Just some pictures to help with Rich's description.

Measuring spring arch. If you don't have a straight edge 5' long, Run a string between the 2 spring eyes.

DCP_1958.jpg

Then take a ruler and measure from the top of the spring to the string. This measurement is free arch.

DCP_1958.jpg


From eye to center bolt, lay tape measure on spring and measure from center of forward eye to center of center bolt. Repeat for rear segment.

DCP_1961.jpg