I recently purchased a 2001 YZ250. I went to the MX tech website (along with some others) to determine what the proper spring rates would be for a 210 lb rider. Most of them agree that 5.0 Kg/mm is what is recommended. The stock spring is 4.9 so I thought "close enough". But when I set the sag to 4 inches, there is no free sag when I am off the bike. Why is this, what spring do I really need?