cotefarmboy wrote:

Paul

the key difference is that HDC allows the car to slowly descend a hill at a safe speed with minimal risk of skid, if you rely on brakes/ABS you don't have the fine control, sure ABS will activate but only when a wheel locks and you have theoretically started to lose control which is dangerous off-road.

Probably some of you should try this offroad in a REALLY steep hill with mud / icy / gravel / rocks mix situation. This simply prevents overheating the breaks and amazingly helps keeping control. I'm talking more than 45 degrees downwards. Unfortunatelly I did not have a device to mesure that..!

When using HDC 'something' has to apply pressure to the braking system, I think the noise we are talking about is in part due to this. If you rely on using the footbrake and ABS to retain control then the nosie you will here is just the ABS (if indeed ABS operates). The noise you hear when using HDC is the systems working to apply pressure (and may be ABS if it opertates) I have used HDC on dry tarmac road on a hill greater the 1:4 (25%), there is noise coming from the wheels nearly all the time. Now this is not beacuse ABS is working, (it is not needed on dry tarmac) the noise comes from the automatic operation of the brake system.

Now I'm not clear on the technical details of the brake system, but would imagine that when HDC operates there is some sort of high speed pulsing generated in the hydraulics, my money is on this being something to do with the source of the noise.

I've put HDC to good use on very many occasions, I think it works very well. If the system is provided in the car then my view is use it.

Avtur, I think in the particular case (dry tarmac) you describe it is not that easy to define where the noise comes from. When using HDC on a steep gravel hill, you hear clearly that one wheel skids shortly. Next the HDS reduces the braking force so the wheel turns again. This happens continuously. (several times per second)

The picture below shows what conditions I mean. (gradient is bigger than it looks)

Click image to enlarge

Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated

Personally 'd give up trying to understand what its doing and concentrate on driving it. Braking on a steep slippery slope in a good way to end up rearranging the body work. Your car doesn't have a low box so you can't use low first, take on obstacle at atime, if the slope is in 2 parts drive it in 2 parts! The newer HDC is much better and quieter than the original!! D4 HSE Lux for me
FL2 HSE Zermatt & Alpacca for the wife now gone
Skoda Yeti L&K for the wife.

Pelyma, I'm greatly interested in mechanics so I try to understand how things work. I'm also convinced that understanding what happens underneath helps to use it in a better way. Forums like this one are most interesting just because you get the opportunity to get in touch with lots of people from anywhere in the world sharing the same interests. Some people say that on suchlike forums too much rubbish is talked and even if sometimes they are right, from time to time you find information you would never get from official channels nor dealers.

That's why I posted this topic. It doesn't mean I would avoid using H.D.C. in critical situations but I still don't see clear the difference between ABS and DHC with regard to descending a steep slope. (exclusive of the "limited" speed)