go cart/a arm construction help please?

Question

on this web site that shows how to construct double a arm this is a side note http://www.sadik.net/gokart/ the pic has measurements of the a arms

"when you use dual A-arms, there's a problem to overcome: when the suspension travels up, the wheels push outwards as the A-arms get closer to horizontal. what you can do to fix this is make the upper A-arm shorter than the lower A-arm. this way, when the suspension travels up, the top A-arm, being shorter, pushes outward at a greater rate, making the top of the tire lean outward. when the tire
leans out, the part of the tire contacting the ground does not move outward." -Eric

can anyone tell me how much smaller the top one should be

Answer 1

Problems
1. He doesn't give dimensions
2. The pictures of the assembled arms look very strongly like the arms are not the same length but the lower is longer. Compare the verticalness of the chassis mount with the slightly lean of the wheel mount.
3. The wording of the quote is misleading - with unequal arms the geometry is more complex than he states, especially if the mounts are not the same distance apart vertically. To do this empiricly if the point on the ground is not going to move, then what ever the distance the arc points of the lower arm might be, the upper arm has to be different by the ratio of the distance from the ground to two pivots. (i.e. If the lower arm is 30.0 inches from the center line in the down positions and 30.5 in the horizontal position and the upper arm is attached exactly the same distance from the lower arm as the lower arm is from the ground then the needs to be short enough for the change in its arc distance from the center line is twice the lower. Usually this is done with the inner mounts being further apart than the wheel mounts.)