Which tiagra? I believe Tiagra 4700 uses a different pull ratio than earlier shimano 10 speed stuff. In any case, Check out the Wolf Tooth Tanpan. It’s a pulley adapter that changes a pull ratio so road shifters work with MTB derailers. I believe they make one that converts 4700 tiagra shifters to the pull needed for newer XT derailers, check Wolf Tooth’s site.