Hill decent and slippery stuff

All my experiences with HDC, and knowing about the use of cruise control to lower or increase speed have been very good.

Nursed my D3 of Mt Pinnibar, which is very steep in places (thank god not wet and slippery) due to a transmission fault using HDC and it is an amazing piece of kit, can put it in neutral if you want (not recommended!!) but tried it non the the less.

Not sure about using it in reverse but as I recall reverse is very lowly geared so in rock crawl you would have lots of engine braking control ? I am sure someone can provide gear ratios.

As has been pointed out, you only control vehicle speed when the tryes have some traction. So no matter what you or the vehicle does, if you are slipping down a track with minimal or no traction only an anchor will assist. I for one do not have an emergency anchor fitted !!

As long as it stayed upright and out of the trees you can look at it as a positive learning experience.

Regards,

George

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Originally Posted by gghaggis

AT tyres will give you little to no grip on clay - most MT's will struggle too. A bit of speed might help clear the tread, but usually they'll just turn to slicks in a couple of seconds or so.

Cheers,

Gordon

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Fully agree with above and I would be interested to hear what your experience/thoughts are regarding the use of tyre chains in extreme clay conditions?

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Originally Posted by brad72

So does the hill decent work in reverse as well.

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Absolutely it does. Again, don't go near the brakes! Nail your foot to the floor if you have to.

Alan

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Originally Posted by gghaggis

AT tyres will give you little to no grip on clay - most MT's will struggle too. A bit of speed might help clear the tread, but usually they'll just turn to slicks in a couple of seconds or so.

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As I found out once with STT's on the D3. Once they were full of mud, all the car would do is slowly pirouette.

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Originally Posted by RichardK

In conjunction with HDC you can use command shift to lock it up in 1 or 2 low depending how slow you want to go, I find using command shift this way I mostly don't need HDC

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The Cayenne has no HDC. When I went down a steep, loose shale and rocky slope, I locked the diffs and went into low range manual 1st. Much more control than I ever felt with HDC on the D3.

It was also when I found out about the benefits of tiptronic gear levers on the steering wheel. I could change between 1st and 2nd without taking my hands off the wheel.

I think that when it comes to slippery mud, particulartly on steep slopes, one needs to ask oneself 'do I need to go this way?'. Losing control can be very costly.

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Originally Posted by Jamo

The Cayenne has no HDC. When I went down a steep, loose shale and rocky slope, I locked the diffs and went into low range manual 1st. Much more control than I ever felt with HDC on the D3.

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Interesting. Of course no machine is perfect and therefore no machine will perform optimally in all conditions.

Personally I hate it when I first lurch down a slope (front or rearwards) until the computer works out what it wants to do, but once it has done that I have every confidence that it will perform as required. Then if traction is lost because of soft or slippery ground then a tweak on the accelerator usually sets it off in the right direction.

In the old Stage 1, going forwards, 1st low and no diff lock. No brakes ever and use the accelerator to maintain forwards momentum. It feels that I have more control and probably I do, but with HDC the control is handed over to Silicon Sue.

But the Stage 1 is a manual box, yes?

Oh, and I didn't mention 'confidence', I only mentioned 'control';) but I suppose in some circumstances lack of one leads to lack of the other.

(My car also has an automatic terrain diffculty alert system. Whenever I have failed to heed her warnings, I have invariably run into trouble!:p)

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Originally Posted by gps-au

Did you use the HDC speed control at all ?

(I have found many D3 drivers don't know about it).

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+

I was using the speed control. It was working untill as pointed out in another thread. Physics took over. 2 tonnes with mud choked tires and a good incline had the car going or starting to go sideways. HDC works and the + & - works well. I read the manual from cover to cover then tried the speed control on a dry slope previosly.
Thanks for the suggestion ( I added note to user guide "nail foot to floor to remove temptation it touch brake while HDC engaged" as I over looked the bit about keeping ones foot off the brake )

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Originally Posted by WhiteD3

I would have thought you'd have HDC selected before you started down? As other have said, select L1 or L2, HDC and stay off the brakes. Use the cruise +/- to change the speed.

What tyres do you have?

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Sorry important bit on information. they are Grabber AT 2.

review at General Grabber AT2 Tires - All Terrain Tire Reviews

the review found they work in mud untill it became deep. The track was slippery as but the mud was less than a few millimeters or a few centimeters deep after I had cut the track a little after the several attempts. Physics took over but the climb out was fun.

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Originally Posted by Jamo

But the Stage 1 is a manual box, yes?

Oh, and I didn't mention 'confidence', I only mentioned 'control';) but I suppose in some circumstances lack of one leads to lack of the other.

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Sorry I didn't express myself clearly enough. What I intended was that when driving the Stage 1, which is manual of course, down an incline requires a specific technique. Since it is manual I am required to pilot it and have control over all the machine's functions to ensure a safe descent. When doing the same with a HDC equipped vehicle there is a technique but it is different to that required when driving the manual Stage 1. In that instance one must pass control over to the computer brains (there are multiple) that control the vehicle's functions.

Tweaking the speed controls adjusts the parameters for the brains but using the brake pedal, or the accelerator pedal for that matter, disengages HDC and is more likely to cause problems than resolve them.

Different techniques but with the same result, hopefully. A safe and controlled descent.

Hope that's clearer.

Alan

I agree. Different techniques for the conditions and the vehicle. And a bare bones D/4 on the same terrain will perfom slightly differently to one that's been loaded up. My D3 weighed around 3tn+.

The HDC must contain the momentum of the vehicle and momentum is a function of the mass. As I added bits I drifted away from using the HDC and towards driving the car myself as I found I was having more work to do with the HDC than when i controlled the descents myself.

The Cayenne is considerably lighter and, having done 165,000km in my D3, I would at this stage say that the aisin warner auto is better than the ZF. But, then again it's almost like comparing apples and oranges. One was 2005 car weighing 3tn and the other is a 2010 car weighing 2.4tn; and that makes a big difference.

Horses for courses.