Comparing the steering performances of skid- and Ackermann-steered vehicles

Skid steering has advantages for military armoured vehicles because it gives greater internal hull volume and improved manoeuvrability. The steering performance of an 18 t 6 x 6 skid-steered vehicle is analysed and compared with that of a similar Ackermann-steered vehicle. The basic properties of the double-differential mechanism used for steering most modern skid-steered vehicles are analysed. A tyre model is used that enables the force characteristics at combined slip to be established from the relatively small amount of pure slip data that are available for truck-sized tyres. A spreadsheet analysis is used for solving the equations of motion. This shows that the skid-steered vehicle is generally neutral to oversteer whereas the Ackermann-steered vehicle is understeer. The skid-steered vehicle is also shown to require more power when cornering because of the power required by the steering mechanism. This will increase the fuel consumption and reduce the range of the skid-steered vehicle.