Out of interest, when towing a trailer with my Electra-Glide I too was advised to power out of a weave, but to do it by steadily increasing the speed. Only had cause to try it once but it did work OK.
Never liked the bike trailer though; only bought it for my ex-missus' sake, she was the type who takes a spare kitchen sink in case the first one gets blocked!
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It is a deep gene pool, and there are some very exotic creatures at the bottom.
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The damping ratio of the vehicle / trailer combination reduces as speed increases, and there is, for a given combination, a critical speed where the damping ratio becomes zero. (Rotational instabilities are quite common in vehicle dynamics, and the idea of a critical speed is not limited to cars and caravans)
Therefore, advice given to speed up to prevent snaking is spectacularly bad. Those who have tried it and succeeded would probably have also found that the oscillation would have decayed had their speed remained unchanged.
The best advice is to avoid the instability in the first place, and the best way to do this is to reduce the yaw inertia of the trailer - to do this, pack heavy items in the car, or, place them close to the trailer's axle rather than at the front or rear extremes of the trailer.
Make sure that the tyre pressures are high enough - the lateral deflection of the sidewall of a partially inflated tyre can contribute to the oscillation.
Make sure the nose weight of the trailer is correct - not too light, and the use of a friction damper between car and trailer can usefully take energy out of the oscillation, and increase the effective damping ratio.
Obey the speed limits for the vehicle / trailer combination, a well designed, maintained, and loaded caravan should have a critical speed which is above the appropriate speed limits.
When travelling at speed, avoid making sudden inputs via steering, and leave larger gaps to prevent aerodynamic excitation of the trailer.
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"the use of a friction damper between car and trailer can usefully take energy out of the oscillation, and increase the effective damping ratio."
My brother used to use a caravan and had a "device" that probably was a friction damper as you say that he said stopped the caravan moving about. It was nearly 20 years ago come to think of it but it definitely used friction to stop the caravan moving about so much.
I'm with TG - towed caravans for target practice. I like big stationary ones.... But I remember the last holiday with my father (it was 30 years ago) - we towed a very large caravan with a Triumph.... we only just got up some hills on the way to the west country.
Edited by rtj70 on 16/12/2008 at 22:44
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NC; when this happened to me it was on the A38 between Derby and Burton. Never happened again (at least not quite so badly) and at the time I put it down to the condition of the road surface, which was somewhat worn and had rather pronounced HGV "tramlines".
I'd checked the loading before leaving (you use a spring-balance on a bike trailer) and also the tyre pressures. Not much else to go wrong rally so do you think my blame theory was correct?
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>>do you think my blame theory was correct?
If you mean the Mrs and the kitchen sink, then, yes, definitely!
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N_C's comments pretty well summarise the research Bath University carried out into caravan stability. For a given combination there is s critical speed, above which, when an oscillation starts, it will increase rather than decay.
The original research IIRC used a well worn Mondeo with a "soggy" rear end for which this critical speed, with the test rig, was not much above 60mph, and the simple version of their advice was to stay below this speed.
Interestingly, while the hitch dampers caused the oscillations to decay more quickly, they concluded that they wouldn't have much effect on the critical speed.
The inescapable conclusion was that more speed would be a bad thing, and that a hitch damper does not confer immunity.
I always pay attention to tyre pressures and noseweight, which is easily checked with Tesco value bathroom scales and a stick. Dampers on the trailer are generally held to help - many UK caravans do not have suspension dampers, though they are easy to add to the standard chassis.
Despite the perhaps obvious dangers of taking TGs jokes as gospel, it was a mistake on their part to risk reinforcing a widely quoted myth.
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Dampers between car and trailer would be a lot better if they were well designed viscous dampers rather than cheap friction types. Where a friction damper can only supply a fixed torque whatever the amplitude and frequency of the oscillation, a viscous damper would react by producing larger damping torques for larger and faster oscillations.
My experience with this kind of work comes from a few projects I did about 10 years ago, looking at the security of rail vehicle yaw dampers. We tested quite a few, and found that the dampers themselves were working well within their (Koni) specifications. We also did some operational testing where the damping forces were obtained indirectly by strain gauging the mountings - the critical speed, and the onset of large damper forces was quite stark.
