Ok,

I've done a search. I understand the debate of DSC/ATC when trying to accelerate or go up hills, sometimes you just need to spin the wheel. My question is more about the understeering. Since I am not talented or crazy enough to push my car beyond 7/10 th's on public roads, the only reason I wanted DSC was for the snow. Beyond the traction control, I don't see that it is of any help. I do understand it is not a substitute for good driving and is limited to the law of physics. I did think it would at least attempt to minimize understeer by tapping the inside brake however. During our recent snow storm, the depth of the snow in the apex corners was well beyond what I could expect all-seasons to be able to handle. During relatively low speed corning the car would unsuprizingly understeer. What was suprizing is that the DSC light didn't come on. In fact the only time it would ever come on is while attempting to accelerate to quickly.

Is this the expected behaivour ? Is DSC smart enough to realize this as a low speed slide and not intervine ? Is it intervining without signaling the DSC light ?

 

The light came on because the TRACTION CONTROL was being activated...odds are, your DSC (stability control) was never coming on. I'm fairly sure that the stability control only comes into play when the car's traveling above a certain speed...and at any rate, stability control has little if anything to do with measuring wheel spin. Rather, it's mostly about reading how far the car is pulling from its center of gravity (some physics person could probably explain this much better than I). Subsequently, for what it's worth, I have no idea why you'd think that stability control would be particularly useful in the snow! No, traction control may be useful in snow...but stability control is mostly for keeping you top side up and on the road during higher speed advoidance maneuvers.

 

>>The light came on because the TRACTION CONTROL was being activated...odds are, your DSC (stability control) was never coming on. I'm fairly sure that the stability control only comes into play when the car's traveling above a certain speed...and at any rate, stability control has little if anything to do with measuring wheel spin. Rather, it's mostly about reading how far the car is pulling from its center of gravity (some physics person could probably explain this much better than I). Subsequently, for what it's worth, I have no idea why you'd think that stability control would be particularly useful in the snow! No, traction control may be useful in snow...but stability control is mostly for keeping you top side up and on the road during higher speed advoidance maneuvers.



So,

The inertia sensors don't detect that the car is understeering or oversteering unless a certain speed is achieved ? Again I don't exceed the limits of adhesion on public roads intentionaly, when it is snowing it can occasionaly happen. This is why I thought it would be useful under these conditions, my salesman had said it would be as well, but of course he would say that. Not the traction control in particular, but the CBC and other aspects of the DSC.

Aparently I had some misconceptions ......not the first time.



So nobody's DSC light comes on while sliding in the snow, unless they are in fact spinning the front wheels or traveling at hich speeds ?

 

Here's a link to an interesting article on BMW World that explains how BMW's DSC works. It does a nice job of breaking out the components of DSC and how each interacts. The bottom line seems to be:
Hope this helps! :smile:

 

Thanks jsun,

The qoute is the perception I had. I expected this exact thing to happen while understeering or oversteering in the snow. It did not, so I am trying to uderstand why. It is my first guess that either the speeds or the gforces were not sufficient during this event to trigger it. It is also possible that the light does not activate during that kind of intervention, or my DSC is malfunctioning and only providing traction control.

I will read the link you posted and hopefully gain the answers I seek.

 

Mine just did exactly that in yesterday's snow...I sped up to go through an intersection (there was a yellow light after all ). I got off the gas to slow down, turned the wheel to make the left turn....there was no traction at all....underteer to the extreme. The DSC kicked in and I felt one of the rear corner brakes kick in. The trottle appeared to be cut too - because I got back on the throttle, but there was no response (by this point, I knew what was going on and I was trying to play with it) I think that the DSC needs to sense a significant difference between your intended inputs to the car's controls and what the car's brain is sensing via the yaw-sensors.

I did get it to "wig-out" a bit one time: I was motoring down a back road, hit an off camber bump with my foot still in the throttle and I think un-weighted one side of the car pretty severly (didn't get air)....this seemed to upset the yaw-sensors. the throttle was cut, and I'd swear one of the rear brakes was on when the car's wieght settled back down.

Now how does the DSC affect hand-brake turns at high-speed in the snow???

_________________
2003 MCS, Indi Blue, Black Roof

 

>> The DSC kicked in and I felt one of the rear corner brakes kick in. The throttle appeared to be cut too - because I got back on the throttle, but there was no response (by this point, I knew what was going on and I was trying to play with it) I think that the DSC needs to sense a significant difference between your intended inputs to the car's controls and what the car's brain is sensing via the yaw-sensors.
>>
This what I expected mine to do as well. I read the article, I am still puzzled. I will have to find a snowy parking lot and try this again. I did do some e-brake slides in a parking lot the other day. The DSC again seemed only interested in wheel spin. If I went easy on the throttle the car seemed perfectly happy sliding and rotating around the parking just like any other front driver.

 

Hey guys, have fun in metro-Detroit with the commute Wednesday? My 8.7mi commute translated into 2.5 hours, normally 20 minutes, 40 with BAD traffic

When snow is deep, skid control does have yaw-sensors (on the MCS it's just under the parking brake, same with many cars). When in snow, your car can have a tendancy to "plow" against it and almost slide over a thin layer of ice/snow/slush. This is one scenario where locking your brakes can sometimes be of benefit (snow builds in front of your tires).
Anyways, I suspect the DSC is confused, because the wheels are still rotating well, yet the car is maintaining the direction (somewhat) you want to go in. The yaw isn't too great and is gradual, so it just assumes minor slip, nothing big. Of course then BAM you hit some immobile
object

I know DSC on my vette is immensely helpful in winter, it keeps it on the road. Granted in deep snow or solid ice, I'm screwed, but I can at least keep it going slowly usually. It does come on in turns, as does my olds Intrigue. With no braking or acceleration. Find a solid ice or very slick parking low. Go say 20MPH, turn the wheel, see what happens. oh yeah, be FAR FAR from anything fixed. Light posts seem to be magnets for cars doing donuts.

I went to the Michigan Tech/KRC/SCCA winter driving school a few years back when I was in school. Regarding skid-control in snow. Some cool stuff, had fun hitting snow banks and driving to the edge in snow!
One technique I really find useful is a "brake tap". This can work in hard-core driving too. As you enter the corner transfer off the front of the wheels and do a quick (light to moderate, but not too hard) tap on the brake pedal. This will put the weight back on the front wheels and allow the steering to gain a bit more traction. Using the engine for braking is good too. Tho I see people be stupid about it. In the storm on Wednesday,I saw someone in a GTI 337 do a hard-downshift on a corner, right into the ditch. He upset the balance it seemed, too much torque, steering and braking for those O-rings to handle! I honestly sometimes wish I didn't have ABS at times, so I could do threshold braking or cadence braking.

cheers,

-Matt

 

Thanks zxfr,

It seems likely that the speed is the most likely factor in me not getting any help from DSC. I was going very slowly in both experiments. I need to try this again at say 20 mph or so, in a empty parking lot of course.

 

Ok,

I had a chance to do a short experiment again as the weather was bad again this weekend.
It would appear to me at least, that because I was attempting to help the car by reducing my steering input, the DSC didn't think it's help was required. If I go ahead and steer in the direction I want to go, the DSC or possibly the ASC+T functions do in fact grab one of the back brakes and help the car rotate. This was a short expirement in a parking lot.
During the rest of that days driving, anytime the car seemed to want too understeer, I would just increase my input, and the car would turn. Not something you want to count on, caution would still be the best idea, but at least the behaivour was as advertised.
We will have more snow in the near future, so I will verify what I observed.