what is the difference between these two. i saw in the owner's manual that one of them is an add on

 

ASC+T is traction control.
If a front wheel spins, it will apply braking to that wheel to divert power to the other one - it might also reduce engine power.

DSC includes all that.
DSC *also* has sensors to monitor the cars direction compared with your intended direction (steering); it can detect the car losing control, and apply brakes to any wheel in an attempt to pull the car back in the correct direction.

ASC+T happens a lot if you accelerate hard while turning, especially if you don't have an LSD.
DSC shouldn't happen unless you push your car seriously past its limits.

 

dsc also uses ignition retard to reduce the power in the first place.

 

Just curious where you got this info, never heard of that exactly before.*

Aricle on how ASC & DCS work:

http://www.bmwworld.com/technology/dsc.htm

Edit: Perhaps you are referring to this? "As with ASC, DSC will if necessary also cut back the engine speed to automatically stabilize the vehicle."

 

As previously posted, ASC is to reduce tire spinning from bad traction on an individual tire; DSC is to help the complete car avoid spinning. DSC works with a combination of selective application of brakes on individual wheels (depending on which direction the car is wanting to spin) and engine power is reduced through ignition retard (although some implementations of stability control will cut fuel to the engine to further slow the vehicle). Don't confuse ASC with a form of Limited Slip Differential (LSD). LSD is a mechanical approach to traction-challenged road surfaces that doesn't apply the brakes, but rather mechanically shifts torque from the spining wheel to the non-spinning wheel.

 

Just to be clear, ASC also cuts the power to the engine; the power cut out felt even more abrupt in the ASC car vs DSC that I've experienced.

 

GBMINI (post #2) mentioned the reduction of engine power with ASC; I was focusing more on DSC.

 

alright thanks for the info. the power cut out when you chirp your tires a little sucks with the ASC. it doesnt happen when i'm in a corner, so is there any problem with turning it off?

 

Turn off ASC or DSC when you are in safe driving conditions with no chance of sudden unexpected slippery roads, avoidance maneouvres, etc.

Some people habitually turn off ASC/DSC - and a (very) few have regretted doing it.

 

thats what i was thinking. i'm not going to turn it off during january or something

 

Let's put it simple :

ASC ==> traction control and stability control, but only with engine's output.

DSC ==> traction control and stability control, but with both engine and individual brakes. It work great and keeps you on the right path if you drive at a safe speed. Back on Quebec, I've came across many severe snowstorms and DSC was a great device... On the highway, I was driving at 90-100km/h in 10cm on snow and takeover SUV and other AWD cars without any stability control... DSC is great!!

I've had a Subaru Impreza (AWD) for 5 years, and think a great stability control, such as DSC, is 1000 times better than an AWD car with no electronic control.

 

Traction control is initially accomplished with application of brakes on the individual wheel that is spinning. If the spinning continues, then engine power output is cut through timing retard.

The principal reason why DSC is so great at avoiding spins of the car is the combination of a yaw sensor with the computer that can individually apply brakes on all four corners in milliseconds - there is no way that a human can do it better.... Also, the best combination is AWD with DSC; but yes, I would agree that DSC without AWD is better than AWD w/o. DSC.