Showa Twin Chamber 49mm conventional forks 96-98 RM125/250 + inverted Showas // RM & DRZ400 shocks & DRZ400 49mm forks!

[Chuck78]

Pictures from Negative_Noel on Thumper Talk:

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[Chuck78]

More, as well as someone's DIY milling of the triple clamp to gain the necessary steering stem height without reducing the available travel on the chrome tubes:

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[Chuck78]

I've got too many irons in the fire so to speak, but have gotten the stem pressed out of the bent lower triple that I had, as a test since the triple was not usable as-is. It easily came out with my 10 ton homemade hydraulic press.
I used my oxy-acetylene torch set to heat the VStrom DL1000 triple to remove it's steering stem, since I intend to use the RM or similar GSXR steering stem in the V-Strom triples perhaps, for some street bike fork swap projects. It came out even easier when heating the lower triple with the torches. No prob.

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I got the longer V-Strom steering stem chucked up in my lathe but had to order a new live center for the tailstock, as my old beat up live center gave me about .002" runout.
As you can see from the photo, this will work out just about right, but I'm going to cut the bottom flange stop on the V-Strom steering stem about 1.25mm shorter to allow the stem to press up into the triple further, as it's cutting it pretty close on the shorter 30x47x12 upper bearing + 3mm spacer on top of the bearing, the bearing will be a few millimeters over the threaded portion of the stem. One nice thing about the V-Strom stem, is that it comes with TWO spanner wrench type threaded locking collars, with a toothed washer in between, so I believe the 3mm difference in bearing height I can just use one of these thinner locknuts as the spacer to make up the 3mm difference in height versus the OEM KDX bearing vs the 30mm i.d. conversion bearing.

Also got a nice new diagonal/diamond pattern knurling tool for stem swaps. I assume most people knurl the outside of the steel KDX stem, although I did read commentary of one person stating that their machinist said they had no tool to knurl the aluminum i.d., which I was surprised to hear someone even considering knurling the i.d. of the triple vs the o.d. of the stem.

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I also got a nice face plate for my South Bend Heavy 10 L lathe, so I can just bolt the RM lower triple to the face plate and shim it until it spins true to the bore, and cut the lower bearing seat down in the lathe. I suppose I could also have just made up a press fit stem to insert into the bottom of the triple from underneath with heat to the triple and a chilled shaft fresh out of the freezer, and cut the bearing surface down that way with the specially cut holding tool chucked into the lathe. That might actually be easier to set up, as the bottom of the cast triple is not guaranteed to be a flat surface perfectly perpendicular to the steering stem's machined bore (as well as the fork tube bores).

One other thing - the V-Strom stem will protrude a bit higher than what I'd hoped above the RM's (or DR-Z400E's) upper triple, so an aluminum spacer may be required, or else cut the stem threads down further and shave the top of the stem shorter in the lathe.


Before I determine how much of the RM lower triple's raised bearing seat step I can machine off, I'll need to pull the forks off of my '99 KDX220R rebuild & mod project bike and mock up a stock KDX / RM lower bearing (same size) to check clearance, as this is a "gullwing" type lower triple - as is typical for non-inverted forks' lower triples. The sides angle upwards, so I can't cut too much off to near flush, as the head tube of the frame then could be dangerously close to rubbing the triple.

I also plan to shave 1mm off the bottoms of the lower triples where the fork tubes slide through, as the KDX frame's taller steering stem / head tube height is pretty close to cutting into the travel range of these forks, and internally lowering at the top-out area of the forks, as is typical, won't fix this clearance parameter no matter how much you lower it internally.

[Chuck78]

I plan to run near zero preload on the fork springs in order to help "lower" the ride height up front (by allowing more sag with rider seated on bike), since it'll be quite a bit taller with the 97-98 RM fork dimensions vs stock KDX or 96 RM.
Running almost no preload is also highly recommended for a woods bike setup on twin chamber / closed chamber forks, to help overcome the ICS inner chamber spring, which does add some to the initial fork movement's spring rate but is there to control cavitation far better than an open chamber fork.

