snow driving question

[canis]

Bear with me, for we only get snow maybe once a year in Memphis so snow driving experience is minimal...

 

It snowed last night, but by the time I got out this morning most had melted. I found a large snow-covered area of parking lot in the shadow of an abandoned building. There was a distinct line where the snow stopped right at the edge of the shadow. *Keep in mind all this was done very slowly, to understand the physics involved (i.e. not balls-to-the wall). Anyway, I would enter the snow area in a right-handed arc (5-10mph), and give it a little gas to simulate oversteering in a right-hand turn. I would countersteer (as if to turn left), and when my front tires would leave the shadow and hit non-snow pavement, the car would lurch to the right (the direction the car was facing, not the direction my front tires were turned).

 

Why did the front tires not pull the car immediately back to the left when they got traction? It did eventually straighten out, but not until the entire car was stabilized on solid ground.

[GTTuner]

From what I understand, the power transfer from front to rear and vice versa could take up to 3 seconds depending on conditions

[robinlsb]

Typical AWD. The car goes where the NOSE is pointed:lol: Exciting,isn't it?

[Scotty]

It's because you are transitioning between two different grip levels. When you are still on the snow, the front tires are still sliding. Once you leave the snow, the front tires gain traction, while the rear are still sliding, hence the abrupt right turn.

 

Any time you wheels are traveling on different surfaces, the handling will always be somewhat sketchy and unpredictable.

 

If you have enough run off space, try this. Line up the car so wheels on one side are on snow and the wheels on the other side on pavement. Now accelerate hard and hang on. If you want to see the ABS work over time, try braking. If you want to go for the ride of your life, pull the ABS fuse and do that same thing. You will want A LOT of run off area if you dare try this.

[fortnern]

Because your slip angle was apparently larger than your steering angle. So even though your wheels were turned to the left with respect to where the car was facing, they were turned to the right with respect to the direction the car was moving, so they still pushed the car to the right. As others have said, once the front tires began developing much more grip the forced the front of the car to the right with much more force than the rear, causing the car to swing to the right.

[DukeTrout]

You went right because your front, regardless of which direction you were steering, was on dry pavement and your rear was still on snow, and still had outward momentum. I'm sure the reason you ended up tracking again was not the interference of AWD but that your rear tires finally got some traction.

 

When your fronts got traction, you transitioned from 4-w drifting to snap oversteer. No amount of countersteer can correct snap oversteer like that.

 

It's been said many times, but it bears repeating: AWD still cannot overcome the laws of physics.

[canis]

Excellent responses. Thanks guys - that makes a lot of sense. Now if it would just snow again so I can keep experimenting!

[robinlsb]

You went right because your front, regardless of which direction you were steering, was on dry pavement and your rear was still on snow, and still had outward momentum. I'm sure the reason you ended up tracking again was not the interference of AWD but that your rear tires finally got some traction.

 

When your fronts got traction, you transitioned from 4-w drifting to snap oversteer. No amount of countersteer can correct snap oversteer like that.

 

It's been said many times, but it bears repeating: AWD still cannot overcome the laws of physics.

 

The front differential is open, the rear is not via limited slip. It's two tires versus one. Guess who wins? Let alone slip angle. Even if all FOUR tires were on snow, the same thing will happen. Try it!!! Makes for exciting driving under power!!!!!!

[trepetti]

Ditto to DukeTrout. When all 4 are on snow, car is rotating roughly agound the center of gravity near the mid-point of the car. When the front tires hit solid ground, they become the fulcrum, and the amount of rotational torque is amplified because the lever just doubled in length. Result - snap oversteer!