Never been stuck in snow with a manual. Auto merc - rubbish.
Auto 4X4, with low ratio option and half decent tyres - goes like a tank!
|
Borrowed a friend's C240 Auto in Switzerland once - think they were a standard set of Michelin tyres but remember that they had picture of rain / snow on the sidewall.
They were most impressive on a very snowy drive from Zurich to Neuchatel.
|
|
|
|
I've got two RWD autos: a 2000 Jag S-Type, which is terrible in the ice, and I avoid using it in these conditions; and a 1999 MB W202 (C-Class) which is much better, although still not as good as a manual would be.
The MB has a summer/winter switch on the gearbox, which helps quite a bit. The gearbox also responds to the selector much faster, which makes it easier to rock out of a depression in the snow.
But I'd much rather have a FWD manual when the snow comes around.
|
Maybe ten years ago I was in the Midlands on a business trip when it snowed far worse than it has recently. The hire car I had was an Omega automatic with heated washer jets. I religiously went out during the day to clear it of snow.... then all went wrong work wise and I didn't the last two hours....
... car was under 2+ inches of snow! Set off for Manchester late evening and the weather was poor and the heated washers froze all the time. When I eventually got to Manchester after many stops (to de-ice) the back-end (rear wheel drive) slid... and for some reason I steered into the skid.... so didn't hit the police car in front ;-)
Since then I have always had front wheel drive but I don't see why RWD would be too much of a problem most of the time for me. Except I don't want a BMW or Mercedes ;-)
|
I think you'll find little to choose between them.
The stranded BMW/Mercs you see in the snow are being let down by the wrong tyres/RWD largely. The gearbox is immaterial. It just happens that giant-tyred cars often have autoboxes. My colleague in his manual 325i with 18" wheels was unable to move at all despite uber-gentle clutch release - the moment of inertia required to make the car roll was greater than the friction available between tyre and snow. (couple of pieces of heavy duty carpet helped out...)
You'll find the crazies in Iceland/Norway who go blasting over pack-snow prefer autoboxes.
|
Either, it matters not a jot you just drive accordingly.
No car on wide (runflats probably worse of all) low profile summer tyres will be any good regardless of transmission.
|
I'm afraid I disagree. When you are on a variable incline/variable traction slope and trying to keep up momentum whilst keeping the revs under comtrol, being able to select the gears at the precise moment you need to keep it in the balance of the two is vital and anticipation will always beat an auto box that can't know what's coming from one half second to the next.
|
Doesn't matter a jot which end drives the car if you don't know how to drive in those conditions.
As for manual or auto; I actually found my old Beemer (525TD auto) better than the Hyundai Coupe which succeeded it, in moderate snow. I am, however, in the habit of keeping some ballast (normally a bag of cement or similar) in the boot of any RWD car I'm in during this kind of weather.
As an aside; since Mrs. H required the use of the i10 today, and using the scooter was not an option unless I was feeling suicidal, I took the old pickup into work. Fortunately it was still loaded with half a ton of felled timber; to its credit it coped admirably and as usual started first time, not bad for 47 years old!
|
>>I am, however, in the habit of keeping some ballast (normally a bag of cement or similar) in the boot of any RWD car I'm in during this kind of weather.
I've never really understood if this works at all, and if it does work, how does it work?
|
My auto RWD car has been surprisingly good during the recent bout of adverse weather.
It doesn't have fancy wheels (just 205/55 R16) or a "snow" mode on it's gearbox, and I have no special skills as a driver.
Yet just taking it steady has resulted in (mostly) surefooted progress. A few slips and slides, but more wobbles than real loss of control.
Funny thing is, weeks before the snow arrived, I was commenting on another thread how worried I was about RWD with winter on the way, and swearing that I'd plump for FWD or AWD in future.....
|
|
|
|
I assume ballast to keep weight on the driven wheels? They used to force the RWD touring cars to carry ballast as a penalty though.
|
I used to keep a bag of sand in the boot of my Spitfire and my Midget. Not so much for ballast but to have something to chuck under the back wheels if I did get stuck.
Edit - sorry didn't answer the OP. Auto or manual ? Don't mind. Different techniques but really don't care.
Edited by Humph Backbridge on 04/01/2010 at 22:57
|
>>I assume ballast to keep weight on the driven wheels?
Yes, I think that's the logic that is being used.
But, of course, this extra weight also needs to be moved, which means that the tyres need more grip to move it - they need more grip exactly in proportion to the added weight. So, how does the added weight help?
It can't be increasing the contact pressure between the tyre and the road, because that is simply the air pressure in the tyre - the tyre's contact patch will increase in area exactly in proportion to the added load. So, there's no gain to be had there.
I suspect it's an automotive equivalent of the placebo effect!
Asking a front seat passenger to sit in the back seat would be helpful - the overall weight of the car doesn't change, but, more weight is over the driving wheels. Although asking the passenger to simply get out might be similarly helpful.
|
No, ballast works, simples, it is needed in the case of RWd simply because mostly the engine is over the front wheels. I drove a Hillman Hunter as a younger man, I therefore know.
