Fork oil: weights and equivalents (cSt)
The "wt" weight is not a standard across brands: two oils of the same wt can have different real viscosities. To truly compare, look at the viscosity in centistokes (cSt) at a given temperature. Also, the bath oil (lubricates lower legs and seals) is not the damper oil, and they should not be mixed. This matters when doing the lower leg service and the damper service.
Buying oil "of the same weight" from another brand seems harmless, but the wt is misleading: what counts is the cSt. And bath oil and damper oil are not interchangeable.
The "wt" problem
The grade or weight (wt) comes from the motor industry and is not standardized for fork oils. Each manufacturer measures and labels its own way, so one brand's "10wt" can be thinner or thicker than another's "10wt". Going by wt alone when switching brands is gambling with the damper's behavior.
The real viscosity: cSt
What truly compares two oils is their viscosity in centistokes (cSt) at a reference temperature (usually 40 °C). That figure is objective: an oil with fewer cSt is thinner and lets the damper move faster; one with more cSt is thicker and slows it down. If you're going to substitute an oil, look up the original's cSt and pick another with a similar cSt, not the same wt.
Bath oil vs damper oil
They are two oils with different jobs:
The bath oil goes in the lower leg service and keeps the suspension smooth; the damper oil goes inside the cartridge and the rebound and compression depend on it. Using one where the other belongs ruins the fork's behavior.
Why not mix
Mixing oils changes the real viscosity (the resulting cSt is neither one nor the other), so you alter rebound and compression with no control. Also, different oils may not be chemically compatible. The rule is simple: use the oil and viscosity the manufacturer specifies for each function, and when switching brands compare by cSt. This is exactly what's respected in a well-done damper service.
Tell us your fork's brand and model and which service you're going to do and we'll tell you the correct oil and viscosity. Message us on WhatsApp
Frequently asked questions
Is the wt the same across brands?
No. The wt is not a standard: two oils of the same wt can have different real viscosities. Compare by cSt.
Are bath and damper the same oil?
No. The bath oil lubricates lower legs and seals; the damper oil defines rebound and compression. They're not interchangeable.
Why not mix?
You change the real viscosity and the damper's behavior, and they may not be compatible. Use what the manufacturer specifies.
Related
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