Since 2009, the EU regulation ECE R117 specifies that the wet grip adhesion must be measured for the approval of tires, and the wet grip index (G) must meet these requirements. To understand wet grip performance, this study performs a set of analyses based on fluid–structure coupling theory in the LS-DYNA finite element software. The impact of both the depth of transverse grooves and Standard Reference Test Tire (SRTT) tread patterns on the wet grip capacity is investigated by simulating the following cases: (1) six SRTT tread patterns, (2) three identical straight grooves with outer transverse grooves of four different depths, and (3) identical straight grooves with inner transverse grooves of three different depths. Results reveal that regarding transverse grooves in the SRTT, tires with outer transverse grooves show an approximately 8% increase in the wet grip compared with those with only straight grooves. With the addition of both outer and inner transverse grooves, the wet grip capacity can be enhanced by approximately 10%.