The fluid weight depends on more factors than just a general number. What works on one car, might not work on yours.
The oil weight is what makes a damper damp. Although an accurate calculation is out of the scope here, you need to understand that it depends on factors like the spring rate, the wheel rate, the sprung weight of the chassis (everything that is attached to the upper side of the damper), the unsprung weight of the chassis (everything that is attached to the lower side of the damper) and the damping ratio. This means that different batteries, different electronics, different springs and even different bodies will make a difference!
What I do to simplify things is to buy 2 different oil weights, one light and the other very heavy and mix them together until I get the desired damping. The process is quite simple: first I setup the car and make it drive ready with battery and body shell. Then I fill the dampers with a light mixture, install the dampers and drop the car from a height of about 4" off the ground, making sure that all the wheels will hit the ground at the exact same time. Since the mixture is very light, the damping ratio is very low, so the chassis will rebound back and will continue 'vibrating' up and down. Next I increase the mixture weight, progressively, by replacing a small amount of the oil mixture with a few drops of the heavier oil, until the car is hitting the ground and is almost not vibrating after the initial impact. When this happens, then you´re very close to the golden number, the Critical Damping.
