I just recently serviced my Fox TALAS fork and i put in fox’s 7wt susspension fluid. My question is what is the difference in the weight of the oil? And what is best for XC and DH racing through full on extream Freeride.
7wt is stock for FOX forks, and I would use stock oil.
OK, let’s step through this:
Damping is the amount of force resisting the movement of your suspension. Compression damping helps your spring resist compression. Rebound damping resists the spring’s tendency to rebound. The ideal amount of damping would give you a ride that is both plush and controlled. Not stiff. Not a pogo stick.
The ideal damping depends on the terrain, the machine and your riding style. There are so many variables here, it’s crazy. Stock forks and shocks come with an adjustment range that suits “typical” riders. Companies like PUSH make a good living at custom-tuning the damping for riders who are exceptionally big, small, fast, slow, aggressive, timid or just picky. I’ve had some shocks PUSHed, and they made my Enduro and SX — both great bikes — phenomenal.
The amount of damping is the product of your oil weight and your valving. If you have an opening of X size and oil of Y weight, it takes Z amount of force to push the oil through the opening. Modern suspension uses a series of ports and shims to provide different levels of damping in different parts of the suspension stroke and even at different speeds. It’s really complicated!
You can change your damping by changing your valving or your oil weight.
Lighter oil reduces your damping. Might be a good idea for a lighter or slower rider.
Heavier oil increases your damping. Might be a good idea for a heavier or faster rider.
But realize that changing your oil weight is a blunt instrument. It changes your damping en masse: low speed, high speed, beginning of stroke, end of stroke, rebound, everything*. Changing your oil is quick, cheap and easy, but you’ll get a more precise tune by changing your valving.
If you’re sensitive enough about your suspension to want to change oil, I think you’ll appreciate a custom tune.
*On a FOX. Some forks use separate compression and rebound oil.