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Snaking

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#1 alano

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Posted 11 September 2017 - 09:15 pm

Hi   I have a Peugeot 3008  with a Elddis Typhoon unit   traveling down the M5 at approx. 60 mph I experienced quite a nasty snake so slowed down to 50mph ok for a few miles then it started again but not so sever this time. Could anyone advise on possible cause. Van was loaded good with heavy stuff over axle, I was thinking may be I need to change pads on my winterhof hitch or may be tow car is over towing limit, although it was towing great until snake started approx. 60 miles into our journey.



#2 blondchaser

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Posted 11 September 2017 - 09:35 pm

Cross winds ?? Tyre pressures set for towing ??
I tow a big Elddis Cyclone with a small Picasso and can't say I've had this problem until over the legal speed limit.
Many years ago I landed with a serious snake situation, and since then I always fit the old Bulldog blade type stabiliser----no probs at legal speed.
Is your car loaded to a higher weight than your van??

Edited by blondchaser, 11 September 2017 - 09:36 pm.


#3 Tuningdrew

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Posted 11 September 2017 - 09:35 pm

Check your nose weight.
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#4 AWanderingLancastrian

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Posted 11 September 2017 - 10:21 pm

Hi alano. Rear tyre pressures along with caravan tyre pressures and nose weight would be what I would be looking at and especially if the snaking started on a slight downhill run.

Also what is your tow-ball height at the center because if the snaking started on a slight downhill run then that will effectively increase the hitch-head weight - it is a part of the dynamics of towing and the effect of weight-shift brought about by the tow-ball being lower than it should ideally be.

 

It should ideally be at 350mm to 420mm at the center and should be set on flat and level ground with everything ready to roll.


Edited by AWanderingLancastrian, 11 September 2017 - 10:26 pm.


#5 Stevan

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Posted 11 September 2017 - 10:29 pm

Although there are lots of known influences on stability there is little or no hard evidence to show exactly how these factors interact or exactly what turns a minor wobble into a major snake.

 

Known factors include:-

Noseweight, end loading, top heavy loading, tyre pressures (all of them), tyre types, suspension type and condition, nose up or nose down (controversial), speed, stabiliser condition, length of rear overhang.

 

 

Tracing a precise cause in an individual instance can be very hit or miss, any permutation of any of the above could be part of the cause. 



#6 banjokat

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Posted 11 September 2017 - 10:39 pm

What is your towing limit? What is the weight of car / caravan? I recently invested in a Milenco nose weight gauge and outfit feels better (although it was never unstable).



#7 Black Grouse

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Posted 12 September 2017 - 05:29 am

Check all the things mentioned - tyre pressures for car and caravan, loading of both car and caravan, noseweight.

 

Yesterday, there were weather warnings about high winds in the South-West reaching up to the Midlands, it may be that which triggered it.

 

I've got a similar journey today, down the M5/A30 to Cornwall, with another weather warning from 5pm.



#8 xtrailman

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Posted 12 September 2017 - 05:55 am

As mentioned IME its nearly always NW. Get that right and the caravan with stabilise.


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#9 charlieboy2608

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Posted 12 September 2017 - 06:05 am

The M5 is notoriously bad for crosswinds-might just be that unless you've used this route before?



#10 JTQ

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Posted 12 September 2017 - 06:07 am

Noseweight is being mentioned rightly so; with few exceptions for improving stability this is best as high a load as the kit allows.

 

Also ensure the cars rear tyres are inflated at least as high as they recommend for a heavily loaded car, even up to what the tyre maker allows; getting the car to be as stiff as possible to side deflections is the aim here.


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#11 CommanderDave

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Posted 12 September 2017 - 06:34 am

A number of reasons a caravan can start snaking as said speed , going down hill , overtaking van or lorry , cross wind , tyre pressures , as well as nose weight .

My TA Elddis used to tow perfectly in calm weather but a bit of wind and I would only be able to tow at 45 mph usually to keep it in the lane on motorways .

Dave

Edited by CommanderDave, 12 September 2017 - 06:35 am.


#12 Lutz

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Posted 12 September 2017 - 07:54 am

Another possible cause that hasn't been mentioned is the weight distribution in the caravan left to right. The Caravaning magazine ran a test a couple of years ago and found out that stability is noticeably impaired if the difference between left and right exceeds much above 70kg.



