Towing Prob

Aug 28, 2005
603
0
0
Visit site
We own a Dethleffs Newline which is fitted with an Alko Stabiliser. We have no problems when passing artic lorries etc but we do find that we swerve a little when being passed or passing smaller vehicles like 7.5 tonners and coaches - does anybody have the same problem and why would it happen with the smaller vehicles and not the larger ones?
 
Jul 14, 2005
99
0
0
Visit site
Hi

Firstly you don't say what your towcar is and the weight ratio you are using. Also you will need to have around 75kg on your tow ball weight. It is possible that you may have too much weight on the rear half of the caravan. All these factors can add up to make the difference.
 
Aug 28, 2005
603
0
0
Visit site
Hi Tom,

The Monkey's other Half here as she cooking the children's tea. Car is a Volkswagen Sharan 1.9 tdi, weight is between 1650-1750 kgs depending on length of Holiday, van quotes 1100 kgs unladen and I would reckon a maximum of a 100 kgs extra stuff on board. (1 gas bottle, awning placed in side locker no other weighty items. the van is level no light some you see (hunched in the middle) and the nose weight is around 70 kgs.

I too thought of the rear loading but if anything is is probably under weight as its not loaded and has a U shaped dinette.

It's a strange thing that we can go or be passed by 44 TONNE six axle artic and not notice it's there (not in the literal sense) yet a high roof transit and the van does move. Not enough to worry me like the wife but an explanation would be well come

Cheers
 
Mar 14, 2005
987
0
0
Visit site
Transit type vehicles cause a slight swerve when passing usually at high speed, they seem to push the same area of air which can cause the caravan to swerve in the vacuume that is caused.

Never had any problem with lorries coaches overtaking. or overtaking lorries.

Followed a large farm grain vehicle on the A14 the other day which was being towed on a lowloader driving at 55 mph , as we got closer to overtake The car and van started to vibrate droppng back two vehicle lenghts behind it, everything returned to normal, We noticed as the grain load was passing large trees by the road side they were all moving as if in a gale, returning to normal as soon a the load passed. Even big lorries who were overtaking were swerving a bit as they passed the load.

Keeping a safe distance from these monsters in the future.
 
Mar 14, 2005
3,004
0
0
Visit site
Hi - I will add my comments as Monkey invited me to on another thread but I am no expert on towing. All I do is be cautious and treat all other drivers as potential idiots.

One thing that helps with the larger lorrys is to move out slightly in your lane as they come up behind you then as they pass GENTLY move in a bit. This helps them move away from your lane and enables you to put as much distance as possible between you and "him"

I have never had a problem with smaller vans and the like. So sorry cannot help you there.

There is a guy who contributes regularly here called Lutz who is based in Germany and would probably have some insight - he is very knowledgeable - may be especially relevent with your make of 'van.

Why don't you flag it up on the other thread with a specific question ? I am sure Lutz would respond.

My only comment would be to look at the noseweight and how the 'van rides - is it nose up or nose down. Nose down helps!!

Also what was the road surface like? We had a terrible problem once with a folding camper that became sensitive to a sparrow breaking wind. What we thought it might have been was these "furrows" that get worn in the inside lane the track of the wheels on the trailer was such that given half a chance it would start to swing from side to side as it got caught in these tracks.

Hope this helps
 
Mar 14, 2005
189
0
0
Visit site
There's something very variable about the aerodynamic "bow wave" in front of large vehicles. It's most noticeable with traffic coming towards you on single carriageway roads. Some large vehicles will create a lot of buffetting while others will not create any, even at consistent approach speeds and lateral clearances. This aerodynamic variation also occurs when overtaking, or being overtaken, by large vehicles.

I vaguely recall that the Caravan Club is sponsoring research into this, possibly at Bath University - I've never seen or heard of any results.
 
Mar 14, 2005
1,476
1
0
Visit site
Monkey ( and husband of course), I experience the same thing which is that artics and even coaches do not cause the van to move but box bodied vehicles cause a minor movement. This is of course most noticeable on the motorway as the oppurtunity for overtaking on normal roads isn't great. I think it may have something to do with speed differential as I normally cruise at 55mph on the motoray and artics are overtaking at 55-60 whereas box bodies are doing 60-70. I think it is also due to the boxiness shape pushing the air to the side of them.

The most buffetting I get is if following a car transporter which definetly causes the air to be turbelant.
 
Mar 14, 2005
9,779
677
30,935
lutzschelisch.wix.com
I haven't got any facts simply because there doesn't seem to be any substantiated information available but I suspect it has something to do with the length of the passing vehicle. In the case of a van, the bow wave is followed almost immediately by turbulence behind the vehicle. When a long truck is passing, the air flow has a chance to stablise a little in between. It's a bit like when you are standing on a platform as an express train is coming through the station. At first you are buffeted by wind as it approaches but while it is actually passing you the air flow calms down somewhat until there is a rush of turbulence again as it leaves.

Also, vans have a habit of passing at higher speeds than trucks and this increases the effect.

Finally, and not to be underestimated, there is the psychological effect of one being prepared for something to happen as a big truck is looming up from from behind but one is easily caught unawares as a smaller van approaches.
 
Mar 14, 2005
17,760
3,172
50,935
Visit site
There was some considerable research looking at fuel efficency of large lorries done in the 1970s, I susspect as a result of the earlier fuel shortages.

Large vehicles that had very sharp corners to the tractor and the payload area could have their fuel efficacy improved by several percent by adding rounded mouldings to the leading edges.

This apparently smoothed out the air flow around the leading edges, making the vehicle slightly more aerodynamic. The reduction in the turbulence caused by the sharp corners, meant that the air flow around the side of the vehicles was less turbulent and will approach laminar conditions on a long artic. It also means that the air flow from the trailing edge would settle quicker as the vehicle passed.

