Effect of Cornering Loads on Vertical Loading

The figure below shows lateral weight transfer measurements with (red) and without (green) the introduction of tire cornering forces. The green traces could be obtained from a pull-down rig (or even a 7-poster), but for a given chassis roll angle, the measurements do not reflect what’s really happening. The red traces, measured on the Morse Measurements K&C rig and including proper tire cornering forces, tell a very different story:

As shown above, front and rear lateral weight transfer is not measured correctly unless lateral tire loads are applied. It is particularly noticeable in the rear of this vehicle, where over 300 lb of additional weight transfer comes from suspension jacking forces. Since total lateral weight transfer is dictated only by the cornering G’s and C.G. height, what we are seeing here is an effective change in roll stiffness when jacking loads are taken into account. The rear suspension is also shown to have significantly more load variation due to friction when properly loaded to simulate cornering. Only a properly set up K&C test will get after this kind of information.

Jacking force influence on weight transfer becomes even more pronounced when suspension rates become non-linear (due to bump-stop or coil-bind situations) and when a vehicle is subjected to large aerodynamic down-force loads. And although this example only shows the lateral weight transfer characteristics, jacking will similarly influence longitudinal weight transfer during both throttle-on and braking.