Land Rover in snow

Diff center diff lock provides traction to all three remaining wheels if one slips. If two slip, on a diagonal or same side, you lose traction as both slipping wheels revolve. How do I know? I've got a little Lego technic model. B-)

Saw and example of same side slip with the snow plough the other day, it got stopped by the couple of foot drift on the slight rise opposite. Short pause then both wheels on the side I could see started slowly revolving to no effect. It backed out and took a bit more a run and got through, still gave it something to think about though. I guess it could have been all four wheels turning but I doubt it without locks for the axle diffs.

I have enough trouble getting my head around diffs in the first place let alone when you have a combination of them. Presumably the Pinzgauer has 5 diffs? One in each axle and two more between those axles.

ROFL.

Probably not. I have the half worn Kuhmo things still on rims in the garage, they are fine in the summer, when it's warm, but have noticeably reduced grip below about 2 or 3C.

Also my fuel consumption has taken at least a 2mpg hit. Now that might be the tyres or it might be that since I put them on there has been less than two weeks (2nd - 14th) when I haven't been driving on snowy/icy/reduced width roads so some what slower and in lower gears than normal. Yes, this is Day 31 of lying snow for this area.

Don't think they do them wide enough for my rims, 255/55R18.

Be good to see that. The type of snow makes an awful lot of difference. It can vary from so light and fine that it's quicker to fan 4" of it away than to try to shovel it, to stuff that is very firm, solid and heavy. I know people take the piss out of the rail companies for the "wrong type of snow" but they have my sympathies. Fine, dry, powder snow, is a right PITA, it's almost "if air can get in, so can the snow".

As has already been pointed out the diffs stay at the same height, but it would give more space for snow to get around the the rear axle. Not sure what would happen when you tried to let it down with the gap full of snow...

Not many hills that I consider steep enough to need it, ie. Ones where the car still runs away in Lo 1 or 2. The steepest around here needs Lo 3 to run away, if it doesn't run away why do you need HDC?

Anyway I find the HDC a bit too fast for comfort and the range of speed between what it slows the car down to and how fast it lets it go before slowing it down, rather harshly, too large. If it held it around 2 or 3mph I'd be a lot happier.

You couldn't feel the braking? Mind you on snow maybe the braking effect doesn't get transfered into the car as much as it does on dry tarmac.

It's one of theose things I'd love to play with on really steep hills both dry and slippy but with space around and at the bottom so if all goes pear shapped you have "run out" space. Not a bend, a wall, or someones garage...

Yes I know how diffs work and what happens when wheels slip, I was talking about the traction control that was specifically mentioned. I've cross-axled my Defender plenty of times, I'd have thought traction control could get out of that by braking the spinning wheels.

No, it only has 3 diffs, and they're in the axles. The rear two axles are close to each other and are permanently powered with a straight solid shaft joining them, no transmission wind-up that it can't cope with. The front axle is only driven when off-road, at which point all three axles get the same amount of torque as they're all driven by what is now effectively a single drive shaft. You can then selectively lock axle diffs to keep all 6 wheels turning even if only one wheel has grip.

A friend has a Tatra 813, that has 8 wheels, four diffs in the axles, two diffs between pairs of axles, then another diff between those two diffs.. They're all lockable. It's quite amusing to see this great big truck suddenly grind to a halt because one wheel has hit some mud and spun, with the diffs suddenly chattering away to direct all power to that one spinning wheel! There's some video of it on the youtube link in my sig below.

That's not quite true Dave. Locking the centre diff means that if (say) you have a wheel spinning-in-place on the front axle, you can still send drive to the rear axle. The non-spinning wheel on the front axle will still not get any drive if you engage centre diff lock, because the front diff will still be sending all the drive to the spinning wheel.

So only two out of the three remaining wheels get traction.

If two slip, on a diagonal or same side, you lose

This is true. Or to put it another way if one wheel slips on each axle, you're buggered unless you also have axle diff-lock.

Well, I think you're most probably right.

