twin axle and noseweight

[Paul_5099000]

hi all

i drag a compass rallye 640 (1900Kgs)

ive been looking looking at the newer type of noseweight gauge, the one that fits onto the tow ball of the tug and the van hitches onto the gauge....

looking at the gauage it would seam that when hitched up,,,the hitch would be about 2 inchs higher than it is when hitched straight onto the towball (IE without the gauge)

my question....if the hitch height is so important, how can these gauges be any good if they raise the hitch when measureing ?

does this make sence ?

many thanks

 

[602]

Hi Paul,

I don't know if it makes sense, but it raises an interesting question. The rules require that everything is weighed when both car and trailer are standing on level grouns. That seems fair.

But suppose immediately before you hitch up, the trailer hitch is just 1mm higher than the towball. This will give you NEGATIVE nose weight, and the hitch will probably lift the back of the car. You will get the oppposite effect if the hitch is lower than the ball.

Does this matter? I reckon it does. Lets assume you are ready to roll off on your holidays, having correctly established the nose weight. Then you, your wife, granny and two kids climb into the car. I'm guessing that the car will settle on its springs. On your way out of town, you pull into Tescos, buy enough food to feed an army for a week, and add 10 gallons to your fuel tank. So much for your careful balancing act.

With a two wheel trailer, loading the car will increase the noseweight, as the trailer leans forwards, taking the CofG shifts forward with it. Probably doesn't mater much with a caravan ..... but try it with an old-fashioned steel skinned, single axle horsebox. I had one once (1974ish). If the hitch was on the ground, I couldn't lift it ..... but weightless when everything was level.

602

 

[ProfJohnL]

Hello Paul,

The fact that the nose weight of a trailer changes depending on the height of the hitch above the ground, means that any difference between the coupled height and the measured height will make the height a critical component in the process.

The degree of inaccuracy depends of a number of factors which cannot be easily guessed, so as the nose weight has a legal implication it is only right to take the measurement carefully and correctly.

For a number of technical reasons, the effect of hitch height on a twin axle trailer is much more acute, so small changes in height can make a big difference in the actual value.

602's response demonstrates how sensitive a TA can be for just a small difference in height.

The type of gauge you mention raised the hitch height and thus will give an inaccurate reading, and I recommend it is not used.

A better solution is to use a set of bathroom scales with a broom stale with a foot to spread the load, and cut to length to match the actual hitch height you have when coupled up.

 

[602]

Hi,

I once towed my boat - four wheeled trailer, with front axle about 15ft behind the towball. Trailer plus boat weighed about 2500kg. Tow car was my 1957 Land Rover (1400kg on weighbridge)

As I approached one particular roundabout, I had to drive across a series of lines painted across the road.

As the trailer wheels crossed the lines, the back of my Land Rover was being shaken up and down .... most unpleasant.

602

 

[602]

Hi,

In the unlikely event that anybody wants to see a pic of my Landy and boat, you MIGHT find it on .....



602

 

[Paul_5099000]

as it seams these gauages, because of theuir design, give a wrong reading, how come they are even made ? they are clearly not fit for the purpose of reading a correct measurement. They seam flawed by design.

I wonder how such a thing even gets made, never mind actually being purchased and used.

 

[ProfJohnL]

I don't know the exact answer, but I suspect that whoever came up with the idea didn't understand the importance of hitch height and load and how it changes due to the relative position of the Centre of gravity about the main axle.

Similar comments can be levelled against all the gauges I have seen, where there is no adjustment for hitch height!

 

[Phillipcharnwoodforest]

I like the series one 602, very nice.