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Yes, I think that partially because of the heavy and long rear overhang of the estate bodywork of our W124, the behaviour in snow is quite benign. I was hoping that it might be more entertaining!
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Today I have driven 2 vehicles in the snow....
firstly my FWD renault, I live on a hill, and found on tuesday it was impossible to get out my uphill drive forwards, so have been parking nose downwards to see if that gave improvement...
in reverse it wasnt easy but i did find more grip and managed to get out without too much problem.
on the road, i felt the car 'floating' a lot, and found the grip to be very low.
Once at work, I had to go out in a lightly loaded sprinter.... what a joy! OK, i had to start in 2nd (as i did in Reggie) and yes the traction light flashed, but no float... and she steered exactly where i pointed her (unlike Reggie!)
I find that having separating drive, and steering, makes for more control.
I do agree that RWD is easier to make 'fishtail' but driven properly (and with weight over the rear axle) ill take RWD every time!
and in the dry? deffo no contest!
Edited by the swiss tony on 05/02/2009 at 20:15
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if sticking it in second and tickling it on idle won't do the trick.
Quite tb.
Isn't the problem with beemers not so much the wide tyres, which theoretically provide more grip even on ice at low speeds, as the sharp clutch and vigorous torque delivery characteristic of 'performance cars' (including fwd ones)?
I repeat, in 1961 or 2 I drove a Vauxhall Victor in snow and ice conditions that stopped all sorts of Jaguars, big Humbers and so on. It was easy because it had a soft little engine and clutch, less likely to break adhesion at the slightest touch on the throttle.
Even in that car one had to pussyfoot. Perhaps BMWs, or most of them, just aren't capable of pussyfooting.
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>>the wide tyres, which theoretically provide more grip even on ice at low speeds
really?
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really?
The difference might be academic, but I would have thought so, yes.
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>>>>the wide tyres, which theoretically provide more grip even on ice at low speeds
How does that work then?
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How does that work then?
However low the level of grip, a wider tyre should in theory supply more of it.
People see this in terms of a narrower tyre, with its heavier loading per square inch, 'cutting through' surface water (or slush or snow) to the grippy surface below. Except that if that surface is ice, it isn't grippy. On that you need studs, which cost a fortune, are easily damaged and tear up roads when there isn't any ice.
I did say any difference would be academic, and theoretical. In practice obviously things are different. Perhaps my point was invalid. It wouldn't be the first time.
But I still think it's because BMWs tend to be relatively violent in their power delivery that they are skittish on slippery roads. Others have said, like me, that much humbler rwd vehicles are more driveable under those conditions. But during these snow panics road conditions can vary enormously. These days main roads are soon reduced to dirty salt slush, but forty years ago you could go many miles on A roads on packed snow, a much more enjoyably controllable surface (until it was rained on in zero temperatures after dark) but now troublesome to most cars and most drivers. Heigh-ho.
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>>However low the level of grip, a wider tyre should in theory supply more of it.
Not necessarily. At low temperatures, one of the area dependent mechanism of providing grip between the tyre and road - the rubber's hysteresis - becomes much weaker, leaving tyre / road friction more area independent than might usually be the case.
>>People see this in terms of a narrower tyre, with its heavier loading per square inch,
Yes, that's definitely wrong - the contact pressure between tyre and road is to a first approximation, simply the air pressure in the tyre.
Wider tyres don't give more contact area.
Thinner tyres don't give more contact pressure.
What does happen is that the *shape* of the contact patch changes.
>>I did say any difference would be academic, and theoretical.
No, I think the difference is not academic - in most cases where forward traction is the priority, arranging the shape of the traction contact to lie along the length of the vehicle rather than across it makes a big difference - to take an extreme example, a caterpillar track.
The wide tyre gives cornering grip at the expense of traction.
>>But I still think it's because BMWs tend to be relatively violent in their power delivery that they are skittish on slippery roads.
Yes, I think there's something in that. Someone also shrewdly mentioned driveline inertia, which makes its presence felt most keenly in the lower gears, and while normally being a hindrance can be good to smooth the power deliver on slippery surfaces.
