TRACTION DETERMINATION BY CHANGING WHEEL NORMAL FORCE

A control system () for controlling an active suspension system () of a vehicle () to determine relative traction levels, the control system comprising one or more controller (), wherein the control system is configured to (): control the active suspension system to change normal force through a first subset of one or more wheels; determine a traction-dependent variable at each of the first subset of wheels to which known torque is applied; control the active suspension system to change normal force through a second subset of one or more wheels; and determine a traction-dependent variable at each of the second subset of wheels to which known torque is applied, wherein the traction-dependent variables indicate relative traction levels.