DRIVEN RIGID REAR STEER
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The most dramatic demonstration we saw was of Tridec's new WST system. This allows the rear axle of a tandem-drive bogie on a rigid chassis to be hydraulically steered, improving manoeuvrability and reducing tyre scrub. Our first attempt to drive through a forward slalom obstacle of cones on a skid pan in a three-axle (6x6) tipper predictably failed due to understeer, sending the truck sliding straight ahead. With the WST rear steer engaged, the truck sailed through, taking each bend smoothly and safely. Off-road mobility is not compromised and overall payload distribution improved, Three Scanias fitted with the device have recently been commissioned by the Dutch fire service, and it may be relevant to larger UK appliances.
The concept was designed to meet a unique Dutch Construction and Use law, which allows rigids at 32-tonnes GVW on three axles as long as the rear bogie wheelbase is greater than 1.8m.
Although not directly applicable to the UK, the concept could prove useful in specialist markets; for example 8x4 tippers delivering aggregate to confined sites, grab loaders used by utility companies in urban settings or vehicles delivering to farms or off-road construction sites.