Stock spring rates in the RM125 are .40kg, and due to being Closed Chamber / Twin Chamber forks and having the ICS spring adding a bit to the initial force required to initiate travel, I absolutely am going to order some Cannon-Racecraft springs in .38kg (what Racetech recommends for me doing singletracks at 30-44yrs old and ***preferring softer spring rates***), and I'll probably also try out the Cannon-Racecraft ICS springs which are listed as a progressive rate starting at 1.2kg/mm and firming up into the 2.-something range. Racetech lists a chart for the ICS springs, and recommends for a woods/enduro/singletrack rider of 160lbs or less, to run their 1.0kg ICS spring. The CRF250X Showa Twin Chamber woods bike forks come stock with a 1.5kg ICS spring. Some people have said that going down to a 1.0 or softer than the fork was designed for just makes things out of balance, as the softer spring allows more cavitation, which alters the way the fork responds, and goes against the design intent and principles of the twin chamber / closed chamber design strategies. RaceTech lists the ICS springs on these RM forks as 2.7kg/mm, which I find VERY HARD TO BELIEVE, but just in case, since I have a stack of these forks now, I'll be able to head to the trail with my Showa fork cap wrench and multiple sets of base valves, since the 98's have the quick change base valve feature at the top of the forks, so I can set up 2 sets of base valves with stock and aftermarket ICS springs, and go for a trail ride with both back to back to test them out.
I have a feeling that the recommended valving which I've stumbled upon and noted in this thread, may behave differently if I go switching the ICS springs out, IF the RaceTech spec of 2.7kg/mm is in fact correct. if it's not, and the ICS spring is much softer, then there won't likely be any drastic side effects to playing with the ICS rate slightly.
Also of noteworthiness, Racetech offers AWESOME products and technical knowledge, but their enduro/singletrack/woods valving recommendations don't always seem to be the best advice... perhaps for motocross and definitely for street/road bikes, they offer a wealth of tuning knowledge, but for off-road trail riding, it seems that they maybe are not the top authority on valving and spring setup, although far better than most of us could do on the first try.

I've read solid arguments that people say that the fork spring rate calculator from RaceTech has too many variables, and that the wide range of results based on the 5 or so different input fields beyond rider weight, is misleading. The argument is that the fork springs really have a narrow range of acceptable variances, as the fork springs need to hold up the bike and rider's weight at a certain stroke height, as that is their job and the valving is then the one that is dependent on compression, travel, plushness, and to some extent bottoming or at least "blowing through the stroke too fast and then encountering harshness deeper in the travel." This does make a lot of sense.
Since I am trying to start out a bit deeper in the travel, I still will go with the Racetech "prefers soft" rate with old geezer inputs (although I look 30-34-ish yrs old, I'm only a few months from surpassing the age range inputted into the Racetech calculator of 30-44yrs old!!!). This way I can have a lot more downtravel in the nasty rocky rutted rooty sections to keep tire contact with the terrain, as well as effectively lowering the ride height of the forks.
I might even try out some of the .36kg/mm Cannon-Racecraft fork springs if the initial effects of the ICS rate + the .38kg/mm fork springs leave a little to be desired.
The stock KDX H-Series fork springs at .35kg/mm or .3475 or whatever they are, I was fine with in my first few years of riding dirt, but once I had just a few hours on the .375kg/mm KLX300R forks' stock springs, more firm fork spring rate that was quite apparent at first on the trail, quickly became much preferred to me as my trail speed at times is quite fast and aggressive nowadays. I think I can get these '98 RM125 forks set up really nicely with a little bit of trial and error, and I stand a darn good chance of getting it really nice on the first try thanks to the valving info I've found and posted in this thread.

[Chuck78]

I've been working on compiling complimentary shock info to any of these modern Showa fork swaps '97-'98, '01+ RM125, '06+ KX250F, Honda CRF250X, 2021+ KX450X etc Showa Twin Chamber forks, or any modern KYB forks as well as they're generally all 1" - 1/14" taller than KDX forks, so matching the rear shock ride height increase is of great benefit to many riders vs lowering the forks.

Showa 50mm piggybacks with independent high speed compression AND low speed compression adjusters on the reservoir are what I'm after, basically '01 or '02+ on most makes/models in the mid to upper tier (any with 50mm Showa shocks).
Finding an older version (including 2002-2024 DRZ400 as it's "old" proven technology reused for ages vs the modern MX bikes going longer length up until 2024) shock that is shorter is critical here if you want to be able to utilize the same or longer shaft travel vs the stock KDX shock.
2001-2004 RM125 shocks are common, DRZ400 or 98-00 RM125 lower spring seats are shorter and best used on these when lowering slightly, to allow full preload range - but this depends on Showa 50mm shock spring length, some are 258mm, 255mm, some shorter versions from newer bikes and Honda CRF's are 243mm and can run the longer spring seat. The shock springs are generally 63.5mm lower i.d. x 66.5mm upper i.d, altough some aftermarket are 66mm-ish i.d. top and bottom with reducer adapters, but this is mostly for KYB use as they are significantly smaller on the lower i.d. on KYB.

