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Suspension Improvements.

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I'm looking for some ways to improve my suspension, mostly the forks, without springing (haha) for an entire revalve. I find that my are really harsh on small stuff yet will still bottom fairly easily. To prevent the forks from bottoming, I have to crank the clickers way in which in turn makes the forks even more harsh. I came across a post in another forum made by a suspension tuner in Aus and it describes exactly what I'm feeling.

The KYB forks have a cylinder valve in the cartridge which allows oil to bleed out in a rather uncontrolled manner. This in turn means there is less oil passing through the compression or base valve. In order to combat this Kayaba has stiffened the base valve significantly in an attempt to try and achieve the same amount of damping with less oil. This results in a harsh action yet the fork will still bottom easily on big hits. The answer is to replace the cylinder valve and lighten the base/rebound valves. The result will be a plusher, more controlled ride with greater bottoming resistance. For some reason KYB have always been down on build quality yet the performance potential of their components is staggering.

How hard would it be to replace that "cylinder valve" and "lighten the base/rebound valves"? If it isn't too hard, I would like to try doing that over the winter when I pull everything apart. I've only had my forks apart once and that was to change the oil.

Right now the forks are set at the stock oil height with 5wt oil in them. The springs are stock as well. I weigh about 160 lbs so spring rate shouldn't be an issue. Is there anything else in the form of oil and oil height that I could try to improve the forks?

Thanks

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try amsoils #5 synthetic fork fluid. It is amazing stuff, and cheap too. Race tech's synthetic is like 4 times as expensive and doesnt work as well as the amsoil.

I would spring for better springs though. even though they are the right weight they do sack out over time, and I suspect the steel used is not as good as the race techs springs.

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I'll give that a try. I had an extra bottle of BelRay 5wt but if you think the amsoil will help then I'll try it next oil change.

What effect does the oil weight have on suspension action? I'm thinking that maybe I should try 7.5wt instead if the 5wt still doesn't work.

What about oil height? What effect does that have?

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In my opinion never play with oil weight only the level.

Okay but what effect does oil height have? Less oil (larger height) means more air and softer suspension right?

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oil height make the initial hit stiff or soft. If it's low it will have more air and will be a softer hit. If it's high it will have less air and will be a stiffer hit. It all depends on how you like the forks to feel.

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In the simplest terms,spring rates affect fork ride height and oil thickness and valving affect fork speed.

The thicker the oil the greater change it will have when it gets hot and thins out (or gets old)thus causing a new variable in the equation.

Oil height is part of the spring side of the equation ( mostly). The greater the oil height, the less prone it is to bottom. (position)

Isn't stock oil height around 120mm? My suggestion is go back to 12C and 10R on clickers and change your oil height to 90-95mm. Go out and ride and see if it bottms on the same troubling jump. Turn the comp clicker in until bottoming stops. If you get below 4-6C you've really got no choice but to get new spring or revalve ( or as last resort add more oil until the recommended max, but watch out as fork seals like to blow at this level).

You might also want to measure the spring for length as when they sack out they are shorter and below spec's. Check the manual.

Make sure your rear sag is correct too as that has an effect on harshness up front.

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I thought that oil heigth only affected the last few inches of travel if there is some bottoming, add oil to bring the level up 5mm and try again. I am running 110mm oil height and do not bottom, but I don't moto and jump big either. Don't run off for a revalve right away--you likely don't need it.

If you have not measured you oil height without the springs in the fork tubes, how do you know it is at stock height? Don't assume. Different people put the forks together. I once sat on a bike in a show room that I could almost bottom the forks and it was obvious there was little if any oil in them. It was an '01 Yamaha YZ250F.

Get rid of the stock oil and put something decent in it like the Amsoil or Spectro full synthetic. Stick with 5wt. Put the forks to stock height in the clamps.

Set all your clickers to stock along with stock oil height. Make sure your rear is set up good too--proper race and static sag and clickers and nut to stock and then test. There are some good sites with proceedures to set up suspension--MX Tech or Race Tech, I forget. But you set up one thing at a time. First set up your rear rebound, then rear compression, then front rebound, then front compression. Leave everything else alone and only test for one thing at a time and save the bottoming in the front on big jumps for last. You SHOULD bottom on the biggest jump on the track if you land it properly. But--the bottoming should not be harsh and you should easily be able to maintain line control and absorb the rest with your body.

Strive to remove as many variables as you can before testing for a problem. By removing varialbes and going back to stock and proper set up per the manual, often times the problem disappears because it was something you unintentionally dialed in. On the other hand, it may be your riding technique. You may simply be landing too harsh on the front wheel and perhaps need to video yourself and make some in-air corrections, or take-off corrections. Certain settings on the rear can also affect how the front behaves and vise-versa. Stive for a balance between front and rear. Opt for plushness over anti bottoming. Most of your riding will be done in the first 6 or 7 inches of travel anyway.

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keeripes, I cant believe I remembered it that backwards. :thumbsup:

Thanks for your post Rudy, it caused me to go back and reread the manual. yup oil height affects the end of the stroke more than it does the beginning.

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I rebuilt the forks last winter and set the oil height myself. I set it at 120mm.

Is it possible to say add another 20mm of oil to each fork leg without having to take the springs out? I'm planning on rebuilding them over winter again but for now I just want to add a bit of oil. Maybe I'll just throw 50mL in each fork and see how that works.

I'm mostly having troubles with it bottoming when landing short on table tops.

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I remember somebody had a general equivalence of teaspoons to mm for fork measurements. maybe do that as a search or topic title if know one remembers it offhand.

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Is it possible to say add another 20mm of oil to each fork leg without having to take the springs out?

Go out and buy a syringe that is used for giving infants liquid medicine ($2 or less). Fill it up with fork oil and squirt it into your bleed air hole on the top of the forks. Do both sides equally until it stops bottoming.

Are you bleeding the pressure in these forks?

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I think somewhere in the manual it tells you how much volume of oil is needed to raise level x amount of mm's.

Putting oil is way easier than taking it out. If you have 120mm level (120 down from top without springs) then raise in increments of 5mm and test well before adding more.

On the other hand, how do the forks work when you don't come up short and land harshly? Maybe they are working well?

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