Snaking!!!

[steve56616]

We collected our new van last week and brought it home with no problems. After taking it out on our first trip on Friday it kept snaking every time I reached 49 - 50mph.
The van is a Avondale Ospray and our tow car is a 2.5 X type Jag.
It was loaded evenly I thought. Awning across axle, water roll and watermaster in the back bathroom. Clothes even all round and that was about it. All water was emptied from all tanks and toilet etc.
Any ideas what I may be doing wrong?

Steve

 

[Damian]

Did you actually check the noseweight

 

[forestgump]

the back bathroom may make the front light as damien says check your front for load .

 

[steve56616]

Nope. Everyone I have spoken to don't seem to check it other than make sure it looks level. Not been caravanning very long as had to take our Luna back to the dealers so got this new one now. So not very experienced to be honest.

 

[Lutz]

That explains all. Sitting level is no indication of how stable the caravan is going to handle and is therefore not a criterion to be taken seriously. As previous posts have indicated, it is far more important to ensure adequate (but not excessive) noseweight.
Snaking at speeds below about 50mph suggests that the noseweight was well nigh zero.

 

[forestgump]

your van will lift as you go down the road so to be level to start with may not be so on the move.

 

[Lutz]

Level or not is immaterial.

 

[steve56616]

Well we all live and learn. Everything seems daunting when your new but we will get there. Funny reading old post how some people thought you accelerated to get out of a snake.... least I new that you don't but thats the fun about caravanning, everyone is happy to help... like when it took us 2 hrs to put the removable towbar on when leaving!!!

 

[Damian]

Steve, I am pleased that you have said that you are not very experienced with caravanning yet, a lot of people would not admit that, so you have my respect for stating what you have.

Noseweight is critical to safe towing and is probably the most overlooked measurement.
The car will have a max weight allowed to rest on the towball, you need to establish that first( should be in the vehicle specifications) and then the chassis has its own max allowable hitch weight, which is 100kg for Al-Ko and BPW.
Your car may have , for example, a max ball weight of 75kg, so in this instance you need to load the van in such a way as to achieve as close to 75kg as you can, without going over it.

The weight is measured with car and van loaded as if towing, and should be done on level ground.
You can buy a noseweight gauge or use bathroom scales and a length of 2x2 cut to give the same measurement as that of the car and van when loaded and hitched.

I am certain that get the noseweight right and your snaking will stop.
Failing to get it right WILL result in your van on its side and your car somewhere else.

 

[Guest]

While I agree with nose weight being quite possibly to blame, I don't agree regards level or not having nothing to do with it, towing nose up can affect balance and produce snaking.
The speed though is interesting, my experience says nearer 40mph is critical for light nose weight problems, 50mph I personally found to be due to the cars rear tyres?
This was not 'snaking' as such but an uneasy feeling of it, a sort of gentle movement side to side? I found this was due to soft side walls on the cheap tyres fitted to the car, as an experiment I put 10psi in the cars back tyres and the problem disappeared, changing to good quality tyres fixed it permanently.
While towing though you should always put a few extra psi in to compensate for the vans noseweight and of course all the extra clobber in the boot!

 

[chopper1]

I took my van out for the first time and inadvertently got above 60mph, and around 65mph I felt the car suddenly being swayed from behind. Foot off the accelerator and the swaying stopped.

The van is a four berth rear bathroom, I had loaded everything heavy over the axle, put some bathroom scales under the jockey wheel to get a feel for the nose weight but no matter what I did, where I loaded anything, it didn't seem to budge away from 80Kg (75Kg limit on the towbar, 50Kg recommended in the manual for the van!). Given the stubbornness of the scales to move away from 80Kg, I assumed I was doing something wrong with the scales and abandoned.

For the return journey, the father in law (a more experienced vanner) just loaded everything forward of the axle in the front seating area, left the bathroom scales in the gas locker but instead we just lifted up the hitch by hand (which would have given an indication of it being too heavy). No idea what noseweight we were actually carrying, but it felt significantly smoother and less bouncy on the way home...

 

[forestgump]

my point was that if it looks levell it dose not mean its ok as was said [it looks levell ]does not mean a thing.

 

[drsorento]

Looking level is no indication of stability under tow, some cars, mine included have self leveling suspension.

 

[Lutz]

Towing with the nose up does NOT affect the balance so long as the noseweight in that condition is still adequate. It is, however, important to compensate for the reduction in noseweight as the front end is raised.

 

[mullsy1]

The only time I have experienced anything close to a snake it turned out to be a rear wheel bearing which was about to collapse.

 

[ChrisUK]

Is it snaking as in the caravan wagging about on the towball if it is it is probably nose weight, or is it simply somewhat unstable as in tyre pressures not correct. It is important to have the car's rear tyres at the "towing" pressure which on some cars is a lot more than normal.
Even though I have towed for years, if I have not towed for a few months, when first setting off I am aware that there is something on the back but within a few miles you get used to it.
On my van I try to load it as little as possible but find I have to put the water bottles at the rear to keep the nose weight down to 100kgs for my car. Having what weight you have got at the front and back does give "dog bone" instability. You really need all the weight in the middle, but they don't make caravans like that. The heaviest object being the gas bottle right at the front.

