RichTextBox tab spacing

How can I change how many spaces are equivalent to a tab in a RichTextBox? At the moment it's on 8 and I need it on 4.

It may look like spaces, but behind the scenes it's actually pixel positions:
ms-help://MS.VSCC/MS.MSDNVS/cpref/html/frlrfSystemWindowsFormsRichTextBoxClassSelectionTabsTopic.htm

Do something like this:

VB Code:

Dim arrTabs() As Integer = {50, 100, 150}
        rtxStuff.SelectionTabs = arrTabs

If you do this before any text is added to the richtext, it will apply to any text you add in.