3 Different front end weights..... and stem length comparisons for KDX use!

[Chuck78]

Well I spent some time today working on my Showa shock retrofit details and figuring lowering spacers vs ride height etc, and also got to tear into the '99 KDX220 as someone wants to buy the stock forks from it, and... I got a pair of KX450X triple clamps the other day, and I was dying to see how they'd fit!

Well, I determined that really the best steering stem length for our frames is 190mm-192mm from outside to outside of bearing surfaces on the steering stem...Chopperpilot's YZ250 2-stroke worked out to be a hair under 194mm and he said this fit perfect, so we are very close in agreeance.
With the KX450X in front of me now, it measures more like 196mm, but this is still very workable, especially as I could just run a 3mm thick or so spacer UNDER the lower bearing, dropping the triples slightly and dropping the upper bearing surface on the steering stem in position better. With my quirky plan of a 28mm upper stem running a 30x47x12 bearing (to have the same bearing races in both bikes if I were to swap forks between them, using a sleeve to drop the 30mm i.d. down to 28mm for the KX450X forks only) would have to be spaced up 3mm from underneath the race, but if using the generic Amazon 28x47x15 bearings, there would be no issue aside from needing a 3mm or 4mm or so spacer on top of the bearing and seal to span the gap between the nut and the bearing if not shimming up the lower bearing from underneath.
This was a pretty big success I'd say, although my desire to run the 30x47x12 bearing is requiring some additional custom spacers machined, With the 28x47x15, you'd just need a couple of steering stem washers or make an aluminum spacer that doesn't have to be terribly precise other than even thickness in the up and down dimension.

[Chuck78]

So I quickly weighed my stock '95-'06 KDX forks without the triples, vs a current model 2021+ KX450X / 2026+ KDX300R Showa 49mm Twin Chamber forks...

KDX forks have unknown oil level (seals were leaking slightly) & stock .35kg springs for a 130lb rider...
2024 KX450X forks are brand new factory take offs, .48kg fork springs and more oil than I'll run. Superlight fork springs are in the mail.


KDX '95-'06 43mm KYB Open Chamber fork legs = 21lbs 4oz
KX450X '21-'25+ Showa 49mm Twin Chamber legs = 19lbs 7oz (same forks that'll likely be on the new '26+ KX300X/ KDX300R

1lbs 13oz lighter for a far more advanced and rigid fork is a nice savings! And also, the springs I have in the mail will be significantly lighter than the stock springs, so that will drop a hair off the brand new 49mm Showas as well... Nick from ApplegateMX had a pair of those Diverse Springs Superlight low friction micropolished fork springs in hand, and thought they were titanium, and said they were the lightest springs he's ever felt! They had the Diverse Spring DS######## part number on them, which is how I instantly was able to identify them...

I suppose only the modern-ish mid-2000's KYB Open Chamber 46mm & 48mm forks will really be closer to 4lbs lighter than stock, oh well on that additional weight savings, closed chamber Showas and KYB forks are the most advanced tech we have available... the Open Chambers get the job done still quite well though!

I'm very excited to have a pair of brand new Showa Twin Chamber 49mm current model off-road forks to swap onto my KDX along with this Showa rear suspension I've been tinkering on adapting a few days a month now for several months... I hope I can get the valving close for the first ride of the season April 4th on opening day at Perry State Forest!

[Chopperpilot]

