After playing with several types of springs for my Dart, I have a formula that works. The site for my shop Bergman Auto Craft is almost finished, where they will be listed. However, I wanted to share a profile shot of the Dart with the springs installed. These are 130 lb springs that have a heavily reinforced front section and sit at the proper height. If you use a 26" tall tire, the height will be 22" vertically from the ground, through the centerline of the wheel up to the wheel lip. The picture is at 21.5" because I use a 1/2" lowering block as well.
