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Calculations: why position of tailgate cables impacts cable tension

The positioning of the tailgate cable on the tailgate and the angle of the tailgate cable affect cable tension.

cable-tension-position-e.pngPosition E
If a cable could be positioned so that it was vertical (which of course it can not be) and attached to the end of the tailgate, the load applied to the tailgate would result in equal increase in the cable tension. i.e. if you applied a load of 500 lbs.* to the outer edge of the tailgate, and the load was equally shared by the two cables you would have a 250 lbs. load supported by each cable and 250 lbs. of tension in each cable.

 

cable-tension-position-f.pngPosition F
If a cable could be positioned so that it was angled 45 degrees from the tailgate, attached to the end of the tailgate and the same load is applied as in position E, the cable tension would be 1.414 times the load. i.e. 1.414 x 250 lbs. or 354 lbs. tension in each cable. Tension = load/sin 45 deg.

Or, Tension = load x (1/0.707)
So, Tension = 250 lbs. x 1.414 = 354 lbs.

 

cable-tension-position-g.pngPosition G
If a cable could be positioned so that it was angled 45 degrees from the tailgate, attached to the midpoint of the side of the tailgate and the same load is applied as in position E, the cable tension would be 2.828 times the load. i.e. 2.828 x 250 lbs. or 708 lbs. tension in each cable. Since the vertical component of the cable tension is twice as much as when the cable is attached to the end of the tailgate: Tension = 2 x load/sin 45 deg.

Or, Tension = 2 x load x (1/0.707)
So, Tension = 500 lbs. x 1.414 = 708 lbs.

 

cable-tension-position-h.pngPosition H
If a cable could be positioned so that it was angled 60 degrees from the tailgate, attached to the midpoint of the side of the tailgate and the same load is applied as in position E, the cable tension would be 2.828 times the load. i.e. 2.828 x 250 lbs. or 577 lbs. tension in each cable. Since the vertical component of the cable tension is twice as much as when the cable is attached to the end of the tailgate: Tension = 2 x load/sin 60 deg.

Or, Tension = 2 x load x (1/0.866)
So, Tension = 500 lbs. x 1.155 = 577 lb

*The load of 500 lbs. includes the portion of the tailgate weight that is supported by the cables.

 

If we move the load to the middle of the tailgate, as shown in I and J, the tension in the cables is one half that of when the load is placed on the edge as in E-H. i.e. the cable tension in F is 354 lbs. and the cable tension in I, which is the same configuration as F, is 177 lbs.

cable-tension-position-i.pngPosition I
Since the vertical component of the cable tension is one half as much as when the load is placed on the edge of the tailgate: Tension = 1/2 load/sin 45 deg.

Or, Tension = 1/2 load x (1/0.707)
So, Tension = 125 lbs. x 1.414 = 177 lbs.

 

Position J
cable-tension-position-j.pngSince the vertical component of the cable tension equal to the load: Tension = load/sin 45 deg.

Or, Tension = load x (1/0.707)
So, Tension = 250 lbs. x 1.414 = 354 lbs.

As you can see from the preceding examples, the geometry of the tailgate cables and the placement of the load on the tailgate both can dramatically affect cable tension.

 

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