2013 KYB PSF updates.

With the ongoing development of the KYB PSF and a lot of really good info coming to the front of the reader’s attention, I’ve been generally silent. (Except for what I put on Face book.) We have been on this Air system for a long time. Early this summer when I read that the PSF was coming I had Kerry Cannon from Cannon Spring making me negative springs ( balance springs) to put in my standard KYB forks so I could do the air conversion myself. I was thinking we could potentially do conversions. And the learning curve was step; the conversion idea was not going to be possible. But I learned a lot. When the real version became available with the Kawasaki KXF450 I got one right away. (Along with the CRF450 that we received in September) The first rides where exciting but then the fork started to present its characteristics and flaws.

My Prototype Air fork. June 2012

In a nut shell the fork works really well on hard-pack, and jump filled tracks that involve rhythm and timing. The lack of friction from the coils of the spring is very noticeable and the fork has a nice fluid feel. However in fast, outdoor tracks with big braking bumps the fork is not so happy and becomes very harsh.  The root cause of the problem is that as the fork reaches the second half of the stroke the natural pressure increase due to volume change becomes very pronounced. In the final third the pressure increase is exponential and the air force is much greater than the valving, spring and air spring of a traditional fork.

We attempted a multitude of fixes and here is what we have found that is useful.  Stiffer midspeed valving (midvalve float) this keeps the bike out of the stroke a little delaying exponential increase in pressure as the fork uses stroke.  We run the Oil as low as possible; this delays the pressure rise until deeper in the stroke. Bottoming tends to start to occur. To better manage the bottoming control we designed and tested a SSBCV (Huck Valve) for the PSF. This makes a huge improvement. We have also been testing a MXT LFPR for the 32mm valve.

This image is the external subtank system we tested. It evolved to be an external volume compensation with dual pressure regions.  This was to precede the following more tiddy internal design,



We have also been testing a MXT LFPR for the 32mm pistons. The steel / Teflon ring seals better, and is more stable and lowers friction significantly.

Where is it going? We tested several types of pressure management systems. Enzo Racing style subtanks etc. The real solution will involve multiple pressure regions that compensate relative to position.   (Pressure) We are working on these designs right now.  If this type of stuff interests you make sure you look at the MX-TECH Face book. I’m always posting models of ideas and projects.

The PSF SSBCV Huck Valve P-types.

If you own a PSF fork now and want to improve it. I would do the following in order of value.

#1: SKF 48KHD seals. They will improve the performance and reliability of the fork.

#2: Lower the oil volume.  This will help the bike work better in braking bumps at the expense of bottoming control.

#3: Change the stock midvalve piston rings to the MXT LFPR. The Low Friction Piston Rings improve the wheels ability to follow the ground which improves comfort and control.

#4: Revalve for more midspeed compression damping, and less high speed. This improves plushness while delaying the pressure increase by reducing use of travel.

#5: Install the MXT SSBCV PSF Huck Valve.

Let me know what you think of this Blog.

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One Response to 2013 KYB PSF updates.

  1. Igor Babiy says:

    Hi Jer!
    I think your blog is very useful.
    I cant revalving and testing this fork yet,
    because winter and a lot snow. But I try to pack more info about PSF.

    Best Regards.

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