>>trying to make such a system work effectively
The vital thing will be setting the gain of the system, i.e., the ratio of drawbar compression to trailer brake force - the aim is a gain of one, but always making sure you stay under 1.
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As a quick thought, does it matter if the 'ratio' is greater than 1 if the ABS is operative on the towed vehicle? Also 'the damping factor and 'time constant' of the feedback must be important, but I will leave you to do the maths!
When my BX went, the guy who took it had a home made A frame with a bowden oprated actuator to the brake pedal. Definately illegal, because as a BX he had to have the engine running on the towed car, to give him any brakes. I also suspect the biggest risk was the towed car overheating and stalling and hence losing brakes. I know that he had sucessfully towed like that for quite some time.
Edited by pmh on 20/03/2008 at 20:14
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The 'A' frames I've seen used to tow behind motorhomes are rigidly fixed to a frame mounted on the towed car. There used to be companies that specialised in doing this. AFAIK the brakes on the towed car were not used.
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After a court case involving the RAC, the law was clarified to prohibit the use of unbraked A-frames on vehicles over 750kg - no matter what the weight of the towing vehicle.
Those Bowden cable arrangements were introduced to get around that ruling and were exactly what I was working on - I'm now fairly confident that it's virtually impossible to make such a system work effectively.
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>>does it matter if the 'ratio' is greater than 1
If the gain is larger than 1, the brakes will tend to grab, and the system will tend towards instability, if it's much less than 1, then the trailer brakes won't be particulalry effective.
I have designed similar systems, albeit rotational rather than translational, where lockup was the desired outcome, and gains above 1 were required.
As the brakes offer a route by which energy is removed from the system, at low gains, they tend to provide all the damping you might ever need. The time constant for the feedback depends upon how heavily loaded the trailer is - for heavy loads, the trailer system has a lower longitudinal natural frequency, and this is inverserly related to the feedback time.
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Some interesting points in this article
www.ukcampsite.co.uk/articles/view.asp?id=18
and a heck of a lot here
www.motorhomefacts.com/ftopic-39142.html
and this appears at
www.ntta.co.uk/faq/default.htm (National Trailer and Towing Association)
I have a motor home and want to tow a Fiat Seicento behind it using an A-frame. This car has a kerb weight under 750 kg so am I legal with this outfit?
Sorry no is the answer. The law regards this as an unbraked trailer and you are allowed to tow up to 750 kg Gross Trailer Weight, not a car?s kerb weight. The figure you have to use is the car?s Gross Vehicle Weight or Maximum Permitted Weight. This is usually at least 300 - 400 kg more than the kerb weight. We have no knowledge of any car sold in the UK that has a GVW under 750 kg. The only vehicle we know that is completely legal to tow with an A-frame is the French Aixam small "car". This is a full four seater and details can be obtained from Aixam UK on 01926 886100. An A-frame or dolly can only be used to recover a broken down vehicle to a place of safety. Transporting a car is, therefore, illegal. A-frames may be offered with a braking system that applies the car's brakes. These do not conform to the law as the car then becomes a "braked trailer" and has to conform to European Directives contained within the Construction and Use Regulations. It does not conform to the European Directive 71/320/EEC and amendments regarding braking requirements in any way. The use of this A-frame for transportation is illegal. It is still OK for use to recover a vehicle to a place of safety.
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PhilW,
Had a look at some of the links - thanks for digging them out.
Seems to me there are a lot of motorhomers out there trying to justify doing something that is at best barely legal/open to interpretation.
Can't any of them accept what in my opinion is obvious - it's dangerous.
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Can't any of them accept what in my opinion is obvious - it's dangerous.
Why?
The point about Gross Trailer Weight is a legal one, not a practical one if the actual weight of the car is <=750k.
The towing vehicale is generally much heavier than the "trailer".
The "trailer" especially if on for wheels is inherently much more stable than a typical caravan.
It is generally known that these arrangements are illegal in the UK and I am sure the majority of people doing it know this; however I believe they are acceptable elsewhere and there are a lot of people doing it. The last two I saw were Smarts.
As to the driving "blind" what does this mean? If the driver has a view behind from the side mirrors, what's the problem whether or not he/she can see the car directly behind and attached - they know it's there?