 

[xtrailman]

The level of the caravan can effect the stability of a caravan, as i found out with the new xtrail, the old xtrail towed level and was very stable, but when i changed tow cars to the new version this tows slightly nose down.
Now i have always found with the T30 that 85kg was the target nose weight for that model, however changing to the T31 gave a very twitchy tow, even small white van man would make its presence felt!

I now tow with 95kg and the rig is once again stable. So even if you think you have sorted your ideal nose weight, a change of tow car can send you back to the drawing board.
As for towing nose up having no effect on stability, well thats hog wash, both the NCC and CC recommend a level or nose down attitude while towing, as do bailey.

 

[GeorgeandAde]

Hi Chopper.
I noticed from your post that you stated you put some bathroom scales under the jockey wheel.
I am not the most experienced caravanner by a long way,but i believe the scales should be under the tow hitch and not the jockey wheel.
I would imagine this may make a small difference to the reading you get.
Adrian

 

[Lutz]

The reason why sources recommend a level or nose down attitude is only to ensure that any noseweight measured before hitching the caravan up is not reduced by raising the front end. However, this condition, and the associated potential stability issue, is avoided if the noseweight is measured with the coupling at the same height as when towing.
There is no reason why a nose up attitude should be any less stable subject to the noseweight being correct.

 

[glenno]

My 2p worth:-

I also tow with a Jag X-type & have done for several years. Never had a snake at any speed & my van weighs 1483kg max. Passing trucks is no drama at all.
Max towing weight for the car is 1500kg & the max noseweight is 75kg. Tyres should be inflated to the normal, not comfort pressure which is lower & will allow more sidewall flex.
Noseweight should be measured under the hitch. Measuring under the jockey wheel will give a higher reading.
I agree with Lutz. Attitude on hitch is irrelevant as long as the noseweight is correct at that attitude.

 

[Guest]

For those that think attitude has nothing to do with stability, the caravan is not a simple see-saw, otherwise I would possibly agree, no, it's eight or nine feet high and towing nose up shifts the centre of gravity both back and higher.
Adding nose weight does not shift the vertical balance forward therefore the C of G is still further back than it should be and consequently less stable. To say nothing of the van floor trapping more air at the front than the equally reduced space at the back can freely allow to pass?!
Otherwise I'm sure, the likely advice to reduce an unacceptably high noseweight would be... tilt the van back a bit mate?!

In short, level or slightly nose down, never nose up!

 

[Lutz]

When compensating for the reduction in noseweight as a result of raising the front end, the centre of gravity is shifted forwards again, back to where it was before the front end was lifted. Therefore, this compensation will restore the outfit back into a stable condition.
At normal speeds encountered when towing, i.e. up to 60mph, the aerodynamics underneath the caravan play a negligible rôle compared with the aerodynamic forces acting on the front face of the caravan and the latter are practically independent of attitude (at least within the normal range of attitude changes).
The statements made in the reply above are therefore incorrect.

 

[ProfJohnL]

Hello Gary,

I do not understand of follow your reference to the ‘Vertical balance’ can you be more descriptive please?

But not withstanding your intention with the “Vertical balance”, I do glean that you understand the position of the CoG is not in the same plane as the axle but above it, and that it must be some way forward of the axle to generate a positive nose load.

The actual position of the CoG within the caravan is not a fixed point for eternity, but is determined by the way you load the caravan, so it will be different for each journey. But having loaded the caravan, the position of the CoG within the structure will remain the same until you change any part of the load. It follows that you can change the position of the CoG within the structure by loading the caravan differently, and this is what you do to trim for the correct nose load.

Because the nose load does vary if you change the height of the hitch, it is vitally important that you measure the nose load correctly. It must be measured with the caravans hitch at exactly the same height as when it is hitched to the car with all luggage and passengers.

Measuring at a different height will give incorrect results when hitched.

To compensate for raising the hitch, more mass needs to be moved forward of the axle to generate the necessary nose load, and this means the CoG will also move further forward. This is where I think you have misunderstood the mechanics of the situation.
Air flow is a different consideration. It is a highly complex subject, and whilst it may seem logical that the underside of a caravan is like a flat board, you cannot consider that in isolation to the effects of the air flow over the caravan, and the disturbed air from the towing vehicle, So it is cannot be a foregone conclusion that a nose up attitude will try to lift the caravan when towing.

 

[Lutz]

Exactly, assuming everything such as noseweight, load distribution, etc., is set up correctly, a nose up attitude is more a case of the outfit "looking wrong" rather than such a condition actually having an adverse effect on stability.
The only real problem likely to be encountered with a nose up attitude is the loss of ground clearance at the back end of the caravan, which could be an issue when negotiating speed bumps, for example.

 

[Guest]

Thats the point,the CofG is above floor level because of all the weight above floor level, ie' the roof and walls, fixtures and fittings and anything in those fixtures.
Maybe then 'vertical balance' is not the the best expression, nevertheless, all this weight is not directly, at least proportionally related to the nose weight, so the CofG's distance in front of axle is not corrected by simply adding more noseweight. As I said a caravan is not a simple see-saw,