Hills, snow and ice

tomstickland

skiddlydiddly wrote: »

You had a response to an input, you were steering the car and it responded by veering off the road.A fairly dramatic response.Your previous experience of grip levels being low on the flat bits should have maybe given you an inkling that when you add gravity into the equation ie the hill that grip levels would drop.

I wasn't steering. I was driving in a straight line down a hill. The rear wheels broke traction and that caused the rear of the car to swing round.

The grip levels were not sufficient for the engine to slow the vehicle. The rear wheels broke away.

tomstickland

darich wrote: »

When grip is that low, it requires experience of driving.....not a degree in physics.

They are not mutually exclusive.
Both allow an informed discussion of what's happening.

-avoid extreme situations by taking less hilly routes
-engine braking, but if grip levels are very low this might cause driven wheels to break away
-if slide develops then get clutch down to regain steering
-careful use of brakes, releasing if wheels locks to control speed

optimus_primera

tomstickland wrote: »

They are not mutually exclusive.
Both allow an informed discussion of what's happening.


-engine braking, but if grip levels are very low this might cause driven wheels to break away
-if slide develops then get clutch down to regain steering
-careful use of brakes, releasing if wheels locks to control speed

In an off road situation,with slippery descents acting like 'your hill', you are taught to use engine breaking,with feet off all controls.
If the wheels lose grip and start to slide then gently apply the throttle to get wheels spinning to match the slide,then take foot off.
NEVER depress the clutch,and don't touch the brakes.
The only difference is use of a low box on a 4x4.

tomstickland

Skid pan courses teach to depress the clutch so that the wheel speed can adjust itself to the rate that ground is going by.

Applying some throttle is the same in principle. How many people could judge the amount correctly on a steep hill though?

I guess that off road with mud is a bit more forgiving than an icy surface.

cyclonebri1

tomstickland wrote: »

Physics doesn't stop if someone is travelling too quickly for the conditions. The point being, the conditions were variable. I negotiated a 90 degree bend at the top without any issues - this being the source material for the estimation of grip levels. The first I knew of the lower grip was the rear of the car sliding into the bank as it broke traction.

The forces needed to maintain a steady speed are the same regardless of the speed. So if I'd been travelling at 10mph down the hill the rear tyres would have been expected to generate the same forces to hold the car at a steady speed. That's ignoring tyre dynamics and steering of course.

Sorry Tom, you can argue untill the cows come home, but on normal roads, ie, ones you can traverse easily in good conditions, the only reason you will skid is either driver inability/or inability to read the signs, or driving too fast for the conditions.


If some planks slews out in front of you, you have a problem, but it comes under the banner of driving too fast for the conditions; ie,

Expect the unexpected,

skiddlydiddly

tomstickland wrote: »

If the forces acting are larger than the grip available then the wheel will lose grip. I incorrectly said "lock up" when I meant "lose grip".

The engine can't speed up if there's not enough grip to apply the force needed to do that speeding up.

How is that any different to if you were in neutral?The same forces would be working on the tyre, so it wouldn't grip either way.

The engine can still speed up.What's easier for the tyre to do?Continue turning(thus turning the engine) or stop turning completely(which would have to happen for the engine not to be speeding up in this example)?For the wheel to stop turning there would have to be a LOT of grip.

skiddlydiddly

tomstickland wrote: »

I wasn't steering. I was driving in a straight line down a hill. The rear wheels broke traction and that caused the rear of the car to swing round.

The grip levels were not sufficient for the engine to slow the vehicle. The rear wheels broke away.

Thats still steering, unless you take your hands off the wheel when you are going in a straight line?

If the grip levels were not sufficient for the engine to slow the vehicle then neither would the brakes.If there is no grip then nothing will slow you down until you hit something or the road levels out.

There is generally some grip, you just have to find the speed at which you can get some by slowing down when its slippery.

cyclonebri1

I've only had 1 accident in the snow and that's in a long driving career.

Picture this
Sunday evening a good 4" of snow over ice. Longish, say 500 yd hill that steepens right up to the tee junction at the top.

2 or 3 cars infront of me all did the same thing, waited till the hill was clear then took a run from the level at the bottom. As the car infront of me, RWD as it happened, stopped at the junction I set off from the bottom. I had to stop at about 50 yds behind him as he could not only get no traction, he could not even hold the car on the hill with hand and foot brakes. I reversed away from him and tried to do a reverse 3 point turn or spin it out of his way but another car had followed me up and blocked me. He eventually hit me square in the passenger door at about 5mph.

Talking to him after the problem was simple, he was a DJ on his way to a booking the rear seats and bout were crammed with amp, speaker and vinyl, ie totally overloaded, simply dragged him backward once he's lost momentum. Something else to think about:snow_grin