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As to the driving "blind" what does this mean? If the driver has a view behind from the side mirrors what's the problem whether or not he/she can see the car directly behind and attached - they know it's there?
Manatee,
All I mean by towing blind is the driver of the towing vehicle cannot see what he is towing.
He has to rely on 'feel' and I just think, for example, if the towed car became detached as the motorhome was bowling down the motorway at 60mph the driver would hardly know.
Surely, anyone who tows something relies at least partly for safety on keeping an eye on what is being towed in the rear view mirror?
I take your point as regards the stability of the rig.
I guess the fact the motorhome driver barely knows the car is there either detracts or adds to my dangerousness argument, depending on your point of view.
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Fair enough. Seeing it might not make any difference to whether it detaches or not, but I confess I like to keep an eye on my trailer - especially the tyres.
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A further point to the lack of vision; how would the driver know if the car starts to break away from the A-frame? It's not common for a conventional rigid trailer to start disintegrating en-route.
While a recovery A-frame is strapped to the lower arms - and isn't suited to much more than a few miles; if firms are selling mounting kits that fix to the car, how do the manufacturers feel about that?
Modern car designers pare weight down to the barest minimum. No car is going to be designed with trailing in mind; the frontal structure is therefore being stressed in ways that were never intended - and some of those pressings are paper-thin and would fail rapidly once cracks appeared.
I was amused by the notion of printing-off and carrying that dubious resume with the intention of arguing the case at the roadside. In my experience, VOSA examiners are not that chatty and would simply look, hand you the prohibition notice and walk away - charges to follow.
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Screwloose,
When I worked in recovery I recall the first job we did with our new A frame was to use a Jag XJ6 to recover a Jag XJ6.
After detaching the propshaft - don't want to seize the autobox, do we? - I was detailed to sit in the towed car because none of us knew what would happen.
I was fascinated by the way its steering wheel turned as if it was driving itself.
Plus, I've never been so close to the car in front at 70mph!
Those two Jags drove pretty much as one, but I still say A frames are only suitable for breakdown work.
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IIH
Oh, they work OK; I've used them numerous times - it's just the thought of the motorhome numpties that use them without a thought for the law - and what might happen if they fail.
A good friend lost his wife when a trailer with a 2" hitch came off a 50mm ball....
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"It is generally known that these arrangements are illegal in the UK and I am sure the majority of people doing it know this; however I believe they are acceptable elsewhere and there are a lot of people doing it."
Not legal anywhere in EU - does "a lot of people doing it" make it acceptable? Must remember that excuse if I am done for doing 80 on the motorway, or next time I get a parking ticket!! ;-)
"it's just the thought of the motorhome numpties that use them without a thought for the law - and what might happen if they fail."
Interesting to juxtapose with Manatee's point above.
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Not legal anywhere in EU - does "a lot of people doing it" make it acceptable? Must remember that excuse if I am done for doing 80 on the motorway or next time I get a parking ticket!! ;-)
I'm not condoning, even less recommending it, and FWIW I haven't a motorhome either. It just seems unlikely to me that it's materially dangerous - like doing 80mph, it presumably can be done dangerously but generally isn't.
The trailer regs clearly didn't consider this - it might have been better if they had, then there would have been a legal way to do it and the more dangerous set-ups could be excluded.
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>>All I mean by towing blind is the driver of the towing vehicle cannot see what he is towing.
>>He has to rely on 'feel' and I just think, for example, if the towed car became detached as the motorhome was bowling down the motorway at 60mph the driver would hardly know.
>>
I had this sort of thing happen a few years ago.
Driving a 5.3 Jaguar and towing a very low trailer with not a great weight at about 60mph on a quiet motorway in Spain, a trailer tyre had a blow out.
The tyre shreaded, hit the muguard, buckled it so that it jammed the wheel and that caused the rim to be ground away while I carried on with it not having much effect on 5.3 performance. My friend in convoy ahead spotted it as a shower of sparks.
It certainly left a long long groove in the motorway.
Fortunately no one came to harm.
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I once helped the owner of a motorhome business deliver stock to a show. There were two kinds of towing arrangements in use:
1) the towed vehicle sat on its own wheels, with a device coupling its steering linkage to the towing dolly so that it followed the towing vehicle.
