An easier KYB Spring Conversion for WP XACT 48mm forks.

Thanks!

I don't think so.  Everything I've heard points toward KTM brands staying on air forks for motocross for a long time to come.  The bikes weigh two or three pounds less and the air-fork is less expensive to produce.

I think the WP XACT fork (2021+) is a big improvement over the WP AER-48 fork (2016-2020) and they are just fine for plenty of riders. Suspension upgrades like this have a place in the world because some guys like a different feel, or demand more from their bike.

There are at least two different heights of KYB oil lock cups that I'm aware of.   The way they interface the lug makes a difference in that height as well as the size and position of the seal head and oil lock piston on the end of the cartridge cylinder.   Actually, there are two diameters of lock cups and pistons too.  My kits are set up for the larger (≈29mm diameter) oil-lock pistons used in later KYB forks.  If your spring perches can slide over the oil-lock piston, it is the early / small (≈28mm diameter).

On the left is the 2006 - 2007 YZ version and on the right the 2008+ version.
( I cannot remember where this image came from, but it shows the difference between OEM KYB parts)

I have two adapter heights and two clicker lengths.  I designed them to have a similar stroke (similar displacement of oil) to the OEM KYB parts in a Yamaha.  My two heights are matched up to form two kits that deal with the two most common cartridge lengths in YZ and KX forks that I've found.

Flipside33, here's the photo you asked for... On the lower left is my kit for the shorter KYB fork cartridge (WP21KKIT-S) and on the upper right is the kit for the longer KYB cartridge (WP21KKIT-L).

The short answer is most years of YZ and YZ-F from 2008 - 2024 as well as any 2009 - 2012 KX450F KYB cartridges.
There are other potentials out there, but I haven't measured them all yet.

I have written up this Technical Information page to help identify compatible cartridges.


If you have a KTM, GasGas or Rockstar Edition, the best performing setup is a 2018 or later YZ450F and 2019 or later YZ250F cartridge and spring with the kit designed for "long KYB cartridges" (WP21KKIT-L). This latest generation of YZ-F fork has a 25mm cartridge with a leaf-spring mid valve.

Any 2010 or later YZ450F and 2014 or later YZ250F or 2009 - 2012 KX450F cartridge is also compatible in the same bikes with that same kit.  My personal bike (the GasGas in the videos) has 2012 KX450F cartridges with (WP21KKIT-L).

If you have a KTM, GasGas or Rockstar Edition and you'd like to save a little money, you can use any 2008 and later YZ125 or YZ250 cartridge or any 2008 - 2009 YZ450F / YZ250F cartridge with the kit designed for "short KYB cartridges" (WP21KKIT-S).   Those older KYB forks can be purchased second hand a little cheaper than the latest version of KYB forks.  Typically those older forks are 24mm cartridges without the leaf-spring mid valve.   Pay attention to the cap diameter with the short KYB forks from the YZ and YZ-F.  They almost all have the large cap diameter that doesn't fit through your top triple clamp.  I will trim them free of charge if you pay the shipping both directions.  If you have access to a lathe, it's a ten minute job to trim the little flange to 53.6mm diameter.


Husqvarna lowered their standard motocross models by 10mm.  The easy and inexpensive solution to this is to use an older "short KYB cartridge" with the kit designed for long cartridges (WP21KKIT-L).  This will preserve the geometry of your bike.   If you aren't sure if you have a 10mm lower Husqvarna model, I created a chart with the upper fork tube part numbers on that Technical Information page.   The same note above applies for the cartridge cap diameter.

A kid I help out won the local series in Schoolboy on his 2022 TC125 running a 2016 YZ250 cartridges with (WP21KKIT-L).

If you have a Husqvarna standard motocross model that is 10mm lower you can run a long KYB cartridge, but you will have to purchase a 10mm fork lowering kit.  I don't know who currently offers that lowering kit.  I will make those parts in the future if the demand for all this stuff exists.

Thanks, that was my goal.

Yeah, you would have to change fork lugs to a set from 2021 or later.  They can be swapped onto any AER-48 fork from 2016.5 to 2020.   It takes a special vise fixture to hold the chrome tube and a bit of heat to soften the thread locking compound.