DRZ400 are same shock but the body has a slightly different reservoir mounting position. It has the compression adjuster in a similar position to the stock KDX shock, almost hidden halfway behind the side plate plastics, whereas the '01+ RM125 and 2024+ KX have the compression adjuster to the right side of the reservoir in the wide open.

The DRZ400SM (Supermoto version) shock uses the "same length*" shaft but a taller valving piston, with the shaft step machined down lower to accommodate the taller piston assembly, effectively making this shaft a 4mm shorter extended length than the DRZ400 & DRZ400E (e-start) offroad models and DRZ400S dual sport models. So the DRZ400 and DRZ400SM shocks would be a good solution, and the 400SM version is already slightly lowered, but will need 6mm more internally lowering spacers (I'll get to this later on).
The reservoir looks to be cocked to the side slightly to match the angle of the bike frame's tubing as well, so this may help also... The DRZ400 shocks gained the high speed/low speed compression adjusters in 2002, '00-'01 just had a single compression adjuster.

I think this along with the KLX650R 115mm or KLX300 117mm aluminum suspension links (& matching longer bolts as they're thicker links both steel and even thicker aluminum versions) will get me pretty close to where I want to be. I'll be running less preload on the 4.9kg Renton Coil Spring titanium rear shock spring to allow for a bit more sag to correct the ride height as well, and make things a bit more plush initially. This is a popular technique (especially on fork springs) to run the spring rates on the firmer side of what's rated for you, but run close to no preload, in order to get good bottoming resistance but still good initial plushness.

2005-2008 RM125 and also RM250 (250 used KYB 2001-2004, but these should be Showa) - very similar shock but 18mm shaft vs previous 16mm shaft, supposedly to allow more oil flow through the shaft damping passages for big hits, as well as I suspect a slightly longer body than '04 RM125 (probably same as RM-Z250, 6-8mm longer, too long for our needs), and a significantly longer clevis. The clevis can be shortened and holes redrilled higher to match the other shocks we're considering, but the body length may be a deal breaker on proper length and travel range unless running the 117's will alter the leverage ratio enough that the shorter shaft travel resulting doesn't lessen the wheel travel, and this will also lower the bike back closer to stock, as these shocks @ 438mm shortened length and stock links will ride 1.8" taller than stock. Edit - later on in this thread, I noted the longer links "soften" the damping and spring rate action by giving less total shock shaft travel for the same amount of wheel travel, so if someone wanted to experiment, those shocks may be very useable and the RM-Z250 especially looks like a nice reservoir orientation, '07-'09 or '11 or so in particular, around then the compression adjuster changed to a newer/larger style - study the clearance on the KDX frame vs the earlier version Showa 2007-???? and vs the '98-'04 RM125

2006-2018-ish KX250F - very similar to the 05-'08 RM & '07+ RM-Z with the longer clevis and likely a longer body, the clevis needs the bottoms chopped off and the lower bolt hole redrilled to the same length as the RM shocks. The KX250F also has the same style reservoir location as the DRZ400 shock and the stock KDX's 44mm KYB. Around 2010 or so, a year before they switched to the SFF forks with one side spring one side damping, the KX250F shocks got a different shock reservoir cap that bulges out for a larger bladder capacity. Apparently these are a pain to remove and everyone uses the aftermarket reservoir caps which also have the extended capacity and a standard schraeder valve instead of a needle fitting.

2007-2018-ish RM-Z250 - same as the KX250F shock but fatter 18mm shaft vs 16mm, and a better extra-capacity reservoir cap design, which is an absolute necessity on these due to the extra oil volume displaced by the larger shafts. Same clevis as the KX250F, needs shortened in the same way.

RM-Z 250 shock 2007-2018-ish:

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One thing of note - the Kawasaki model shocks in the OEM parts fiches break down every single part. The Suzuki shock OEM parts fiches only show the shaft and piston and all attached pieces available as one complete assembly.
The aftermarket sealheads between the 18mm shaft 2005-2008 RM shocks vs the 2007-2018 RM-Z250 shocks don't show the same part number interchange despite being the same style of Showa 50mm shock body/cylinder & the same oversized 18mm shaft, and no Kawasaki models use the 18mm shaft, so I'm not certain on any of the parts breakdowns for the larger shaft versions since they are Suzuki-only. The parts are available outside of the bike manufacturers through places like Showa Parts Europe, or better on the navigation via Teknik Motorsports (in Australia). The 16mm shaft is still significantly fatter than the stock KDX shock shaft, but the hollow shaft bores do have a lot to do with the damping abilities as far as maximum flow capacity for the rebound especially, but this may only apply to extreme use (pro racers). Without a rebound separator added to the shock, the compression is slightly affected by the shaft flow as well, but not in a significant way although adding a rebound separator will slightly alter the shim stack requirements, but this is definitely for the better.

