleration (a spirited left turn). The driver steps to 100% throttle (point #1) which causes the rear wheels to start spinning. Prior to spinning up the tires, the TCS system doesn’t know much about the road surface conditions. It could be wet, dry, gravel, coarse concrete, smooth asphalt, etc. To determine the surface condition the engine torque is allowed to increase until the wheels start slipping a certain amount (point #2). They would continue to slip at this torque level so torque is quickly reduced to stop the slipping (point #3). The initial engine torque that caused the wheels to slip along with how much torque needed to be removed to reduce the wheel spin are used by the TCS to calculate the type of surface the car is on. Once the surface grip is known the torque is added back in to maintain an amount of slip that’s appropriate for that surface (point #5).





The drawback to this method is that the wheels have to over-slip past the ideal target at the start. This disturbs the cornering of the vehicle and requires the driver to adjust the steering angle. Further, bringing the wheels back down from the initial over-slip with a torque reduction dramatically reduces acceleration in order to regain stability.

The use of the PTM switch tells the car that it is definitely on dry asphalt (or wet asphalt in in mode 1) and that the driver is prepared for some amount of wheel slip. Since the surface is known the PTM system can make a good approximation of the maximum possible engine torque that will not over-slip the tires based on how hard the car is cornering and how fast it’s going. This torque estimate is used as a starting point (since no new information about the surface is needed in PTM) and then depending on the amount of slip that results more fine adjustments can be made. As the driver unwinds the steering wheel the tires gain grip and torque will be fed back in due to the lower slip. See Fig2 for the same maneuver described above but using PTM mode 2 this time.





As you look at these two examples one thing to note is how much more gradually steering and lateral acceleration can be reduced on corner exit in PTM vs normal TCS (Red and Tan lines). The initial over-slip in normal TCS is what prompts the driver to make this abrupt steering adjustment.

Each of the Traction Control modes in PTM are differentiated in two ways. First, the target slip levels are lower in the lower modes as you would expect. Second, the estimate we make for the starting torque is lower. In DRY we err on the low side with our estimation and may have to increase torque to reach the target slip. In RACE we err on the high side and the driver may have to use more steering correction to manage the extra slip in the rear until the target slip can be recovered.

Along with the traction control, the other chassis subsystems are modified for the conditions expected in each mode. The following is a chart of the status of each subsystem for each PTM mode:





Mode uses:
WET: This mode is intended for any driver who is on a wet track. The track should be wet enough to be glossy, not just damp. A damp or drying track will require the driver to decide between WET and DRY modes to get the best performance. Standing water is not recommended as hydroplaning is possible and no TCS system can accurately control a tire that is hydroplaning.

The slip targets are very low, lower than in standard TCS. The MR is in tour mode to maximize mechanical grip since the lower cornering forces don’t require the extra control offered in Sport or Track. ESC is on and uses the normal calibration, not the competitive calibration.

DRY: This mode is for a novice driver on any track or an experienced driver learning a brand new track. I also use it to warm up the tires or run the mold release off of new tires, especially if it’s cold out.

Slip targets here are very similar to normal TCS but will feel very different due to the entry prediction. MR is in Sport to compliment the usage we expect in this mode. ESC is on but uses the competitive calibration.

SPORT 1: This mode is for any driver who is ready to run very competitive lap times while still having stability control on in the background. I use this mode whenever I have a passenger, possible distractions such as data collection, or as I am continuing to become more familiar with a new track.

Slip targets are higher here than in normal TCS. MR is in track mode and ESC is on using the competitive calibration.

SPORT 2: This mode uses the exact same traction control settings as SPORT 1 but turns off ESC completely. This mode is designed as a way to turn off ESC while maintaining a fairly stable TCS calibration. I use it very often. Basically any time where tenths of a second are not critical to my testing or when the tires are getting too hot or wearing out. After 10 to 15 consecutive laps it is likely that your fastest times will be achieved in SPORT 2 rather than RACE.

Slip targets here are the same as SPORT 1. MR is still in track mode and ESC is turned OFF.

RACE: This one is pretty self-explanatory, it’s as fast as we know how to make the car go. This mode is for a well prepared car on relatively new tires with an advanced driver that is completely familiar with the track. The track should be somewhat warm and the tires should be up to temperature.

