Lay out an equilateral triangle. all sides equal. lay out the equilateral triangle for the center lines of the three parallel pipe. Multiply the desired altitude times 1.155 and add or subtract for the (example: diameter of the 2 7/8) outside diameter of pipe/tubing used.
Example; 32 desired finished height; subtract 2.875 from 32 equals 29.125. Multiply 29.125 times 1.155 equals 33.640. Subtract 2.875 from 33.640 equals 30.764. This would be the distance from bottom/inside of saddle to bottom/inside of saddle to space three parallel pipe equal distance to provide a 32 inch tumble pipe stand.
Or, cut three short lengths of pipe and play checkers on the floor with them until the height and sides are right.