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>>yes it was a Kia but a Sorrento 4X4 not a Rio<< Actually it was neither - have you even watched the episode? It was a Kia Cerato.
Well, I got the Kia bit right :-)
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I attended an accident on the motorway in the eighties. A four wheel double horse box had overturned with the poor horse lying on it's side and struggling to escape. We got him out ok and he wasn't injured, thankfully.. I'm not sure how much a horse weighs together with it's trailer but I'm sure it must have been slightly over the limit for the Marina 1.3 pulling it !!!!
Ted
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I speak from experience of towing quite a lot of trailers, caravans, boats etc.
1) I would say that adjusting the load distribution is crucial, but the actual weight not absolutely critical as long as there is a reasonable positive downward load on the coupling. A negative load is a disaster.
2) The height adjustment of the coupling is important. The trailer chassis should be roughly horizontal, or possibly slightly tilted down at the front.
3) With a 4-wheel trailer the height adjustment becomes critical. Nose weight is harder to determine, but the load on the two trailer axles should be equal.
4) The weight distribution in the trailer should not only give the right nose weight, but be concentrated over the axle(s), not distributed at the extreme ends.
5) Speed is the most important factor, especially downhill on over-run. The critical speed is much much lower downhill than when powering up a hill.
6) The relationship between tow vehicle and trailer brakes is important. Snatching trailer brakes, or incorrectly adjusted over-run that cuts in too early or too late, introduces instability.
Within these overall guidelines, I have found that in moderation, a tiny touch of accelerator can correct a minor wobble, but only if followed by very gentle deceleration.
It is crucial to keep a very close watch on the trailer behaviour, and be aware of any minor tendencies long before they can develop into a snake. You certainly can't afford to breeze along forgetting about the trailer - towing requires very concentrated attention.
Carrying something live like a horse makes everything doubly critical. If the horse lurches or stumbles, the effect on the trailer stability can be devastating.
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To echo an idea on another thread on here, what about a towing driving test ?. No pass this test, no towing a trailer / caravan/ horsebox .
It seems strange that you can pass your test one day and then immediately hook up a great big horse box and set off . As towing anything can completely alter the handling characteristics of the vehicle being used, this would surely be a sensible approach in order to cut down on accidents.
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YES!
And then if somebody is caught towing a 25 foot speedboat with a 1.1 Fiat Uno, or similar, he should be banned for life!
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"It seems strange that you can pass your test one day and then immediately hook up a great big horse box and set off . "
You can't if you passed your test after 01.01.97. You need a trailer test to tow more than 750kg, and that would include most empty horse trailers, and all loaded ones.
The incident referred to was a trailer with three bullocks. They are normally free inside the trailer, so if even one moved forwards/backwards/sideways it would seriously upset the dynamics. Horses are always tethered, so there is less chance of such large change in the C of G.
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You can't if you passed your test after 01.01.97. You need a trailer test to tow more than 750kg and that would include most empty horse trailers and all loaded ones.
Almost correct. If you passed after 01.01.97 you can tow a braked trailer of more than 750kg provided that the combined maximum authorised mass (MAM/GVW) of the car and trailer is no more than 3500kg, and provided that the MAM of the trailer does not exceed the unladen wieght of the vehicle. This can seem a bit odd because it means that you could potentially tow say a 1400kg MAM caravan with a Mondeo/Vectra type car with a MAM of under 2100kg, but with something like a Shogun with a MAM of 2800kg, arguably a better towcar for that weight, you would be limited to 750kg.
The official version of these rules is very confusingly worded - The Camping & Caravanning Club website explains it quite well.
tinyurl.com/5sfz5o
If you passed before that date, then generally you can tow a combined MAM of up to 8.25 tonnes until your licence expires.
All assumes that the trailer is within the car's towing limit.
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So the simple answer is that nobody tows anything until they have completed test and have that fact placed on their licence and also they must display a plate on the back of the towed item to show that such a test has been passed. Nice big fine for those who use the plate when not in possession of a pass cert. Job done
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I presume you don't tow then Mr X, otherwise the cost of what you are suggesting test would just be another tax on the motorist?
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