Currently, to specify the start and end values for an an axes, you right-click on the axis, select "Edit Axis...", then in the Range section of the 'General' tab you enter the numerical values for the Start and End values.
It would be most helpful if you could use parameters to specify these start and end values. It would make it easier to experiment with the look of a chart while building a view, but perhaps even more importantly it would enable Tableau Reader users to adjust the look of the view. Currently (as far as I know) there isn't a way to give a Tableau Reader user this functionality. It would be particularly helpful in situations where their quick filter specifications dramatically impact the chart's appearance.