The axles themselves and the front and rear diffs don't present a huge obstacle. For a short distance in snow you'd get a 'plane' effect at the front where snow was lifted over the axle (until it wedged on the frame and did pack down, of course). If the problem was only a short hump, you would most probably have cleared it.

Aside: I used difflock properly for the first time today (just to test it, VBG), on the Circular Road on the Downs - it was only a few inches of slidey, slushy snow & ice, reasonably flat and with no obstructions, for a mile or so.

I think it's working, as the transfer box lever moves to (and stays at) all corners of the '8', and I certainly had pretty good traction. To be honest I didn't need it, as the basic 4x4 would've been quite adequate, but it was good to check it out. I need to fix the indication tho, but that can wait.

I did an 'entertaining' sideways slide earlier, on Redcliffe hill right in the middle of town - turned out of an icy side road onto what looked to be cleared dual carriageway, to find it had a patch of black ice in just the wrong place! No harm done though as very little traffic about.

Anyone else noticed a suspicious absence of 3-series BMWs recently? I think they're frit!

Cheers, S.

PS: loved the pics, BTW.

wheels

Plays with model and pays a little more attention. Yep, the non slipping wheel on the same axle as the slipping one does not drive.

Except of course with the center diff lock engaged all wheels rotate at the same rate(ish) so the slipping wheel isn't actually spinning anymore just not providing any drive and simultaneously not letting the other wheel on the same axle provide drive either.

Much simpler explantion.

Apparently they're s**te in the snow, one of the few web boards I'm on reckons the 3-series beemers are worse in the snow than the Lotus Elise (!), due to the rear weight distribution (most of the weight at the front on the beemer, most at the rear on the Lotus, both cars rear-wheel-drive). This was from owners of both Lotuses and Beemers. One chap controls the BMW fleet for a police force in the UK and grounded all the beemers for the duration of the slippery stuff as they were turning out so shit. Front-wheel drive cars are apparently doing better due to more weight over the driving and steering wheels. 4x4s are of course doing the best, particularly those with sensible tyres, i.e. knobbly ones!

If you stop one wheel on an axle and let the other spin, then the spinning wheel will rotate at twice the speed that the wheels would be turning if they weren't spinning. Also if a wheel has no grip and power is applied to it, it *will* spin. Where does the engine power go in your scenario above, one wheel without grip, one wheel with grip, engine power applied to prop shaft, but in your case no wheels spin? In reality the wheel without grip will spin.

Sorry misread.

Plays with model again, you only need to brake one of them (solves the two slipping wheels on different axles problem) and I was surprised that the TC didn't do any thing effective. The pump fired up and there was the occasional clunk clunk clunk with small jerks associated with them but maybe I was too frimly stuck... The TC does work with a single wheel spin AFAICT, at least the pump fires up and the car keeps going.

Now that is getting unstoppable...

ARGH! And presumably a computer to drive the locks. Or do you just start at the beginging of the drive chain putting in locks until you start moving again.

I did know.

I'm surrounded by them here (probably 100+ in a 1000yard radius), and I've never seen what the point was (except the old estates, which were nice).

Wide wheels, low-profile tyres, all the weight at the front but rear wheel drive - nice for the skid pan at Castle Combe, otherwise rubbish.

The trouble is, Bristol's full of 'em. At least this week the owners (mainly) seem to have seen sense. Last week they were just road obstacles everywhere, and being driven round by Fiat 500s, etc.

Well I've been driving my 330i about although not until the roads have started to de-ice a bit tis true. Why put yourself in a difficult and possibly expensive situation when there is a 90 in the drive. :-)

Most BMWs have a 50/50 weight distribution or thereabouts, they pride themselves on it. Their problem is the wide low profile high performance road tyres (no grip on snow) coupled with the rear wheel drive, and yes I have seen Mercs in trouble too with the same problems. Front Wheel Drive cars without the prop shafts and diffs have most of the weight at the front over the driven wheels which are pulling the car along. I have driven the Hardknot and Wrynose passes in quite heavy snow 4 up in a FWD car but I know the 330i would not get to the first corner in those conditions although, on thinking about it, a couple of years ago up on Exmoor I kept going when others didn't.

