I have tried to do my home work on these springs asking a lot of questions along the way. Before I bought these from Eric Wracks71 I made a call to Flex form to see what they would recommend for my application. Mark of flex form recommended I run there 250 rate spring with there 4 inch free arch. So I ask him(Mark) if he could look up Eric's order and see what his springs were? They are exactly what he had recommended for me so I saved myself some money and bought them. I still have reservations about them working for me as the car is a 65 Dart estimated weight is 2950 at race weight with me in it. The front will have 1.14 T bars with QA1 single adjustable shocks. So I'm guessing that the reason they work for some and not others is mismatch suspension components. Or just to stiff of a spring rate to begin with. I guess we will see if I can make them work or not.