Slip targets are 100% optimized for forward acceleration, any small variances in the track or tires can result in momentary overslip that will have to be managed by the driver.

A few notes about RACE mode: I approach this mode as a tool to go faster meaning that I think specifically about it when I go to WOT and I try to change or optimize my throttle application point and steering to help the computer do its job. It can do the job better than me but only if I give it good information. A specific example is how I unwind the steering wheel mid corner and as the corner opens up. When learning to drive on track it is good practice to automatically unwind the steering wheel as you apply throttle regardless of the vehicle response (a string tied from throttle toe to steering wheel is the analogy used by some instructors). The problem in RACE PTM is that by doing that you are telling the car you are ready to go straight. It will add power and drive you to a wider line. The best results are found by holding the wheel as steady as you can and pointing the car to corner exit only when it’s time. Obviously you have to be ready to correct for overslip but as you gain trust you will find this is required less often than it feels at first. It is very useful to practice using PTM in the lower modes where you can focus on letting the car go where you point it and not correcting your steering too early.

We find that the calibration settings that achieve the fastest lap times often result in expert drivers feeling like they are being held back slightly on corner exit. Most of the time that extra little bit of slip that an expert driver wants is over the traction peak of the tire and may feel good but is wasting forward acceleration. The restrictive feeling is not there as a safety net, rather, it’s as close as we can operate to the peak capability of the tire in a robust way.

Other notes: The eLSD “PTM mode” is only a slight alteration of its normal track mode. This alteration is required since it is likely to see engine torque values that would not occur without PTM. However, the philosophy of what it’s trying to do and how it’s controlling vehicle dynamics does not change between PTM and TCS/ESC OFF mode.

As for the nannies, that term is a big gray area. I would personally call TCS, PTM, ESC and active rev match nannies but would not call the eLSD or MR dampers nannies. ABS is very gray. ABS, TCS, PTM, ESC and active rev match are trying to do a better job of something you normally do as a driver, steering, throttle, brake or shifting. However, no driver ever controls a differential directly or a shock absorber directly. They are part of the base chassis tuning and can be thought of as a calibration component like a spring or anti roll bar.
ABS is more of a gray area but it is not allowed to be shut off because the capability of the vehicle is so limited without it. You may need 200 bar of brake pressure to get max decel from a wheel that’s on the outside of a corner but the inside wheel would be totally locked at 50 bar. Unless you want a lot of flat spotted tires you need ABS in that situation. Also, somewhat like eLSD and MR, individual wheel brake pressure is something even the best driver can’t physically control without the electronics.

That’s a long way of saying you can shut off TCS, PTM, ESC and active rev match but you can’t shut off MR, eLSD or ABS.

Z06NJ

Did you feel comfortable on that autocross road? It looks very uneven and not smooth.

Bill Dearborn

The autocross road is actually a Go Kart track. I started auto crossing at that location in 2001 and participated in multiple events there since then so am quite familiar with the track.

Yes, it was uneven due to thin pavement constructed to support couple hundred pounds of Go Karts Vs 2500 to 5200 lb cars/trucks running at close to 70 mph. The track has been around 40+ years and the asphalt has broken up and been patched with concrete in a number of places. In fact we weren't using a part of the track we used previously since heavy cars had broken the pavement up to the point we would have been driving on dirt Vs pavement.

A hell of a lot more comfortable to ride around in a car Vs a Go Kart that doesn't have a suspension.

Bill

JohnC7

I was surprised stability was interfering in Track > Race at corner exit to the extent you can mash the throttle because that is not what the manual indicated. But that is exactly what it does. The reason I am looking at the forum is that the car is not giving full beans at corner exit! UPDATE: PTM is defiantly on in Track > Race. If you cannot feel it until you are going fast enough for it to kick in. Lack of power at corner exit. You can mash the throttle and nothing will happen until you straighten up a bit and then power will come back. You can drive the car like an absolute loon but ultimately it is frustrating.

orca1946

I have only been to the track once and the instructor said leave it in basic track mode for me as a new driver to the track in Joliet,il.

Bill Dearborn

Just turning the **** to Track Mode is sort of undefined. Once in Track Mode you need to push the center button twice and once Wet is displayed in the DIC turn the **** to one of the 5 selections. Wet works very well on a wet track. The Spring Mountain Corvette New Owner school recommends Sport 1 for most drivers running on a dry track.

Bill