FAR from presenting a more difficult problem than other types, the six-wheeler can be made to give better braking performance than any, these authors contend. They are less likely to skid than either four-wheeled straight trucks or tractor-semi-trailers, they continue, and in general stopping ability they rate high. However, they acknowledge the complaints against the six-wheeler for behavior known as “bogie hopping” and loss of steering control when brakes are applied on slippery roads.
Comparing the three principal types of commercial vehicles, they conclude that the complaints on this score are based if at all upon something other than dynamic weight transfer.
“The reason why the problem is so acute with six-wheelers is that the supposedly rigid alignment of the rear bogie wheels constitutes a resistance to steering and that, therefore, any tendency for the front wheels to lose traction is of graver concern than with either a four-wheel truck or a tractor-semi-trailer.” Calling this the crux of the six-wheel steering problem so far as brakes are concerned, they declare: “for six-wheelers, therefore, a relay valve to speed up the application of the rear brakes and a quick-release valve for the fronts seem essential,” while a brake distribution quite different from that of the four-wheeler is required.
“Bogie hopping,” they say, “as in the case of steering ability, is affected by weight transfer,” and, according to the authors, it is not an inherent fault of six-wheelers, but “merely a manifestation of faulty design which can be completely overcome by employing a bogie which is torsionally balanced.”
