The desire to obtain a higher share for silica in tire compounding has been one motivation in the development of silane coupling agents. This development has reached a stage where at least a partial replacement of semi-active and active carbon blacks with silane-modified white fillers is technically feasible although costs are still too high. Nevertheless, silica tires with bis-(3-triethoxisilylpropyl)-tetrasulfide (TESPT) have been built on a development scale and tested under various conditions. Over the last ten years, the coupling agent TESPT has developed into a special rubber chemical. This is due to its simultaneous capability of forming equilibrium cure systems, polysulfidic crosslinks with extremely high thermal stability, and rubber-to-filler bonds to improve silica-rubber interaction. In conjunction with silica, TESPT gives superior physical vulcanizate properties such as low heat build-up, better performance under continuous deformation, and better tear and cutting resistance than vulcanizates with carbon black only. Its present main application is in truck, off-the-road, and earth-mover tires to solve specific tire problems.