If the center of mass is not in the axle plane, the weight distribution among the wheels will depend on the car's orientation. The following short video shows an easy way to copy the slope of the test ramp to the scales that will be used for weight distribution adjustment.
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Note: The procedure above assumes that the table is uniform, the thicknesses of the wheel cradles are identical, and that the incremental thickness of a sheet of 20 pound copier paper provides sufficient granularity. Note that the cradles are attached to flat bases so that the depression in the center of the scale pan will not distort the measurements.
Here are spreadsheets for planning weight distributions to use in aligning your car. Save one to a folder in which you have both read and write privileges since spreadsheet files get altered during spreadsheet program operation. (I usually put such files on my desktop until I decide whether I want to keep them or not.)
Underlined cells are for data input. Other cells contain computation results, etc. Many of the underlined cells have data from one of my test cases. Your car and weight will probably be different, so enter your own data.
Spreadsheet for Microsoft Works
Spreadsheet for Microsoft Office
Spreadsheet for Open Office
The bias ratio should usually be in the range of 2:1 (67%) or 3:1 (75%) depending on how well the rough alignment is done. Either should produce good alignment for most cars.
I puzzled over whether to construct detailed instructions for use of the spreadsheet. For now, I think better service is provided if the reader puzzles it out himself in order to better understand and apply the information. (I may change this opinion later based on feedback.)
Now we have scales adjusted to simulate the slope of the alignment board, we have weighed the car and the bias weights and we have computed how much weight should be on each wheel to achieve the target weight bias for the alignment runs. The next step is to adjust each bias weight assembly to produce the desired axle loads.
Note that if wire is bent so that the bias weight is moved laterally, i.e. side to side, the load on the front wheel does not change. So, the adjustment of the wire assembly is easiest if the bias weight is first adjusted to achieve the correct front wheel load. Then, compare the rear wheel scale readings against the target readings and bend the weight wire to move the weight left or right to the right location... bend and wiegh, bend and weigh, ...
The weights do not have to match the targets exactly, but try to get them within about 0.1 ounces.