Reading back, I guess I see how someone could take my comment that way. However, if you think about it, I am also saying to turn "into" the skid. If you were on a two-lane country road and suddenly found yourself sideways, you certainly aren't going to want to keep the wheel straight...you're pointing towards the ditch, and you don't want to go there. You also wouldn't want to turn in the direction you're coming from, because you don't want to go there either (you've already been there, right? Why visit the same place twice?). Naturally, you'll want to have the front tires parallel to the yellow line in the center of the road...that's where you want to go. As the car corrects itself, you'll gradually reduce your steering input until the wheels (and the car) are again going straight down the road.

Inexperienced drivers often tend to over-correct on the steering input (turning too much into the skid). This usually causes the car to gain momentum with it's tail, and now you'll be skidding in the opposite direction. For most people, this goes on about 2-3 times before they hit the ditch. (If you ever watch Rally races, you'll notice the drivers actually use this effect to their advantage...they call it the "pendulum effect." They purposely steer opposite of the turn to get the tail to swing, then cut hard towards the turn. This builds up momentum in the tail and makes the car turn tighter into the corner). With experience, you'll actually find that turning the wheel less results in killing the skid quicker. It all has to do with the car naturally not wanting to skid (yes, ALL cars have this property, not just the ones with VDC).

KOLIA: I want to address your statement about FWD and AWD. There really isn't any "force vectoring" that can be done on pavement with these cars. This stems from the basic principles of tire adhesion...if the tire is already skidding, there is nothing you can do with it; you can't accelerate or turn. NOW, on dirt that is a different story. Big, knobby tires can grab hold of the dirt and fling it in any direction they care to, and this helps the car turn in that direction.

Here's a test you can try. Take a FWD car in a large empty snowy parking lot. Get going about 10MPH in a straight line, then crank the wheel and simultaneously hit the gas. What happens? The car will continue to move in it's original straight line. What you did was overload the tires by trying to accelerate, and so there was no grip left for turning. If you lift off the gas, you'll notice the car will start turning again. FWD cars are inherently stable, because when all else fails, they go straight. And they'll go straight into the ditch, if you let them.

On a RWD car, it's a crapshoot. likely, the rear will swing to one side or the other when you mash the pedal because the back tires are trying to outrun the fronts. However, you will notice that you can TURN AND ACCELERATE with a RWD at the SAME TIME, unlike FWD. However, doing so will cause the car to spin (i.e. it turns TOO much).

Anyway, the point of all this is to say that VDC is a proven technology. It helps make RWD cars a little more predictable if you happen to get into trouble, but like any technology, you have to understand its limits. I wouldn't say that you have to re-train yourself to drive with VDC, you just have to keep in mind that the system will do what it can to match your command (i.e. steering wheel angle). But, if the system detects that you've commanded too much steering angle or tire slippage (that would cause a skid or a spin), it will no longer follow your command and will try to make the car go straighter.

 

We pretty much agree here.

Dynamic friction is a lot less than static friction, it’s not zero. Even a spinning tire will give some amount of thrust.

Granted, a nose heavy FWD with open differential and summer tires won’t have much going for it on a snowing bend. But it will still turn some. Put snow tires on it, and it will fare much better, event on full steering lock and WOT. An LSD will help greatly.

Even on pavement, turning the wheel and flooring it will get the car turning. It’s not the best or fastest or most elegant way around, but it works. Noobs do it all the time at the race track. They usually stop when someone explain it to them or they run out of front tires…

 

Something about this description doesn't sound right.....In the scenario where you're turning left, oversteering and countering with right input, it wouldn't make sense to brake the right front wheel. The car is already "diagonal" to the desired direction of travel with the right front wheel being the most forward point in the slide. Braking the right front wheel would cause a forward weight transfer that would load up the right front corner further inducing the oversteer. It would make more sense to brake the right REAR wheel to "pull" the front end of the car back into the cornering line, wouldn't it?

 

No.
Because the rear wheels have already lost traction, remember? (Oversteering…) It would be like pulling the e-brake if it did that.

The front right wheel is the one with the most vertical load at that moment, but less load than a second before the oversteer started. So it can still work for us. And we have ABS to prevent it from locking up anyways.

The rear wheel braking is used in the event of understeer.

 

This makes sense to me. The VDC has no direct control of the steering, but braking the right front wheel essential forces the steering to the right, as if the driver had counter-steered manually. What is curious, if the VDC is reacting to your steering input (i.e. counter-steer), then braking the right-front wheel would seem redundant. It is this feeling that the car is forcing you toward the ditch that bothers me. If I'm doing it, I know that I'm doing it and I can see the ditch coming. I don't think VDC can see the ditch!

 

I've read through the several chapters and posts of this thread...mostly anyway. There's only so much of this "we sound like a bunch of women" drama I can take.

Anyway, Jvanquish: Good writeups. Keep the information coming. It all boils down to "you do what you do, I do what I do". And everyone is responsible for their own choices. But I welcome the information.

To everyone else: Eliminating a "safety net" does not make a car more dangerous. It makes the driver more dangerous. It is up to each driver to make choices based on their skill level. Poor choices result in poor situations that are only the responsibility of the person making the choice. 60 mph on a tight bend, VDC, TCS, or not...it's going to bad.