2) the front wheels sat on a special dolly which had its own wheels. This was used to tow quite heavy loads - I remember one camper pulling another, smaller one, by this method.
The question arises as to which component is actually the "trailer". If the towing dolly has over-run brakes, does that mean the "trailer" is regarded as braked, albeit only on the front wheels?
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Not so sure about the constant referencies to these people being "numpties" - no-one has checked to see if they have actually researched it and if their set-ups are safe - just wild assumptions that they are unsafe... a little unfair, I feel...
Now if you want numpties in this respect they were mentioned earlier - and I'm sure we've all seen them - cowboy builders driving their Transit at 80mph with a generator attached to the back that they definitely can't see, is weaving all over the place and bouncing up and down at the same time...
I'd be after them before some guys driving a Motorhome at a lot slower pace and, from what I've seen of them, in a lot safer manner...
Or is it just an excuse to have a go at motorhome/carravaners??
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"a little unfair, I feel..."
Except that, from my reading of links above, it is illegal - though I could well be wrong. I wonder what their insurance company would say if there was an accident?
"an excuse to have a go at caravanners??"
Nope, I'm not much into self-abuse!!!
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Fair enough - looking at a google search it would seem as though its definitely illegal, though:
"It is well known that some countries in the EEC tend to overlook the regulations (the UK included) but some countries don?t. The situation regarding enforcement could change at any time and, as a result, the only safe way to transport another vehicle behind a motorhome is on a car transporter trailer. Play safe! Don?t take the risk!"
says an awful lot - a small two wheeled trailer for something like a Smart wouldn't take up too much room, though!, could even store it sideways on the site!
I'd still rather the Police clamp down on those builders and others that go shooting past me a 80mph on the motorways with trailers swinging along behind them - they are far more dangerous than the OAPs that tend to drive the Motorhomes.... (oops another generalisation....!)...
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Cliff
Towing dollies are another can of worms; but can be legal if used and equipped correctly.
b308
Yes; it was indeed me that referred to them as numpties. I find a significant proportion of motorhome owners are from the shallow end of the gene pool, are frighteningly gullible and seem to have far too much time and resources to spend on yet more worthless tat to further encumber their primary obsession.
Little wonder that unscrupulous traders home in on them and easily con them into believing that it's possible to durably attach an A-frame to a modern car - and that it's legal to do so.
Your point on builders' similarly cavalier attitude to trailers is also very true. About 20 years ago, a lovely young lady colleague, mother of twins, left her job at Polegate AA box, just after dark, to drive only a mile home. A freshly-detached, unlit, builder's trailer lying across the middle of the A22 ensured that she didn't make it.
So, after losing two friends to careless hitching; forgive me for having a bit of a bee in my bonnet about trailer safety.
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No idea of the legality, but I have seen the big Winnebago type motorhomes towing little cars such as Fiat Pandas.
Maybe these behemoths are classified as HGVs and different regulations apply?
Certainly a different driving licence is needed AFAIK.In a specialist magazine I even saw a motorhome with a car in an integral garage!
Edited by Glaikit Wee Scunner {P} on 22/03/2008 at 11:05
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Doubt it. I know a chap who used to use a converted coach to transport his stock car and the rest of it was motor home. He was assured by the police the vehicle in question was legal as a motor home, could be driven on his car licence yet as anyone who has read a coach weight details, had a GVW in excess of 7.5 tonnes by quite a lot. He did actually get an HJV licence as the matter still concerned him.
AFAIK the regulations on motorhomes still allow this, although I've not looked into it as I've no wish to drive one!
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I used to travel around with Graham Blundell in the 70s in his converted coach - I'm sure he said they needed an HGV licence for it, but not a PSV!
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You sometimes see travelling fairs pulling a string of assorted trailers and caravans, often ending with a car. I know they probably have to have a special (HGV?) licence to drive it, but that is not the same thing necessarily as it being safe.
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Cliff
I believe that the extensive "Showman's Haulage" exemptions come with a 20 mph speed limit - I'm not certain if the 750kg unbraked limit applies to their train of trailers, but it certainly does to a normal Goods vehicle.
They are also, usually, extremely practical people who are well able to make sure that their trailers are securely attached - and, to keep their LCV C+E [HGV 1] licences, they make sure that they stay that way.
