I moved my axle about one inch forward with rear springs. The front spring bolt is like one inch back of stock and my shackles just bearly hit the frame on compresion. But once the shackles hit the frame the springs are already flat so it doesn't do anything, just rubs. I have 2 inch lift shackles. So if you move the axle forward 2 inches with rear spring the shackle won't hit.