Thank you modern engineering (stability control)

[rcy]

Aside from purposely engaging stability control systems (playing around in a snow covered parking lot), I've had no real world experience with either the GM Stabiltrak in my wife's 2010 Equinox, or the VDM (vehicle dynamic management) in my Lexus RX400h.

Today, while driving to work, I exited the highway (100km/h) to the off ramp at my exit. The exit lane itself was mostly dry, but melting snow had run across part of the lane and refrozen. As I started to follow the curve to the right, I hit the ice and felt the slide begin.

I started to steer into the skid (i.e. turned steering wheel left as rear end began to slide left) but before I could really react, I felt/heard the ABS cycling, vaguely noticed the light flashing on the dash, and suddenly I was on the straight and narrow again.

Now there's no defeating the laws of physics, and had the entire ramp been ice covered, I doubt the Stabiltrak would have been as effective, but it definitely kept me going the way the vehicle was aimed until the tires bit into pavement again.

Nice, and I encourage everyone to experiment with these systems (and ABS) in a safe location so you know what to expect when they are called into play.

 

[pbm]

That's good to hear.
My 2002 Buick has 'ABS and 'traction control' and it is
great in the snow. I can see why some have called 'tc' "poor man's 4 wheel drive".
I have heard it engage in similar situations a few times over the years and I was glad to have it.

How do you like the Equinox?

 

[rcy]

It's the wife's company vehicle, but I will admit, having never been a GM fan, I'm impressed. She has the 3.0 DI 6 cylinder and AWD.

And just to clarify, this was not the traction control kicking in (it has that too) but the Stabilitrak or 'vehicle stability control' for the most generic term (most manufacturers have different names/acronyms for this technology - Honda is VSA, Subaru is VDC, GM stabilitrak, Lexus VDM etc.)

 

[Captain_Klink]

the stability control in my 08 Subaru Impreza, it feels like a giant hand comes down from the sky and straightens up the vehicle. this is completely different from traction control that my Crown Vic had. with the Impreza, the computer takes the car out of the skid/fishtail/sideways-slide and straightens it right up - totally awesome and amazing.

 

[eljefino]

So was your foot on the brake when this happened or did it selectively brake some wheels as necessary?

 

[d00df00d]

Would it be a buzzkill to point out that, all else equal, a lighter vehicle with a lower center of gravity would have had less of a problem in the first place?

 

[rcy]

Originally Posted By: eljefino
So was your foot on the brake when this happened or did it selectively brake some wheels as necessary?


No braking on my part. Had slowed down from highway speed before entering the actual curve of the off ramp. I'm guessing it selectively applied the brakes on the driver's side rear for sure and possible the front as well.

 

[rcy]

Originally Posted By: d00df00d
Would it be a buzzkill to point out that, all else equal, a lighter vehicle with a lower center of gravity would have had less of a problem in the first place?

I know you're joking (soft of), hence the smiley, but it was ice. Any vehicle would have slid, light weight or low centre of gravity or not. Now if it had rolled over after sliding, then yes, lower center of gravity would have made a difference.

 

[440Magnum]

Originally Posted By: d00df00d
Would it be a buzzkill to point out that, all else equal, a lighter vehicle with a lower center of gravity would have had less of a problem in the first place?

But that might not be very true. Center of gravity mostly affects tendency to roll over, and only has a 2nd order effect on lateral traction because it increases weight transfer. A lower CG vehicle might have done *slightly* better in a curving exit ramp scenario with patchy ice... but my guess would be that the margin of difference is almost negligible.

 

[G-MAN]

Originally Posted By: pbm
That's good to hear.
My 2002 Buick has 'ABS and 'traction control' and it is
great in the snow.


Don't confuse ABS and traction control with electronic stability control. Different animals that use some of the same hardware. If you're in a situation where stability control is warranted, ABS and traction control aren't going to help you.

 

[rcy]

Originally Posted By: 440Magnum
...curving exit ramp scenario with patchy ice...


This is exactly the scenario. The ice was not the entire ramp, just where the melting snow had run down the grade and frozen.

You're in Texas...how'd you know this?? It would be like me saying "curving exit ramp scenario with blazing hot asphalt"

 

[d00df00d]

Originally Posted By: rcy
Originally Posted By: d00df00d
Would it be a buzzkill to point out that, all else equal, a lighter vehicle with a lower center of gravity would have had less of a problem in the first place?

I know you're joking (soft of), hence the smiley, but it was ice. Any vehicle would have slid, light weight or low centre of gravity or not. Now if it had rolled over after sliding, then yes, lower center of gravity would have made a difference.

Not joking at all. Just not making a particularly serious comment.

I know any car would have slid; the point is that a lighter, lower car would have been easier to get back into line (less momentum and more grip).

But again, not a serious objection. Stability control is a wonderful thing sometimes. Just making the obligatory jab from a sport GT driver to an SUV driver.

 

[Bill in Utah]

Originally Posted By: Captain_Klink
the stability control in my 08 Subaru Impreza, it feels like a giant hand comes down from the sky and straightens up the vehicle. this is completely different from traction control that my Crown Vic had. with the Impreza, the computer takes the car out of the skid/fishtail/sideways-slide and straightens it right up - totally awesome and amazing.