OK, quick update on YZ triple clamps with some good and bad news. Good news! The 2010 22mm offset YZ450 clamps, with the 'medium' stem length fit up fine on the kdx frame with a KDX lower stem bearing and the 28 x 47 adapter upper bearing. The upper nut threads are just a skoosh below the upper bearing race, and the nut can get full thread engagement. As I thought, with the KDX lower bearing installed, this stem is either perfect or a touch too short, depending on where you like the threads to stop!
Now the bad news! I thought I would be able to use both these clamps interchangeably to see if I liked the 22mm offset vs the 25mm offset. The upper clamp diameter is the same. Unfortunately the lower clamp diameter is .5mm different between the 48mm fork legs and the 46mm fork legs. Because the 46s are so rare, nobody really talks about the lower clamp diameter on them. The 2010 lower clamps will 'tighten' on them, but you can tell that they slide over waayyy too easy to be right. The 2003 clamps measured 58.42mm and the 2010 measured 58.90mm....... so close. Maybe cut up a beer can for a shim?? Guess I'll have to keep an eye out for 48mm OC or some SSS fork legs. I think the 48 OCs and some early SSS had a bigger top clamp diameter. It looks like Kawasaki 48mm KYBs had the smaller 54mm top diameter, like my clamps. I was really looking forward to the 2 different bar mount locations on the 2009 clamps.

[Chuck78]

I worry about not having exacting sized triple clamps made for or exactly matched to the forks being used, as if one end upper or lower is slightly off in diameter vs fork tube, or they are off by slightly differing amounts, it will clamp the tubes in sideways out of vertical plumb, and they will no longer be parallel, causing stiction and binding. I cringe when I read of people saying "they're close enough to work" when mismatching forks and triples....


I'm very sorry to hear of your fitment issue.

So with the medium steering stem height, the threads extend down just a hair below the top of the upper bearing, so that most of the upper bearing is still on the stem's bearing surface?

What was the length difference in the bearing height bottom of lower seal to top of upper seal on the bearing areas of the medium vs YZ250 2-strong long Yamaha stems? So the long stem worked perfect and would allow proper torque + a thread or 2 for bearing wear to be further tightened in the future? Or is a washer/spacer a good idea on the long stem?


I've got a CRF450 triple on the way now to verify, but noted aftermarket steering stems for aftermarket triples have stamped CR250 / 450 on them and the CRF450 '08 triples that someone said fit their KDX on here as well as the CR250 2002 stem drawing I posted show this to be perfect height, as did eBay seller photos of this 2018 CRF stem, so I think it's around the same as the Yamaha stems and virtually perfect for the KDX, AND 30mm upper bearing so I can use NTN Japanese bearings from Pyramid Parts (they sell with the right sized seal, and if you get the more expensive option from eBay, it comes with two spacers same as the All Balls conversion bearing kits).

[Chopperpilot]

I feel the 'long' YZ (2 stroke 250s) stem is the perfect length. The threads stop just a skoosh (a highly scientific term) above the bearing race. The nut is still able to be torqued to cause steering drag without a seal ring installed (and presumably stop steering movement if I continued).
The 'medium' YZ stem (four stroke 450 and 250 IIRC) is also perfectly acceptable and the threads are just a skoosh below the bearing race (I'll get pictures later) and the bearing race is absolutely located on the bearing surface on the stem. I guess what would be beneficial is if someone gets a look at what the factory setup is (are the threads 'exactly' at the bearing race? a touch above? a touch below?). I can't do that any more (more accurately I don't want to bang out my upper adapter race to see) because I have the adapter race in now.
BTW, there's a nice park bicycle tool for knocking out headset bearing races that make it a breeze (RT-2) about $42. I already had one because you're not smacking randomly on bicycle head set cups and frames.

[Chuck78]

I still have the stock bearing race in my KDX frame, I'll dig the triple out when time allows and check this before I bang out the race. Coincidentally my wife has that exact park tools headset cup remover! Before my HVAC career, I was a bicycle mechanic for a decade myself!