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Narrower tyres provide more grip in slippery conditions (snow, mud, etc.). Or so I thought. The reason being they cut through instead of sitting on top of the slippery stuff.
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think you are right rtj.
Stood watching Tuesday - a big Volvo unable to get up a snowy residential road followed by an A4 estate which also failed after numerous tries. At one stage a 307 pulled up a bit behind the Audi, stopped, saw he was stuck and pulled out past the Audi and continued smoothly up the hill with no problems. Was the difference was the much thinner tyres on the 307?
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I repeat in 1961 or 2 I drove a Vauxhall Victor in snow and ice conditions that stopped all sorts of Jaguars big Humbers and so on. It was easy because it had a soft little engine and clutch less likely to break adhesion at the slightest touch on the throttle.
My old Mondeo TD was victorious over far more exotic machinery in a very muddy Goodwood Festival of Speed car park a couple of years ago for, I suspect, similar reasons. Gentle clutch, and soft response in the early stages of throttle travel.
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For snow, read mud. Took the Jowett to a regular steam fair and it turned into a mudbath. All the modern cars were just spinning but anything with thin tyres was just driving out normally, as was my car on 5.25 X 16 crossplys. They were cutting through the mud and finding solid ground. They were all rear drive. The steamrollers could only spin as well, in spite of being several tons.
I remember you couldn't steer a Hillman Imp in the snow and many owners put a 3 X 2 concrete flag in the boot at the front.
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Similar reason why wider tyres aquaplane more. The car's weight is distributed over the larger area and so does not cut through the water the same. So snow and mud would be even worse.
One of the best 4x4's for mud was the original Panda 4x4 because of the narrow tyres (M+S ones) and the 4x4 system.
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The car's weight is distributed over the larger area
No - the area is the same.
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I have harped on about this on this forum so will bore you all again.
(I have driven various 3 and 5 series in the snow).
To drive well in snow:
you need narrow tyres to increase contact points and ensure tyres do not slip on loose snow.
You need low speed torque delivered linearly at low revs so you do not spin the wheels.
You need more weight on the driven wheels to maximise grip 50/50distribution is NO good - FWD is nearer 55% front)
You need an engine which is not set up to accelerate its revs quickly - ie. you do not want a light flywheel and fast throttle response.
The steering should not react to small inputs so the differentai friction on the front tyres casues it to turn in one direction due to patches of snow.
And finally you need a driver who drives with light feet, slowly, brakes gently and is happy to dawdle along.
Nuff said.
My Yaris diesel is good on snow: wife's 106 diesel is better (less power, thinner wheels)
An Austin A30 with winter tyres can beat them all: higher wheelbase, narrower tyres and less power.= even with rwd,
We once had about 100cms of snow . My fwd Rover 800 diesel got up a very steep hill by dint of much slithering and sliding, My friends BMW525td (diesel again) got one quarter of the way and stopped with wheelspin. Both had summer tyres. About standard performance I would say.
People round here with rwd cars tend to drive a small fwd car in snow - or not drive...
EDIT
On ice: you are stuffed. FWD or RWD. Unless you have studded tyres.
Edited by madf on 05/02/2009 at 16:47
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On ice: you are stuffed. FWD or RWD. Unless you have studded tyres.
Which is why some 4x4 drivers feeling overly confident of their grip levels can get into trouble. They assume they have more grip. But when they lose traction they will get into trouble. And because they probably did have grip until they lost it they will have been going faster.
Reminds me of some of the problems with the original Audi TT. Some of the accidents that caused them to fit the wing were down to driver error as much as anything.
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Reminds me of some of the problems with the original Audi TT. Some of the accidents that caused them to fit the wing were down to driver error as much as anything.
Yes, I'd heard something similar.
I've also read in a few well respected publications that the pre-mod cars were actually much more of an enthusiasts drive than the later / modded ones due to lift off oversteer in fast corners, and much more front end "bite". The downside of course was that they would (and did) punish you if you were careless.
Both of these traits were dialled out with the addition of the wing and the suspension mods that went with it.
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And one of the ones caught out (and killed) by the pre-mod TT was a rally/race driver I believe.
