Robbie,
There is another issue to consider regarding pre-load.
Over time and many miles the main spring may lose some of it's initial spring and length, so nullifying any initial pre load.
If you were to shorten the lower spring, then later on in the life of the assembly you might find that it becomes sloppy with free play and require the lower spring to be replaced.
If this were to happen, would it not be possible just to insert a spacer of some sort below the rebound spring, until it just kisses the stub axle collar? Easier than buying a pair of new rebound springs with the hassle of installation etc surely?
