On the return from Birdsville last year, we came across a new Roadstar "offroad" van, driven by a novice on his first outback experience. The Roadstar uses a 3-tonne Simplicity suspension.
This guy had blown the right hand front tyre on the van (no one told him about dropping tyre pressure). He hadn't noticed it, shredded the tyre, then ground the rim down to the brake drum. With the brake drum hanging near to the road, it was only a matter of time before it dug in. When this happened it sheared the stub axle & stuffed the suspension. The inside of the van was extensibly damaged due to the rough ride.
He hadn't noticed anything wrong with the way the van was travelling. How he didn't notice the excessive dust cloud, I don't know.
Need to be careful
Just another comment that I read on the internet:
"Simplicity have one major problem with the tandem unit in as much as the front wheels are on a Leading Arm (Rear are Trailing Arm). This puts massive loads on all components, especially bushes. A leading arm cannot rise unless it first moves forward. In other words it moves against the direction of travel of the trailer."
This is another interesting comment. If you picture the leading wheel going into a pothole and hitting the far edge of the hole, it is prevented from swinging upwards in a forward arc and therefore would have to transmit the full shock loading directly back into the suspension mount and the van frame. While it's never a good idea to rubbish your competitors, you could give this as another reason why Phoenix eliminated this type in favour of Al-Ko's trailing arms.
Add it to the armoury!
It hadn't occurred to me that the Simplicity system, while effective in transferring weight from wheel to wheel when travelling over undulating surfaces, is potentially very destructive in the event of a flat tyre.
With progressively less load being carried by the deflating tyre, the other wheel keeps trying to transfer load to the damaged wheel, driving it harder and harder into the road surface, destroying firstly the tyre, then the wheel, the hub, brakes, suspension and possibly the van.
In the dust and noise of dirt roads, this would be easy to miss. I've always felt that the load-sharing systems that transfer weight back and forth between adjacent wheels, while fine in theory and easily
demonstrated at very low speeds, simply wouldn't function at road speeds where a bump strikes the two wheels a mere millisecond apart, leaving no chance of transferring the impact from wheel to wheel.
Al-KO's axles, while not doing the same job at low speeds (where it doesn't really matter, so long as each axle is up to the job of briefly carrying all the weight), doesn't have the same potential for
disaster. I'm pretty happy to have a much-less-complex and virtually maintenance-free system that confines any damage to an easily-replaced tyre.