Leaf Spring Relocation Kit

Bill Crowell said

Spring relocation reduces the effective spring rate in the rear, because the spring is working against a shorter axle lever arm, and therefore has less leverage than it had when it was in the stock position. The lower spring rate changes the handling quite a bit for the worse, IMHO. I think it is necessary to correct for this. I'm not a suspension expert, so I will leave it to others to perhaps discuss this further.

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This is true. Moving the springs any amount inboard increases the lever arm between the center of the contact patch and the spring by that amount, so, the wheel rate is effictively changed. A greater force is applied to the spring. The further the springs are moved, the more force is applied. So, the spring rate has to be increased to compensate. For a 1/2" offset the difference is minimal. For the 3" relocation the difference is more significant. But higher rate leaf springs are easily obtained, and the factory rear spring rate wasn't as far off as the spring rate of the torsion bars in the front. A lot of these cars actually end up tail happy (loose, in oversteer mode) with just the addition of a rear sway bar, so it's not that big of a deal. A larger rear sway bar can be used to correct the roll stiffness. I run an E-body rear sway bar on my car with a 1/2" offset, so does 72bbswinger and his springs are relocated 3". It's one of the reasons I only went to a 1/2" offset, but with a Duster I can fit 295's with just the 1/2" offset, so that was a consideration too. I don't need any more tire than that anyway.

It's something to consider, especially if you're looking at autoX or road racing, but it's not at all difficult to deal with.