All of these shocks in addition to the clevis shortening on the KX250F/RMZ250 versions, will be best to be lowered with a 10mm sealhead external spacer or with internal spacers, or at least have the preload backed out, as the KDX linkage rocker will top out on the frame before the shock is fully extended, so the shock will never see the top end of travel otherwise. I'd originally figured 440mm was the magic number, but now after remeasuring, 438mm looks to be a better bet to avoid the cast aluminum rocker knuckle from smacking the frame on suspension top-out full extension moments.

I have some KLX300R pull rod aka dog bone suspension links, both the 117mm steel KLX300R/KLX250 links (like the KDX's 112.5mm steel links) that are a direct swap onto the KDX, and a set of identical length 117mm aluminum+stainless reinforcing bushings KLX300R links (thicker) with their longer mounting bolt hardware.
These will lower the KDX around 15/16" in the rear, but since these shocks are 1" taller physical shock length but will need lowered to 438mm (13mm longer than stock '95-'06 KDX shocks), multiplied by the linkage leverage ratio of around 2.5, it seems these longer links will be very useful in dropping the height down to match the taller forks at around 1" taller. Lowering links generally advertise that a 1" lowering link won't alter the suspension rate too drastically (slightly alters the progressive / rising rate curve however), but any longer links for additional lowering will really start to alter the geometry of the linkage significantly, as well as causing hard bottoming out of the swingarm/chain on the upper chain guide and tire buzzing the fender.

Being that the KDX came with 5.0kg shock springs and the RM125/250 came with longer links and softer springs at 4.6kg to 4.8kg, I think that the RM shocks will already be slightly more plush mounted to the KDX (longer links and the KDX rocker rotated beyond stock to absolute top-out against frame - will perhaps soften the MX valving some?). I may fabricate my own links as well if I determine something around 114mm would be more ideal due to damping and leverage ratio curves.
EDIT - The fairly scarce '93-'96 KLX650R are of the aluminum KLX300 style AND 115mm! Thanks to Chopperpilot for that tip. The bushed alloy KLX300R dog bone links sure are nice, and these are basically the same but closer to stock length.

[Chuck78]

(both photos show my buddy David on a mostly stock KDX200H picking the *easier* lines through the rocks on trail 11 at Redbird Crest OHV trails in Daniel Boone National Forest Kentucky, my (currently-) KLX-forked purple KDX is parked in the foreground as I was snapping these photos to show people the gnarly terrain that can be found at these amazing and seldom visited trails - and what we like to pilot our bikes through)

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At Redbird Crest OHV trails in Southern Daniel Boone National Forest Kentucky or the Buffalo Mountain / Rock House trails in the Hatfield-McCoy trail networks of Southern West Virginia, I do always notice that in the really rocky sections that we we ride in, that I'm always banging my toes on boulders and big loose rocks, as well as smacking the skid plate a fair bit. I know that a firmer suspension would keep me up away from the rocks a bit further with more compression damping and/or .40kg springs, but I really like the plushness in this terrain of running .38kg fork springs, and backing off the preload adjuster on the KDX shock even more on our trip to Redbird last week. I think this was one of the factors contributing to me making it up sections that I'd never made cleanly before on the most challenging technical areas, but made rather cleanly on this most recent trip.
springs 1 step on the softer side than the stock KDX 5.0kg (for my 15lbs weight) and a good woods valving, plus the added ground clearance of the taller forks and shock, will definitely be an upgrade and fit in well with my suspension setup/upgrade strategies here...

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(pardon the blurriness, I had to zoom in substantially on the camera to get the up close perspective, no time to run on foot up there while he was crawling through this section)

All the while, I absolutely love the way my bike handles with the stock KDX shock rebuilt and with preload set pretty soft/saggy, and the stock-ish KLX300R 43mm inverted forks. I am ready to be blown away when I revalve these upgraded shocks and swap to even better forks. My other KDX220R badly needed a complete rebuild anyways, so I figured why not just go all out with the upgrades on this machine and go for some serious 49mm Showa conventional forks and a shock to match...the 49mm Showa RM conventionals or similar external appearance DRZ400E forks seemed the answer, or newer Showa Twin Chamber inverted. I absolutely hate how often mud gets packed up into the seals on all inverted forks in our riding group's bikes... the ultimate conventional forks seemed to be a great answer, plus less chance of suffering rock damage to the chrome tubes since inverted forks are right down there in all the boulders and rock gardens we ride through on my favorite terrains...

