1The design of a novel apparatus, the Glen Withy torque tester (GWTT), for measuring 2 horizontal shear properties in equine sport surfaces is described. Previous research has 3 considered the effect of vertical loading on equine performance and injury but only limited 4 discussion has concerned the grip or horizontal motion of the hoof. The horizontal support of 5 the hoof by the surface must be sufficient to avoid excess slip without overloading the limb. 6The GWTT measures the torque necessary to twist an artificial hoof that is being pushed into 7 the surface under a consistently applied vertical load. Its output was validated using a steel 8 surface, then was used to test two sand and fibre surfaces (waxed and non-waxed) through 9 rotations of 40-140°, and vertical loads of 156-980 N. An Orono biomechanical surface 10 tester (OBST) measured longitudinal shear and vertical force, whilst a traction tester 11 measured rotational shear after being dropped onto the surfaces. A weak, but significant, 12 linear relationship was found between rotational shear measured using the GWTT and 13 longitudinal shear quantified using the OBST. However, only the GWTT was able to detect 14 significant differences in shear resistance between the surfaces.