VSC Sport and Trac Off don't work

[Stang70Fastback]

Originally Posted by reeves

Well I was only sliding for like a second (maybe two at the longest). Maybe traction control is more aggressive towards the rear wheels?

Nope. It treats both ends equally. It shouldn't even allow a fraction-of-a-second of slip without stepping in. When I put my floppy winter tires on the car, I can cause the stability control to freak out just by gently swerving back and forth. The front end isn't actually losing grip, but the winter tires are so floppy, and deform so much more than summer tires, that the extra split second it takes for the car to actually start turning makes the stability control THINK the front end has lost traction, and it brakes the rear wheels to compensate. I even have video of it.

[ame="https://www.youtube.com/watch?v=w1vDOxXH9Pw"]Winter Tires = Confused Car - YouTube[/ame]

[Geese1]

Originally Posted by Stang70Fastback

There are really three core systems you need to understand. I'll try to make things as simple as possible, but still thorough.

ABS: This system is designed to prevent wheel lockup under hard braking, or braking on slick surfaces. The basic way it works is that each of your four wheels has a wheel speed sensor, which measures the rotation speed of the wheel. The car is always comparing the rotation speeds of all four wheels, and it uses these sensors to detect when a wheel has "locked up" (stopped spinning) due to a loss of traction; either you slammed on the brakes too hard, or one of your tires hit some snow/ice/oil/etc... When it detects this, the car can individually cycle the brakes on the wheel(s) that have lost traction. This is done VERY quickly - many times a second - and is basically the car releasing and re-applying the brakes over and over. (That's the buzzing you feel in the brake pedal when ABS is operating.) This lets the wheel keep rotating, rather than simply letting it lock up and skid, which in turn allows it to maintain some degree of grip on the road, and therefore allows you to maintain control of the car. ABS actually increases stopping distance, since you're basically cycling the brakes on and off, but in exchange, you retain the ability to steer the car, which is generally more critical in an emergency situation.

Traction Control: This system is basically the opposite of ABS. Rather than monitoring for wheels that lock up, it uses those same wheel speed sensors to detect TOO MUCH rotation, which is a result of applying too much throttle for the situation. Doing a burnout, for example, or accelerating and spinning your wheels on a wet/snowy/icy road. Traction control resolves this situation in two ways. First, it cuts engine power. You can have the throttle pedal completely buried to the firewall, but the car will basically step in and say, "You're being an idiot. You're just spinning the rear wheels. Let ME manage this," and it will reduce engine throttle until the rear wheels stop slipping. Remember modern cars are drive by wire, so there is no mechanical connection between the gas pedal and your throttle body. So even if you have the throttle pedal fully depressed, traction control allows the car to override that command and say, "He wants 100% throttle, but he is on ice, and we are only going to allow 7% throttle, because any more than that just spins the rear wheels." In addition, Traction Control can also leverage the car's ABS system, to individually brake either one of the rear wheels if they are spinning too quickly.

So far, we have two systems that work in tandem, doing their best to basically ensure your wheels are always spinning at the same speed that your car is moving.

Stability Control is the most advanced system. Its job is to keep the entire CAR pointed in the direction that the driver intended at all times. At its most basic level, it is designed to monitor for two things: understeer and oversteer. Understeer is when you turn the steering wheel, but the front wheels lose traction, and the car continues in a straight line, or turns maybe a little bit, but not as much as it should. For example, if you've ever driven in snow and tried to make a left turn and the car just didn't want to turn and you almost slid straight into a curb... that's understeer. Oversteer is the opposite of that. Basically the car turns TOO much, and the rear end steps out. Think drifting. Or if you've ever tried to swerve and wound up spinning the car around. Or doing donuts!

Stability control's job is to prevent either of those things from happening. It does this by monitoring a whole host of things. It knows how fast you are going (wheel speed sensors), it knows the angle of the steering wheel, throttle position, etc... Based on those things, it knows exactly how much lateral (side) force, and how much rotational (yaw) force it should be experiencing. The car has accelerometers on board that allow it to detect all of these forces. If you turn the steering wheel, and the front wheels lose grip, that will be immediately identified by the car, as it won't "feel" the car turning as hard/quick as it should be. Basically the car says, "We are going 30 MPH, and he just turned the wheel XXX degrees. My math tells me that should result in YYY G's of lateral force, and we should be turning at ZZZ degrees per second. But my sensors are reading much lower numbers, so clearly the front tires aren't turning us as much as they should be." So it responds by doing a whole host of things. It can cut throttle, which helps shift more weight back to the sliding front tires. It can also brake your inside rear wheel, which helps to "drag" the car around the turn, to help it turn better. It continues to do this until everything checks out, and the car is pointing where the driver wanted it to point.

If it detects oversteer (the rear end coming out too far and starting to slide) it will also cut throttle, and it can brake various wheels to help control that slide and bring the rear end back under control.