#13 ChrisUK

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Posted 12 September 2017 - 08:14 am

Interesting. We are just back from a two site stay, no problems on the motorways on the first two legs, but on the final trip to home the van was very nervous over 50mph. Half way home I stopped to check tyre pressures and all was OK.  When home I noted that my nose weight was about 80 kg instead of the usual 100kg, I was also running with less weight over the caravan axle (we had eaten it!).  I'm surprised that 20kg would make so much difference.

I have always carried my 2 aquarolls + waste container in the end wash room,  I have always wondered if this exaggerates the "dog bone" effect.

For the questioner, I have occasionally forgotten to drain the hot water heater which is front right, and this is quiet noticeable on stability. 


Another possible cause that hasn't been mentioned is the weight distribution in the caravan left to right. The Caravaning magazine ran a test a couple of years ago and found out that stability is noticeably impaired if the difference between left and right exceeds much above 70kg.

Good point but not easy to measure.  Anyone any ideas?



#14 Stevan

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Posted 12 September 2017 - 08:16 am

A number of reasons a caravan can start snaking as said speed , going down hill , overtaking van or lorry , cross wind , tyre pressures , as well as nose weight .

My TA Elddis used to tow perfectly in calm weather but a bit of wind and I would only be able to tow at 45 mph usually to keep it in the lane on motorways .

Dave

I think that we need to make a distinction between causing a bit of a wobble (crosswinds and/or overtaking a large vehicle etc.) and the wobble turning into a snake. 

 

Any outfit will wobble, as above, if the external conditions happen, although in some outfits you may barely feel it. What turns that wobble into a snake is far more complex.



#15 Lutz

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Posted 12 September 2017 - 08:59 am

I think that we need to make a distinction between causing a bit of a wobble (crosswinds and/or overtaking a large vehicle etc.) and the wobble turning into a snake. 

 

Any outfit will wobble, as above, if the external conditions happen, although in some outfits you may barely feel it. What turns that wobble into a snake is far more complex.

 

That is correct. A snake is usually understood to be a condition of instability which will not recover on its own without some sort of active external intervention, either by an electronic stabilising system or by the driver himself.



#16 CommanderDave

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Posted 12 September 2017 - 10:18 am

It is usually a contributing factor that will cause a snake like a passing lorries bow wave especially going down hill .


Dave

#17 Stevan

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Posted 12 September 2017 - 10:36 am

It is usually a contributing factor that will cause a snake like a passing lorries bow wave especially going down hill .


Dave

Can't agree, the passing lorry causes a wobble, for this to turn into a snake requires instability in the outfit.


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#18 ancell

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Posted 12 September 2017 - 10:55 am

My Elddis Typhoon single axle was susceptable to snaking and not only downhill!
It was especially prone to winds on either rear quarter.
Tyre pressures-noseweight and loading helped-especially keeping heavy stuff out of the back end.
Towing up and down the A9 it was subjected to some pretty high winds but of course crosswinds are not restricted to up here eg crossing the border on the west coast M6 A74M.

#19 joanie

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Posted 12 September 2017 - 11:03 am

all of the above, We travelled home yesterday at no more than 50 mph. It took 6 hours to travel 200 mls.  We were held up because of a broken down lorry , plus a couple of stops, but no way would OH increase his speed in those winds. We have had a bad wobble once when we were overtaking a lorry and a white van sped past, frightened the life out of me. All I can suggest is check everything .



#20 AWanderingLancastrian

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Posted 12 September 2017 - 11:04 am

Can't agree, the passing lorry causes a wobble, for this to turn into a snake requires instability in the outfit.

 

Hi Stevan. I am sorry do differ with you on this one BUT if any outfit has started out with a slightly higher nose-weight than would be optimum and the rear of the car/nose of the van or ridding low and the load inside of the caravan shifts even as little as a few inches then the whole outfit WILL become unstable and especially when on a descent and an HGV/Tour Coach passes either at speed and or to closely then the bow wave will result in a Snake and also could possibly cause yawing and when the two are combined a snake will quickly generate.

 

There was a member of CT Forum that was known as The Flying Tog (aka Simon Barlow) he is the author of an absolutely essential bit of reading for newbies/novices and even those that believe that they know it all.

 

It is called The Dynamics of Towing and can be found here within the technical topics on CT Forum.

It covers single axle,twin axle and 5th wheel outfits and can be found here in the three parts of the article :--

 

www.caravantalk.co.uk/library/files/Beginners-Guide-To-Towing-Dynamics.pdf

 

https://caravanchron...of-towing-pt-2/

 

https://caravanchron...being-overtaken

 

 

What is actually going on behind you can be real horror story if allowed to go uncontrolled - the split-second between normal and utter panic can be very very costly.







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