Setting Lines and Arcs to Equal Length

Does anybody know if there is a sketch relation or some other function that allows you to set a straight line and an arc to equal length? See the attached image for example. I want the two dimensions that show 13.132 to always remain equal. In this sketch, I have the 5.500 dimension as driven, but in reality, it is the dimension that I would like to be able to vary along with the diameter.

Thanks for your help.

SolidworksGeneral