In normal mode, these systems are SO sensitive, that they generally step in almost before anything even happens. You won't get a massive burnout going before the car steps in and stop it. Instead, you simply won't get more than maybe a slight chirp from the rear wheels. Even if you rev the engine all the way up and dump the clutch, as SOON as the rear wheels start to slip, the car will cut all engine power, and brake the rear wheels. Same goes for stability control. In normal mode, it will detect the rear sliding even really before the rear tires fully lose grip. They are VERY good systems for someone who doesn't know what they are doing, though more skilled drivers often find them too overbearing. However, between those three systems, it's VERY difficult to completely lose control of the car unless you do something monumentally stupid. Generally speaking, there is no solution for too much speed. If you plow into a corner going faster than your tires have grip for, even the most advanced driver aids can't do anything to help you. These systems help you regain traction, but they don't magically give your tires MORE traction. If you are stopped on ice, and you floor the car and swerve violently, the car will manage all that stuff and keep the car under control. If you are stopped at an intersection, on a snowy road, and you want to make a right turn, and you just bury the throttle and turn the wheel, the car will cut power, and manage your wheelsping, and you will make the turn as fast as the car will allow you to. However, if you plow around that turn at 60 MPH, the aids will do their best to help you complete that turn without losing control, but your tires won't have enough grip to do so. So the result will be a nice, controlled, accident where the car just doesn't turn enough and you slam straight into the curb on the far side of the road.

Hopefully that makes some sense...?

Awesome write up, much thanks for taking the time to type all of that up! I was already familiar with ABS, but it was pretty informative reading more in depth on the other two systems.

So basically, in the new 2017 and up cars, the TRAC button (the car with the squiggly lines) turns the traction control on/off, and by holding it down for 3 seconds will turn both traction control and stability control off completely. And there is also the TRACK button, which when pressed lowers the intrusion factor of the traction control and stability control systems, but both are still active (just at a lower limit). This is what I am getting by looking at the explanation given in the manual,which combined with your excellent write up actually starts to come together.

Or at least I think so. I still may be totally off here!

[reeves]

Originally Posted by Stang70Fastback

If you turn the steering wheel, and the front wheels lose grip, that will be immediately identified by the car, as it won't "feel" the car turning as hard/quick as it should be. Basically the car says, "We are going 30 MPH, and he just turned the wheel XXX degrees. My math tells me that should result in YYY G's of lateral force, and we should be turning at ZZZ degrees per second. But my sensors are reading much lower numbers, so clearly the front tires aren't turning us as much as they should be." So it responds by doing a whole host of things. It can cut throttle, which helps shift more weight back to the sliding front tires. It can also brake your inside rear wheel, which helps to "drag" the car around the turn, to help it turn better. It continues to do this until everything checks out, and the car is pointing where the driver wanted it to point.

Originally Posted by Stang70Fastback

Nope. It treats both ends equally. It shouldn't even allow a fraction-of-a-second of slip without stepping in. When I put my floppy winter tires on the car, I can cause the stability control to freak out just by gently swerving back and forth. The front end isn't actually losing grip, but the winter tires are so floppy, and deform so much more than summer tires, that the extra split second it takes for the car to actually start turning makes the stability control THINK the front end has lost traction, and it brakes the rear wheels to compensate. I even have video of it.

Hmmm... maybe my traction control really is malfunctioning or simply not working for my front wheels.

I started to suspect something after replacing my rear wheels with Continental DWS 06. Going over a few rough patches on the highway (50+ mph) caused the traction control to kick in, similar to your video. This is with the brand new DWS 06 on the rear wheels and the worn out Michelins on the fronts (the same Michelins I slid around on last night). I then switched the Continentals to the front & put my worn out A/S 3's on the rears just to see what would happen. And going over those same spots on the highway (at the same speed), the nannies never intervened! Heck, I even starting accelerating & speeding over those same rough spots just to try to induce the nannies to come out. For whatever reason, my car's nannies just trusts Micheline tires more than they do the Continentals haha.

Aside from the nannies issue, I just didn't like how 'lazy' & numb the DWS 06 made my steering feel. So I ordered 2 Pilot Super Sports to replace them. (*Side note: To answer your previous question about only getting 2 MPSS tires) I always only get 2 tires initially if I've never had experience with them before.. for this exact reason. I bought the DWS 06 because of the great reviews on here and other sites = totally failed for me. The only positive here is that I didn't buy four of them! I hardly thought the MPSS would fail the same way, but I've never had them on my car before so I had to make sure (they're great btw ).

Anyway, I'm digressing. And I'm not too worried.. I was only slightly curious. I'd be relieved if the nannies really aren't monitoring my fronts lol. I'll soon have another pair of MPSS for the front wheels so I'm just going to enjoy the understeer slide in the rain while I can (while no other cars are around of course).

Thanks for the informative write-up on the ABS, Traction, & Stability Controls too btw!

[cjd]

Never buy just two tires... Unless its for a motorcycle...

I would expect fresh tires in the back, worn on the front, to be more likely to trip intervention because less traction for steering input you might not yet need... But worn on the back is still more dangerous (a shop will refuse to install that way usually). Also could be different sidewall stiffness in the mix... I assume the tires are the same size, but if not that also does weird things.