I know someone with an A6 3.0d Quattro who like to power round things on bends thinking "see I've got al lthis grip" except one day he'll save a lot of speed and lose traction and it will be too late.
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3 series tried to overtake me today in the uncleared 3rd lane - I saw him pull out, start to fish tail, then very meekly pull back in again.
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3 series tried to overtake me today in the uncleared 3rd lane - I saw him pull out start to fish tail then very meekly pull back in again.
Yes I was late for my Dynamic advertising strategies: A guide to strategically advertising dynamically seminar. Thanks a lot.
Edited by mss1tw on 05/02/2009 at 17:30
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As I understand it, the problem with the original TT was a combination of weight distribution and aerodynamics.
There was a very heavy front bias anyway (can't remember the figure, but it was something mad like 70-30%) and the original shape generated enough lift that at speeds above about 130 or so the balance was 100-0% to the front (all figures not correct as from memory, but you get the idea).
So, in the UK there was no problem. Those killed were all killed on fast autobahn corners where they could quite legally and legitimately go into a corner at those sort of speeds. With no weight at all on the back wheels, the car would swing out far further than was recoverable before the lift was lost and the back end touched down again. Driver skill didn't come into it.
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Very interesting... my neighbour in a Saab auto diesel didn't make it through the snow, had a real fright by all accounts. A work colleague with a Touareg auto diesel commented how useless it is in snow, another work colleague with a Fiat Panda 1.1 manual sailed past a load of stuff stuck on the hill! My Octavia's been fine, all week, as long as TT is turned off and a dab of handbrake to bring the rear around when needed.
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I once had an old 735i auto. In 'winter' mode traction was not a problem in the snow; far better than the front wheel drive Mitsubishi Galant that I also had at the same time.
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All this talk about cars having "too much power for snow" is not really true is it?
What it comes down to is drivers not knowing how to use their cars.
Manual gearbox: start off in 2nd or 3rd and apply the throttle gently, try not to lose momentum going uphill.
Auto gearbox: select winter mode if it has one, manually select higher gears if you can and be extra gentle on the throttle.
Oh, and most obvious of all, use engine braking and anticipate what you're doing, avoid the brakes if possible. Take corners very slowly...
If everybody did that they'd be hardly any problems, FWD or RWD.
Edited by TheOilBurner on 05/02/2009 at 20:00
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>>use engine braking
This piece of advice, frequently repeated, has puzzled me for a while. Why would the engine braking be preferable - it might easily lock the wheels where a gentle application of the brakes, perhaps under the auspices of the ABS controller, would not.
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Imagine doing 30mph approaching a right turn, if you let off the throttle and move into 2nd gear, the car will slow itself right down for the turn and you'll approach at a nice gradually slowing pace.
No risk of wheels losing traction at all, which even ABS can't help much on ice and snow where to stop the wheels locking may result in effectively no braking at all!
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My E46 is utterly utterly crap in this weather. I think is a combination of stiff suspension, 245/45R17 runflat tires and lousy traction control system. All that happened this morning was when you put your foot down the revs would increase to 2000rpm and the TCS light would flash continously and you got nowhere except maybe slide sideways.
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Engine braking is much better. Go down a steep slippery hill is first at idle and it will not slip at all, go down with the ABS chuntering and you'll go faster and faster and faster all the way down, of course a mixture of the two is good too. I don't see how you will lock up with engine braking unless you turn off the engine.
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>>I don't see how you will lock up
Yes, perhaps lock up was the wrong choice of words - begin to slip grossly would have been a better description.
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Our downhill cul de sac is sheet ice at the moment. 1st gear and feet off all pedals - no drama whatsoever - 5mph max full control. Touching the brakes would see me with an insurance claim.
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Engine braking is not always desirable in a RWD vehicle, taken to extreme's where trucks which are all RWD (not incl the trailer or semi trailer) will lock the driven wheels when empty using a high performance engine/transmission brake under slippery conditions and often have a switch for reducing or turning off the retarding effort, very unpleasant experience to get the driven wheels lock up when negotiating a slippery bend with an artic.
