A vehicle drive speed control system is provided for a vehicle having driven rear wheels, driven steerable front wheels, a powertrain for driving the front and rear wheels at controllable speeds. A control unit controls the powertain so that a front/rear wheel speed ratio is a non-linear trigonometric function of a sensed steering angle signal. The front/rear wheel speed ratio increases as the steering angle increases. The relationship of the front/rear wheel speed ratio to the steering angle is represented by a curve which is concave in a direction of an axis of increasing speed ratio. With a mode select switch, an operator can selectively cause the control unit to control the front/rear speed ratio according to a first normal or a second more aggressive predefined relationship.