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KYB fork, less oil = faster rebound? Kevin Walker


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Was watching Walker test 2020 or 2019 Kawi 450 with ML. He said during the video that Kawi only has 310 oil as standard, and therefore also rebound felt fast and nervous.

Never heard of this myself?

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Doesn't make any sense to me.  Oil quantity in the outer chamber only factors in as air spring pressure.  Less oil would slow rebound somewhat from deep in the stroke, other than that it's not relevant.

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Agree. Outer chamber oil height only affects spring in last 1/3 of the stroke. Does not have much affect on damping in last 1/3 either. If the forks are in the last 1/3 of stroke a lot they need a stiffer spring. 

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Tested it myself this weekend. Went from 300 to 340 on my WP KYB cartridge-kits. 

As usual, forks just rod higher in the stroke in general and better bottoming resistance.

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I put 310cc in my KYB AOS to try and get some softer initial fork reaction in the slow stuff. I now have a woods bike and want to turn this bike into a sand whoops/open terrain bike. Would 330cc (factory fill on the GG forks) do the trick or use that as a starting point and go up?

As it sits now I can hit 1 or 2 whoops before it causes me to bounce off to the side or I get way out of shape. (Yes I can ride whoops on other bikes)

Edited by gez300
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What I mean to ask is. Is having less oil in the outer chamber affecting the forks performance over repeated fast hits? 

A revalve is an option I'd try also.

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47 minutes ago, gez300 said:

What I mean to ask is. Is having less oil in the outer chamber affecting the forks performance over repeated fast hits? 

A revalve is an option I'd try also.

The outer chamber oil height determines the air spring effect which helps bottoming resistance on the last 1/3 of fork stroke. Within reason. You can’t make up for too soft of springs with oil. For a fast sand whoop area I usually like less rebound but stiffer compression. Adding too much rebound in sand buries the front end in fast sand turns, with a quicker rebound the forks seem to bounce off the sand once it digs in so deep where as slower rebound let’s it keep burying. That’s just my take and experience. I do run more rebound in the shock which also helps keep the front moving along in soft sand….. too much and you will ride to low in the stroke over sand fast whoops. Then it kicks. If you run a quicker rebound in the shock you can use throttle to control your rebound. Again, my experience. These other guys actually know what they are talking about

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16 minutes ago, hondaman331 said:

The outer chamber oil height determines the air spring effect which helps bottoming resistance on the last 1/3 of fork stroke. Within reason. You can’t make up for too soft of springs with oil. For a fast sand whoop area I usually like less rebound but stiffer compression. Adding too much rebound in sand buries the front end in fast sand turns, with a quicker rebound the forks seem to bounce off the sand once it digs in so deep where as slower rebound let’s it keep burying. That’s just my take and experience. I do run more rebound in the shock which also helps keep the front moving along in soft sand….. too much and you will ride to low in the stroke over sand fast whoops. Then it kicks. If you run a quicker rebound in the shock you can use throttle to control your rebound. Again, my experience. These other guys actually know what they are talking about

Thanks for the input, like I said I can now delve into making this bike more focused on faster rough terrain.

I'm at the lighter end of the spring's weight (I'm 65kgs). I always thought it needed more rebound, I guess I've been going the wrong direction with clickers.

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3 hours ago, gez300 said:

Thanks for the input, like I said I can now delve into making this bike more focused on faster rough terrain.

I'm at the lighter end of the spring's weight (I'm 65kgs). I always thought it needed more rebound, I guess I've been going the wrong direction with clickers.

Repeated fast hits can cause the fork or shock to pack and ride low in the stroke so you run out of travel. Too much rebound damping and/or too little compression damping can cause the same thing. Spring rate might be a factor, but if you are already light for the spring that is probably not the problem.  You can try adding oil too (and it may help a lot) but get the clickers dialed in and go from there. If you find yourself at the end of your clicker range but still want more or maybe you get to the end of the range and it feels good then a revalve comes into play. A fork revalve can change high speed compression/rebound where the clickers don't have as much effect.

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6 hours ago, gez300 said:

What I mean to ask is. Is having less oil in the outer chamber affecting the forks performance over repeated fast hits? 

A revalve is an option I'd try also.

Oil level has an impact you notice pretty much everywhere on the track. So going up in oil level (general stiffening), it will bring you more stability over repeated bumps. Maybe not the best tool, but it works.

It is also that I'd you have 200 oil, and go to 250-290, you will notice it less on the track in general and more just for bottoming. Going from 300 and up it will impact turn in into corners, whoops, braking bumps, ruts, flat corners etc.

The 1/3 being affected, makes it sound like you only notice it when bottoming which is typically not the case.

WP KYB, around 290-300 is where i use all the stroke. Higher then this and it pretty much is like making the fork longer for every 10ml that goes in. 5+5ml very hard to notice, 10+10 absolutely, 20+20 huge difference.

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