Most modern car braking systems are perfectly capable of coping with most snow conditions, only rarely will anyone experience that moment when full lock up would have been desirable at (usually) slow speeds on very slippery road, as Hamsafars example correctly describes, i experienced this speeding up whilst abs braking coming off an old badly worn transporter body in icy weather, not nice.
Traction control is a pita when trying to climb a hill as it usually cuts the engine power at the crucial moments often making the difference between a successful hill climb and not, but it does help prevent the more inexperienced from over powering on the twists and turns.
All my own opinion of course.
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>>very unpleasant experience to get the driven wheels lock up when negotiating a slippery bend with an artic.
Yes, it was in particular RWD vehicles that I was thinking about, and almost that exact scenario.
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I think it depends on the car and the surface. I have two FWD's and three RWD's. None of the RWD cars would get up my drive this morning...a C Class Merc, W124 E230 TE Merc and a E28 535i, all on different width tyres ranging from 185 to 225 section. The two FWD's , an Escort on 195 and a Almera on 175 both went straight up once I managed to get the RWD's out of the way. Once moving on treated roads with a bit of ice and snow and the like I prefer the RWD as it gives you the option to steer from the rear if needs be but if you lose a FWD it ain't that easy. On the hill that is my drive, the RWD cars tended to slide out backwards when ever any camber was involved.
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Oh yeah....Hello, by the way. I'm Rob, and that was my first post here.
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Don't ask me to properly explain the reason why but a technique I was taught many years ago to get a RWD vehicle moving in slippery conditions does seem to work.
If you are failing to get traction in a RWD, ease the handbrake on until it is just biting. Not so much that it will lock the wheels but enough to feel some resistance. Keep it in that position but keep your hand on the lever ready to release it as soon as you start to make progress.
Attempt to move off and for some reason the car will have more traction. I can only assume that the resistance created by the handbrake sort of tricks the diff into a state where it supplies equal torque to both wheels or something.
Anyway, whatever the explanation, it works, I used to use this trick a lot in ancient times north of Hadrians wall.
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>>where it supplies equal torque to both wheels or something.
That's exactly what the diff does before you apply the handbrake.
Applying the handbrake a bit stops the wheel that would spin from spinning up to speed - the slow slip can sometimes create more traction than fast slip.
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Using the handbrake on a RWD car will cause a spinning wheel to slow down, transferring some torque through the diff to the other wheel that is sitting and not moving.
Think of it as a poor-man's LSD.
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Think of it as a poor-man's LSD.
Ah, didn't twig it till you posted, our pick up has LSD, is that why its so good for a RWD thats fairly light at the rear? if so its worth having.
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Drove an agricultural tractor with a diff lock.
That would keep going through almost anything.
One problem - you can't steer with both driven wheels turning at the same rate.
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>>where it supplies equal torque to both wheels or something.
That's exactly what the diff does before you apply the handbrake <<
Not quite true - the diff allows wheels to rotate at different speeds - the torque is diverted to the wheel that can rotate fastest in a normal diff.
If a wheel is on a near frictionless surface such as ice, the diff sends the torque to this wheel allowing it to spin wildly while the wheel with grip sits motionless...
Imagine if you then (being Geoff Capes!) grabbed the spinning wheel and held it tight - the torque would then be transferred to the stationary wheel enabling it to start turning.
This is basically what happens as the handbrake is applied - you are reducing the turning force at one wheel causing the diff to transfer it to the other. By partially locking the wheel with the brake, rather than completely locking it, you can then enable both wheels to rotate giving you 2wd rather than 1wd.
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>>Not quite true
Alas, it's exactly true - it's how diffs work.
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>>Think of it as a poor-man's LSD.
Yes, in the past, this is exactly how I've thought of it, but, as I thought about my post above, I began to doubt that explanation.
Whatever happens with the brakes, the standard diff still split the torque in each driveshaft equally. Having the handbrake on a bit will not magically make the wheels turn at the same rate like a LSD will.
The problem with the LSD like explanation is that the braking is applied to *both* wheels - the one that's spinning, and the one you're hoping will being to drive you forward.
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Whatever happens with the brakes, the standard diff still split the torque in each driveshaft equally <<
When you are driving in a straight line, and neither wheel is spinning this is true.
