[moldcad]

Howdy. I know this horse has been beaten to death already, but I just had an incident in my xDrive F10 that - according to my technical knowledge about how DSC/xDrive are supposed to work - should have never happened, so I'd like hear your comments.

I was cornering rather fast on my superb Michelin PSS tires; should I have been in an RWD car with DSC off I would've expected to fish-tail on the curve exit. But with xDrive and DSC on, and on dry surface - the very moment oversteer was detected I would expect most of the torque to be transferred to the front axle. Should that have been not enough to pull the car out of the curve without spinning around its own vertical axis, DSC was supposed to mitigate the engine output while applying some braking to the spinning rear wheel...

Well - nothing of the above happened, and if I didn't just spin around was only thanks to my steering wheel action (being an unconditioned reflex with my previous experience of sporty driving RWD cars). Nevertheless, I must admit I lost control - luckily the road was empty; otherwise - at that angle to my intended direction - I would have kissed some other car!

I went straight to my dealer and asked them to check for any errors stored in my car's ECU - there were NONE!

So I'm asking you guys with xDrive BMWs: did anything like that ever happen to you? I perfectly understand the laws of physics cannot be changed by even the best traction control and or AWD system that exist, but believe me - I was driving fast, but within reasonable limit...

Opinions welcome!

[Breach]

Glad it turned out alright. Did you notice whether DSC engaged at all?

[moldcad]

No - the light didn't even blink.

[CmdllbF11]

Try to engage DSC functionality again by kicking out the rear/over steering and see what happens (I mean in a controlled environment!!).

I don't know much about xDrive (I have F11 with RWD only) but did have a xDrive M320d as a courtesy car for a coupe of days and put it through its paces.

I managed to spin wheels in comfort mode but DSC did kick in.

As it did that in Comfort, I didn't have the balls to put it in sports+ whilst driving aggressively.

Be interested to see results/updates.

[bimmertaxi]

Originally Posted by moldcad

I was cornering rather fast on my superb Michelin PSS tires; should I have been in an RWD car with DSC off I would've expected to fish-tail on the curve exit. But with xDrive and DSC on, and on dry surface - the very moment oversteer was detected I would expect most of the torque to be transferred to the front axle. Should that have been not enough to pull the car out of the curve without spinning around its own vertical axis, DSC was supposed to mitigate the engine output while applying some braking to the spinning rear wheel...

You were driving too fast and the rear wheels lost traction. Breaking the rear wheels will not help regaining control. Lifting the throttle will shift weight forward and the rear wheels will have even less weight on them. Your only option was to countersteer.

xDrive does not mean that the tires have better grip. Don't drive faster than you would in a RWD car, unless you are on a track and have the space to correct (by applying throttle) when sliding out.

[moldcad]

Originally Posted by bimmertaxi

You were driving too fast and the rear wheels lost traction. Breaking the rear wheels will not help regaining control. Lifting the throttle will shift weight forward and the rear wheels will have even less weight on them. Your only option was to countersteer.

xDrive does not mean that the tires have better grip. Don't drive faster than you would in a RWD car, unless you are on a track and have the space to correct (by applying throttle) when sliding out.

All true, but my expectation was that with the onset of oversteer, most torque will go to the front tires thus preventing the rears from actually loosing traction. Well, seems like I expected to much of the "most intelligent AWD system that exists"...

[lovec1990]

as bimmertaxi said, did you hold gas during your situation?

this is why are so many AWD cars and SUVs in diches during the winters they think AWD would save them.

in my opinion xdrive is unpredictable so i prefer RWD cars

[moldcad]

Originally Posted by lovec1990

in my opinion xdrive is unpredictable so i prefer RWD cars

Now I know the above is true, unfortunately.

And yes - I kept pressing the gas pedal as together with the steering wheel counter-action, it's the only way to exit a curve with the rear wheels spinning. But DSC must have been doing its job after all when I recollect now, as my pressing the gas pedal didn't accelerate the car enough to leave the drift gracefully. Perhaps it's just the DSC light that is faulty?

[AP]

I'd have thought that the outside wheels would be braked to yaw the car back to where you were trying to steer.
So if you were in a left hand bend for example and the car over steers, the right hand side wheels would be braked to yaw the car round to right - into the skid.

May be DSC did kick in but it was beyond the law of physics.

