How to Use a Lightweight Powerplant to Increase Payload

The advent of turbine power for commercial vehicles raises the question of how best to convert the promised weight saving into an equivalent increase in payload. The practical importance of the method adopted to maintain maximum axle load limits, in the case of truck tractors, lies in the profound effects on ride of the wide changes possible in the dynamic index.

This paper reviews the basic principles of weight distribution effects on vehicle ride to bring out the quantitative significance of the dynamic index. This criterion is then applied to the prediction of the consequences to riding quality of any combination of fifth-wheel offset and wheelbase, at constant axle loads. General equations are derived and their use is illustrated for the case of a typical tractor, with assumed powerplant weight reductions up to 2000 lb.

The principal conclusions are:

1. 1.
   Axle loads should be maintained by using the shortest possible wheelbase combined with slight increases in fifth-wheel offset.
2. 2.
   Powerplant location should be as far forward as possible, preferably ahead of front axle.
3. 3.
   In general, the design objective in adapting a lighter powerplant should be to attain the highest possible dynamic index within practical limits.