That question has been asked so many times over the past couple of years. You will really be better to just hit the search button and punch in lower pulley, lightning, or whatever keywords you want to try.

The short answer is 8# for Lightning = roughly 6# for HD. The upper pulley being the reason that the same size lower gives the different amount of increase for each truck. Sometimes it's easier to use the pulley diameter to be clear which one you are referring to.