INFLUENCE OF SUSPENSION, TIRES, AND SHOCK-ABSORBERS ON VIBRATION IN A2-HORSE TRAILER

Combinations of vehicle suspensions (leaf-spring and torsion-bar), tir es bias-ply (311 kPa), normal-pressure (344 kPa) and low-pressure (172 kPa) radials, and shock absorbers were evaluated for smoothness of ri de and common frequencies of vibration using a two-horse, bumper-pull, tandem-axle, forward-facing trailer. Accelerations on the x-axis (dor sal-ventral, upward-downward) were measured on each wheel and each cor ner of the trailer while the trailer was driven over fourteen 25-mm-di ameter cables spaced at 4.8-m intervals at three speeds (40, 56, and 7 2 km/h). Twelve combinations of suspension, tires, and shock absorbers were tested in all. Initially, five steel barrels filled with 1000 kg of water (total mass) were positioned in the trailer to mimic the bod y masses of two horses, The leaf-spring suspension with low-pressure r adial tires and without shock absorbers provided the smoothest ride in terms of the lowest root mean square (rms) accelerations (P < 0.05), but the leaf-spring suspension combined with bias-ply tires and withou t shock absorbers also had similarly low mts accelerations, The torsio n-bar suspension combined with normal-pressure radial tires was the ro ughest (in terms of rms accelerations) combination tested. Generally, the addition of shock absorbers did nor improve ride quality in terms of x-axis acceleration. Several combinations of suspension and tires ( leaf-spring suspension with bias-ply, low-pressure and normal-pressure radials, and the torsion-bar suspension with normal-pressure radials) were chosen to test with four live horses riding in the trailer (hors es were transported two at a time). Root mean square acceleration valu es (x-a;xis only) were measured on the left and right front trailer su bframe, the left front hoof and left trunk of one horse, and the right front hoof and right trunk of another while the trailer was driven ov er smooth and rough roads. The leaf-spring suspension with low-pressur e radial tires provided the smoothest ride. Horses traveling on the ri ght side of the trailer experienced more vibration than horses on the left side of the trailer, perhaps because of the poor conditions of as phalt roads near the shoulders.