[SS109]

Man, you really dive deep in to it!

I'll give you a little food for thought. RaceTech has always seemed pretty spot on with their spring recommendations IMO/IME. For me, a 45+yo, desert, B rider, they recommend .38 up front a 4.74 rear, However because I didn't shorten my forks internally, and have them pushed up in the clamps, I went .40 up front to help keep the forks from hitting the fender/lower triple (really scary thought!) on big G-outs. At this same time I set the preload at zero on the springs. All I can say is that it works great and it soaks up the trail junk great. The stiffer spring with zero preload allows that first bit of spring movement to be really soft yet it holds the bike up in the proper sag range so the valving can do it's work for great handling everywhere. As I'm finally learning, it even handles riding the whoops very well yet still eats up the small stuff.

As to dialing back the preload on the shock spring, there is a contingent over at GasGasrider.org that swear by doing that very thing. I plan to try it on my Gasser once it's completed. They normally run at the stiff end of the spring range for their weight (if they are borderline they'll step up to the next stiffer spring IIRC), set it for proper sag to make sure it works for their weight, then dial back the preload adjuster until it is only preloading the spring 10mm. They say it really plushes out the rear but still allows it to take the big hits without hard bottoming. Of course, like I said, I haven't tried it myself yet so take it with a grain of salt.

[Chuck78]

Another deep dive for ya, Kelly!


Doing a little bit of number crunching...

'95+ KDX rear ride height with a taller shock:
448mm length '01-'04 RM125 (*only around 440mm is useable without KDX frame mods)
-vs-
425mm length KDX H-series shock.

So an 01-04 RM125 shock = 23mm - longer than the KDX shock.

SS109 said his H-series KDX with an 01-04 RM125 shock rode significantly taller than stock.
He also said the RM125 shock was so much longer, that it couldn't install at full length, and that the suspension rocker linkage topped out against the frame and he had to compress the shock around 1/4" total approximately, to get it to just mount on the KDX rocker linkage. (I've checked this myself, and this actually ~8mm)

95-06 KDX have 11.8"/300mm advertised rear suspension travel.

95-06 KDX shock travel is 118mm 127mm (edited - lower spring perch bottoms against sealhead bump cap with 11mm of shaft never able to be used)
01-04 RM125 shock shaft travel is 130mm minus a couple millimeters with foam bottom out bumper compressed fully - they go from 50mm+ foam thickness down to just 2mm-3mm!)

That's 12mm additional shock shaft travel over stock on a shock that's 23mm longer than stock (& '96-'00 RM125/250 are 454mm, +29mm longer vs stock KDX200H/220R), but we cannot utilize the full length of these shocks, and so clevis and/or shaft travel are where we make up the difference unless cutting and extending/welding the upper shock mount 6mm rearward and 10mm-16mm upward.

So we'll figure we need to lower the 50mm Showa '01-'04 RM125 shocks 10mm internally or with an external Zeta Racing 10mm sealhead lowering spacer. A DRZ400/400E/400S 2002-2024 shock would need nearly identical lowering, but will be 2mm less travel than the RM shocks.
(KXF and RMZ Showas have substantially longer clevises, which need shortened and redrilled to match the RM/DRZ400 clevis length, but also bodies that are a bit longer perhaps 4mm or 6mm longer?)


23mm longer minus approximately 10mm lowering = 13mm taller than stock still.

***The math below is *approximate guesswork* due to the complex engineering nature of rising rate linkage designs, although I had read heresay that the KDX has a fairly linear rising rate linkage.

300mm stock rear wheel suspension travel out of a 118mm travel shock, 300÷118 = 2.5424 *average* suspension leverage ratio of the stock shock length and rocker position, rear wheel travel vs shock travel (rear wheel travel is also altered by chain length / axle position, FYI! Moving the axle position rearward with longer chain is more rear wheel travel as well.)

