1.0 is pre compression, it basically is how much the suspension sags into its travel when you spawn into the game. You can lower the number but eventually you will hit a point where the suspension will break and the truck will either be undrivable or crash the game. The lower the truck sits, the lower centre of gravity it has, thus the faster you could drive because the weight is less likely to upset the truck turning. I have never run any lower then 0.9 because anyone who knows the shocks2 line knows how to properly lower the truck using the other numbers.