Thanks for the question, and corresponding answer, regarding the CG Long, it was causing me to scratch my head. Would I be correct in assuming, for the sake of the analysis, that my rear lower pickup points are centered at the hub? I'm using a Cougar upright and there are two pickup points, one would be +X and one would be -X. As wishbone only has one input value, I'm assuming the X values cancel each other out and become zero but would like some verification.
I haven't done a IRS but it should follow the same dimension rules as for a IFS.
For people just starting out with wishbone;
"X" measurements are taken down the length of the car. Plus numbers are entered for stuff in front of the front "axle" line. Negative numbers are entered rearward of the front axle.
"Y" measurements are the height above the ground to the thing being measured. These numbers are entered as + numbers.
"Z" measurements are taken from the center line of the car to the respective "X" points. These numbers are entered as + numbers.
WARNING -- all measurements have to be within 1/16" or better
! As you approach the sweet spot of getting the desired geometry even 0.050" from the "correct" measurement (or construction of the parts) will affect the results.
In an IRS both the "forward" and "rear" mounting points of the upper and lower A-arm mounting points in the "X" plane would be entered as negative numbers since they are well rearward of the front "axle". The upper and lower "ball joints" would be the heim (or other) joints at the hub.
Each A-arm has three points to be measured. In order as they appear on the wishbone data entry form they are,
1. The rear mounting point of the upper (or lower) A-arm closer to the center line of the car.
2. The forward mounting point of the upper (or lower) A-arm closer to the center line of the car.
3. The lower and upper ball joints (at the outer end of each A-arm).
There is no "cancellation" of numbers. All these measurements assume a symmetrical A-arm layout on the left and right side of the car so only one side needs to be measured (remember that "Z" numbers are from the CENTER LINE of the car to the "X" point being measured).