1.  Field of the Invention
The present invention relates to a tire rubber composition, more specifically, to a tire tread rubber composition capable of providing a tire tread having a good balance between the rolling resistance and the coefficient of sliding friction on wet road surfaces. 
2.  Description of the Prior Art
With the current worldwide concern for saving resources and energy, car manufacturers are making intensive efforts to achieve better mileage economy.  To meet this end, it is essential that tire manufacturers find effective ways to minimize energy loss resulting from the motion of tires. 
Two principal functions of tires are to support the weight of the automobile and to transmit the driving force of the wheels.  As is well known, the energy loss resulting from the friction between a tire and the road surface or from the heat generated by the tire itself, has an appreciable effect on the fuel consumption of a car.  However, the energy loss attributable to the tire itself, i.e., its rolling resistance, cannot be reduced without also decreasing the coefficient (.mu.w) of its sliding friction against a wet road surface.  In other words, a tire with a small rolling resistance has a great tendency to cause skidding.  It is therefore very important for tire manufacturers to obtain a good balance between the rolling resistance of the tire and its coefficient of sliding friction on a wet road surface.  A need therefore continues to exist for a tire which exhibits a good balance between its rolling resistance and the property of the tire to skid on wet road surfaces all the while exhibiting minimum energy loss.