Does anyone know the correct way to measure toe-in, without going to an alignment shop ? The manual lists the toe-in for a 72 240Z as 1.59-5.56mm. Is that measured from the leading edge of the tire to the trailing edge, measured at the center height, or is it from the leading edge of the tire to the center of the wheel ?

One would result in twice the toe-in as the other.

If you started with your front wheels pointing straight forward, you would be @ "0" toe. The dimension given for toe-in will be the total of both wheels, not each wheel. So, toe-in is the total toe-in of both wheels, from "0", at the leading edge of the wheels. Hope this helps you out!

This is the way I measure toe-in. Imagine a horizontal line through the center of the wheel (running front to back, in line with the car). Measure from the inside face of the wheel rim at that horizontal line on the front side of the wheel to the same location on the other wheel (left to right). Then measure at the same spot but on the rear side of the wheels. (measuring points will be in front of and behind the control arms)

The difference between those two measurments should be within the range you have listed from the FSM. With the rear measurement being greater than the front measurement.

Hope that makes sense...