So when you are wheelspinning your nearside wheel, and the offside is sitting doing nothing there is equal torque split occuring?
Umm, no - that's where it stops working. The torque being applied to the stationary wheel is virtually zero.
Braking one wheel does divert torque to the other wheel, which is indeed reduced in turn by the effect of the handbrake, but you can get a balance so both wheels have some turning force.
A handbrake has nowhere near the effectiveness of a true LSD, but it does enable a little more traction from the other wheel. It can help in a borderline case of being stuck but won't pull you up the Eiger.
5 million Swedes can't be wrong ;-)
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this is true
It's *always* true with a standard diff.
>>there is equal torque split occuring?
Yes - I think you're confusing torque with speed.
I think the handbrake trick can work, but, I don't think the mechanism is the LSD like explanation.
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Absolutely right NC - slip of the fingers - the torque is always the same, the speed/power output at the wheels may vary from each side.
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>>the torque is always the same, the speed/power output at the wheels may vary from each side.
Yes, I agree.
I think that if you could apply the brake only to the spinning wheel (like some tractors) then the tractive effort could be moved from side to side in pretty much the manner you wrote, and I had thought until earlier this evening. I think the real explanation of how gently applying the handbrake helps is just a little bit more involved.
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If you put your foot on the brake, the "retardation" is constant - with "engine braking" the effect is of "pulses". Perhaps there's something in this - certainly I remember the reverse being discussed, i.e. of "why grip is better with a motorbike with fewer cylinders", WRT Ducati machines.
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I wold have thought the gyroscopic effect of a faster-spinning, heavier multi cylinder engine would inhibit changes in direction more than a slower spinning 2-cylinder machine.
Possibly has something to do with COG of the engine design too ?
Should have no effect on true grip levels other than this.
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My old SAAB (sadly missed) had a front handbrake which could be used as a poor man's limited slip diff. Obviously inefficient, when partially applied it could apply braking torque to the uselessly spinning driven wheel whilst allowing a sufficiency of torque to the wheel with grip to get things moving. As well as all of the usual measures - high gear, low revs, careful clutch control etc. - I found the trick was to release the handbrake as soon as you achieved some vehicle movement. This technique served me well once or twice.
Most limited slip differentials are quite useless on ice as torque is required to give the necessary reaction force from the diff pinion of the slipping wheel to lock the multi-plate clutch. I well remember comfortably out-running an Opel Monza (with LSD) up an icy hill in my SAAB - wish I still had it.
659.
Edited by 659FBE on 05/02/2009 at 22:58
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As an example, if a car needs a total of 1000N to move it up a slope, and one wheel on ice can develop 300N, and the other on less slippery ice can develop 800N, how can the vehicle move?
With only a standard diff, and no handbrake trickery, the wheel on ice spins at 300N, and the stationary wheel also develops 300N - a total of 600N, not enough to move the car.
What level of handbrake effort (at the road), applied to each wheel will produce the "poor man's LSD" effect, and allow the vehicle to move?
Edited by Number_Cruncher on 05/02/2009 at 23:20
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I would assume it works as a result of variations in static/moving frictional coefficients between the speed of the wheels on the road surface, the brake pads and drums/discs, and breaking the car's inertia.
As has been mentioned it tends to work momentarily and in the past when I have tried it, it is only useful for the initial shove - it certainly doesnt allow a prolonged drive with both wheels acting as if a locked diff has been created.
I was never that good at mechanical and civil engineering, and it's way to late to even try to work out what's going on!
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1. Narrow tyres cut through snow better than wide tyres which tend to push the snow before them. That is why the old SAAB rally cars used to do so well in snowy conditions.
2. Winter tyres are made with a special compound that remains very flexible below 8 degrees C. In addition they have lots of sipes and a block type tread to gain grip and stay clean. Vredestein is one of the best makes. There are others.
3. 100kg of ballast properly secured in the boot, a full tank of fuel [more ballast] and a set of narrower steel wheels [you'll need different bolts or studs to your alloys] with snow tyres will enable most rear wheel drive cars to do just as well in the snow as a 4x4, many of which are on performance road tyres rather than off road tyres so they do not have the grip owners might otherwise expect.
