Here's a great diagram showing the tie-rod end/kingpin relationship and how they'd be placed in a "perfect" Ackerman situation.
In practice, if the two lines join either 1/3 the wheelbase length infront or behind the axle C/L, it is considered acceptable.
I have studied many different theories and experimented myself on radio controlled cars. The difference between having perfect Ackerman, C/L rear axle, and "almost" perfect is not a great deal.
To figure out the steering arm offset:
Measure the length of the steering arm (kingpin to TRE)
Mulitply that by the front track width.
Divide the answer in half
Divide the wheelbase dimension.
Eg: (inches are easier 'cos they's bigger....)
Steering arm: 7"
Therfore your steering arm offset should be set at 2.1"
"Obviously your ambition outweighs your talent" Casey Stoner to Valentino Rossi. 03/04/2011