If you have databound the XValue of the chart DataPoints (like adding an ItemMapping for XValue) you can take advantage of the TicksDistance
property of AxisX. This property defines the minimum distance between two ticks along the X axis. In case there are lots of items, RadChart will calculate the ticks and label in a way that ticks are no closer than the value of this property.
If you are not setting XValue, TicksDistance will be ignored, so you may consider using the LabelStep
property. Setting it to 3 will force the chart to display only every third label.
the Telerik team