4. If you are having trouble going up a hill in a front wheel drive car, then turn the car around and go up in reverse - you'll have far better grip as the weight transfers to the driving wheels which are now at the rear.
5. For the very few days we get tricky weather, get a pair of snow socks for the driving wheels. They take up no room, are easy to put on and cheap to buy [£40-£60]. Google will pull up at least 4 options in the UK.
6. Use your gears - even on an automatic - to control the car's speed on snowy/icy surfaces rather than the brakes. Keep a far bigger distance from the car in front, especially if the idiot behind is too close and do everything - steering, braking, accelerating - very gently.
7. Please clear ALL your windows from snow and ice before setting out and make sure your windscreen wash bottle has good a antifreeze screen wash in it.
7. And finally, is your journey really necessary? And if it is, take some warm clothing, fresh water and a few Mars bars just in case you bite off more than you can chew!
Edited by noobytoogy on 06/02/2009 at 01:41
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in reply/agreement to noobytoogy's post.....
1/ to put the wide/narrow tyre explanation simply - think snow shoes!
2/ exactly, normal tyres are too hard, - think F1 different hardness compounds for different heat tracks
3/ just to say, make sure the ballast is as close as possible to being over the axle, too far back it can act as a pendulum, not nice!
4/ exactly what i have done it works! (have i converted Reggie to RWD?)
5/ cant say ive heard of them, Ill have a look later!
6/ deffo.... drive like you have an uncooked egg under your feet... and dont grip the steering to hard, white knuckles dont allow the feel!
7/ 'letter box' driving is no good to anyone, also think about keeping a premixed supply of antifreeze screenwash in the car, for when the washers run out!
8/ may also be worth taking more than one mobile phone, of different airtime suppliers, in case you cant get a signal on your main phone........
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8/
A mobile phone will make an emergency call on any network it can find. Obviously, this doesn't help if the battery has gone flat. ;-)
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Just to add to noobytoogy's post (all of which I agree with and is spot on), here's my experience of two different cars(both FWD) in this years snow:
Car A with 225 michelen tyres - not very good in the snow, not bad enough that I was getting stuck but progress was slow. Tead pattern and tyres design more suited to warmer/wet conditions.
car B with 215 very cheap budget tyres - a more traditional 'block' type tread design / all season tyre - the levels of grip were very good, I reckon it would outperform an X5 with wide summer tyres.
Also saw many 4x4 drivers going way too fast for the conditions. They seem to forget that all car have 4 wheel braking.
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I can verify that tyres make a huge difference. There are mud & snow tyres on my old Landrover and it's been fine all week, haven't even needed the centre diff lock despite 4-5 inches of snow in places.
To pick up on someone else's point, it has a huge flywheel so driving smoothly is a doddle.
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So when my rover 25 FWD is sat on snow with the clutch out and one wheel spinning and the other wheel motionless, if I were to gently apply the footbrake with my left foot and gently apply the accelerater to prevent stalling , will the motionless wheel start to rotate giving it the chance to gain some traction?
I think I remember doing this many years ago in a marina and it worked but if you needed to go for the brake quickly your right foot stamps on your left foot and you stall when braking to a standstill with your left foot trapped under your right.
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I meant fiesta not marina.
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"why grip is better with a motorbike with fewer cylinders" WRT Ducati machines.
I think it was Bike magazine which explained it as relating to the power delivery of the twin being kinder to the tyre than that of an equivalent four. In essence, the twin has fewer power strokes per engine revolution than a four, which means the tyre has more time to recover grip between each power "pulse" from the engine.
Could this also be a factor in BMWs poor snow performance - the heavy bias towards six pot engines? Are the fours any better?
Cheers
DP
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"Are the fours any better?"
Based on my experience? Nope.
318i spins very readily in snow.
It's the design..
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On all my trips to the States, I have been hard pressed to spot a BMW that isn't 4 wheel drive, denoted by the 'x' on the back. eg. 325ix, 530ix, etc.
I don't think it's even an option here.
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