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Old 02-13-2019, 01:12 AM
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DSC demonstration (drifting in snow)

I've been wanting to do an experiment with DSC ever since I read how it works.

In the experiment I did, I took 240 frame per second video of me drifting strings a corner with DSC on.

I took frame grabs from the video sync'd to the rear wheel each half of a revolution. (Approximately 1/7th of a second) then I put guide lines on to show the relative change in rotation of the front wheel.

What happens: when the yaw sensor detects that the car is turning mathematically faster than it can based on the steering angle and the speed of the car, it knows the back end is "fishtailing" and works to correct the slide.

It does this by primarily applying brake to the left front wheel in this case. (I'm intentionally causing an oversteer situation by applying gas when taking a corner at the limit of grip)

What amazed me in this experiment was how quick the system worked and how there is absolutely no visible skidding of the left front tire that is being braked on packed snow (almost ice)

(Actually shortly after this video was taken I did the experiment and hit the gas too hard on a part of the drive that was more icy and with fresh snow, I overwhelmed the DSC and actually got perpendicular!)

Enough talk, here's the photos:

https://www.icloud.com/sharedalbum/#B0SJ5HumnJrCUob

It just dawned on me I need to do the test with DSC disabled for comparison. Hopefully I can find a similarly slick surface.

One thing I wanted to mention was how neat the tire tracks were. The tread left what looked like little white worms behind, and where I was drifting, the "worms" shot out to the outside of the curve just outside the track of the tires I'll have to get a photo next time!

It was the first time I've actually seen my tires leave tracks without perfect (non slipping) tracks.

Take note how the sliding left rear tire is kicking up a berm of snow.

I drift plenty in the X when there is fresh snow on the ground, and when you are just at the limit of grip you can drift for an extended time, if you over do it like my perpendicular example, the car tells you in no uncertain terms you went too far, it feels like a mechanical bull ride, but if you limit the DSC activation to 2-3 times per second it will let you drift continuously.

One other experiment I did during my first winter in the X5, was to disable DSC when I was at the limit of grip on a big sweeping curve in a large parking lot, at the very next bump that caused a fishtail event, the car spun 90 immediately!

The X5, at least pre x drive where the front axle can be disconnected absolutely requires DSC on low friction surfaces! I'm not even kidding!

Here's an example of why: say you are driving on a road where half the lane is ice: if you give it gas, the wheels with traction will torque the car quickly toward the icy side, you will find yourself immediately pointing in a new direction, and depending how hard you hit the gas that could easily be a 10-20 yaw shift, that will quite easily put you into the curb, a parked car or pole or worse: oncoming traffic!

I'm not exaggerating! Ask anybody that's driven a pre face lift X5 on icy roads!

If I programmed the DME on the original X5, I would have programmed automatic transmission failsafe 4th gear and top speed of 30mph any time DSC was disabled and the ice warning (3/37) was enabled.

I'll try to get a demo video of that situation it's panic inducing! Very scary!
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Last edited by andrewwynn; 02-13-2019 at 01:30 AM.
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Old 02-13-2019, 01:13 AM
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Placeholder post for the DSC off version


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Old 02-14-2019, 03:56 PM
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This is a cool test, and thanks for posting the data.



That said, I have a pre-xdrive X5 and live in an area that gets lots of snow and ice. Driving on straight up ice, flooring it and losing traction doesnt really turn the car at all. You may spin out easier, but it never turns the car in a direction you dont intend for it to go. If you leave your foot in it, the car cuts throttle pretty quickly anyways. It's more intrusive than other cars I've owned, surprisingly.
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Old 02-20-2019, 12:09 PM
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I've gotten perpendicular but only when trying. I've used full throttle when going straight the DSC does a marvelous job of keeping things under control.

That said with DSC disabled the car is unsafe on icy roads. When one side of the car has better traction the car steers itself like a bobcat and it can be a very quick very dramatic change in direction.
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