SNAKING

May 25, 2005
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We have recently purchased a Volvo XC70SE AWD Cross Country with which we tow an ACE Award Dawnstar 2004 model. First time out we experienced a phenomenon which in 20-odd years of caravanning has never occurred before. I understand when heavy vehicles, ie lorries, coaches, etc., overtake I am going to experience some snaking through suction - that I can cope with. However, we are now experiencing snaking of the caravan when we overtake a heavy vehicle at 60mph! I can only suggest this is due to the fact that the towing vehicle is an AWD. Any suggestions would be welcome.

Previously we have towed with a Volvo V70 D5 and experienced no problems.

The caravan is loaded correctly and well within the 85% loading.
 
Mar 14, 2005
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Ann - Years ago when we first started vanning, we changed our tow car to a Volvo 240DL estate - a big heavy tank weighing about 1400kg, with which we pulled a very light Perle Olympus with a laden weight of about 950kg. The first time out we had our first & only snake. Why? Because we hadn't increased the rear tyres pressure to the laden setting. This car had very high profile tyres, which I think that your Volvo may have the more modern equivalent fitted. Try pumping them up to the manufacturer's laden pressures - this made a big difference with our old Volley and stopped the problem. Also check your van & car's noseweight limits as this can have a big effect too.
 
Mar 14, 2005
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Here we have yet another example of nervous behaviour of 4x4's when towing and a good case comparison of towing the same caravan behind a conventional car.

The problem is almost certainly due to excessive lateral compliance in the suspension system and tyres of the average 4x4. High profile tyres and their relatively soft sidewalls don't provide as much support as those typically used on cars. Unless you want to re-equip the 4x4 with other footwear, the only option available is to increase the tyre pressure.

Only because of the generally good weight ratio of most 4x4 combinations does 'twitchyness' not develop into anything more serious.
 
Mar 14, 2005
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An interesting point Lutz about the high profile tyres

We have no instability with the X-Trail when towing and I do use the highest tyre pressure recommended by Nissan

What I do find though is the car has a tendency to drift from the straight line solo if my attention wanders a fraction.

I put this down to the high centre of gravity but am wondering whether to have the steering geometry checked.

Has anyone else found this with these vehicles.
 
Apr 13, 2005
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seems to be the norm with 4x4 towcars, i suffered exactly the same problems towing my coachman laser with a discovery the discovery was a superb car but put the van on and it became very twitchy and nervous despite perfect loading and tyre presssures. we changed to a ford galaxy with the same van and the outfit was steady as a rock, we have since changed the van to an ace twin axle and the car to a seat alhambra both a joy to drive and tow, however on one occassion i needed to take the van to the dealer and my wife had the alhambra so i used my dads shogun and back came the snaking every time we overtook another vehicle or exceeded 50 mph. I loved my 4x4 but was a nervous reck every time we arrived on site so it had to go.
 
Mar 14, 2005
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Where to start (and is this going to be another long post) with this apparent fault with 4x4's. To begin with, John, go and have a look at the width of the tyres on your 4x4. You will be amazed at the size, now if you put the same width of tyre, low profile or not, onto a standard car you will experience the same problem of needing to be alert to drifting as you do in your 4x4. Trust me, my son has done it with a Vauxhall Corsa (typical chav!) and the thing won't go round corners for love or money, he's not bothered because he's got 19 inch rims under the wheel arch.

Lutz, you may have something about there being more flex in the sidewalls of a 4x4, but I wouldn't say there is much of a difference. Once again, go outside and push your car sideways, you will notice quite some movement on an ordinary tyre; the difference is the amount of movement is restricted by the short sidewalls. Good thing? Nope, I don't think so; imagine an elastic band, once you run out of the stretch what happens? The higher profile tyre is more forgiving, they provide as much support but where a short sidewall stops, the taller one will keep on giving.

4x4's roll too much, really? They do roll slightly more due to their higher profiles, but nowhere as much as you think. Go outside and if the Leaning Tower of Pisa is in your back garden, climb onto the first floor and look out, this place really isn't level, is it, now climb onto it's roof and look down, blimmy, it's a wonder this place can stay up, get me down quick it's going to fall! Has the tower leaned more since you climbed further up? No, it's just a matter of perception. Something ably demonstrated by seeing both a Toyota Landcruiser and a Volvo estate take the same corner at a reasonable speed in procession. The Toyota was more noticeable, but the Volvo leaned more.

The size of the 4x4 is what makes it better for towing due to its weight ratio. Most definitely! However it is not the only reason. I used to have a Grande Vitara, and once, a couple of years ago I had a snake. It was my fault, travelling to fast for the conditions and over taking a truck at the same time, how did I notice the snake was taking place? Through my mirrors, not by the seat of my pants, after the initial reaction and alarm I realised that the tail was not wagging the dog, I just eased gently off the accelerator and eventually it stopped. Is it because I was in a huge 4x4? No, the weight of the good old Suzy is comparable to a well-equipped Ford Mondeo,

Take a look at the max tow figures for 4x4's and you will see some of them are rated much higher than their own weight, they are rated so high for a good reason. There are a lot of factors to look into scientifically before you can say any particular vehicle dynamic causes snaking. I myself would look at the caravan first, you all know the reasons why, but it could be simply that the caravan and car do not match, it happens. Does not mean the car or van cant cope, it just means they cant cope together.

