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Fork oil

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So me and my buddy are change his fork oil for the first time and was just curious do you use the same oil for the outer tube as you do for thin internal. And also what is the best brand to use?? It's on a 2006 yz250f and could someone give me the oil specs for each, he doesn't have a manual for his bike.

Edited by hartman534

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Have never heard of using  different oils for the forks. In 40 years.  A thinner specific use oil is used for the shock though.

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Different oil in the inner and outer chambers of twin chamber forks is common. Typically the inner chamber would use thinner oil. It's also common to use the same oil in both chambers since they do eventually mix.

Yamaha specs yamalube S1 oil for both chambers. 300-375 cc's outer and about 200 cc's inner.

Edited by bg10459

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Have never heard of using different oils for the forks. In 40 years. A thinner specific use oil is used for the shock though.

I've never heard of this either. Must be some garage rebuilder. Guarantee FC,PC, Enzo ect is doing no such thing.

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Different weight fluid inner and outer is yet another adjustment available. Simple as that!

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Different weight fluid inner and outer is yet another adjustment available. Simple as that!

I would bet your yearly income that in a dbl blind test, NO ONE could tell if different weights had been used. In fact I'll double that bet! 

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Well, George, if I were you I'd hold off on the bet unless you're pretty wealthy.

 

Using a heavier than specified oil in the outer side of a KYB twin chamber is one of my favorite tricks.  Remember that the outer side oil does only two things that are relevant to suspension action (unless you count lubrication); oil bottoming oil locks, and the "air spring" effect, controlled by the total volume.  Since the oil locks present a "fixed orifice" flow restriction, heavier oil makes the fork more resistant to bottoming out in the last inch or so.  That can allow you to reduce the total volume of oil in the fork, which increases the air volume captive in the fork, which in turn gives a plusher ride deeper in the stroke. 

 

On a YZ450, I use a lighter oil, such as for a shock (~3wt), in the cartridges, and a heavier oil (~5-7wt) in the outers, and cut the oil down from 350 to 320-325cc.  Works great except that you have to step up the oil changes to take care of the mixing problem. 

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Different oil in the inner and outer chambers of twin chamber forks is common. Typically the inner chamber would use thinner oil. It's also common to use the same oil in both chambers since they do eventually mix.

Yamaha specs yamalube S1 oil for both chambers. 300-375 cc's outer and about 200 cc's inner.

Thanks! We plan on getting it done this weekend.

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Well, George, if I were you I'd hold off on the bet unless you're pretty wealthy.

 

Using a heavier than specified oil in the outer side of a KYB twin chamber is one of my favorite tricks.  Remember that the outer side oil does only two things that are relevant to suspension action (unless you count lubrication); oil bottoming oil locks, and the "air spring" effect, controlled by the total volume.  Since the oil locks present a "fixed orifice" flow restriction, heavier oil makes the fork more resistant to bottoming out in the last inch or so.  That can allow you to reduce the total volume of oil in the fork, which increases the air volume captive in the fork, which in turn gives a plusher ride deeper in the stroke. 

 

On a YZ450, I use a lighter oil, such as for a shock (~3wt), in the cartridges, and a heavier oil (~5-7wt) in the outers, and cut the oil down from 350 to 320-325cc.  Works great except that you have to step up the oil changes to take care of the mixing problem. 

CK whose money I was betting. I respect your input but am still skeptical what would be the outcome of a blind comparison.

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If you put a thicker oil in at the same amount I think you would feel it , lowering the level then brings the total stiffness down to similar levels as before , but with the benefit of a smoother midstroke as the oil doesn't hit the spring perches as much , it's these that give a big change in feel

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Wow, the variables are endless. I have had at least 15 revalves on cartridge fork bikes and have never had a tuner mention using different weights in the forks. Still skeptical of its value for the typical rider, 90% of which are C riders. Whether they will admit it or not.

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Tuning is all about balancing variables to achieve a set result , it's a shame you have not had a more positive result , tuning should make your bike feel how you want it

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Yep. Previous bikes have been a very simple process to get things right. Frustrating. 

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