2012 KX450F - Min/Max Fork Oil Volume Range

I am messing with my fork oil volume (and obviously clickers) to try and get rid of some mid-stroke harshness. Before I go to a revalve, I am just messing with the variables to see what happens with the changes. The stock spring rates are fine for my weight.

Anyways, I'm going off of memory here, but I think the owners manual says the adjustable range for oil volume is from 310cc to 380cc. It seems that most suspension guys like to run between 335cc and 350cc with how they set up suspension.

I recall having Factory Connection revalve some YZ suspension a few years back and the guy there told me that, below a certain oil volume, you can damage internal components -- or at least I think that is what he told me.

So, my question is, has anyone gone as low as 310cc to 320cc with their oil volume, or is that getting too low and could it damage any internal components for not having an adequate oil volume in the forks?

I got the same bike recently after having a 08' CRF for many years. I am amazed by how much more sensitive these KYB forks are to bleeding off the air screws before each ride. On my Showas, it was a good idea to bleed the air off; but only had a minimal effect. It could be how the suspension was set up for the previos rider (my same ability height and weight). It would seem, unless im just imagining what I feel, that these forks would be sensitive to oil height.

I have 11 forks on my 06. They have non-stock valving, but I can still give you meaningful info on what you've asked.

You can use the minimum spec outer oil volume with no extra chance of wear on internals. That's for sure. The oil volume is meant to be adjusted to vary the amount of air spring effect in the lower half of the stroke. The amount of travel is sensitive to oil volume. I assume the reason KYB give us such a huge range to play with is because different riders like different things, incl diff spring rates. Some riders want more or less air spring effect. If your springs are in the ball park for your weight, then mid range on the oil volume would make sense (to me at least).

I have 0.47 fork springs and I weigh 165 lbs bare. I find that 325ml is good for getting more travel on tight tracks with small jumps. If riding some larger jumps or anything involving substantial hard/flat landing, then adding 10ml per leg (335ml total) makes a huge difference to bottoming resistance. But that extra 10ml does make them a little more harsh and a little harder to compress for turn-in on tight corners.

When changing the outer oil remember it takes a few hours for most of the oil to run out and also off the spring. So you need to be patient if you want to measure how much oil you've currently got in there. It's still really worth your while to check, and check both legs.

Edited by numroe

Hey numroe, thanks a ton for that feedback. I was actually running 345cc in the forks, and I went down 10cc and they felt progressively better. So, I went down another 5cc and they worked even better. That obviously puts me at 330cc, but I guess if you are saying that maybe 320-325cc is still okay, I'll probably keep fine-tuning it. But you are right -- that 15cc does make a big difference. When you think about it, I dropped the oil volume by only about 4%, which seems insignificant, but it really does make a big difference on the margin. Cool stuff, man!

You're welcome.

Always start low then add, through the air bleed holes in the caps. I began testing at 315.

If necessary, thoroughly clean those bleed holes and screws when each cap is off.

A 10ml oil change might be 4% oil but its a much larger % of remaining air space when the fork is compressed.

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