They also have a different arch and a different spring ratio.
The spring rates are supposed to be the same.
Off the top of my head DC/MP books had their SS Springs listed as 160 lbs/in.
Spring ratio is the relative stiffness of the front segment to the rear segment. Those numbers are in the same DC Bulletin.
The difference in arch and ratio is to better load the tires during launch and maintain the anti-squat and help the chassis rise, transfering more weight onto the rear tires.
