Castrol Fork Oil 5W is an advanced mineral oil-based suspension fluid designed to provide maximum damping performance in all on- and off-road suspensions. Highly refined base oil and natural high viscosity index provide superior damping performance that does not fade over a wide temperature range. Castrol Fork Oil allows air release and performance that doesn t wane even in the toughest racing conditions. At low and high speeds there is minimal "static friction" of the suspension unit with good operation of the suspension units over a wide range of operating conditions.