Passenger tire having low rolling resistance with improved wet traction and treadwear

Abstract

A tire having a tread includes an outer tread layer and an inner tread layer. The inner tread layer includes one of a first elastomeric compound and a second elastomeric compound. The outer tread layer includes the other of the first and second elastomeric compounds. The second elastomeric compound has a lower rolling resistance and greater resistance to treadwear than the first elastomeric compound. The inner tread layer increases in thickness across at least a widthwise portion of the outer tread layer with a maximum thickness of one of the inner tread layer and the outer tread layer occurring near at least one of a first shoulder and a second shoulder of the tread. As the tread wears, the inner tread layer defines a greater proportion of a running surface of the tread.

What is claimed is: 
     
         1 . A pneumatic tire comprising:
 an outer circumferential tread having an outer tread layer in direct and continuous contact with an inner tread layer, the outer and inner tread layers together defining the tread thickness, the inner tread layer comprising a first elastomeric compound or a second elastomeric compound and the outer tread layer comprising the other of the first elastomeric compound or the second elastomeric compound, the second elastomeric compound having lower rolling resistance and greater resistance to treadwear than the first elastomeric compound, the inner tread layer increases in thickness across at least a widthwise portion of the tread with a maximum thickness of one of the inner tread layer and the outer tread layer occurring near at least one of a first shoulder and a second shoulder of the tread, whereby as the tread wears, the inner tread layer defines a greater proportion of a running surface of the tread.   
     
     
         2 . The tire of  claim 1  wherein a maximum thickness of the inner tread layer is approximately equal to the tread thickness. 
     
     
         3 . The tire of  claim 1  wherein a maximum thickness of the inner tread layer is located near the first shoulder. 
     
     
         4 . The tire of  claim 1  wherein a maximum thickness of the outer tread layer is located near the first shoulder. 
     
     
         5 . The tire of  claim 1  wherein the maximum thickness of the outer tread layer is near the first shoulder and a minimum thickness of the outer tread layer is near the centerline of the tread. 
     
     
         6 . The tire of  claim 1  wherein the outer tread layer continuously increases in thickness from a minimum thickness to the maximum thickness between the first and second shoulder, respectively. 
     
     
         7 . The tire of  claim 1  wherein the variation in the thickness of the outer tread layer from the maximum thickness to a minimum thickness is approximately linear. 
     
     
         8 . The tire of  claim 1  wherein the outer tread layer continuously increases in thickness from near a central region of the tread to near the first shoulder. 
     
     
         9 . The tire of  claim 1  wherein the outer tread layer continuously increases in thickness from near a central region of the tread to near the first and second shoulder. 
     
     
         10 . The tire of  claim 1  wherein the first elastomeric compound has a greater peak in tan δ at a higher temperature than the temperature at which tan δ peaks in the second elastomeric compound. 
     
     
         11 . The tire of  claim 1  wherein the first elastomeric compound has a greater wet traction than the second elastomeric compound. 
     
     
         12 . The tire of  claim 1  wherein the first elastomeric compound contains a greater portion of silica than the second elastomeric compound. 
     
     
         13 . The tire of  claim 1  wherein the tread comprises a tread pattern including tire grooves that extend through the outer tread layer and into the inner tread layer, and wherein the tread is configured to wear such that the rate of exposure of the inner tread layer substantially compensates for a reduction in the volume of the tire grooves. 
     
     
         14 . The tire of  claim 13  wherein the inner tread is exposed in the tire grooves. 
     
     
         15 . A pneumatic tire comprising:
 an outer circumferential tread having an outer tread layer in direct and continuous contact with an inner tread layer, the outer and inner tread layers together defining the tread thickness, and a tread pattern having tire grooves extending through the outer tread layer and into the inner tread layer to define valleys, the valleys of the tire grooves being devoid of the outer tread layer,
 the inner tread layer having a maximum thickness near a central region of the tread and comprising a first elastomeric compound; and 
 the outer tread layer comprising a second elastomeric compound having lower rolling resistance and greater resistance to treadwear than the first elastomeric compound, the outer tread layer increasing in thickness across at least a widthwise portion of the outer tread layer from near the central region of the tread to a maximum thickness near at least one of a first shoulder and a second shoulder of the tread to provide longer lasting wear resistance for the tire at the at least one shoulder, whereby as the tread wears, the inner tread layer defines a greater proportion of a running surface of the tread. 
   
     
     
         16 . The tire of  claim 15  wherein the tread is configured to wear such that the rate of exposure of the inner tread layer substantially compensates for a reduction in the volume of the tread pattern. 
     
     
         17 . The tire of  claim 15  wherein the variation in the thickness of the outer tread layer from a minimum thickness near the central region of the tread to the maximum thickness is approximately linear. 
     
     
         18 . The tire of  claim 15  wherein the first elastomeric compound has a greater glass transition temperature than the second elastomeric compound. 
     
     
         19 . The tire of  claim 15  wherein the first elastomeric compound has a greater wet traction than the second elastomeric compound. 
     
     
         20 . The tire of  claim 15  wherein the first elastomeric compound contains a greater portion of silica than the second elastomeric compound.