Tuesday, Mar 25, 2008 at 10:17
I must say that I'm surprised at some of the first replies. I thought that WDHs had long ago moved from the realm of "debate" and were accepted as sound and sensible safety engineering.
When we first looked at vans about five years ago, we were told at the BT stand at the Sydney show that BTs "didn't need" WDHs. Just inside the pavilion next to BT, Hayman Reece had a 4WD hitched to a tandem axle van with all eight wheels sitting on scales. The demonstration left no doubt that the addition of the WDH evened out the weight on all wheels, which was clearly out of whack without the WDH. To the eye, everything looked OK but the scales told a different story.
Over the next couple of years I monitored the forums while choosing our van and listened to some pretty qualified people stating the case for WDHs. I'm not an engineer, but it's pretty easy to summarise the advice from the experts.
Firstly, that changes to the tow vehicle's rear suspension do not change the effect that towball load will have on the front wheels. It's a simple and logical concept: the rear axle is a fulcrum upon which the tow vehicle pivots like a seesaw. If you add weight to one end (the towball) the other end must rise. It doesn't matter what suspension you use. In fact you could beef it up to solid steel blocks - the front end must still lose weight if you add weight to the towball. The removal of weight from the front wheels will be exacerbated by undulating road surfaces, reducing the load on the front and therefore the grip on the road, braking effectiveness and wheel camber angles.
This doesn't mean that suspension changes are not a good idea, but for a different reason. Our 100series TD has had its suspension modified. But the modifications were determined by the overall load to be carried by the truck, not just the ball load of our 3 tonne van.
Another way of looking at it is to think of the WDH bars as wheelbarrow handles. Lift them up and the weight is sent to the front wheels.
An acknowledged authority on many caravan and motorhome issues, Collyn Rivers, was one of the major exponents of WDHs on this and other forums. I recall once that, when finding himself preaching to a brick wall, he asked just how much loss of front-end control the non-believer was prepared to accept. The answer, of course, should be none.
I started this thread when I saw the unchallenged statement on the other BT
forum. We had just had the experience of arriving on the scene moments after a caravan went out of control and overturned on the road out of Busselton in WA. The driver was pretty shaken, couldn't remember what had prompted the incident and claimed that everything had always been OK. The van went into its death throes, sending the rig across three lanes and leaving it facing the opposite direction, on its side and with the tug suspended in the air on the hitch. The van was a tandem axle and the driver thought it was correctly loaded and had been travelling perfectly. It didn't have a WDH. It was a reasonably busy 110km stretch and it takes little imagination to see how this ordinary incident could have created headlines but for a fluke of timing.
I see that within a few hours of starting this post, it appeared to prompt a response on the other
forum by somebody who suggested the WDH unbeliever might be being a bit cavalier. Disappointingly, there is still no response from BT.
Michael
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