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Discussion Starter · #1 · (Edited)
As I am in the process of installing aftermarket fully adjustable fork cartridges/inserts I did some research.
I can imagine our community can benefit from it as well so here goes nothing:
In my manuals (200 and 390 first-gen) the amount of fork oil is stated at 450 ml/per fork leg.
When changing fork oil and/or fork seals you will most likely not be able to drain all the old oil so the best way to do this is to carefully drain as much oil out of the fork leg and replace this with the same amount you drained.
This will probably present a challenge when you've been riding with a leaking fork seal.
In this case, it would be good to measure out 440 ml of new fork oil and fill it off with this volume.
Whatever you do, make sure both fork legs are filled to the same level.
I have so far been unable to find any measurement in mm from the top for our bikes BUT my new insert supplier's manual says 140 mm.
In contrast to engine oils, fork oil is not bound to standardisation rules, for some reason.
This makes it pretty difficult to find the best fork oil.
One thing that seems to hold out along the different brands is the viscosity (4W, 5W, 7W etc).
My manuals (as well as the new fork inserts) say I need to use 5W fork oil, so that will be used.
According to many suspension guru's, to chose the best fork oil in your viscosity range, the decisive factor is the VI or viscosity index.
It is claimed that the higher this number is, the better the fork oil will work over the 40 - 100 °C range.
 

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Super Moderator
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Discussion Starter · #2 ·
Obviously, there is also Öhlins fork oil in 5W BUT there is absolutely no info on their oils as there is with most of the other brands mentioned.
Even the Öhlins dealer in Thailand was not able to give me this info, hence they are not on my list.
 
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