The fork lugs changed on 2021 and later WP 48mm air forks and that's what my kits fit.  Specifically the fork lugs with the hex machined directly into them. 

I can convert the older forks too, that's actually how this design started back in 2020...   I haven't decided if I want to do a production run of those AER-48 kits yet.  They require removing the fork lugs anyway because the WP oil-lock and blue hex adapter have to come out and my adapter oil-lock has to go in.  That kit uses a different rebound adjuster as well.

If you do want to swap your lugs and you order one of my kits, put a note in the order that you'd like a set of new o-rings for the lugs.
I'll put a pair in the box for you, but you've got to remind me.   The o-rings get messed up sometimes when you disassemble that stuff.

I have been shipping the two conversion kits above for the 2021+ fork lugs and I have plenty in stock.

https://dialedmfg.com

If you buy a set of KYB donor forks, make sure you get the correct kit based on cartridge length.  There's a "Technical Information" page on my website, but you are welcome to ask me directly.

If your question was about conversions for the 2016.5 - 2020 AER-48 fork lugs, I haven't manufactured a production run of those yet. I would like to get them on the machines in 2024 in time for spring or summer.   

The design for those AER-48 lugs was actually the first conversion design I came up with.  They require removing the lugs and swapping out the WP oil lock (bottoming cup) and the blue spacer puck for my adapter, so they don't drop in as easily as the 2021+ kits.   The WP oil lock cup interferes with the KYB spring, so it makes a simple drop in kit unrealistic.   That kit will also include a new rebound adjuster so that the fork lugs don't need to be drilled out or machined in any way.


There is a potential work-around for 2016.5 - 2020 AER-48 fork lugs  (requires machining):

A few guys have asked about using my current kit in those AER-48 (2016.5 - 2020) fork lugs.  It is possible, but I haven't tested it.
It would require using what I call the "Short KYB Cartridge" with my kit designed for the Long KYB Cartridges.  This is because the older AER-48 lugs cause the adapter to sit about 9mm higher in the fork than they do in the 2021+ XACT Air fork lugs.  The difference between my two kits is about 10mm, so your fork would be within about 1mm of the original KTM/WP length.   The downside is that you need to remove the fork lugs and cut down the gray WP oil lock cup from the damping leg to match the blue hockey puck in the air spring leg ( ≈ 19mm final height).   You also need to bore the bottom of the fork lug to clear a 21mm socket so you can tighten the new rebound adjusters in my 2021+ kits.

...I'll post photos that show the differences between the two types of lugs and how the conversion parts fit into them.

 

The two types of WP air fork lugs.  The gray oil lock cup and the blue "hockey puck" are only used in the early AER-48 fork lug.   

I like to refer to the 2016.5 - 2020 WP forks as "AER-48"
I like to refer to the 2021+ WP forks as "XACT Air"

Thanks for the feedback!

You are probably the first to use Honda CRF450R cartridges.
I don't have any data on the length of the Honda parts, but the assembled fork length must have worked out ok.

Thanks a lot for the kind words.

My primary business is production CNC machining.  I do a lot of design and development work with my wholesale customers in the 4x4 and monster truck industries as well as a few other niche areas.

I had considered doing service and assembly, but I lack the tuning and valving experience vs your favorite suspension shops.   Also I'm a one man band, so attention to customers would be sub-par if I take on the responsibilities of a full-service suspension shop.

Suspension tuning is a very customer service oriented business.  I don't want to be the guy who neglects that by reaching too far.  To reduce the time I spend answering questions I've tried to write quality technical information and create acceptable video instructions.  So far, that seems to be good for 95% of the questions out there.  For the direct questions I do my best to answer e-mails within a few hours or at worst the same day.

Later this year (spring / summer) I want to do a production run of the kits for the older WP AER-48 forks (2016.5 to 2020 models).   I am considering the best way to help guys remove their lugs and install the adapters.   I may offer a service for that and/or offer tools to hold the lower fork tubes for lug removal.