Here are some preload clips for the Losi Micro-T or similar vehicle. I made them for my JJRC LT832. They have different thicknesses ranging from 1mm to 5mm. They allow you to fine-tune your shocks without purchasing new springs.
I found that with softer rear springs the truck cornered better and spun out less. Softer springs allowed the truck's weight to shift toward the outside of the turn, putting less pressure on the inner tire, allowing the differential to give a little more power to the inside tire preventing spin outs. With stiffer springs my truck landed jumps better, but spun out more easily.
I recommend cutting the 1-2mm clips using a knife or small wire cutter so they don't break (see last picture for where to cut). You should be able break off the thicker ones without them breaking.
I recommend printing these slowly as they are pretty small. I printed them with no shells and got good results.