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.