Nose weight

[CaptainKangaroo]

If for example your car has a noseweight of 75kg which is the mean, and you van excerts this force when stationary, what is the force from the van when on the move as the van is a dynamic load? Will it be much greater than 75kg?

 

[Lutz]

How the noseload changes dynamically depends on speed and road conditions. At speed, the noseload will decrease due to the air pressure acting on the projected frontal area of the caravan. Under adverse conditions, it could even turn into a negative value, which can cause severe instability problems.

Of course, if the road is bad and potholed, or during braking and accelerating there will be additional loads acting on the towball due to pitching. I would estimate that the peak load when driving over speed bumps, for example, would easily be in the order of 4 to 5 times the static noseload.

To cover worst case conditions, towbars tested for type approval according to Directive 94/20/EC have to meet dynamic requirements which are even more stringent. The directive specifies a dynamic force acting at an angle of 15

 

[CaptainKangaroo]

Thanks Lutz for your comprehensive reply.

As the loading is 4 to 5 times greater due to the van being a dynamic load, why do car manufacturers state such a low noseweight? Surely if you were 10 or even 20kg over the noseweight it wouldn't make much difference? and therfore the manufacturers noseweight is really only an advised weight as the car can take much much more?

 

[ProfJohnL]

The designers will establish the static download force to keep the tow hitch within the legally require hight above the floor.

Increasing the imposed force above that limit Will depress the toe hitch further than is permitted, and prosecution could follow.

 

[Lutz]

John L is right but equally important is the structural integrity of the vehicle underbody. Constant shaking up and down at the towball can cause fatigue failure of the body attachment points over the lifetime of the vehicle so the car manufacturer must undertake measures to limit the stresses imposed.