Ligands mounted to surfaces via flexible polymer tethers represent a growing class of molecules used to engineer adhesion in drug targeting, biosensing, and self-assembling nanostructures. The Surface Forces Apparatus was used to characterize the specific bridging forces imparted by such molecules towards model receptor surfaces. Specifically studied were the effects of polymer chain length, grafting density, and ligand-receptor bond energy on the binding efficacy of both bimodal and monomodal architectures. These measurements validate analytical expressions that we have derived for the specific bridging force. Also explored are the grafted chains' nonspecific repulsive interactions with model membranes, their adhesion under flow, and implications for targeting polymer-coated particles towards biological surfaces. Importantly, we show that the adhesion strength can be tailored by controlling the ratio of ligated to non-ligated tethers without reducing the probability of initial cell capture.