[akhter]

i remember from my one spin on black ice in a e36 many years ago that the whole thing happened so fast and i was so focused on counter steering and staring at the opposite side of the road while doing 2 360s on the freeway that I don't think i would have noticed the blining dsc light.

on my e90 335 it was on all the time

[ezmaass]

Not having been in the car, it's hard (probably impossible) to really say whether the event was within or outside the correctable realm of DSC and xDrive. However, what concerns me about the story is the lack of DSC engaging/blinking on the dash. I've been in plenty of situations before (~14 years of BMW driving) where DSC engaged but couldn't really "fix" the problem - including a situation similar to the highway 360 story about. In all circumstances, the system at least engaged and gave it the old college try. In the case of my highway 360, not only did it try, but when it couldn't "help" it cut the gas completely to the engine, and as the car came to a stop from a wild ride, the engine was off with the car still in drive. My BMW dealer confirmed this was the "expected behavior" when the car detects a situation that it expects may end in a collision. Lucky for me, my driving skills (and a bit of luck) saved it.

In the multiple times where I've broken the tires lose and had the back kick out on me (by accident), the DSC HAS absolutely engaged, and in all circumstances one of the behaviors was to cut engine power. If you're going quite fast, I think there's a limit to how much braking intervention (if any) the car will apply - above a certain MPH range, I believe the car won't try to correct using braking (seen as dangerous, I guess?)... but instead relies mainly on torque vectoring and cutting engine power to get wheels away from spinning.

The 550 is my first xDrive car, though, and I've yet to get the DSC to engage. All of my prior experience with DSC was with RWD. And quite honestly, it wasn't all that impressive. In most cases I found it was most successful and useful when attempting to control minor issues below 30mph - such as starts, stops, and turns on less than perfect pavement and traction conditions. But anything at truly high speed was next to worthless for DSC to correct... and most of what I witnessed was just cutting engine power at those speeds.

So anyway - long story short, my biggest concern in your story isn't whether or not DSC was able to help or not when your tires broke loose, but rather why it seemed to fail to engage altogether.

[moldcad]

These were exactly my thoughts - after many years in the E46 330i RWD, with DSC acting (and blinking on me) very often and distinctive, my first conclusion after the incident was that DSC in my 528xi didn't kick-in at all. But when I recollect what happened within a second with a cool reasoning rather than emotions, I'm almost positive it did engage - unfortunately it only made things worse by severely limiting the engine power, which is why I couldn't drift out of the curve in spite of the gas pedal all the way down to the floor...

Also my dealer, when checking for any errors stored (which he didn't found - not a single one) has told me that with xDrive cars DSC acts much more discreetly than with RWD. Your story seems to confirm this; nevertheless I invite others to chime in and comment on their RWD vs. AWD experience with DSC.

[Grover432]

You should disable the DSC and take the same exit under the same road conditions and see where your car ends up.

[grimlock]

^this

have you driven other BMW X-drives or other 4WDs?

I don't think what you expected to happen with the BMW 4wd program is what BMW thinks should happen.
Why would power to front wheels increase in oversteer in a curve? That would be dangerous and make the situation worse, not better.
Maybe once you have corrected on exit, but perhaps the program requires you to regain traction first.

I was in a friend's TT once going really fast in a flowing curve, not a 90degree turn, the car was drifting and slowly drifting off course at high speed. My friend increased the throttle to increase power to front wheels and the car responded as expected - the front end overtook the rear end and was saved.
The difference is in a 90degree turn, there is no way to save by powering the front wheels - that would be disasterous. It can only brake and hope there is enough space to regain traction. Powering the front wheels in this situation would ram you into the curb at high speed, or spin your rear out breaking traction even more.

[Grover432]

Originally Posted by grimlock

^this

have you driven other BMW X-drives or other 4WDs?

I don't think what you expected to happen with the BMW 4wd program is what BMW thinks should happen.
Why would power to front wheels increase in oversteer in a curve? That would be dangerous and make the situation worse, not better.
Maybe once you have corrected on exit, but perhaps the program requires you to regain traction first.

I was in a friend's TT once going really fast in a flowing curve, not a 90degree turn, the car was drifting and slowly drifting off course at high speed. My friend increased the throttle to increase power to front wheels and the car responded as expected - the front end overtook the rear end and was saved.
The difference is in a 90degree turn, there is no way to save by powering the front wheels - that would be disasterous. It can only brake and hope there is enough space to regain traction. Powering the front wheels in this situation would ram you into the curb at high speed, or spin your rear out breaking traction even more.

Once you start the car sliding sideways (AWD or RWD), what are the car electronics supposed to do? They can brake the vehicle (won't help), they car brake the inside wheels to draw the car to the inside of the circle (won't help if the car has gone past the limits of adhesion), it can transfer power to the front wheels if the rears are slipping (my car has done this several times in the winter while rounding a corner), but again, if I've gone past the limits of available traction, what can the car's electronics (DSC) do?

if the OP reads the owners manual, there is a statement saying DSC adds safety but cannot overcome the laws of physics - in other words, don't so unreasonable stuff and then expect the car's computer to save you when there is no "saving" possible in the situation.