This isn't a terribly accurate method to calculate the difference in rear wheel ride height, but I think it'll be close at least:

13mm taller shock (after 10mm lowering spacer) x 2.5424 = 33.05mm taller rear ride height... That's only 1.3" taller than stock...
I believe I measured 1.8" taller fully topped out ride height with the longest shock possible (438mm or 440mm) vs stock topped out, so this points to the fact that rotating the rocker knuckle further back in it's stroke than the stock shock length ever allowed, in fact does get us further into the "initially plush" leverage range - making it softer initially although it will give more rider sag aka race sag (seated on bike, all body weight on bike at rest) than the standard suspension, so this needs to be kept in mind when setting proper sag - leave it a little on the long side (more sag with rider weight and more static sag with no rider weight on bike).
[/i].
The KLX300 or KLX650R suspension pull rod links & matching longer bolts, at 117mm & 115mm vs the '95+ KDX's 112.5mm links, will lower a topped out rocker linkage '95-'06 KDX to a ride height of around 3/4"-1" taller than stock from my initial testing.

The DRZ400 shock will be similar. (shorter body, slightly shorter shaft, 5mm longer clevis vs '01-'04 RM125 shock)

@SS109, does that sound like how much taller your rear fender sits?

Around 1" of ground clearance gained will help in the big rock gardens and log hopping/climbing/sliding, but will still allow me, at 5'10" & 32" inseam, to comfortably touch my toes or the balls of my feet down on the ground.

I'll have to hang the rear end from the shop ceiling and drop the shock bolt and measure the total available extension on the shock install height with the rocker bottomed out or topped out against the KDX's frame, and then I can fine tune any internal lowering spacer length needed if trying for maximum shock shaft travel.
The 96-98 RM triple clamp offset (22mm? iirc) + the forks' axle lug offset equates to nearly the same trail geometry as a stock KDX, so we're not changing the bike's geometry much at all, only softening the initial rear suspension leverage but also running a more stiffly valved MX shock that should still be revalved to be better suited to woods riding.

I'd prefer the rear to be a bit taller than the increase in height added by the RM125 / KX250F / etc fork swaps, so that I can back out the preload on the shock spring some to lower it via more seated rider sag. That'll allow more traction in the nasty uneven terrain when the wheel drops down in between rocks and ruts/roots/etc... So I might end up running some 115mm KLX650R aluminum suspension links, keeping the swingarm vs linkage geometry closer to the stock KDX 112.5mm steel links.

[Chuck78]

I'm still on the fence of whether or not I can reasonably run the .40kg/mm RM125 fork springs. I'm leaning towards .38kg Cannon-Racecraft springs due to what I've been reading about twin chamber forks' internal chamber pressure springs (same function as the nitrogen charge in the rear shocks, but no rising rate linkage to make the fork plush like the back end has), adding to the initial force needed to initiate travel. generally the answer is to run the fork springs at nearly zero preload to compensate for the small coil spring in the damping assembly. I also may just switch from what Race Tech alleges are 2.74kg internal chamber springs to Race Tech or Cannon-Racecraft Showa Twin Chamber ICS spring that is a 1.2kg/mm rate... Those are way cheaper than fork springs as well. That should make initial travel require less force, giving more bump compliance.

RaceTech 2610 Series Pressure Spring offerings:
FRPS 261010 (26.2 x 102mm) - 1.0 kg/mm - $79.99
FRPS 261014 (26.2 x 102mm) - 1.4 kg/mm - $79.99
FRPS 261018 (26.2 x 102mm) - 1.8 kg/mm - $79.99
FRPS 261022 (26.2 x 102mm) - 2.2 kg/mm - $79.99

Cannon-Racecraft ICS (Inner Chamber Springs) offerings:
Showa: 100mm length
Straight Rates: 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6

If Race Tech is correct in stating that the stock '98 RM ICS spring is 2.74mm, the fact that neither of these companies offering different rates of replacement springs makes anything over a 2.2 (R.T.) or 2.6 (C.-R.) tells me that perhaps I shouldn't even bother using the stock ICS springs IF in fact they are 2.74kg/mm/ I suppose I could make up a basic spring holder to place on a scale while placing the scale in an arbor press, and make an approximation of the rates, but it will be just eyeballing a ruler etc and noting the increase in scale measured weight.
I have the 1.0kg 102mm RaceTech springs here already. I may re-measure the stock spring length and then order 1.2kg versions and 1.4kg versions in the Cannon-Racecraft most likely.
Unfortunately the other pair of more modern current model (2019+ KX, 2017+ RM-Z & CRF?) '24 KX450X Showa 49mm inverted Twin Chamber forks that I have now use the FRPS 2810 ICS springs, 99mm length, so I no overlap in spare parts there beyond perhaps the fork seals... Perhaps it is Cannon-Racecraft who uses the more universal Showa ICS springs then @ "Showa = 100mm" vs Race Tech @ 99mm, 102mm, and (KYB?) 112mm...


