Tow ball height on witter bar / Sorento car ?

[Mike_5041040]

Hi,

I,ve just had a witter tow bar fitted to my Sorento and was wondering which of the two available height settings for the tow ball was recomended / advised by forum users.

Thanks,

Mike.

 

[Lutz]

The centre of the towball should be between 350 and 420mm above the ground when the car is standing on level ground and fully laden (with or without the caravan hitched up, it doesn't matter, although, of course, it is easier to measure without it being hitched up but then you've got to simulate the noseweight).

 

[Saladdodger]

The centre of the towball should be between 350 and 420mm above the ground when the car is standing on level ground and fully laden (with or without the caravan hitched up, it doesn't matter, although, of course, it is easier to measure without it being hitched up but then you've got to simulate the noseweight).

Hi Lutz

I didn't think the 350 - 420mm height of towball was applicable to 4x4s.

 

[Lutz]

The centre of the towball should be between 350 and 420mm above the ground when the car is standing on level ground and fully laden (with or without the caravan hitched up, it doesn't matter, although, of course, it is easier to measure without it being hitched up but then you've got to simulate the noseweight).

In order to cater for off-road use it's not a legal requirement for 4x4's but it's still advisable to stay inside those limits if you want to tow a caravan because caravans are designed to be used with the towball at that height.

 

[RichardS1]

Hi Mike, we have the Witter towbar on our Sorento with the towball fitted to the lowest setting. Caravan then sits very slightly nosedown when hitched to the back of the car.

 

[Lol1]

I didn't have a witter tow bar, but had the choice of two heights anyway. Towing a twin axle, the lower hight was too low, a single axle won't be effected so much by ball hight. If you have a twin, it might be best to look at both heights, you want a level or slightly nose down attitude to the caravan.

 

[Lutz]

Actually, a slightly nose up attitude of the caravan is not, in itself, necessarily a potential cause of an unstable outfit. It is first and foremost too low a noseweight which is really to blame although a nose up attitude may mislead one to think that this is the case. However, if the noseweight is right at the height at which the caravan is hitched to the car then the outfit should still be stable even if slightly nose up (subject to everything else being set up properly, too).

The only real basic disadvantage of a nose up attitude is the loss of ground clearance at the rear end of the caravan.

 

[Lol1]

I'm surprised Lutz, it's not like you to give advice like that. Try googling the subject, I was always taught, never tow with the caravan nose pointing up.

http://www.exploroz.com/Vehicle/Caravans/ChoosingandSettingUpaTowVehicle.asp

 

[Lutz]

I know a lot of sources state that the caravan should not point nose up but none of them say why. I reckon the recommendation was based on the assumption that if the caravan was nose up then the noseweight cannot be correct and this concept has snowballed into general acceptance to a stage where nobody questions it any more. I still maintain that the only reason that stands up to scrutiny is the loss of ground clearance at the back of the caravan but maybe some vehicle dynamics engineer will convince me otherwise.

 

[vauxhall2]

hi.if the caravan is towed nose up this will give a sail effect on the floor of the van giving lift and make the noseweight far too light.the caravan should be level or slightly nose down.

 

[WatsonJohnG]

Hi Michael and Merry Xmas

I would have thought that if the nose on the van was higher the the volume of air "scooped" under the van would be compressed more as it got to the lower section at the rear and thus cause more lift at the rear and increase nose weight.

To us purists it don't look right to have the van tail down.

I had damage to the rear steady pads when coming off a ferry with a level/nose down outfit so it could be a problem with the tendency for longer vans these days.

 

[Lutz]

The 'sail' effect that Michael is referring to is too small to make any difference. The real reason for noseweight to decrease with increasing speed is the air drag on the projected frontal area of the caravan. As the centre of the frontal area is considerably higher than the axle, this causes a moment about the axle tending to lift the front end up.

 

[gary]

Merry Christmas all

I would not tow nose up from experience of trying regardless of any other evidence.

I have always thought Watson's explanation was the reason why but wind tunnel tests appear to prove Micheal's to be correct.

Whichever way round it is,IMO it cannot be sensible to allow more space at the front for air to enter than spaces allows beyond to exit.

To my mind your creating a windsock!!

 

[Lutz]

The towcar in front is going to break most of the airflow under the caravan but the frontal area of the caravan which projects beyond the roof of the car is still substantial and provides massive wind resistance which causes the front end to lift, far more than any airflow effect under the caravan.

I'm not advocating a nose up attitude, I'm just saying that I'm not aware of any documentary evidence that stands up to scrutiny that it alone causes instability.

 

[WatsonJohnG]

Understand your point Lutz(compliments sof the season)

There was wind deflector on sale about 5 years ago that looked like a Formula 1 aerofoil and bolted onto the towbar.

This was supposed (and probably did) deflect air over the caravan and reduce the frontal wind pressure thus reducing lightening of nose weight etc.

After reading the data I stopped using a Windslammer !!

 

[clivea]

Hi,

I have a Brinkmatic towbar fitted to an 04 Sorento. The van sits level when the car is fully loaded but with the Sorento's self levelling suspenion (by SACHS) taking about a mile to pump it back to level the van sits slightly nose up when running. The total van length is 7.02m and I hav enever had any problems grounding the back on roads, fileds or ferries. The outfit is very stable and I run at the van's maximum noseweight which is 100kg with most of the van's load then stowed over the axle area or towards the front of the axle. It takes us longer to then re-stow it once we are on site but I guess that's my hangup from having lighter cars nearer the 85% ratio. The current Sorento :van ratio is about 63%.