[Gilgorm]

I agree with Grover. The angle of the car probably made it impossible for DSC to correct your unique situation.
I had a retired E60 that was hit from the side and spun three times. At highway speeds its impossible to see a single light on the dash. My car did not turn off and was still driveable off the highway. Once stopped, I realized every dash light for ABS and DSC and traction control was on and stayed on until restart. The systems were simply overwhelmed for the situation and threw in the towel(light).
In your case, perhaps there was nothing to be done to help you out. I do not believe that power would have shifted to the front axle, nor would you want it to. The systems are all connected principally to the brakes and not the engine other than a possible power reduction. While my E60 didn't turn off its possible F10s are different or simply the fact that your driving wheels were stopped so quickly that the engine essentially stalled. My E60 slowed from 120kph to 0kph in seconds but I had been modulating the brake and the car was actually sliding backwards in Drive so the engine had a chance to adjust.
My F10 DSC only blinks occasionally on ice or wet leaves at slow speeds. Even on hard full throttle takeoff it has never even blinked. I guess I don't push the car enough to have it function at higher speeds.
If in doubt have the dealer do a more thorough inspection.

[moldcad]

My 528xi is tuned to some 310 PS / 440 Nm, and with the lightweight nose the car can be driven through curves in a very similar fashion an RWD can. After learning my above described lesson, I went to the local track (well, not a track really - just an unused fragment of the local airfield runway) and trained the technique with considerable success on a slightly wet asphalt. I did it at some 80 km/h, in Sport Manual mode of the SAT, using gear that would give me the most torque and power (around some 3,500 rpm) upon exit from intentional drift; what I achieved was not typical RWD fish-tailing, but rather 4-wheel slides the WRC cars do.

So - while I admit the incident described in the OP was due to my inexperience with AWD and RWD "unconditional reflexes" - it can been done if you know what you are doing. It takes some guts, too - you cannot enter a curve cautiously and only apply power on exit like with RWD; you must use speed to have enough inertia to toss the car into a 4-wheel slide like this. Especially one with just some 300-ish HP rather than a 500 HP M5 or alike...

[Super6]

Exactly how fast do you have to be going to achieve a 4-wheel slide? I have done some suspension mods, and I can take corners pretty quickly and flat. I have to tried to break them gradually, I just haven't had the balls or the space to do so yet. I am thinking its going to violently break away. I think to produce a 4-wheels slide you would have to be going extremely fast.........speed I would only do on a track or airfield.

[bimmertaxi]

Found this site: A driver's guide to oversteer

About 4 wheel drive:

Four wheel drive vehicles can oversteer as much as rear wheel drive cars, depending on setup. However, due to the sharing of drive forces over all four wheels, there is less risk of oversteer due to too over-exuberance with the throttle pedal. Treat as a rear wheel drive vehicle and you won't go far wrong. With particularly powerful four wheel drive vehicles it may be possible to enter a 'four wheel drift'. This is a particularly spectacular way of exiting the road!

Of course, this works best if the video clip is uploaded to Youtube

[SomeRandomer123]

Originally Posted by Grover432

You should disable the DSC and take the same exit under the same road conditions and see where your car ends up.

DSC works quite a bit in the background without flashing the light you see on the dash. DSC works with the E-Diff to allow it to behave a little like a limited slip diff so as you're power on in a left-hander, the inside wheel will have braking applied to prevent it from spinning up.

DSC off has the effect of locking the diff up, hence why you're able to kick the arse out.

xDrive is very intelligent but as others have said, AWD is unpredictable on the limit and should not be relied on.

[moldcad]

Originally Posted by Super6

Exactly how fast do you have to be going to achieve a 4-wheel slide? I have done some suspension mods, and I can take corners pretty quickly and flat. I have to tried to break them gradually, I just haven't had the balls or the space to do so yet. I am thinking its going to violently break away. I think to produce a 4-wheels slide you would have to be going extremely fast.........speed I would only do on a track or airfield.

Yes - speed and very sharp steering wheel action are necessary. And yes - it does break away extremely violently; you literally need to toss this heavy vehicle into a slide. Please don't get me wrong: F10 (especially its least powerful version, the 528xi) is not a car to do it casually, like many of us with RWD cars of even less power do on sharp corners. If I did try to check and train it a little was only because I wanted to find the limits and learn how to drive safely after the incident I described in my OP.