The Stovebolt Site Forums The Shop Area Driveline Measuring for shocks

Actually all you need to do to measure actual suspension compression is to measure the space between the axle and the snubber. It's actually harder to determine how much to allow for shock extension, although you could do that buy jacking from the frame until the wheels come off the ground, and measure again between the axle and snubber. Subtract that from the measurement you took with the truck sitting on the wheels and that's the extension of the shock. As Jerry said, adding an inch or so in both directions would work.