This is true.

With normal 2WD single diff system yes. But not with a 4WD system and the center diff locked. The wheel with no grip rotates at the speed of the wheels that are not slipping. Trust me I have the model, one wheel hanging in mid air, other three on the desk apply drive and it just wants to move, the free wheel does not spin. The drive comes from the two wheels on the other axle. If I let the model move the free wheel rotates like all the others.

The tricky bit is showing that the wheel on the same axle as the spining one also loses drive. With drive applied and each wheel lifted lightly so that it just slips only the two wheels on the other axle will slip. Indeed provide you have two wheels on the same axle on the ground it doesn't matter what the other two do they can be in free space but you still have drive from the two wheels on the ground.

On a 2WD system I agreed but not on a 4WD system and center diff locked. Loss of grip from any one wheel (or both wheels on one axle) does not generate wheel spin and all the engine power being dumped to the spinning wheel(s). The power just goes to the two wheels on the axle with out the spinning wheel and keeps you moving when you would otherwise stop.

This wasn't a short hump it was about 40' to the safety of treated road. B-) There was snow rammed pretty much around and up against everything underneath, forward of the rear axle. I suspect it was coping until the rear axle required pushing through the snow as well.

Well if the requirement for diff lock could be equated to the TC waking up it stays resolutely asleep in normal driving on packed or deep rutted snow or moderate slush. It does wake up in up on up hills occasionally or really heavy going situations like trying to be a snow plough.

Careful that's what took out my previous Disco...

No but I have noticed a higher percentage of 4WDs and tractors or is just that there are less ordinary cars about?

You'd only need to brake one spinning wheel to get drive to the non-spinning wheel on that axle, but you'd want to brake both spinning wheels on both axles to get drive to the two non-spinning wheels on both axles.

I don't know how they work but it won't be by computer, that's for sure!

We're not talking about the same situation. I'm talking about a vehicle that's immovable with spinning wheels, you're talking about one that's still moving. The rest of your post is similar, if you're stuck with two wheels spinning, what I said applies.

I had a 90 a few years ago with front and rear axle diff locks. Brilliant in mud or with one side in ruts. Front lock wasn't much assistance on hill climbs as most of the weight was on the rear wheels.

Possibly not. I had the dealer downgrade the wheels that came with my (2nd hand Disco td5 XS) to those on a lesser spec when I bought it 'cos they were narrower and I thought they'd be better able to cope with the bad weather. Very surprisingly, they did it for nothing!

Well, you don't but nice to know it works :) I do remember being impressed when descending the 'test track' at the dealer. Felt like about 1 in 1 and it didn't go ar$e over Tot

Agreed

Yes, I could feel the braking. I was a little surprised by the car's desire to continue straight on when I was turning left and must go out to 'test' it again before the ice goes.

or in my case, some trees. But then I suppose they'd stop you demolishing the stables....

Cheers Please reply to group - email address is not monitored Ian

There's a 265/65R18 BFG AT but it's unlikely to fit inside the wheel arches. It has an OD similar to 7.50-16 and 235/85R16. Suitable rim width is similar to that for a 255/55R18.

Awsome roads!

Mrs_D had to wait as the lady down the road in her Merc sat with the wheels spining blocking our drive. Eventually she asked Mrs_D if she was waiting to go. but advised her she had no chance "..in that!", being our Renault Laguna. Mrs_D pulled off the drive and up the icy bank (4 up) and that was the last we saw of Mrs Smug Merc owner... We have however seen her car, parked outside her house for the last week or so... going apparently no where.

I have to say the RR has been parked up too, but thats in case some c*ck runs in to it. The 110 has been doing a stirling job getting us out to the folks cottage and delivering water when their mains in to the house froze up. Also two trips out for them to escape for essentials. I even invested in some snow chains from ebay. Yet to be used in anger but given the reliance on the car for above duties had things worsened then they were ready to be used.

Lee D