'08 KYB fork oil - 2.5wt?

On my '06 YZ250F I changed out the stock 5wt oil for 2.5 for riding trails and it was a much better improvement.

I now have a '08 YZ250 smoker with the same fork, but I'm not sure how different the valving or spring rates are from the 250F. Its a little stiff/over damped for trails unless I'm hitting things pretty hard and fast.

I'm just looking for some tips from people with experience working on this fork. Will I achieve the same results changing oil to 2.5wt as I did with my 250F? And, should I leave my oil height the same or take some out?

FWIW, I am a fast Vet B/mid Vet A off road racer, and I'm about 175lb nekkid.

The rear suspension is bone stock but the low and high speed is backed off a little and feels wonderful. Wouldn't change it. The front feels a little too stiff compared to it.


What 2.5W did you change to on the 250F? Yamaha S1 oil is basically equivalent to most manufacturers 2.5W oils.

I start with fresh oil and a lower level. It's easy to add more oil if you have bottoming issues, it's hard to take out measured amounts of oils to try lower levels.

hmm... If I can recall the stock Yamaha stuff was 5wt. I put in 2.5wt Motul to the same level and the difference was noticeable on the trail.

Here's a very good read


At the bottom is a chart showing how all sorts of different oil rank in terms of viscosity. Yamalube is a 5 wt, but falls on the very light end of the spectrum, in line with many manufacturers 2.5 wt oils. You can see that some oils (PJ1 Fork Tuner 2.5 wt for example) fall way outside their claimed rating.

More questions -

when you changed oil, did you do the inner and outer chambers?

Was any other maintance done at the time?

Yea I was replacing seals and took everything apart.

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