m_wheel2.createFixture(fd);
WheelJointDef jd = new WheelJointDef();
Vec2 axis = new Vec2(0.0f, 1.0f);
jd.initialize(m_car, m_wheel1, m_wheel1.getPosition(), axis);
jd.motorSpeed = 0.0f;
jd.maxMotorTorque = 20.0f;
jd.enableMotor = true;
jd.frequencyHz = m_hz;
jd.dampingRatio = m_zeta;