Re auto/manual, no odds, I am tootling around in the wifes Steyr at the moment.
Absolutly no problems, auto bos and RWD,( it is selectable 4WD, but therefore no centre diff)
Anyway one can nudge the lever down the gears if so desired, though I have not found the need.
I would agree it is the fact that most auto cars have bling tyres(kinda)
|
|
Plus if one looks at the agric side, tractors require ballast for arable draft operations like ploughing, ditto loader work.
|
>>tractors require ballast for arable draft operations like ploughing
Yes, because the load to pull the plough through the soil is much larger than the tractive effort required to overcome the tractor's inertia. With a car, all the tractive effort goes into moving the car's mass. It's a different situation, and what works for the tractor doesn't automatically work for the car.
|
>>No, ballast works, simples
How do you *know* it works? Whatever you've driven, you either have ballast in, or you don't. You would not know if you would or wouldn't climb a hill with or without ballast.
In the past, I've added weight to the back of RWD cars, Cortinas, BMWs and the like, because it's the done thing. I didn't give it any thought at the time, but, looking back, I can't be sure it helped at all.
It isn't "simples".
The extra weight you add needs to be moved, which needs extra grip.
it is needed in the case of RWd simply because mostly the engine is over the front wheels.
Yes, a front wheel drive does have more of its weight over the driven wheels - but, that's not the same as adding weight to the car. Many RWD cars have a 50/50 weight distribution, and so, it isn't as though there is no weight over the back axle.
|
The tyres on the car make much more difference than the gearbox (or indeed whether front, rear or all wheels are driven).
You can control revs easily in an auto car using the low ratio settings if you need to.
You want narrow tyres in snow, or ideally you want winter tyres.
It's the big fat tyres on performance cars which tend to struggle in the snow and ice, so we can all get a nice dose of schadenfreude when passing a BMW or Merc in the ditch in our little runabout :-)
|
we can all get a nice dose of schadenfreude when passing a BMW or Merc in the ditch in our little runabout :-)
Yes, I had great fun last February driving up a snow covered hill from a standing start round a Merc whose big wide wheels were spinning away helplessly. My "little runabout"? The same automatic Merc, but with winter tyres.
They really do make all the difference and obviate the 'need' for a 4x4.
Edited by boxsterboy on 05/01/2010 at 11:37
|
|
The 'tiptronic' auto box on the Prelude works pretty well this weather - seems to provide all the engine braking needed and is a bit quicker than using the lower ratio locks by moving the lever through the auto selector gate. I still think an early Renault 4 on narrow tyres is the answer, though.
|
Mr NC; it works on the same principle as my lorry having more traction when it's loaded than when it's empty. Having driven the beasts for the past twenty-odd years, I don't think I need a knowledge of physics to know that it just does.
You may have noted from my previous post that I used my pick-up t'other day as it had a load of timber on the back. Had it been empty, it would have been a waste of time even trying to get it out of the yard because the wheels would have spun.
Since I often drive on my own, having a front seat passenger move to the back is not an option, hence the bag of cement. Incidentally, should I encounter a situation where I need a lump of summat heavy behind the back wheels to stop the car sliding away it serves for that too.
|
>>it works on the same principle as my lorry having more traction when it's loaded than when it's empty
But, it also *needs* more traction to move the thing when loaded.
I don't know what you carry, but at a guess, I would imagine that everywhere you drive your truck loaded you also drive it again unloaded.
Yes, you may find it easier to spin the wheels when empty, that's just because the engine has more reserve power - between the power you're demanding to move the truck, and the engine's maximum, when you're unladen.
Edited by Number_Cruncher on 05/01/2010 at 12:47
|
I still think an early Renault 4 on narrow tyres is the answer though.
Nah, 2CV is what you want. No coolant to freeze.
Mind you, the roof is a bit sparse in the insulation department!
|
|
2CV? I thought they were notorious for not wanting to start at all when its cold.
|
|
Only if they are out of tune/flat battery, etc. - much like most cars. You still see quite a few in the Swiss Alps because of their snow-ability.
|
N_C: Friction is a funny old thing, isn't it! No more so than for tyre vs. roadsurface. The equations show that increasing weight simply increases the force required to move that weight, cancelling out each other, but we know in practice this isn't the whole story.
As tyres are compressed, the rubber itself spreads, altering its shape and changing it's ability to grab the road surface. Perhaps this alters the pressure under the tyres changing the melting characteristics of the snow/ice ? Perhaps the tread pattern changes slightly to improve it's grip ?
Does ballast increase grip ? Although the total weight to be moved increases, the weight over the driven wheels increases proportionally so the driver would notice more 'bite' with the real wheels (or less of an ability to spin the wheels given the same throttle/clutch inputs).