Each design of vehicle will have its on characteristics which will change with speed, but as Lutz points out the two events of the leading edge and trailing edge will occur more rapidly with a short vehicle.

In general, the easier a vehicle can slip through the air the smaller disturbance it will cause to other road users.

Theoretically, the worst case scenario for a caravan is to interact with a vehicle of similar size, If we assume the bow wave with tend to push adjacent vehicles away, and the trailing vortex will tend to suck adjacent vehicles towards it then the following sequence of events will occur.

Transit sized van begins to over take. Initially the bow wave from the van will tend to push the rear of the caravan to wards the near side. This slightly turns the caravan and its track will begin to drift towards the off side.

As the vans bow wave draws level with the caravan axle, there is no net turning force, but a general shove towards the near side.

When the vans bow wave moves forward of the axle, the front of the caravan begins to experience a turning force towards the near side, but at the same time, the vans Tail vortex is also pulling the rear of the caravan towards the offside. These two forces are additive, and considerable. The caravan will try to track towards the near side.

As the van passes, the tail vortex will eventually begin to suck the nose of the caravan back towards the offside.

If the van were longer or a full size lorry, the bow wave and tail vortex forces would not occur in phase with the caravan and thus will have less of marked effect.
 
Mar 14, 2005
4,638
0
0
Visit site
I find the worst vehicles for this are loaded car transporters.

The Alko stabiliser I find is very good for counteracting the effects of overtaking lorries etc and seems more effective than blade type stabilisers.

I wonder if this is because the hitch "floating" on the ball as the caravan catches up to the car is eliminated by the tight grip of the friction hitch.

Downhill also seems more stable for the same reason I think.
 
Mar 14, 2005
9,779
677
30,935
lutzschelisch.wix.com
In principle, there is no reason why a blade type stabiliser should be any worse than an integrated one like the AlKo. After all, they both work as frictional dampers (except for the Straightliner which is a viscous damper).

Car transporters are obviously the worst offenders because their sides are anything but smooth. From an aerodynamic point of view they can be considered as a truck followed by a couple of cars or vans in quick succession.
 
Mar 14, 2005
4,638
0
0
Visit site
In principle there may be no difference between the expected performance of hitch and blade type stabilisers but I am talking about in practise.

It seems to me from my own use over 3 years of the Alko that the outfit is more stable on the over-run(ie when the caravan is catching the car)and you get to that floating on the ball sensation when the steering feels lighter.

It seems to me that the tight grip on the ball must eliminate this and this is not a property of leaf type stabilisers or the excellent Straightliner which I have retired from service (anybody want to make an offer ?)
 
Aug 28, 2005
603
0
0
Visit site
My thanks for all of your replies - it has really been fascinating finding out what can cause it - and guess what it turns out I'll just have to avoid white van man - no miracle cure!!!!

I will keep you all in mind when I need advice again!!
 
Mar 14, 2005
459
0
0
Visit site
Yep same problem on the M40 notrhbound.

Passing some artics at 57 to 60 mph and taking into consideration the suction as you pass the last HGV,stabliser on, less than 60% van match to vehicle ratio. All balanced correctly and nose weight and tyres o.k. Then what happens Large ridged van approx 25ft passes in the outside lane at 65-70mph, van all over the place.Side draught from outside and suction from nearside lane HGVs caused havoc with handling,super twich from van and me. The only other time was when a coach passed me on the middle lane at 60mph on the M56 and I was doing 58-60mph again twiching badly. I have always watched the mirrors to try and anticipate what is coming up and even if you try and put as much width between you and the other vehicle its still hairy.

Rob
 
Mar 14, 2005
9,779
677
30,935
lutzschelisch.wix.com
The main disadvantage of blade type stabilisers compared with the integrated type is that they are more dependent on the owner setting it up correctly each time and, of course, you've got more to do every time you hitch up. In the case of a stabiliser integrated in the coupling, there is nothing special to watch out for except that the brake pads are clean and not worn but that applies to the blade type too.
 
Mar 14, 2005
4,638
0
0
Visit site
I think that we are on parallel topics Lutz

My point really was the floating on the ball second is avoided with the tight grip of the coupling hitch.

Maybe floating balls are more apparent with advancing years!!

Another major benefit is clean trousers and little fingers from the dry ball.
 
Mar 14, 2005
9,779
677
30,935
lutzschelisch.wix.com
I don't know quite what you mean by 'floating' on the ball. Do you mean clearance between the ball and the coupling? If so, this should be minimal when hitched up (in the order of a millimetre or so) even without pads to grip tightly. This should have no effect on the stability of the outfit.
 
Mar 14, 2005
4,638
0
0
Visit site
Just a little techno speak from the Straightliner instruction sheet.

"Even the most docile of trailer can go wildly out of control at speeds over 50mph downhill as the kinetic tension between car and caravan slackens"

This is what I am trying to express as floating on the ball and I believe that this is where the Alko type scores as it does not allow the slacknes even of one millimeter (greased) so the tendency to sway is damped before it gets going.
 
Mar 14, 2005
9,779
677
30,935
lutzschelisch.wix.com
Now that we've solved the nose down issue we can return to this topic. The 'floating' that you refer to is the tendancy for the caravan to go its own way if not restrained by the towing vehicle. However, whether the forces to restrain the caravan come from direct reaction of the towball (the usual stable situation) or by friction from the stabiliser (when instability is about to occur) is really immaterial. If your experience is that the integrated AlKo type stabiliser works better then this reflects more on the quality of the product than a superior design concept.
 

TRENDING THREADS

Latest posts