Nearly lost it today on ice

[CMJ]

Hi all. We were around Clitheroe / Lancaster / Trough of Bowland earlier today and on approching a 13% Hill which was clearly very icy I stopped. Engaged low range and decided not to use Hill Decent as the hill was very very icy and braking was not going to assist. That is what I thought !! We started to decend and the car started to slip side ways, I adjust the steering and we started to get a wag on from side to side. My wife told the children to hold on and I starting choosing which tree we were clearly going to hit as we were out of control and gathering speed !!! I then quickly grabbed and engaged HDC and like magic the car lost all its speed as if another lower gear was selected and we straightend up and stopped fish tailing. I started to laugh nervously but would love to understand a) Should I use HDC on icy hills b) How the hell did it stop us from crashing ?
Car is a L322 Range Rover 4.4 2003 and is quire amazing in these conditions !!

[JW911]

HDC is a wonder to behold. I played with it a little today on a quiet icy road. Hands and feet off, flicked the switch at around 15mph and it brought itself down to a slow walking pace in a dead straight line with no inputs whatsoever.

AFAIK, it works by braking each wheel independently until lock-up (a bit like ABS) then releasing, if it doesn't detect engine braking. You'll hear a rumble from each corner as each wheel starts to slide, then it applies electronic witchcraft. You'll note that it won't bring you to a complete halt.

a) Yes
b) Magic

Don't touch it in traffic though - the brake lights don't come on.

Edited by JW911 on Sunday 10th January 00:33

[Ed]

HDC has a set 'target' speed which it aims for. This is primarily to aid engine braking in extreme off road and was first designed for freelander which has no low range. When it senses the target speed is about to be exceeded it triggers ABS to hold the car at that threshold. You can select the target speed upto about 30mph with the cruise control buttons...great feature for towing heavy kit down steep hills or as you have found out, snow.

You can't break the laws of physics...but this seems to stretch them very effectively.

How did it stop you crashing? It simply managed to drop the cars road speed down to the same as the wheels. If you start to slide down mega extreme off road inclines you first accelerate to 'reengage' the tyre with the surface you are on, and when the speeds are realigned the wheels are more likely to have the friction they need to act on the road surface....you then get out and empty you boxer shorts and 'Oust' the drivers seat.

Edited by Ed on Sunday 10th January 01:12

[kVA]

HDC works by not braking a wheel that has no traction. If you are going down a steep hill, your rear wheels have much less grip than the fronts, due to weight transfer, so applying even engine braking alone can cause them to lock.

When a wheel locks on a slippery surface it will immediately try to get in front of the rest of the vehicle - hence the sideways slide!

HDC basically controls the brakes (and throttle) to ensure that the rears don't lock before the fronts and that neither of the fronts slip before the other - hence keeping you straight. If it had been SOOOO slippery that all 4 wheels lost traction at the same time, you would still speed up, but should still stay straight... Clever stuff!

[JW911]

Told you. Magic.

[red_slr]

The difference is the HDC will sample all its sensors much quicker than you can decide which level of brake force to use, and then it can also brake each wheel indipendantly as with EBC on other cars.

Giving all is inputs and the speed at which it can modulate the brakes, it works a lot better than you can ever attempt to do by normal driving.

[JW911]

Having lost the back end on a 1:10 ice laden country lane in the Chilterns today (first gear, low ratio), HDC got it back nice and straight very well. All I had to do was steer where I wanted to go. Superb.

[2 5HAN]

Tried it today on my parents road a very steep hill covered in ice and snow, well done LandRover excellent bit of kit.

[r1chardh]

I agree - HDC has been great in the Freelander2. Gives a lot more confidence in this weather, and it's amazing when you can hear each wheel slipping and re-gripping.

[ilaishley]

The one thing to remember with HDC is that if you opt to use it then please read and understand how it works. When engaged you are basically giving all drive control other than steering over to the on board computer. If you engage HDC at the top of a hill as you descend you do not touch any of the pedals. Its very hard not to hover over the brake pedal, but if you do press the brakes you override the HDC and it cannot perform its job. No matter how steep the hill just let the car roll down with HDC engaged and you'll be amazed how controlled the vehicle is. Obviously you need to brake at some point but I would avoid doing so on the descent. Braking and accelerating whilst in HDC only temporarily overrides it: It will return to full function when you take your foot of the pedals.

I have used it in both my FFRR and my D2. The FFRR is far more refined, whereas the D" works fine but sounds like the Titanic about to sink when HDC is working.

Ian

[ChrisRC]

Another factor to consider will be the tyres. Our 58-plate TDV8 Vogue SE has 20" wheels shod with Pirelli Scorpion Zeros, which was how it arrived from Land Rover. Looking at the Pirelli info on their website, this is a tyre right at the so-called 'High Performance' end of the tyre range, no obvious concessions being made to off-road or non-summer running.

In the recent unpleasantness, we've found that braking is about as bad as it could get (of course, being an LR or a 4x4 offers little in straight braking performance on low-friction surfaces). It was also a bit clueless off-road in the snow around the farm; the Terrain-do-da is all very well, but there are times when locking diffs are still the answer. The local LR dealer is fitting winter tyres next week.