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Just to go back to the original post - just how many of these cars have actually come adrift from a motorhome, if any?
Or are we more likely to get hit by an uninsured driver.....
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No one has posted to say they've seen or heard of a car coming adrift from a motorhome.
Towing this way appears no more dangerous than any other form of towing, so I would guess you are much more likely to be hit by an uninsured driver, or even an insured one!
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Whilst the concensus is to suggest it is illegal it has to said lots have been sold and enough time gone past to see if lots of incidents have happened. One of the things that also should be pointed out is that these are fitted to commercial based vehicles where chassis and brake set up is quite substantial.
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The crucial difference with this set-up is that the entire braking force of an, illegally over-weight, unbraked trailer is passing through a detachable A-frame with cobbled-together, inadequate, mountings.
The A-frame on a normal trailer is an integrated part of the structure and designed as such. The design for the front members of a car has no consideration for such destructive stresses.
On a motorhome with a long overhang, which is most of them, the front of the car is first wrenched one way and then the other on every corner; the perfect recipe to fracture sheet steel.
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I must admit that I would be unhappy at being behind a typical European motor home towing a car. I'm thinking of something like a Cit/Pug/Fiat chassis with a lightweight skin to provide the carcass of the motorhome section. In the US, I have seen much larger vehicles (RVs) towing a small Honda and that always looks to be perfectly reasonable.
I met a guy who was buying a larger Merc chassised motorhome with an integral garage. He was toying between a short tall garage suitable for a Smart, or a long low garage suitable for an MX5. Very very expensive!
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When I was out with the dogs earlier, there was one of these American behemoths (on an UK C plate) parked up in a beauty spot car-park obviously overnighting with no regard to the locality. There was a Pug 106 hooked up to the rear with an A frame. There was a suspicious looking liquid discharging from one corner of he van, a Tesco bag full of rubbish underneath its front axle, will check to see tomorrow if they've left it behind. No doubt stocked up to the ginnals with food from their own local supermarket where it took up a fair proportion of the car-park. In other words visiting my little corner of the world contributing nothing and taking a lot.
In answer to ifithelps I feel that there is more chance of being struck by an insured or uninsured car than a wayward ex-towed vehicle from behind one of these, simply because, thankfully, the horrid anti-social things are rare and I hope they're taxed to extinction.
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. In other words visiting my little corner of the world contributing nothing and taking a lot.
PU,
Reminds me of an unguarded remark made a few years ago by someone tasked with promoting tourism in the north of England.
When asked about caravanners, he said something like: 'They bring a clean shirt, a £10 note, and change neither.'
A little bit of holiday-related humour for an Easter Monday.
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Don't wish to rake over old ground, but I saw a good one today.
It was a motorhome towing a Smart car on an A-frame with the brake lights of the Smart wired to come on with the brake lights of the motorhome.
Clever, I thought.
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Don't wish to rake over old ground but I saw a good one today. It was a motorhome towing a Smart car on an A-frame with the brake lights of the Smart wired to come on with the brake lights of the motorhome.
In the US there's a device sold which presses the brake pedal on the towed car (so that would turn the brake light on) although such a device seems OTT for a Smart!
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BP,
Must say I hadn't thought the Smart's brakes might be on as well.
Do you mean a hydraulic rod like a Krooklok?
I wonder how it's actuated.
There wouldn't be much braking power without the servo.
OTT for a Smart? I should have mentioned it was a four door - practically a limo.
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There wouldn't be much braking power without the servo.
There isn't much braking power in a single axle caravan either if you compare the braking ability of a car to that of a caravan - the majority of braking is done by the towing vehicle in most car/trailer set-ups, thats why the larger the car the better braking there will be - I suspect that a "mobile home" will have sufficient braking capability for something as small as a Smart hitched on the back...
I suspect that the "push on effect" of that set-up would be less than in most car/caravan combinations you see out on the roads...
Edited by b308 on 19/04/2008 at 10:38
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I wonder how it's actuated.
This is what I was thinking of (there are others too):
www.brakebuddy.com/
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BP,
Thanks for that.
Looks like the answer is remote control, although I'm still not entirely sure what the driver does.
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