Picture your motorcycle with a 4" long swingarm, yes, 4 inches... now imagine the angle that would be created during the suspension cycle... meaning the suspension fully extended to fully compressed. You'd have almost no travel due to its short length, in addition, the angles required to achieve full suspension travel would around 45 degrees, way beyond an ideal figure. By the time you reached the bumpstop (compression) your swingarm would be pointing almost at the sky. Now picture your current swingarm... as the tire goes up and down through the travel cycle the angle of the swingarm stays in a reasonable relation to the ground... this is nowhere near as severe as you'd have if your swingarm was shorter. Radius arms are very similar. The longer the radius arm, the less severe the working angle of the suspension, this means more travel and less bind. Building a longer radius arm in most cases is not for strength, it's to allow for additional wheeltravel without the increased working angle of the suspension. Now picture this... as the tires of a radius arm equipped truck extend into the droop region of the suspension cycle, the radius arm is following a natural arc, since the radius arm length remains constant, the tires and beams must follow whatever arc the radius arm happens to be traveling in. A supershort radius arm would cause the tire and beam to travel backwards as well as down. Longer arms help prevent this to some degree.
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Think about the arc that the two lines above would create if they could move from a fixed point at the left, now think about how much more the longer line can travel up and down in relation to the shorter line if you kept the lines parallel. The tire is represented by the | |
If you still don't understand it just say so.
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