I am looking for some advice about calculating Tow ball and tow vehicle weights. Is it reasonable to add only the weight of the spring lifters that are clamped to the A Frame into the tow ball weight, and all other components weight to be added to the tow car (and back axle) weights?
The simple answer is all the parts of the weight distribution hitch are weighed with the tow vehicle, except for the 2 snap up brackets that are attached to the caravan.
-- Edited by Gundog on Thursday 9th of November 2023 10:03:39 AM
I am looking for some advice about calculating Tow ball and tow vehicle weights. Is it reasonable to add only the weight of the spring lifters that are clamped to the A frame into the tow ball weight, and all other components weight to be added to the tow car (and back axle) weights?
Yes. However, weights are a complicated issue, understood by very few, and the much-adored WDH is NOT the cure-it-all that many believe it to be. A WDH can cause more problems than it "cures", and in many cases one is not needed.
More often than not it is used in an effort to make a car do things for which it never was designed, when really what is needed is a better car. Car manufacturers sometimes recommend using a WDH simply because they know that their vehicle's rear axle's carrying capacity is too low.
Consider the enormous added stresses placed on all parts of your car, van and towbar structures by a WDH.
What car do you have, and what is your van's ATM? Happy to do all your figures for you.
You may be aware that if safety is of any concern, always the weight on the wheels of the car should be at least 10% greater than the weight on the wheels of the van. Simple physics to minimise the chances of the "Tail wagging the Dog".
You seem to be taking your weights seriously, which is commendable, but matching your tow vehicle to your van is far more important than trying to make your car do things for which it never was designed. Good luck! Cheers
P.S You do understand that any weight applied to a car's rear axle is around 1.45-1.5 times the towball weight, so a 300kg towball weight adds around 435-450kg to the car's rear axle. This varies with wheelbase and towball overhang etc.
-- Edited by yobarr on Thursday 9th of November 2023 12:22:34 PM
Last para above:
Hence the advantage of a WDH to transfer downforce to the front wheels to alleviate the excess downforce on the rear and prevent skywalking under braking of front wheels.
Last para above: Hence the advantage of a WDH to transfer downforce to the front wheels to alleviate the excess downforce on the rear and prevent skywalking under braking of front wheels.
???????? If your car is so poorly balanced that 150kg less weight on the front axle is calamitous, then you may need to seek lessons in set up. Is a car undriveable without a Bullbar? Cheers.
-- Edited by yobarr on Friday 10th of November 2023 04:11:30 PM
yobarr wrote:If your car is so poorly balanced that 150kg less weight on the front axle is calamitous, then you may need to seek lessons in set up.
Yobarr, that statement of yours explains a lot about why you seem to never appreciate the value of a WDH. While that 150kg is certainly an improvement in the front/rear balance, it is only a starting point to what happens on the highway.
As I have said on here before, the beauty of a WDH is how it dynamically increases the tension when it is needed more, and reduces the tension when it is needed less. As you would know, highway travel is constantly causing the vehicle springs to compress and decompress. The vehicle rises and falls. The van does the same, but as it is behind the tow vehicle that rising and falling occurs maybe half a second later. So they are out of synch. That is what can cause oscillation or porpoising. First the car lifts up, which lifts the drawbar, then the van wheels are lifted, but by now, the car is on the way down.
So while the car is rising, the WDH tension is reducing and there is less of that 150kg on the front wheels. Once the van is rising and the car falling, the angle of the drawbar to the car chassis increases, which automtically adds tension to the WDH. So it is no longer just 150kg on the front wheels, but substantially more. This suppresses the bounce.
In the past, you have referred to the WDH as a stiff board. A pretty good analogy. But the more the front of the car wants to rise, the stiffer the "board" gets. And vice versa. The drawbar only needs to be raised a few inches to completely detension the WDH. In reverse, pushing down on the drawbar radically increases the tension.
So, 150kg is just the starting point. On the highway it constantly changes from much more to much less.
Just as importantly, when braking, the caravan tilts forwards. That tilting puts a lot more load on the tow vehicle rear end, which in turn lifts the front wheels a bit. Result: lack of traction on the front wheels. Again, the dynamic nature of the WDH puts a lot more on those front wheels .... just when you need it.
yobarr wrote:If your car is so poorly balanced that 150kg less weight on the front axle is calamitous, then you may need to seek lessons in set up.
Yobarr, that statement of yours explains a lot about why you seem to never appreciate the value of a WDH. While that 150kg is certainly an improvement in the front/rear balance, it is only a starting point to what happens on the highway.
As I have said on here before, the beauty of a WDH is how it dynamically increases the tension when it is needed more, and reduces the tension when it is needed less. As you would know, highway travel is constantly causing the vehicle springs to compress and decompress. The vehicle rises and falls. The van does the same, but as it is behind the tow vehicle that rising and falling occurs maybe half a second later. So they are out of synch. That is what can cause oscillation or porpoising. First the car lifts up, which lifts the drawbar, then the van wheels are lifted, but by now, the car is on the way down.
So while the car is rising, the WDH tension is reducing and there is less of that 150kg on the front wheels. Once the van is rising and the car falling, the angle of the drawbar to the car chassis increases, which automtically adds tension to the WDH. So it is no longer just 150kg on the front wheels, but substantially more. This suppresses the bounce.
In the past, you have referred to the WDH as a stiff board. A pretty good analogy. But the more the front of the car wants to rise, the stiffer the "board" gets. And vice versa. The drawbar only needs to be raised a few inches to completely detension the WDH. In reverse, pushing down on the drawbar radically increases the tension.
So, 150kg is just the starting point. On the highway it constantly changes from much more to much less.
Just as importantly, when braking, the caravan tilts forwards. That tilting puts a lot more load on the tow vehicle rear end, which in turn lifts the front wheels a bit. Result: lack of traction on the front wheels. Again, the dynamic nature of the WDH puts a lot more on those front wheels .... just when you need it.
Hi Steve, That is a good, comprehensive and mostly accurate explanation of the workings of a WDH, but again I will iterate that a WDH is used ONLY by people who are trying to make a car do things for which it never was designed.
When I bought my van I was convinced that "You MUST use a WDH with a van that size", so I forked out $600. Bad move.
While setting up my car and van I did many tests, with and without a WDH, tensioned and untensioned, and quickly established that it was a con-job.
First up, the WDH weighs 30-33kg so immediately it is fitted you've ADDED around 50kg to the car's rear axle, plus you"ve increased TBO (towball overhang, or distance from rear axle to hitch point), which immediately further multiplies the weight added to the car's rear axle when a van is connected.
PLUS you've increased the chances of Yaw, or the "Tail Wagging the Dog", which is a major cause of caravans going RSup.
There is much more that I could add to assist newbies and those willing to learn, but enough for now.
A WDH is NOT the Universal cure-it-all that many believe it to be, and in many cases a WDH causes more troubles than it "cures".
Eventually I gave mine to a person that I dislike. Good riddance.
Get a BIGGER CAR or a LIGHTER VAN. Cheers
P.S How to waste Thousands of Dollars to gain VERY little if you wish to tow safely.
-- Edited by yobarr on Friday 10th of November 2023 09:01:58 PM
