You can try setting RadChart1.AutoLayout to true
as shown in this online example
. You can also consider modifying the plot area margins and the x axis item labels rotation angle as shown in this online example
. This would be done in code-behind like this:
RadChart1.PlotArea.Appearance.Dimensions.Margins.Bottom = Telerik.Charting.Styles.Unit.Percentage(20);
RadChart1.PlotArea.XAxis.Appearance.LabelAppearance.RotationAngle = 45;
Hope this helps.
the Telerik team