Practical applications of friction/moments of inertia are as close to voodoo physics as any mechanical science I can think of. Why does dropping your tyre pressure from 30psi to 10psi make a noticeable difference on snow/ice/mud/sand? Partly it is increased contact area (with reduced contact pressure per given contact area), partly it is friction between materials, and I suspect partly it is because tyres are very naughty when it comes to the normal rules of friction.
**EDIT** I know it's not directly related to this topic, but I remember when VW were showing off the pulling prowess of the Touareg 5.0 diesel they had to put nearly 2 tonnes of ballast in the Touareg (making it 4 tonnes) to manage to pull a 747, as otherwise it would slip the tyres and not break the moment of inertia required.
**EDIT 2** www.automotoportal.com/article/volkswagen-touareg-...7 - it was 4.3 tonnes ballast lifting it to 7 tonnes!
Edited by Lygonos on 05/01/2010 at 14:13
|
it was 4.3 tonnes ballast lifting it to 7 tonnes!
I find that more impressive than the fact it could pull a 747 - seems like a heck of a weight to put in a car, even a big 4x4.
|
Yes, I agree, tyres are odd things.
When cold, one of their friction generating mechanisms, hysteresis, is much reduced, add in the wet which effectively lubricates the contact, and the other friction generating mechanism is much reduced also.
The 747 is an interesting example. If the 747 has a mass of about 200 tonnes, then, adding 4 tonnes or so of ballast represents about a 2% increase in the tractive effort required, BUT, the ballast represents an increase of over 150% in the vertical load on the tyres, so, yes, in that case, balast would definitely help!
I think that adding mass is, at best a neutral thing to do in a car, and adding the mass over the driven wheels is probably the least bad place to put it.
The closest I can come to a plausible explanation is that the extra mass simply makes the control less sensitive, and makes the driver less able to do something to provoke a skid.
|
Friction: reductio ad absurdum. Imagine a RWD car with its engine mounted so far forward that the car is balanced on its front wheels. There is no friction/contact/grip for the rear (driven) wheels. Put a bag of sugar in the boot, and there is friction, so the car is more likely to move. Put a sack of sand in the boot, and there is more friction, so the car is yet more likely to move.
So ballast can make a difference.
However, imagine a more normal car with an engine in the front, and a selector that allows you to choose between FWD and RWD. Clearly the car's weight is more to the front than the back. RWD is less likely to get you moving than is FWD.
Not sure whether any of this helps much.
|
This is getting interesting!
Putting together the bag of sugar reductio ad absurdum, and thinking in terms of proportions as per the 747 example, I can see it working now.
As an example, take my W124 - it weighs 1800kg. With a driver in, the front axle and rear axle both have about 900 kg of load on them.
If I put 200 kg in the boot, I now have about 22% extra traction available, but have only added 11% of the total vehicle mass.
Again taking an 1800kg RWD car, but this time beginning with 1200kg on the rear, and 600 kg on the front.
Adding the same 200 kg to the boot gives only 16% extra traction but has still added 11% to the total mass.
This gives rapidly diminishing returns if the axle you add ballast to is already the heavy one, so, it wouldn't be much use adding a bag of sand to the bonnet of a fwd diesel.
I think there's some fresh information there. Yes, adding ballast can help, but the best effect is obtained when the drive axle was light to begin with.
|
Well
Doh!
I think a Hillman Hunter could have been described as a bit light of the back end, unless ballasted. With pax or bagged grit/cement
cheers
M
|
|
my 325 RWD auto with 19" run flats is hopeless in this weather, i've been unable to shift it for 3 days
|
|
Don't worry - it would be the same if it was a manual ;-)
|
|
have you considered complaining to watchdog?
|
|
I'd go the SOGA route first BB.
|
My friend lived in a cul de sac at the bottom of a hill, every time it snowed I'd get a call, his big heavy RWD but tail-light Camero would sit there spinning it's fat wheels, I'd tow him up the hill in my 875cc Hillman Imp - RWD, rear engined with narrow tyres, it pulled like a train in the snow!
I find autos are quite good in the snow as they apply power softly, on the down side if you're on sheet ice and RWD you can actually accidentally sit there slowly wheel spinning if you don't push the brake pedal hard enough to bring the rear brakes into play! Most of the problems I've observed over the years are due to poor driving, I've driven all sorts of big RWD cars in poor conditions and have not had problems driving round stranded cars supposedly better suited to winter conditions.
|
Don't worry - it would be the same if it was a manual ;-)
Not sure I agree, my 330d manual touring (albeit with non-bling 17" wheels and 225 section runflats) has been pretty good this past few days, no worse and probably better than the FWD A4 B7 manual which preceded it was in last February's snow.
|
I think the consistent theme through all of these snow-driving threads is the type of tyres.
Winter/Mud-snow construction tyres are inherently better by design, but lower profiles, stiffer sidewalls, and wider tread sections all seem to count against getting/maintaining traction on snow.
|
|
|
|
|