It's like what we who don't have stability control do. Get off the GAS so you don't get any deeper in trouble. (ie.. common sense)

My 2005, 2007 and now 2011 Tundra work trucks have it. Personally I don't like it because at the smallest point it "thinks" you are going to "loose" it, it kills the power. A lot of time its just slightly spinning the rear tires on some slush and nothing makes the heart pound faster than pulling onto the main road with traffic going 50 and your engine dies. (or feels like it)

It wakes up once you are straight, but its VERY protective.

That's okay. We will all have it on every vehicle soon and be paying for it. $$

Bill

 

[Bill in Utah]

Originally Posted By: eljefino
So was your foot on the brake when this happened or did it selectively brake some wheels as necessary?


With active systems it will kill the throttle mostly. Some do throw in select brakes but very slightly.

 

[rcy]

Originally Posted By: d00df00d


I know any car would have slid; the point is that a lighter, lower car would have been easier to get back into line (less momentum and more grip).



Wouldn't more grip be "mostly" dependent on tires, rather than centre of gravity or weight?

I would have liked to have run the same exit in my vehicle (also an SUV with stability control, but winter tires) and observed if the winter tires would have made a difference.

 

[rcy]

Originally Posted By: Bill in Utah
Originally Posted By: eljefino
So was your foot on the brake when this happened or did it selectively brake some wheels as necessary?


With active systems it will kill the throttle mostly. Some do throw in select brakes but very slightly.


In my case, there was much brake application, as I could hear the ABS motor cycling.

Are you sure you're not talking about traction control? Those are known to kill the throttle as well as brake the offending spinning wheel. Accelerating in snow as you mention in your other post and having the rear wheels spinning would activate traction not stability.

Stability control, while it may involve throttle modulation, is more about selectively braking certain wheels to prevent under/over steer, and having experienced it under controlled conditions, I'd say the brakes are not applied slightly, but agressively.

 

[rcy]

Originally Posted By: Bill in Utah


My 2005, 2007 and now 2011 Tundra work trucks have it. Personally I don't like it because at the smallest point it "thinks" you are going to "loose" it, it kills the power. A lot of time its just slightly spinning the rear tires on some slush and nothing makes the heart pound faster than pulling onto the main road with traffic going 50 and your engine dies. (or feels like it)

Bill


A lot of how it feels (and works) is vehicle specific as well. Some are known to be too agressive (activates at slightest wheel spin or skid). I can compare my two vehicles, which both have stability assist.

The Lexus kicks in very early, but is very smooth. A light on the dash and a beeping alerts me to the fact that it's doing it's thing. The pulsating and ABS activation is subtle amd mpt very noticeable (though that might be the actual design of the ABS motor/system.

The Equinox lets the vehicle hang out much more (when playing in an empty snow covered parking lot, I can start a sideways drift before it kicks in - the Lexus will have none of that behaviour), but when stability assist kicks in, it's sudden - the ABS activation is loud and noticeable in the brake pedal. A light flashes on dash, but no warning chime.

 

[Bill in Utah]

Originally Posted By: rcy
Originally Posted By: Bill in Utah
Originally Posted By: eljefino
So was your foot on the brake when this happened or did it selectively brake some wheels as necessary?


With active systems it will kill the throttle mostly. Some do throw in select brakes but very slightly.


Are you sure you're not talking about traction control? Those are known to kill the throttle as well as brake the offending spinning wheel. Accelerating in snow as you mention in your other post and having the rear wheels spinning would activate traction not stability.

Stability control, while it may involve throttle modulation, is more about selectively braking certain wheels to prevent under/over steer, and having experienced it under controlled conditions, I'd say the brakes are not applied slightly, but agressively.


Not on ice. And on situations like I said above (getting on a main road with slush/snow/ice) all it does is kill the throttle until it straightens up then allows the gas to slowly come on.

I can spin the tires quite a bit before the traction control comes on IF I'm going straight. If I'm in a turn its the stability control kicking on. Also major difference between the two systems.

I've been in pure ice too many times and it does nothing for braking if you are getting out of control. Why? Nothing to brake on.

As far as hard surfaces that are dry, never had the system activate it since I don't take a 6000+ lb truck and get it going to the wrong way...

Bill

 

[rcy]

If I take my vehicle out on ice, get up to a decent speed (say 40 km/h), let off the gas (or even slip into neutral) and then crank the steering wheel to induce a skid, I guarantee you that the stability assist system will start braking wheels to try to keep the vehicle on it's intended path. There will be no throttle to modulate.

But these systems are very complex, and different from vehicle to vehicle. Some may use wheel braking only, other's a combination of wheel braking and throttle modulation, but I think no matter what, wheel braking always has be be involved in the equation.

I'm not a friction expert, but I don't think rubber on ice has a coefficient of friction of zero.

 

[d00df00d]

Originally Posted By: rcy
Wouldn't more grip be "mostly" dependent on tires, rather than centre of gravity or weight?

It's tires and vehicle together. A heavier vehicle has more momentum and requires more friction to keep in check.