It looked like it had been squashed flat, lying on the central reservation just before the road goes down to single carriageway, with the 4x4 that pulled it across on the other side of the road looking pretty sorry; it looked like it had rolled at least once.
The eastbound carriageway was blocked for ages as police cleared away the debris (and presumably the occupants of the 4x4); there were bits of caravan and it's contents all over the place.
It's pretty common for vans to snake down that hill for some reason. Looks like this one went too far...
My (basic) understanding of ABS is that it prevents the wheels from locking up, thus enabling you to retain steering control of your vehicle. My (basic) understanding of a typical snake is that the trailer starts dictating the direction of the towing vehicle. The received wisdom (Clarkson excepted) is that you touch neither accelerator or brake, but allow the outfit to pull itself out of the snake. How would ABS (a) prevent a snake or (b) control a snake once it had occurred?
What does ESP type ABS do that ordinary ABS doesn't? I thought ESP was a means of distributing engine power to the various driving wheels rather than a form of anti-lock braking.
Snaking essentially involves the trailer (caravan) exerting a strong sideways force on the rear tyres of the towing vehicle (car) - so strong that the wheels are pushed sideways. That's right, isn't it? Presumably the wheels don't stop rotating when this happens, which is what ordinary ABS is designed to prevent by releasing and reapplying the braking force on the stationary wheel(s).
Leyland_Leopard, when you say that the received wisdom is that you touch neither accelerator or brake, what's the advice if you are already braking to hold the car+caravan at a constant speed on a hill? When you say "don't touch the brake" do you mean that you should you keep the same brake pressure or that you should release the brake (without applying any throttle) which will have the effect of allowing the vehicle to accelerate since you are on a hill?
I'd always understood that with a front-wheel drive car (where there's no danger of increased power to the back wheels worsening the side-slip) you should accelerate very gently (either under power or by releasing the brakes a bit on a hill), to encourage the rear wheels to pull back into line. I presume it is *theoretically* possible to counteract snaking by judicious counter-steering, but that's not advised because there's too much risk of over-cooking it and turning the desired negative feedback into positive feedback and making matters *much* worse ;-)
I seem to remember from the early 70s when my parents had a caravan that there was a system of hydraulic struts that you could buy which ran from the front corners of the caravan to points either side of the towbar on the car, which normally moved freely as you steered but which would automatically lock as the snaking vehicle went through the straightahead position during its oscillations, temporarily turning the car+carvan into a rigid vehicle, if snaking was detected. I was only about 7 at the time, so I may well have misunderstood, but does this description ring any bells?
Nope. It does fancy things like braking the rear left wheel if the front end's understeering and you're trying to turn left, turning the car left for you and getting the front end back on line. Fit an ABS system to a caravan, fit a few acellerometers and rig up a brain, and get it to brake its own wheels to a) provide decent caravan braking and b) provide vaguely safe caravans. If you wanted to go the whole hog, you could tap into the steering sensor on the car and have it know whether or not you're trying to go straight or round a corner.
Snaking is caused by the caravans centre of gravity and centre of aerodynamic pressure combined being too far back to its wheels for stability. As speed goes up the C of G does not move but the unstable effect of a big square increases. So it needs more weight on the towbar for stability to return. Ie move the wheels back, or put a bag or two of cement in the front of the caravan. They dont make them this way because you would need stronger rear springs to cope. Like a artic truck... They dont snake.
Your earlier post suggested fitting ABS onto caravans in order to prevent a snake, or to reduce the effects from it. Now your post is saying that fitting ABS would probably have no effect. That's helped us all a lot, many thanks!
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