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I would have to break out my engineering background to do a free body diagram to prove it, but it seems to me that tying the tires to the deck keeps the center of gravity at the trailer deck level, versus tying at a higher point on the UTV. I am thinking in terms of motorcycle riding - you stand up on the pegs to lower the c-o-g on rough terrain, versus keeping your butt on the seat. I can say with 100% certainty, that tying the wheels to the deck feels, on my setup, way more stable than when I used straps on other frame components and compressed the shock absorbers. With the tires secured, you can see the machine "float" on rough terrain, absorbing the bumps. When I tied to the frame, the trailer hopped on the bumps as the weigh of the machine went up and down...the shock absorbers on the UTV were unable to function as intended. To each, his own.