Remember, this isn't like the F-16's use of Fly by Wire. The Z is not inherently unstable without the "safeties". It is just more constrained and reduces the impact of certain poor decisions.

And to attempt to put an end to all this... VDC On = Full safety system, VDC Off (button) = Partial disable..some VDC systems will still engage. Eg. if you left-foot brake, such as you would to trail brake, then then remaining safeties will still engage (braking, ignition retard, etc.). VDC OFF (using new switch) means that ABS is retained and the entire VDC/TCS system is disabled.



Cheers,
-Smoky

 

Wow... when i sell these switches the arguements will be over... track season is right around the corner!!!! once you feel the difference that the complete diable gives. you will recognise what jav is talkin about. (unless your a serious driver you wont notice the difference.) but for those of you who will take the car to its limits, u'll feel it

 

Dunno about sellin' those switches, man. There's a DIY right here that you can do yourself for like $1.50.
https://my350z.com/forum/exterior-and-interior/174120-1-50-vdc.html

 

I think we're confusing issues here. You're right about sliding (dynamic) and static friction, but that's not what I'm referring to. There is a physical property of tires that dictates if you use 100% of its grip in one direction, you will have 0% of grip in any other direction. It's all derived back to the FRICTION CIRCLE. If you have the tires locked up with the brakes, you cannot turn the vehicle at the same time because you're already using 100% of the tire's grip to stop the car...there's no grip left to do anything else with. You can, however, use 50% for braking and 50% for turning, or any other combination that adds up to 100%. The sliding and static friction determine the overall level of where the 100% of the tire grip is. For the sake of everyone's eyeballs, I won't get into the lengthy details. There are entire books dedicated to this very subject...if you want to truly understand why your car does what it does, it's vital that you understand this concept.

With your comment about "flooring and turning" to get through the turn, I hope you were referring to RWD cars. This method will certainly put you in the grass with a FWD...unless you apex way, way late or have a puny engine that can't spin the tires.

You have to be careful about LSDs. They do not help a FWD turn better, they help it accelerate better. With all other things being equal, it will actually make a FWD turn worse. At low speeds, it reduces the ability of the inside and outside tires to rotate at different rates, and at high speeds if both tires are overcome by the motor, then there is nothing left to help turn the car. (With an open diff, one tire can spin while the other turns the car...remember the 100% rule?...one is 100% acceleration while the other is 100% turning)

 

Archman350Z, we will lose a lot of readers if we keep this going!

I know of the traction circle. I wasn’t referring to a car with locked wheels in my previous post. All cars will behave pretty much the same way once all 4 wheels are locked. You know that.

I should have said “Turing and flooring” instead. I was talking of a FWD then, and it is the way to go fast on a track with a FWD car. Get a late turn in, get the rear end loose, straighten the steering and accelerate hard to pull the car through. Some management of the throttle is still necessary of course.

If you take a few steps back and visualize the car as a set of 4 vectors applied at the wheels, acting on the CG of the car, you will see that we don’t need to turn the steering wheel to turn the car. In a turn, if the outside front wheel is still providing traction (because of an LSD) it will rotate the car. That wheel has the most grip available because it’s the one getting the most load from weight transfer. Without an LSD, we loose all effective traction, the spinning inside wheel will even push the car into understeer. Overall, slowing the car down.

I can recommend some readings on the subject if you want.

 

I think you're right! But, I like to be careful with information given out about vehicle handling...if a person doesn't fully understand what is going on or gets the wrong information, it's quite easy to get into trouble. (It's also quite easy to distrust electronic aids like VDC for all the wrong reasons).

I still maintain that a LSD will make a FWD push more (but this can be compensated by some suspension tweaks), but the end result is usually a positive anyway...if you can't accelerate cleanly out of a corner, it's a lot worse than having a car push a little more in the corners.

This also reminds me: Those with VDC should take great care when modifying suspension components. If you make too radical of changes, it will change the effectiveness on the VDC system to do its job. I've not heard of any incidences where suspension mods have caused the VDC system to crash the car, but you have to keep in mind that it might not be able to correct the skid as well as it did when the suspension was in stock form.

 

First, congrats that you were able to save the situation!

Second: You shouldn't be too proud of it. I can imagine how you feel, like the king having saved the world. But I would bet with you that out of 10 times something like this happens you will not be able to save it everytime. How often you are able to save it depends on skill. Even a professional race driver with 30years more experience than you will not get to 100% at all times.

Just because you saved it this time, don't expect that you will save it next time.

Third: It's more fun like that, disabling the VDC, and feeling it,... but don't try to convince yourself that it is safer in your case to leave it off.
It's a good sign that in the back of your head there is probably still a voice, telling you to leave VDC on on public roads (especially in snow/rain), otherwise you wouldn't try to convince this voice with your post.

So I agree with Kolias and other's responses along those lines.

 

Yeah... but as a proper male, i have to say "i saved the world"
Yes, it is safer to drive with VDC on during rain/snow situations...
but actually i've driven mine right after the 17" + blizzard storm that we had in pennsylvania, without VDC, and i was determined to go SLOW... and just counter-lock through the corners ... (had to get towed out once by my boys in a truck but hey thats just life)
out of anything its SPEED that kills...

 

Yep !

Yours or that of the overconfident/frustrated soccer mom in her Excursion...


hehe, teasing you...