I know it's not documented/unsupported atm, but just tryin out from the Vehicle class:
Found these, but crashed on my first try (if anyone figures it out let me know) :
//Tires
virtual int AddTire(float x, float y, float z, float mass, float radius, float width, bool steering, float suspensionDamper = 200.0, float suspensionSpring = 2000.0, float suspensionLength = 1.2, float lateralStiffness = 20.0, float longitudinalStiffness = 100000.0, float aligningMOmentTrail = 1.5) = 0;//lua
virtual void AddAxle(int lefttire, int righttire) = 0;//lua
//Optional settings
virtual void SetGearRatio(std::vector<float> forwardGearRatio, float reverseGearRatio) = 0;//lua
virtual void SetTorqueCurve(float topSpeedKPH, float idleTorquePoundPerFoot, float idleRPM, float peakTorquePoundPerFoot, float peakTorqueRPM, float peakHorsePower, float peakHorsePowerRPM, float redLineTorquePoundPerFoot, float redLineRPM) = 0;//lua
//Build
virtual bool Build() = 0;//lua
//Control
virtual void SetAcceleration(float engineGasPedal) = 0;//lua
virtual void SetSteering(float steering) = 0;//lua
virtual void SetBrakes(float brakes) = 0;//lua
virtual void SetHandBrakes(float brakes) = 0;//lua
virtual void SetGear(int gear) = 0;//lua
virtual void SetTransmissionMode(bool automatic) = 0;//lua
virtual void SetEngineRunning(const bool running) = 0;//lua
//Information
virtual Mat4 GetTireMatrix(int tireindex)=0;//lua
virtual int GetGear() = 0;//lua
virtual float GetRPM() = 0;//lua
virtual float GetSpeed() = 0;//lua
virtual int CountTires()=0;//lua
virtual float GetTireLateralForce(const int index)=0;//lua
virtual bool GetEngineRunning()=0;//lua
virtual float GetTireSlip(const int index) = 0;//lua
static Vehicle* Create(Entity* entity);//lua