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You ask why one doesn't see caravans with the rear end shunted. Easy, the difference is not that large that it would account for an appreciable frequency of such incidents. From what I recall, it was only about a 10% improvement in stopping distance.
If I can't find the article I'll get in touch with the publishers and maybe they can send me a copy.
If I can't find the article I'll get in touch with the publishers and maybe they can send me a copy.
No real experience of caravan and car except pulling up 'very sharp' one day caused no problems whatsoever.
However I did used to tow a 25cwt trailer a lot with an 18cwt Hillman Imp?...well the sporty version of the Imp!
The mis-match to say the least is excessive! and it was drum brakes all round, but, even in these strange conditions braking was never a problem under any circumstances I came across and there were many?
It was obviously never a 'fast' combination but I can say this for certain, I tested it in around an inch of snow from around 25mph, it stopped near dead! far better than I expected and totally took me by surprise.
I put it all down to the far greater load per square inch on the trailer tyres giving far better grip than the four car tyres.
One other thing was no fancy hitch dampers either, just an old fashioned spring and the towbar mounting was just two 12mm bolts which suggests the load on any towbar is never very great?
However I did used to tow a 25cwt trailer a lot with an 18cwt Hillman Imp?...well the sporty version of the Imp!
The mis-match to say the least is excessive! and it was drum brakes all round, but, even in these strange conditions braking was never a problem under any circumstances I came across and there were many?
It was obviously never a 'fast' combination but I can say this for certain, I tested it in around an inch of snow from around 25mph, it stopped near dead! far better than I expected and totally took me by surprise.
I put it all down to the far greater load per square inch on the trailer tyres giving far better grip than the four car tyres.
One other thing was no fancy hitch dampers either, just an old fashioned spring and the towbar mounting was just two 12mm bolts which suggests the load on any towbar is never very great?
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Steve L, makes a very valid point. All the talk in the world (and I know I'm accused of that) cannot displace the real life situation.
I have tried emergency stops with trailers, but not in a scientific, manner only to prove the brakes do work. And in my experience on a an older vehicle without ABS, it was possible to lock the cars wheels and leave skid marks, but never from the trailer wheels, yet the stopping distance never felt unreasonable.
During the manoeuvre I felt and heard the characteristic thump from the trailer coupling, but what alerted me to the probability the noise was generated by the extension of the overrun, was that under gentle braking the I didn't notice the thump until I pulled away.
I think Ray is trying to play devils advocate with his last posting re crumpled back ends of caravans. Whilst I am certain that under some conditions the braking performance of an outfit can be better than a solo car, I don't expect the difference to be massive more likely a few percent better, and with some outfits where things are not optimally adjusted the distance may be worse.
Chrissbee, the proportioning valve may well be open wider with a fully laden car, but it does not necessarily have to be fully open. The manufactures may well keep some adjustment in reserve for conditions like towing where the dynamic load transfer may exceed the static load limit for the axle.
I think I have stirred the soup enough o this thread so this is my last contribution here.
I have tried emergency stops with trailers, but not in a scientific, manner only to prove the brakes do work. And in my experience on a an older vehicle without ABS, it was possible to lock the cars wheels and leave skid marks, but never from the trailer wheels, yet the stopping distance never felt unreasonable.
During the manoeuvre I felt and heard the characteristic thump from the trailer coupling, but what alerted me to the probability the noise was generated by the extension of the overrun, was that under gentle braking the I didn't notice the thump until I pulled away.
I think Ray is trying to play devils advocate with his last posting re crumpled back ends of caravans. Whilst I am certain that under some conditions the braking performance of an outfit can be better than a solo car, I don't expect the difference to be massive more likely a few percent better, and with some outfits where things are not optimally adjusted the distance may be worse.
Chrissbee, the proportioning valve may well be open wider with a fully laden car, but it does not necessarily have to be fully open. The manufactures may well keep some adjustment in reserve for conditions like towing where the dynamic load transfer may exceed the static load limit for the axle.
I think I have stirred the soup enough o this thread so this is my last contribution here.
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I got in touch with the publishers regarding the article that I mentioned and they told me in which issue it was. Had a look around at home to see whether I still have it, but to no avail. I'll give them a call again on Monday and ask if they can send me a copy (they said they would).
- Mar 10, 2006
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lutz
While we await your article.
Given that you claim up to 10% better braking while towing, why then do all the motoring organisations etc, always recommend leaving a LONGER braking distance between the vehicle in front when towing?
Last year we had a nutter that sped past our rig, he tail gated the vehicle in front, which then braked and caught him out, he had to carry out an emergency stop, his caravan brakes locked up although he did stop in a straight line.
I was under the impression that once a wheel locked, then braking efficiency was impaired?
I find it hard to see how under these conditions, that rig will stop 10% shorter than the car solo.
While we await your article.
Given that you claim up to 10% better braking while towing, why then do all the motoring organisations etc, always recommend leaving a LONGER braking distance between the vehicle in front when towing?
