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

[HeyItRuns]

Okay. Forgive me, but I just want to clarify.
Is that all crf250x/250r/450 years?
99-05 KX 125/250/250F are good donors. Are the other Kawis mentioned (the 250F from 2005 on, or later KX models) possible candidates using the generic bearing, or do they require a stem swap?
No YZ125s are good.
All YZ450s are good, some are long stem and are very good.

[Chuck78]

Okay. Forgive me, but I just want to clarify.
Is that all crf250x/250r/450 years?
99-05 KX 125/250/250F are good donors. Are the other Kawis mentioned (the 250F from 2005 on, or later KX models) possible candidates using the generic bearing, or do they require a stem swap?
No YZ125s are good.
All YZ450s are good, some are long stem and are very good.

To the best of my knowledge all of the Honda CR 250 2-stroke and CRF250 / 450 4-stroke models that I have seen dimensions on are all the same steering stem which is nearly perfect for the KDX frame constraints and steering head tube frame height.
I cannot speak for the CR 125 2-stroke, although my brother has one 70 miles north of where I live, if I can ever get him out to ride with us again in the woods, I'll try to measure his.

KX250F 2006+ are the Showa Twin Chamber forks through I believe 2018. 2019-2025+ KX450 switched to Showa 49mm Twin Chambers, 2019-2024 KX250 (4-stroke KX250F without an F designation) went back to KYB AOS (same as the YZ forks 2005+) until 2025 when both KX250 & 450 are equipped with Showa Twin Chambers.
I'm not sure what year it changed, but the newer KX steering stems are about 7 mm too long, although this can work out in your favor as the upper bearing seating area on the steering still extends down low enough, but the top will need a spacer. I say it can work out in your favor because that will allow you to slide the fork tubes further up through the lower triple clamp just to meet the upper triple clamp, so unless for some reason the fork tubes are even longer which I don't believe they are any different than my 1996 KX forks, then you get a little bit of free lowering action just by sliding the forks up without affecting The handlebar clearance whatsoever, although this will raise the handlebars up higher and if you like low handlebars, will require lower bars even.


YZ125 forks will work great as long as you use YZ250 2-stroke triples. Those would actually be even better because they may have a slightly lighter spring in them stock, depending on what you do as far as spring rate versus valving. Modern forks seem to come sprung incredibly stiff compared to decades old schools of thought from the 1990s and 2000s on spring rate, which extends to the current Race Tech recommendations as well, versus suspension tuners who really like to spec them stiff. Suspension tuners generally cater towards racers, however, who always require firmer springs because they are absolutely hammering it over everything, and even a fast aggressive trail rider will find eraser type setup a bit harsh unless they are in fact a racer and very young, or run a fairly low PSI/equivalent in their Tubliss or Mousse setup, which would be counterintuitive to aggressive race pace riding to some degree, you're going to feel the stiff springs regardless of the valving.
I like to compare Race Tech spring recommendation vs Teknik Motorsports in Australia, who are generally about one spring rate more firm than what Race Tech quotes. It's nice to get multiple opinions on things.

As best as I can tell almost all forks are candidates for swapping with either the 30x47x12 or the generic-only 28x47x15 &/or 28x47x12 bearings, however there are a few older models which use a 26 mm inside diameter upper steering stem bearing. That would be excluded from this although conversion bearings might exist for that size.

I would always try and avoid doing a steering stem swap, because nearly every Fork you are going to swap will have a much higher quality aluminum steering stand versus the hefty steel KDX stem. The aluminum stems are thicker, but it's still a bit of weight savings, and the KDX is a fairly top heavy bike to begin with having a thick seat, longer rear seat frame made out of steel, larger fuel tank, and primarily the perimeter frame with two tubes cradling the fuel tank which keeps the fuel weight up higher than a center spine frame. It's a better frame design technically, but it keeps more weight up top which makes the bike feel much heavier than modern bikes unless you run less gas in your fuel tank always... So dropping a little bit of steering stem weight as well as a significantly lighter Fork swap will do wonders for the perceived weight feel of the bike. Does KYB open chamber forks even the 48 mm versions will be considerably lighter than the stock forks. The closed chamber forks will be 1-2lbs lighter. If you go with a modern Fork that is on the list of diverse springs Fork spring offerings, their Chrome Silicon Steel SuperLight Fork Springs are so light you would think they were titanium, so you could drop a little bit more weight from the closed chamber and twin chamber forks that way since those forks inherently weigh a bit more having the compression damping cartridge at the very top instead of the very bottom. It's a trade-off as you get a better handling bike with less weight being unsprung, meaning the wheel and the axle and the portion of the forks attached to them, but you have more weight up top (higher center of gravity you feel more) in the forks although the forks are still lighter. Reducing unsprung weight will give you better suspension action by far, although closed chamber designs always take a lot more work to get the initial plushness of open chamber forks.