[Chopperpilot]

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Here is the pictures of the 2003 'long' YZ 250 stem and the 'medium' 2010 YZ450F/250F. I included two pictures of the 450 stem, one with bearing uninstalled, so you could get a feel for how far 'down' the threads were. You can see the 250 2 stroke 'long' stem threads go to just above the bearing race. I went ahead and mounted the 2003 stem (due to the 2010 clamps not fitting my forks). I used a wallowed out KDX upper seal + the frame rubber cover. Now that I look back on mounting it....... I was able to get the nut tight enough to start to create steering drag. I continued to tap the nut tighter and tighter (be careful, this is aluminum we're dealing with!) and noticed the drag didn't really change. Now keep in mind the drag I'm talking about means if I put the triple trees into a position, they do not 'flop' anywhere else of their own accord. Including when I just put 1 fork leg in that weights one side (note to self, I should look up actual procedure for stem torquing other than the German way). I was still able to change the amount of steering drag to slightly less. So maybe the 'long' stem is a touch too long and could use (or not) a slight spacer? I have the Yamaha versions to use as well, my top bearing will be the most sealed ever!

[Chuck78]

If you're not happy with the top seal setup, the first time I bought a pyramids part conversion bearing a year or so ago, they sent me the wrong seal with it, 30mm ID bearing and 28mm ID seal! So I could potentially post you this seal. This week is a busy one for me though, and I'm not sure I'd have time to get it out before later next week.


Thank you for posting up this photos! I kind of suspected that a thin spacer / washer might be necessary to get the nut slightly higher up, but it does seem that either of those would work out well. The benefit to the taller stems is that although raising the handlebars up higher as the upper triples will be higher, sometimes a good thing sometimes not preferred by certain riders, by having the upper triple elevated higher, the taller forks can sit flush while actually being lowered in relation to the lower triple, so it reduces the right height somewhat.


I have a 2018 CRF 450 triple clamp in the mail, and although I believe the Honda and Suzuki lower bearings are smaller O.D. like the Yamaha, I may buy a few more lower bearings since I have multiple triple clamps to test out. Maybe I can buy one of those bearing puller tools that can clamp around underneath the stem bearing and extract it more readily and just pull the one off of the KDX triple clamps and use a Dremel flap disc of the radial variety and clearance out the inside a little bit just for testing purposes.

[Chuck78]

2003 YZ 250 - 193.675mm to the bottom of the threads for the upper bearing

2012 YZ 450F - 190.5mm to the bottom of the threads for the upper bearing

So...the 4 stroke stems were 4mm shorter than the 2 stroke 250 stems.

The long 2 stroke 250 YZ stem does appear to be the 'perfect' height. The top bearing (when stem is 'torqued' down and starting to create steering drag) sits just a smidge below the threads (somewhere between .5 and .8 mm).

So it seems like around 192 mm would be the perfect perfect size for a stem, bearing distance measured on the outer ends, based on your pictures and measurements.
The CR250/CRF250-450 stem according to that CAD drawing is 191mm and reportedly works quite well.

So it seems like the CR250/CRF250+ stems or the YZ250 two-stroke stems are going to be the #1 preference although somewhere in the middle between those two would be more perfect, & the Yamaha medium-like stem still being an acceptable size. I do like the fact that the Honda stems use a 30 mm upper bearing I.D., so one can run the Japanese bearings.
If All Balls took the time to look at this, they could easily capitalize on making a mild interference fit tight push-in fit upper bearing sleeve that would make their 30 x 47 x 12 bearing into a 28x47x12, with the spacer flange at the top sandwiching the seal between the bearing and the flange on the top side of the spacer... I believe I mentioned this to them in my brief email, but being such a big corporate conglomerate, this type of request is probably less likely to be heard by anyone or at least be passed along.

[Chuck78]

Some more info passed on to me from a local KDX/vintage street bike guy David McClain:


AOS/SSS fork interchange
All 2006+ 48mm KYB SSS forks have 59.0mm lower clamp.
2006-14 2 strokes: Upper 56.0mm.
2006-09 YZ450F: Upper 56.0
2006-12 YZ250F: Upper 56.0
2010-15 YZ450F: Upper 54.0.
2013-15 YZ250F: Upper 54.0
2006-2012 KX450F: Upper 54.0

Different 2008-up front brake mounting bracket change is one variable I know of.

