load levelling/distribution on caravans and trailers

[warra]

Has anyone developed a mathematical explanation for the effects of a load levelling/distribution device on a car trailer/caravan.

Vehicles without the device tend to sit lower in the rear suspension and the front steering is lighter as a result. The drawbar of the trailer/caravan also dips downwards.

After the distribution device is added the combination of car and trailer sits flatter with the load over the rear axle of the to vehicle reduced and increased over the tow vehicles front axle (improves steering feel). The load on the trailer/caravan axle is also increased.

The overall affects of the device is to produce a more stable combination between tow vehicle and trailer.

I would appreciate looking into the maths of the loadings on the axles before and after the fitment of the device.

Warra

 

[GregLocock]

Yes they have. The SAE has recently introduced a standard for testing trailers on light trucks and passenger vehicles, which incorporates consideration of the load levelling devices. I don't know of any non-proprietary discussion of this, your google-fu is as good as mine. I would have thought a single axle trailer on a two axle vehicle was a pretty easy case to work out by hand.

Cheers

Greg Locock


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[warra]

Thanks Greg,
Do you have a SAE publication number.

What seems a little tricky in the maths is that the tow ball is the pivot point (or hinge) between both vehicles. A turning moment between the vehicles is generated by the load distributor or torsion bar(s) which then inputs to the towbar to lift the load off the back wheels and onto the front of the tow vehicle. The apparent reduction in weight over the rear of the tow vehicle is also transferred to the trailer axle as well. Am I to assume that the increase in weight over the trailer axle and the front tow vehicle's axle is equal to the reduction over the rear of the tow vehicle?

I am just seeking the maths to explain the various moments involved.

Warra

 

[GregLocock]

Yes, the total of the axle weights remains constant. You'll need to invoke compatibility, that is, you need to know the spring rate of each axle on the car and the wheelbase.

The standard is SAE J2807, I think. see also

https://www.sae.org/works/documentHome.do?comtID=TERTH

Cheers

Greg Locock


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