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Fork Oil Weight effect on Bottoming


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I've spent some time using the search feature and think I know the answer, but I'd like some verification.

Does the weight of my fork oil have an appreciable effect on bottoming resistance?

My reason for asking, is I'd like to soften the fork's response to small bumps, but my bottoming resistance is just about optimal right now for my weight. I'm currently running 7 wt. oil in my '97CR250R--and yes I know that the bike is legendary for having harsh forks. Would going to 5 wt. oil give a more supple response without loosing bottoming resistance?

Thanks!

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I'm no expert so maybe someone more knowledgeable will chime in, but from my understanding bottoming resistance is based more on oil level rather than weight. I just rebuilt my forks a couple months ago and raised the oil level for that very reason, it helps stiffen the final couple inches or so of travel.

In that case, you could drop down to 5W and raise the level a bit to help.

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Within limits, a heavier oil in the inner cartridge won't have much effect. The valves themselves are de facto pressure regulators, and to the degree that they can, they will simply open up farther to allow a heavier oil to pass through at the same rate with the same pressure differential. Bleed passages that are a fixed orifice, like those controlled by the clickers, will react to the heavier oil, but once these are compensated, the fork will behave somewhat the same.

One of the major components in bottoming resistance is the "oil lock", or bottoming brake in the outer chamber. In your fork, this is a cone shaped extension in the lower fork lug that slides into a socket in the bottom of the cartridge as the fork nears the limit of its stroke. Since this amounts to a fixed, non-adjustable oil passage, it will respond to a heavier oil, and a heavier oil will generally help reduce bottoming because of that.

I run a lighter oil in the cartridge, and a heavier one in the outer for this reason.

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