Paul owns a 2006 WR250F, weighs 90kg (that's about 200 pounds) and wanted to know about spring rates with and without a YamaLink.
Our reply: Your 2006 WR250F stock rear spring rate is 5.1 kg/mm
BEFORE the YamaLink is installed, RaceTech recommends a 5.5 kg/mm spring rate with the stock suspension to achieve proper sag and the best handling. Too much sag due causes understeering, bottoming and wallowing. You say you're not bottoming: was the bike purchased used and from a heavier rider who put a heavier spring on??
WITH a YamaLink on your bike a 5.8 kg/mm spring is recommended otherwise it will bottom too easily and understeer more.