My understanding is that if you have a trailer/caravan that is well matched to the weight of the towing vehicle, and if you have lowed the trailer/caravan well and have an appropriate nose-weight, then you are unlikely to get a snake. Poor driving - inappropriate speed for the conditions (including hills, side-winds, overtaking etc) might well also contribute. I suspect that its never going to be as safe as an artic, but it is much less likely.
Incidentally, following all of those rules, whilst towing our caravan for a number of years, I have NEVER experienced a snake, either.
Another good reason to ban them and their inconsiderate drivers from the roads. Was stuck behind one today that decided he was going to use the entire length of a 3 mile crawler lane to overtake a truck that was going 0.5mph slower than he wanted to drive at. Much to the annoyance of the 30+ cars that were still stuck behind him and the truck by the end of the crawler lane.
Oh, I thought it was only artics and other HGVs that did this ;-) The two-lane A34 in Oxfordshire is often reduced to a crawl when one speed-limited HGV decides to try to overtake another and then sits dead level with it for mile after mile. Result: a 70 mph road reduced to 50 mph - or less if the overtaker decides to try this selfish manoeuvre on a hill! Fortunately the police are wise to the problem: I've seen several HGVs pulled over, presumably to be read the riot act. When I was learning to drive, my instructor drummed into me that unless you anticipate being able to go at least 10 mph faster than the vehicle that you are planning to overtake, don't even think about it - and if you find that your car has run out of power and isn't gaining on the other vehicle, don't be afraid of braking and pulling behind it again.
Conor wrote in snipped-for-privacy@news.individual.net:
Really? I thought all caravans had over-run brakes which worked if the caravan started to go faster than the car, compressing a spring in the towing hitch so as to operate the caravan's brake. I remember my parents'
1970 caravan having this and I thought it was standard even then. What about small trailers - are they generally braked or unbraked?
I have memories of towing a caravan at 90 around the M25, it was going berserk but because it only weighed 10cwt, and my van two ton, it didn't affect me at all.
ISTR seeing something like that advertised. One previous garden shed, which used to be a caravan, had an anti-snaking device which consisted of a flat bar connected to the tow vehicle via a hinge next to the tow hook. That ran through a friction brake on the caravan, which controlled the speed at which it could change its angle to the tow car.
You don't need the ABS fitted to the caravan. Some of the fancier German cars have a type of traction control fitted that will control a snake in a caravan already. I can't remember all the details- I'm pretty sure it was Mercedes and I think you had to switch on the programme when towing. I cant remember where I saw it. It may have been the Caravan Club magazine.
Because they operate on a completely different principle. On an artic about
25% of the weight of the trailer is supported by the tractor unit at a point in front of the rear axle. Any load from the trailer is then spread proportionally between the front and back axles of the unit. A caravan is designed to support its weight on its own wheels. Any load transferred to the car via the towbar ( behind the rear axle) will be added to the load on the rear axle and also be reduced on the front ( steering ) axle, altering the steering characterisics sometimes quite drastically. The only reason for any static vertical load on the towbar is to ensure that when the whole circus is bouncing down the road the caravan coupling is not exposed to any net upwards force. Most caravan manufacturers consider 25kg to be sufficient. Larking around with bags of cement or other ballast is likely to end in tears. At the end of the day, all caravans and trailers with axles in the middle will oscillate sideways, it is when the the weight distribution is unfavourable (ie. to much weight too far from the axle) that this initial small motion may start to resonate and become uncontrollable.
Thats what I just said above! Centre of grav well in front of the wheels causes stability!!!
Any load from the trailer is then spread
As it would be if you moved the caravans wheels back...
A caravan is
Well since the towbar is so close to the rear wheels it would take an awful lot of weight to effect steering! Trust me a bag of cement (or all the heavy lugage in the caravan) under the front seats cures the weaving.
The more there is the greater the lateral stability though. Correctly loaded caravans do not snake. Its simple physivs!
You mean not doing so will (and often does) surely!!! Sticking the heavy stuff in the front end is all thats required.
In the same way that an eirofoil on an aircraft is stable (neutral actually) when the centre of pressure and the centre of gravity are in the same spot - so is a caravan. Make a plane fractionally tail heavy and it does what the occilating caravan does. Its "unstable" in pitch. And it gets worse with each occilation. Moving the weight (cargo/fuel whatever) forwards slightly returns it to a neiutral stability configuration. Moving the C of G too far forwards results in an over stable (and hard to turn, pull up, etc with heavy controls) aircraft. The same things apply to our caravan.
When the centre of grav and the centre of pressure (the wheels) are in the same place we get a balancing caravan. If we ignore aerodynamics for a moment it would be neutral. Not stable but not unstable. But we want "stable" or any wind or whatever that knocks it off course will continue to sway back and forth. So then we need some weight on the tow bar. Now we have the c of g in front of the c of pressure (its wheels.) Now any swinging will tend to diminish naturally. Exept that our "stability amount is marginal" So the faster we go the greater the aerodynamic stability of a square box becomes. And it increases with the square of the speed too! So we get to a certain speed and it starts swinging from side to side. All thats required is a) a big virtical fin! Which looks daft and would be counter productive in croswinds... Or b) the c of g moving further in front of the axle(s), Either by moving it/them back, or adding / transfering some weight forwards untill the trailer becomes nose heavy and puts more weight on the tow bar. And "damping" kits sold do not really help, because they are addressing the result of a different problem after the event. And the actually disguise the small movements resulting in a false level of driver security and so he goes a bit faster until suddenly its all gone badly wrong.
I remember being caught in exactly that situation some long time ago. I was a passenger in a car towing a glider in a trailer - these trailers tend to be about 7.5 metres long, so more difficult to handle than the average caravan. The guy driving was obviously so impressed with the stability of the rig at 70mph that he commented on it.
That was until we went over the brow of the hill - then the trailer started to snake viciously - we ended up with it pulling the car round
90 degrees so we headed right across the central reservation (this was a dual carriageway) and we came to a stop with the nose of the car buried in the bank on the opposite side of the road - the trailer came to a stop on its side across the whole carriageway. The car (a one year old Audi) was basically a write off.
My main memory was of the pre-tension seat belts going click...
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