The drive of my house is steep and surfaced in tarmc with a general smattering of loose stones which have come loose from the tarmac.
I have had two diesel automatic Mercedes' on the drive this week, both RWD. Neither would slowly reverse up the drive without lots and lots of wheel spin and smoke from the tyres. Both flashed the traction control light, but the TC did not kick in (because in reverse)? I could get them up at speed, but as they were not my cars I didn't fancy crashing into my car or a wall.
We have had the following cars in our drive regularly since we bought the house three years ago: -
Hyundai Trajets (V6 and Diesel)
Volvo S80 2.9
Subaru Foresters Turbo and NA
Suzuki Wagon R+
Honda CR-V
plus lots and lots of run of the mill FWD cars
and none of them gave a moments cause for concern except in very icy conditions, during which time the 4x4 cars were a doddle.
What is going on?
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Espada III - well if you have a family and need a Lamborghini, what else do you drive?
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If they were reversing up then mabey they spun as there was less weight over the wheels whereas a FWD has all the weight on it.
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Neither would slowly reverse up the drive ...
Reverse into your drive? Why don't you go forward into your drive and back out into the traffic/pedestrians like a normal person? Make sure your windows are iced-up for even more fun.
;-)
Hawkeye
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Stranger in a strange land
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You forgot the sudden clutch and out-of-tune motor necessitating high revs until warm, Hawkeye. The real story's always complicated whatever people may say.
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The last RWD car we had was a Fiat Mirafiori estate in 1981-2. It was marooned in the garage, at the foot of a few yards of very gentle slope, in a cold spell that winter. Never again.
(It also let SWMBO and three small children down 3 times in its first and only year, from new, with us, but that's another story.)
The Renault 20 we had then came out without trouble every day, without even any need to shovel snow or ice.
As I'm sure I've said before, RWD is great (without icy conditions) if you drive to the limit. For most of us there isn't anough difference in the handling to make the inconvenience in bad weather worth risking. But each to their own - I'm not denying that BMWs and may other RWD models are fine cars.
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I remember going to work at Sparrows o'clock one winter morning when my MG Metro was the first vehicle up a steep hill covered in snow.
Having failed to get up forwards, the car romped up in reverse with the extra weight on the driven wheels. In fact it was almost like the snow didn't exist.
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Last winter I had our Lexus ES300 (Toyota Camry) out on our slightly inclined drive in front of the garage. There had been a very light covering of snow - about half an inch. Despite the very mild gradient I could not get enough traction to drive the couple of feet forward into the garage - the wheels just spun and the car slid from side to side.
Eventually, hot water and de-icing fluid around the front tires gave me a little traction and I just made it. After that, I avoided stopping on the drive if there'd been any snow.
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We may need a professional engineer to answer this one authoratively. For example, reversing up an incline may alter the weight distribution in favour of the front wheels ~ I'm not sure about that one. The weight transferance due to acceleration will certainly be from the rear wheels to the front.
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L\'escargot.
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Not just weight distribution the gearing is lower in reverse which helps. BUt yes reversing will cause a weight transfer away from the direction of travel, just when you don't want it in a RWD car.
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I thought so. Pity, I had thought of getting a Merc in the next year, but daren't chance it after this experience, even without any frost or snow.
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Espada III - well if you have a family and need a Lamborghini, what else do you drive?
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I thought so. Pity, I had thought of getting a Merc in the next year, but daren't chance it after this experience, even without any frost or snow. --
Did you press the W button? That makes it start in 2nd gear in *both* forward and reverse.
It may be a lot to do with the tyres too - I'm not talking about fitting winter tyres, but some of the summer we use all year round are just useless in cold conditions.
I must admit, after 15 years of FWD, I am terrified of being stuck somewhere in my Merc. I keep thinking of buying some AutoSocks, but of course I'll wait until after I'm stuck until I actually do that!
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You could always get a 4WD 4Matic Merc, assuming they´re imported into the UK. Aprilia would know.
Probably pricy though.
They don´t sell that many over here, certainly not as many as Audi do with the quattro.
