The best way to measure the toe-in is to stretch a tape measure between the spoke ends, not the rims. It's much more accurate this way (and easier, too!) The fronts of the wheels should be closer together by about 1/16". Once you've got this set, get the trike up to about 10mph, stop pedaling, and release the handle bars. If the trike tracks straight then everything is set properly. However, if the steering begins to oscillate wildly, then the toe-in needs a bit more adjustment.