[Chopperpilot]

Ok, snow is starting to melt and the following snowfalls won't stick around long so I'm getting the KDX back together. Put the 2003 YZ250 front end on (I still need to fab frame/fork stops for it). Couple of things I noticed..... the triple tree bar mounts put the bars up slightly higher than the KLX/KX setup I was running by a few mm, I consider this a bonus. The KDX brake caliper fits the YZ front end. I bought a YZ wheel/axle setup and of course that works. I test fit my KX (94? ish) wheel to see if I would have a back up. I will! Woohoo, with using the factory KX seals/spacers, I'll just need to add a 5.5-6mm axle spacer on the brake side. So for any like me double converting USD forks onto a KDX, I think with some spacers, pretty much any 20mm MX front wheel setup could be made to work.

[Chuck78]

Ok, snow is starting to melt and the following snowfalls won't stick around long so I'm getting the KDX back together. Put the 2003 YZ250 front end on (I still need to fab frame/fork stops for it). Couple of things I noticed..... the triple tree bar mounts put the bars up slightly higher than the KLX/KX setup I was running by a few mm, I consider this a bonus. The KDX brake caliper fits the YZ front end. I bought a YZ wheel/axle setup and of course that works. I test fit my KX (94? ish) wheel to see if I would have a back up. I will! Woohoo, with using the factory KX seals/spacers, I'll just need to add a 5.5-6mm axle spacer on the brake side. So for any like me double converting USD forks onto a KDX, I think with some spacers, pretty much any 20mm MX front wheel setup could be made to work.

I'm using a '99-'02 KX front hub for my '98 RM125 forks! I liked the idea of keeping a Kawasaki rotor bolt pattern, and being able to use KDX/KX rotors still. Also, I liked the style of the KX / KDX rotors better as well.

My other bike is likely going to run the same KX front wheels, although the newer 2024 KX450X that these forks came from use a 22mm front axle. I'll be machining some adapters on my old lathe for this purpose...

[brademan76]

Some more info passed on to me from a local KDX/vintage street bike guy David McClain:


AOS/SSS fork interchange
All 2006+ 48mm KYB SSS forks have 59.0mm lower clamp.
2006-14 2 strokes: Upper 56.0mm.
2006-09 YZ450F: Upper 56.0
2006-12 YZ250F: Upper 56.0
2010-15 YZ450F: Upper 54.0.
2013-15 YZ250F: Upper 54.0
2006-2012 KX450F: Upper 54.0

Different 2008-up front brake mounting bracket change is one variable I know of.

Chuck, seems the 08/09 KLX450R had the AOS forks. Thoughts on this fork design for single track use? Those triples/forks should be an easy swap, right?

*I guess I'm reading the klx300 was the direct swap, so maybe not...

[Chuck78]

I believe the KLX450 is based on the KX450 motocross bike. Being a heavier nike, unless you are a heavier rider, the valving may still need adjusted to be more plush after you swap to a lighter rate spring.
The compression base valve cartridge on closed chamber forks generally may need a softer internal compensator spring swapped to allow more initial plushness, around 1.5kg is what the CRF250X woods forks use. I bought 1.1kg ICS springs for my '98 RM125 Showa Twin Chamber forks, have yet to install, but I'm 160lbs and lightening up my KDX's as much as possible including lots of titanium hardware (I'm slightly worried that may be too soft and allow more cavitation of the damping oil on faster sections though, but thus was Race Tech's recommendation per their charts for my weight and general bike weight).
The ICS springs in the forks do the same thing as the nitrogen charge in the shocks (except that the shocks have a progressive linkage to create more initial plushness, forks do not!!).
You don't want to go too soft, but finding out the stock ICS spring rate from Race Tech via their product search (sometimes it simply says "please call us"), is very helpful. The KLX450R is probably more like the new KX450X, I'd imagine more oriented towards woods racing, but perhaps not, as the KLX line has generally always been a casual woods bike otherwise, BUT this one IS is based on a motocross model the KX450...