These forks as they sit stock, just compressing on the shop floor, really do not feel like typical harsh MX forks to me... I might even just put some fresh oil in a set and bolt 'em up to my 99 with an RM125 shock and KLX300R suspension links, and back out the compression clickers, and take 'er for a good test ride! I think it might surprise me, as I've read of a lot of woods riders being pleased with these forks bone stock.

I'm very pleased with my KLX300R .375kg/mm fork springs now.
Teknik Motorsports tells me that for a KDX220R at around 154lbs rider weight and slightly more with hydration pack, saw, phone, & a few tools), I need .40kg fork springs and 4.73 to 4.8kg shock springs on a KDX. I've got what I believe are two 4.9kg RM250 springs and one 4.6kg RM125 spring, all purple 1998 models that fit 98+ RM and KX250F 50mm Showa shocks.
Teknik is apparently of the way of thinking that the spring needs to support the rider's weight, and is less dependent on riding style, as the springs need to keep the rider's weight held up to the proper height in the fork travel regardless of terrain, age, riding style, etc.

Racetech has lots more options for tailoring spring rates to your needs, and tells me:
(inputs - singletrack trail riding, age 30-44, Novice/B-Class, standard stiffness, 159lbs (added a few lbs for water pack and saw), .38kg fork springs and 4.64kg shock springs. I have one KX125 1998 purple shock spring that is probably a 4.6kg (what RT says I need on the KDX for my 153lb rider weight without gear), and 2 springs that measure slightly thicker, one off an RM250 and one off an RM125, same thickness, probably the RM250 4.9kg or optional rates in between, 4.75-ish.

[SS109]

SS109, does that sound like how much taller your rear fender sits? Granted @ 1.95" taller is at the rear fender position at the very back directly above the axle where wheel travel is measured, seat height would be less than 1.95" taller if the forks were only 1" taller or less, splitting the difference at about 1.5" taller.

Yeah, that sounds about right. I can take a measurement if that would help? Remember, I only weigh 140 without gear and I'm currently running .38 up front and a 4.8 rear. I can get the rear to bottom out on a fairly regular basis and the forks will touch the fender on the nastiest g-outs once in a great while. I think you would be fine with the same but you never know until you try it!

[Chuck78]

SS109, does that sound like how much taller your rear fender sits? Granted @ 1.95" taller is at the rear fender position at the very back directly above the axle where wheel travel is measured, seat height would be less than 1.95" taller if the forks were only 1" taller or less, splitting the difference at about 1.5" taller.

Yeah, that sounds about right. I can take a measurement if that would help? Remember, I only weigh 140 without gear and I'm currently running .38 up front and a 4.8 rear. I can get the rear to bottom out on a fairly regular basis and the forks will touch the fender on the nastiest g-outs once in a great while. I think you would be fine with the same but you never know until you try it!

Yeah if you don't mind measuring, that'd be greatly appreciated! Stock rear fender? UFO version? Maier MX KDX fender?

I'll definitely be running the thicker shock springs of the 3 purple '98 RM springs I have here, 2 of them are a 4.9kg or maybe a 4.7kg. White paint dot code for 1998 RM's, no clue where to find a chart stating the rates, but they list stock rate and optional rates in the parts fiches, just not correlating paint dot code or wire diameter.
Stock '98 RM125 was 4.7kg (62211-36E20), optional "firm" rate was 4.9kg (62211-36E30), optional soft rate was 4.5kg (62211-36E10).

[SS109]

I have the Maier MX fender. Measurement with bike under it's own weight is 35.5" at center of rear axle up to fenders lower edge.

[Chuck78]

I have the Maier MX fender. Measurement with bike under it's own weight is 35.5" at center of rear axle up to fenders lower edge.

SS109, I'm not exactly sure how you measured to get 35.5"???? posting photo below. center of axle to bottom of rearmost frame section seat frame - fender support tubing underside.

[Chuck78]

I have the Maier MX fender. Measurement with bike under it's own weight is 35.5" at center of rear axle up to fenders lower edge.

SS109, I've got only OEM fenders here on both 220's. Can you check that measurement again, with the suspension topped out, from center of rear axle up to the bottom of the end of the frame tube, I believe there's a plastic cap in the end of each rear seat frame tube, the underside of the horizontal portion of the rear end of the seat frame tubes behind where they bend and turn down.

