Question about RockShox Vivid Coil Ultimate RC2T C1

For a weight of 65kg, the correct spring size for this shock is determined by the spring rate for that weight. RockShox recommends using their spring calculator to choose the correct metric spring rate for this shock. The spring is sold separately and should be chosen according to your weight and riding style.

In short, there is no one size of spring specified directly, but you must select a metric spring with the correct spring rate for 65kg via the RockShox spring calculator.