How do I add preload

[Acelay]

I was watching a vid of a new rc8 and they added preload to the suspension to help it clear the jumps better. How can I add perload? What is preload? Thanks

 

[Rolex]

Spacers you add to the top of your shocks. They compress your springs and as a result, stiffer suspension.

 

[Acelay]

Thanks, thats what I thought..