[GKP]

Interestingly HDC did the exact opposite for me last year. Trundling down an icy, steep, off camber slope with a 90 degree bend at the bottom. Second gear low, feet off, all going smoothly well and under control. I hit the HDC switch as an experiment and amongst all the brake pulsing the whole car slewed to the left and tried to follow the camber of the road towards the ditch.
I hit the switch again to turn it off and calm and control was restored.

In 99.9% of situations it is a wonderful tool, but it's not a cure-all panacea.

[r1chardh]

ilaishley said:

The one thing to remember with HDC is that if you opt to use it then please read and understand how it works. When engaged you are basically giving all drive control other than steering over to the on board computer. If you engage HDC at the top of a hill as you descend you do not touch any of the pedals. Its very hard not to hover over the brake pedal, but if you do press the brakes you override the HDC and it cannot perform its job. No matter how steep the hill just let the car roll down with HDC engaged and you'll be amazed how controlled the vehicle is. Obviously you need to brake at some point but I would avoid doing so on the descent. Braking and accelerating whilst in HDC only temporarily overrides it: It will return to full function when you take your foot of the pedals.

I have used it in both my FFRR and my D2. The FFRR is far more refined, whereas the D" works fine but sounds like the Titanic about to sink when HDC is working.

Ian

Ian, after reading this explanation, I wondered if you could explain what the snow setting actually does, too?

or anyone else!

Thanks!

Richard

[kVA]

r1chardh said:

Ian, after reading this explanation, I wondered if you could explain what the snow setting actually does, too?

or anyone else!

Thanks!

Richard

Grass / gravel / snow setting dampens the throttle response (so you can't accidentally dump too much torque at the wheels), pulls away in 2nd gear high range or 3rd gear low range and modifies the gear-shift map (auto only), pre-loads the differential(s) to minimise slip, increases the sensitivity of ABS and DSC and switches on HDC with a very low target speed.

Note that the so-called 'snow' setting is intended for packed snow (i.e. on the roads): If you are in deep soft snow (powder) you may get stuck, as there is too much intervention from DSC and TRC... Best to use Sand mode in really deep snow - just to try and maintain momentum.

HTH

Edited by kVA on Monday 11th January 22:32

[ilaishley]

kVA said:

r1chardh said:

Ian, after reading this explanation, I wondered if you could explain what the snow setting actually does, too?

or anyone else!

Thanks!

Richard

Grass / gravel / snow setting dampens the throttle response (so you can't accidentally dump too much torque at the wheels), pulls away in 2nd gear high range or 3rd gear low range and modifies the gear-shift map (auto only), pre-loads the differential(s) to minimise slip, increases the sensitivity of ABS and DSC and switches on HDC with a very low target speed.

Note that the so-called 'snow' setting is intended for packed snow (i.e. on the roads): If you are in deep soft snow (powder) you may get stuck, as there is too much intervention from DSC and TRC... Best to use Sand mode in really deep snow - just to try and maintain momentum.

HTH

Edited by kVA on Monday 11th January 22:32

That sounds exactly right. I have been using Snow/ Gravel all week and it is a god-send, especially in in a TDV8 which is more than sprightly off the mark. To be fair I have done some "testing" of the settings. In other words I have tried flooring the RR in both "special programs off" mode and "snow/ gravel" mode on in the snow/ice. The car did not deviate from straight line running at any point. It was slightly less controlled with programs off. I tried it again the next night in the Discovery 2 and actually lost the car and was lucky not to hit the opposite kerb. The disco 2 was superb though for towing the stranded cars up the hill outside my house, as it as grabber AT Tyres which are fantastic

Ian

[r1chardh]

thanks both, and that's an interesting point about the sand setting in deeper snow.

richard

[tomw2000]

I don't 'trust' HDC and am scared to use it

It's on our RRS TDv8 and when the snow hit us just before christmas I went out to 'rescue' some friends who'd been stranded. I nearly fell at the first hurdle on my own long, steep drive.

Admittedly I set off down the drive a tad quick, then realised it was slightly too quick for the condtions and braked...then started slewing towards our gateposts....so now...all in slow motion...I remember HDC...I frantically look for interior lights, so I can find HDC and then I press HDC...still skidding towards gateposts....

I then thought, "Hmmm HDC brakes...that's gonna make things worse". So I turned it off.

In the end I managed to almost stop, missed the gatepost by inches and got out ok.

I think, havng read this thread, I never really gave HDC a chance to work properly and it probably would have been fine...and I was braking on and off myself, so would have interupted with it's functioning anyway. But it still scares me

[GreenVault]

Just a word of caution- I relied on HDC in our Disco3 last winter and promptly slid down my (long, steep and at that point icy) drive into the garden wall. Not the car's fault, I naively asked it to do the impossible- combine three tons of metal, a steep downward slope and sheet ice and there is not a huge amount that even an incredibly clever braking system can do.

Edited by GreenVault on Friday 15th January 10:35