this is probably a stupid question…….but how do you measure the preload in a coil shock. Is it the amount you turn the screw when it first touches the spring?

Check the FAQ’s on TFTuned.com

Yes, no more than 2 full turns on a fox spring if that help.

interesting……i posted the same query on the MTBR forum and got the following reply

Yes, you have the right overspring, but do not use it as a preload to set your sag…

…when off the bike, just tighten the spring and perhaps it give an extra quarter twist, then use your air pressure to set the sag…get your air pressure to the point where the shock compresses about 1/4″-1/2″ when you lightly sit on the bike…remember if the pressure is too low, the shock will bottom out and could damage not only the shock, but may crack the frame.

Does anyone know the advantage of doing the above?