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No, seems that they aren't or the BMW equivelent. What about an Audi Quattro model. Mabey it would be easier to make the drive flatter or put a grippier surface down.
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We may need a professional engineer to answer this one authoratively. For example, reversing up an incline may alter the weight distribution in favour of the front wheels ~ I'm not sure about that one. The weight transferance due to acceleration will certainly be from the rear wheels to the front. -- L\'escargot.
There are a couple of things going on here which conspire against RWD.
1) A stationary, or non-accelerating car on an incline suffers weight transfer down slope because the centre of gravity of the car is not at ground level. This is a small effect for small inclines, but once the car is on steep ground, it must be accounted for in determining the gradeability of the car.
2) If you then need to accelerate the car in reverse (e.g. to move off from rest) then you get further weight transfer - again because of the height of the c of g. In the example given of reversing up a drive, this weight transfer is the exact opposite of that which causes nose dive under braking.
So, if the car starts out with a forward weight bias, and then has the two weight transfer effects listed above acting against it, wheelspin and difficulty on a steep drive sounds likely.
Incidentally, effect 1 can be used if you wanted to measure the height of the c of g of an unknown car. You measure the vertical load at each tyre with the car on flat ground. From this, you find the fore/aft location of the c of g. Then,you jack up one end of the car, and repeat the measurement with the car at a known angle. Then, its some trig and schoolboy maths to give the height of the c of g.
Number_Cruncher
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Do BM's and Mercs have a winter mode if its an auto. Our C5 had one and our Saab. I know it would do no difference in reverse but am just curious.
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You should be OK with tarmac underneath the loose stones but incredibly you can't always rely on a modern 4x4 where you start from standstill on loose surfaces. There are reports from Australia on X-Trails in particular being left immobile on gravel because the computer can't work out where to allocate traction so gives up!
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Sold as 4 wheel drive, but in reality only one wheel is driven in slippery conditions! Unless there is a lock-up differential on both axles, they're usually most are no better than a fwd for traction. Traction control might help: but thats not a prerogative of 4wd.
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Why not reverse in and drive out forwards
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Espada III :-
"We have had the following cars in our drive regularly since we bought the house three years ago: -
Hyundai Trajets (V6 and Diesel)
Volvo S80 2.9
Subaru Foresters Turbo and NA
Suzuki Wagon R+
Honda CR-V
plus lots and lots of run of the mill FWD cars
and none of them gave a moments cause for concern except in very icy conditions, during which time the 4x4 cars were a doddle.
What is going on?"
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No doubt, if you reversed these cars onto your drive. You would still have the same problem, all to do with weight transfer. The fwd cars would have the weight over the rear wheels on your drive not the front, as you would when you drove on the drive as previous. Except the Subaru I might add, it would make no difference being constant 4wd.
Its like some of the winter driving tips for when trying to drive up a snow covered hill in a fwd car, and you lose traction, reverse it up with weight over the wheels.
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During the worst part of the worst winter of the sixties - can't remember if it was 62 or 63 - I and my new bride went to Plymouth and back in a hired turquoise Vauxhall Victor. Looked like a contemporary US Chevy suffering from a severe wasting disease, but heavily made up. However owing to its lightness and relatively low power it proved able to go up hills a lot better than some other cars (I remember a Humber Super Snipe for example that was all over the place and unable to move forward). It also had a magnificently powerful GM heater, only matched in my experience by the one in an otherwise horrible Lada. In four days of thoroughly entertaining, often sideways, motoring we were only brought to a halt once, on the way back, as the temperature dropped below zero and rain started to fall on the packed snow. When it became impossible to hold the car in a straight line as it kept slipping down the road camber even at walking pace, we parked it on a hill in Cullompton while looking for a pub with a room. When we returned to the car it had slid twenty yards down the hill. Under these conditions a very gentle throttle foot and a higher gear than usual will keep you going when 'clumsy' or heavy footed driving will put you in the ditch. Doubt though if I would undertake the journey in those conditions now.
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I suppose you could move houses to one on the flat with ample parking space.
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