Now, having completed my first Technical post, to my liking I await your response, with baited breath and an awe like posture.

By the way, The Volvo V70 is a slightly raised normal road car, not a typical off road 4x4, ask Kanga.
 
Mar 14, 2005
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Ann, I would look at the tow ball height, could be that the new car is slightly higher and it conflicts with your present van.
 
Mar 14, 2005
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Lol I don't need to look at the tyres as I have lifted the spare out of the boot and it IS wide AND heavy !!
Yup, don't fancy having to do that, lift the wrong way and you're a prisoner of the "bone doctor" for years

One of the good things about the Sorento, the wind down spare wheel. It might get dirty but at least you have a fully functional spinal cord afterwards....
 
Mar 14, 2005
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Haven't you contradicted yourself in your own arguments, LOL? You say, quote:

.... imagine an elastic band, once you run out of the stretch what happens? The higher profile tyre is more forgiving, they provide as much support but where a short sidewall stops, the taller one will keep on giving.

It's exactly that elastic band effect that causes the trouble. When the caravan is threatening to go into a snake it is imparting high lateral forces to the towbar on the car. If the towbar is now at the end of an (effectively) elastic band, the whole system will be bounced from side to side. Depending on the natural frequency of articulation between car and caravan the whole outfit can become unstable and the oscillations will increase with each cycle. The stiffer the system is, the higher the natural frequency and the less likely the caravan will ever sway so quickly as to reach such an unstable condition.
 
Mar 14, 2005
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It's less a question of how long or short the elastic band is but whether it is hard or soft. The soft one will get unstable earlier when you shake it at the other end than the hard one and a soft one that allows more travel, i.e. a long elastic band, will be worse than one which hits an end stop earlier.
 
Mar 14, 2005
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So the hard one hits the end stop earlier, ok, got that bit. So, what happens when indeed that "stop" is hit, bearing in mind that the soft elastic band is yet to hit the "stop".

Excuse me if don't continue with this tonight, "Lost" is on TV soon and its my time to imagine I have control of the remote control.
 
Mar 14, 2005
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When the end stop is reached the system cannot accept any more influence from outside forces, if it tries, it will loose control.

Stop answering so fast, I should be downstairs in front of the TV.
 
Mar 14, 2005
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Now I know why your name is Lol.

If you hold a ball at the end of an elastic band it won't move and if it won't move it can't get out of control. That's exactly what happens when the end stop is reached.
 
May 25, 2005
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Hi lol

The Volvo XC70AWD has a self-levelling suspension! I may have to contact Volvo direct and ask their advice on this point.

Thanks everyone for your responses.
 
Mar 14, 2005
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Ann, the towball height should be between 350 and 420mm from the ground (measured from the centre of the ball). As your car has self-levelling suspension, the towball height should always be within that range. For vehicles without self-levelling suspension, the heights quoted apply only to the fully laden (hitched) condition.
 
Mar 14, 2005
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Ann, my car has self-levelling suspension too, but for the type of van I tow, I found the ball itself to be too low. Luckily the ball could be moved up and it has improved the tow. Your tow ball may indeed be within tolerances but if it is adjustable in any way it might be worth some experimentation. Make sure you have tried the easier remedies first such as tyre pressure on van and car, loading of the hitch etc. Your Volvo should tow like a dream.
 
Mar 14, 2005
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Ann, my car has self-levelling suspension too, but for the type of van I tow, I found the ball itself to be too low. Luckily the ball could be moved up and it has improved the tow. Your tow ball may indeed be within tolerances but if it is adjustable in any way it might be worth some experimentation. Make sure you have tried the easier remedies first such as tyre pressure on van and car, loading of the hitch etc. Your Volvo should tow like a dream.
Out of curiosity, did you need to clean your new tow ball i.e., remove the paint, before you hitched it up for the first time?
 
May 25, 2005
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Out of curiosity, did you need to clean your new tow ball i.e., remove the paint, before you hitched it up for the first time?
No Lol. We were assured (very definitely) by the Volvo dealer that we didn't need to strip the pain or clean the towbar before setting out!!! We thought it odd as in previous times we had to ensure that the towball was absolutely clean.

When we arrived at our destination the paint had disintegrated into a powder which just fell out on unhitching.

Towing back home was a little less of a problem.
 
May 25, 2005
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Teh Volvo has no problem towing our van Lol. The problem lies with the van when overtaking lorries or coaches at 60mph when the downdraught causes the van to wriggle about!
 

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