Look into it, they are great forks, but the amount of tuning required is unclear. Closed Chamber forks can be set up very plush, but it just takes a bit more effort than with Open Chamber forks, and sometimes compromises the closed chamber advantages to a certain degree, of reducing and nearly eliminating cavitation in the fork oil on rough washboard sections and aggressive racing use.

I doubt the steering stems will work on the KDX the same as a KLX300/KX500 stem, as it's likely a 28mm i.d. upper bearing and likely slightly longer than the KDX stem. It could be adaptable with a generic Chinese 28x47x12 Amazon eBay bearing (not an industry standard size) or an All Balls or Japanese NTN 30x47x12 + some machined adapters though.

[brademan76]

Good info, thanks. I'm 205 in my birthday suit, probably closer to 220 fully geared. I have .42 springs in my stock forks with racetech GVs now and don't feel oversprung. The stock springs in the klx450r is 0.44.

Racetech lists the FORK CARTRIDGE PRESSURE SPRINGS - Recommended Pressure Spring Rate: 1.4 kg/mm (Use closest available) Stock Pressure Spring Rate: 1.9 kg/mm (Stock)

[Chuck78]

I bet those forks would do quite good for you. I'm not really sure about how they are set up, you might just want to look up some reviews of that model online and some feedback from owners as well from forums. If it's a really detuned woods oriented bike and not an enduro racer type setup, they might be really good as is for singletrack use. I find that even stock KLX300 1990's-2008-ish fork valving Works quite well on single tracks when paired with a 90/100-21 Shinko Fatty Cheater + Nuetech Tubliss @ 7.5psi-8.5psi... any shortcomings in the stock valving are really assisted / compensated for by lower PSI Tubliss on good Shinko Cheater tires. I run the Shinko 520DC rear (dual compound gummy) & on the KTM 200 (wife's ride), a Shinko 525 Cheater rear. This setup is FANTASTIC.
It's pretty similar with the closed chamber forks but you need to be a bit more intentional about the valving setup and pressure springs. Some people run less preload or basically no preload on the main fork springs on closed chamber forks in order to compensate for the initial pressure applied by the compression valving ICS springs. closed chamber forks have two different grooves to run the spring seat clip in, but also I have seen videos of suspension guys machining another groove into the cartridge assembly for a different alternate spring seat location, or aftermarket parts from ride jbi that give a different spring seat location groove as well.

[brademan76]

I doubt the steering stems will work on the KDX the same as a KLX300/KX500 stem, as it's likely a 28mm i.d. upper bearing and likely slightly longer than the KDX stem. It could be adaptable with a generic Chinese 28x47x12 Amazon eBay bearing (not an industry standard size) or an All Balls or Japanese NTN 30x47x12 + some machined adapters though.

Quick tape measure on the stem of the klx450r shows 7-3/4" from bottom bearing to bottom of threads just above upper bearing surface. So maybe just need to shim between the nut and the bearing a little. Will see when I have time to put on the kdx with one of the adapter bearings.

[Chuck78]

I doubt the steering stems will work on the KDX the same as a KLX300/KX500 stem, as it's likely a 28mm i.d. upper bearing and likely slightly longer than the KDX stem. It could be adaptable with a generic Chinese 28x47x12 Amazon eBay bearing (not an industry standard size) or an All Balls or Japanese NTN 30x47x12 + some machined adapters though.

Quick tape measure on the stem of the klx450r shows 7-3/4" from bottom bearing to bottom of threads just above upper bearing surface. So maybe just need to shim between the nut and the bearing a little. Will see when I have time to put on the kdx with one of the adapter bearings.

As long as the bearing area on the stem extends down far enough. 192mm-ish (190mm-194mm) / 7-9/16" seems like a pretty ideal distance from the bottom of the lower bearing seat area to the bottom of the threads on the stem nut, for our frames. So the KLX450 has typical late model KX steering stem dimensions, which are appearing to be the same as the 2019 to 2024+ KX