Last year we had a nutter that sped past our rig, he tail gated the vehicle in front, which then braked and caught him out, he had to carry out an emergency stop, his caravan brakes locked up although he did stop in a straight line.
I was under the impression that once a wheel locked, then braking efficiency was impaired?
I find it hard to see how under these conditions, that rig will stop 10% shorter than the car solo.
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I did not claim a 10% improvement in braking performance. 10% is what I recall from memory of the report and is not a claim that I have made. I was only relaying information from other sources but the explanations given seem plausible to me. Besides, the improvement applied only under certain defined conditions. Let's await the details of the report to see what they were before discussing this issue any further.
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I got in touch with the publishers and they promised to send me the full report by post, but I have already received a short summary by fax. The results are quite surprising so I thought I'd already mention them here now:-
TEST CONDITIONS
Test vehicle was a BMW 530xd Touring. It was tested both lightly laden with 140kg payload and fully laden with 340kg.
Two caravans were used, one at 1200kg, the other weighing 1800kg.
All tests were conducted both in the dry and in the wet, and all braking distances measured stopping from 100km/h.
TEST RESULTS
A set of test results for 5 different conditions are mentioned in the summary:-
1. Lightly laden car, solo.
Braking distance, dry, 39m
Braking distance, wet, 42.5m
2. Lightly laden car towing 1200kg
Braking distance, dry, 41m
Braking distance, wet, 51m
3. Fully laden car towing 1200kg
Braking distance, dry, 42.5m
Braking distance, wet, 50m
4. Lightly laden car towing 1800kg
Braking distance, dry, 42.5m
Braking distance, wet, 54.6m
5. Fully laden car towing 1800kg
Braking distance, dry, 43m
Braking distance, wet, 60m
CONCLUSION
It is apparent that, in the dry, overall weight has relatively little effect on braking distance and there is even little difference between the solo vehicle and when towing. The picture is, however, markedly different in the wet.
TEST CONDITIONS
Test vehicle was a BMW 530xd Touring. It was tested both lightly laden with 140kg payload and fully laden with 340kg.
Two caravans were used, one at 1200kg, the other weighing 1800kg.
All tests were conducted both in the dry and in the wet, and all braking distances measured stopping from 100km/h.
TEST RESULTS
A set of test results for 5 different conditions are mentioned in the summary:-
1. Lightly laden car, solo.
Braking distance, dry, 39m
Braking distance, wet, 42.5m
2. Lightly laden car towing 1200kg
Braking distance, dry, 41m
Braking distance, wet, 51m
3. Fully laden car towing 1200kg
Braking distance, dry, 42.5m
Braking distance, wet, 50m
4. Lightly laden car towing 1800kg
Braking distance, dry, 42.5m
Braking distance, wet, 54.6m
5. Fully laden car towing 1800kg
Braking distance, dry, 43m
Braking distance, wet, 60m
CONCLUSION
It is apparent that, in the dry, overall weight has relatively little effect on braking distance and there is even little difference between the solo vehicle and when towing. The picture is, however, markedly different in the wet.
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Lutz
Those results are certainly interesting, about what i expected, but the extra braking distance towing in the dry, is less than i would of thought, so yes, interesting.
However, unless my memory fails me, 2 year ago you made claims, that the results showed a car towing, would stop quicker than a car solo?
From the results you have posted, you were wrong, i was right?
Those results are certainly interesting, about what i expected, but the extra braking distance towing in the dry, is less than i would of thought, so yes, interesting.
However, unless my memory fails me, 2 year ago you made claims, that the results showed a car towing, would stop quicker than a car solo?
From the results you have posted, you were wrong, i was right?
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Admittedly the results supplied do not confirm what I wrote back then, but even so, they were not my claims. I can only state what I have read elsewhere as I am not in a position to be able to collect or verify such data myself. It was not purely an assumption on my part. Obviously, the source had either made an incorrect claim or the conditions were different.
The report referred to above was published in September last year, i.e. after the previous thread on the subject of braking distances that you mentioned. It is not the same report. I can no longer trace the earlier article.
Nevertheless, I think the results that I have obtained now, in particular the conclusion, are worthy of note.
The report referred to above was published in September last year, i.e. after the previous thread on the subject of braking distances that you mentioned. It is not the same report. I can no longer trace the earlier article.
Nevertheless, I think the results that I have obtained now, in particular the conclusion, are worthy of note.
It's a pity that in the study that Lutz refers to they didn't give figures for a fully laden solo car as test 2/3 would seem to suggest that when towing in the wet a loaded car would stop more quickly than a part loaded car. This reinforces the thinking that it is better to carry as much of your weight in the tug rather than the caravan, something I'm sure we all strive to do anyway.
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I would imagine that all tests were carried out on the level and in a straight line as anything else would add further variables requiring definition (how steep the hill?, what radius the long sweeping curve?, etc.) into the equation, making the study even more complex.
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