I've got 26-1/4" center of axle stright up to the underside of the last horizontal bit of seat frame tubing, pardon the tattered rear fender and sub-par dual sport tires, this is my old retired and mostly stock '99 220 that's slated for a rebuild ASAP:

KDX-rr-susp-ride-height.jpg (77.2 KiB) Viewed 13337 times

That'd be a more accurate comparison as I have no Maier MX fender. THANKS!

[Chuck78]

Here's the valving info that I meant to post here a while back:

MID VALVE LOW SPEED COMP:
{starting stack from the mid piston face}
13.2x.10 mm : bleed shim
[6] 20x.10 mm
collar/sleeve 8mm o.d. - modified in length to create mid valve float
11x.10 mm
11x.20 mm
Base washer
Running .21 shim float on the sleeved shim stack { most important procedure of the build }any more than .25 float should require a check spring and retainer to be fitted {otherwise noisy}. i sanded that collar/sleeve to the required height always checking the size all around it with the vernier.

as follows from the piston face:
REBOUND
[2]20x.10 mm
10.2 mm
20x.10 mm
17x.10 mm
14x.10 mm
10x.10 mm
9x.20 mm
11x.2
12.5x2.5 washer
High speed dual stage race tech shim stack is as follows
20x.10
11x.10 :crossover shim
[6]20x.10
18.3 x.10 that's all i had,call it an 18 mm o.d.
16x.10
14x.10
13x.10
12x.10
11x.10
10x.10
9x.10 on a FMGV 2320 gold valve
The figure in brackets being how many of that shim ie:[6] and the rest is only a single shim.
running 420ml of Motorex 5wt in each leg

I'll probably be leaning towards running that valving but perhaps with just a touch softer mid valve or some additional sleeve extender shims, based on what negativenoel had to say about not being able to run any more than .21mm of float.

I tracked down some .37kg Eibach 983.037.1 springs direct from Eibach Direct Australia, although I believe they only make .39kg+ or .40kg+ currently (I likely got the last sets of these new in box that were available anywhere). Racetech lists the .39kg versions as availalble, but the stock .40kg springs are probably worn in to give a realistic rate of .39kg by now, so no point...

Racetech recommended oil level for my inputs is 405cc's, which is the minimum of their spec range.

I've also ordered a pair of Race Tech ICS compensator springs for the inner chamber base valve assembly, in their recommended 1.0kg rate (lightest) for my weight / enduro spec riding. This will allow them to cavitate slightly in the fast rough choppy sections in my opinion, but will help them be extra plush. I'll probably try 1 rate higher 1.2kg/mm or 1.5kg/mm most likely if these soft ICS springs seem to allow noticeable damping fade during faster riding. They're very simple to pull the whole base valve cartridge on the '98-currrent Showas and swap these springs from the top of the fork without hassling with anything else, even at the trailhead... I likely will build a couple sets of these base valves to swap out while testing and tuning, as well as bring a second shock with alternate settings just in case my re-valving was too far off base to be willingly rideable.
Cannon-Racecraft also sells a version of the Showa ICS springs, and it seems theirs vs the Race Tech are slightly different lengths - RaceTech uses one spring for KYB and Showa, Cannon-Racecraft sells separate springs for each, with different lengths listed... [/I]

5WT oil or 0w20w Mobil 1 (reportedly very slick and works well in place of 5wt suspension fluid)

very minimal preload on the fork springs if possible (2.5mm?)

SKF Low Stiction Seals and wipers

I'll also be looking at the stock base valve piston vs the Race Tech FMGV 2320 Gold Valve, and comparing the shape of the piston's ports. If the stock is not as smooth of corners on the openings, I'll consider dropping $155 for the Race Tech Gold Valve kit to reduce potential for cavitation with the more rounded ports.




.




and more general valving and setup info:

Best advice on twin chamber / closed chamber forks is to use low stiction SKF seals on these forks
(-negativenoel on KDXRider.net)

From Heart_Of_Darkness on Vital MX:
The stock pistons have large ports, they're not a restriction.


I've been reading about Twin Chambers & cavitation vs plushness, ReStakor has amazing writeups about this - but it seems as if you can get away with a softer TC ICS spring if yourbase valve ports are shaped in a way to minimalize cavitation - so perhaps the FMGV 2320 (97-98) & FMGV 2040 could still perhaps be beneficial? I'll have to tear a pair of these down to check the stock port shapes soon. See ReStakor cavitation articles
-Chuck78


A good woods re-valve is a two stage base with greatly softened high speed, a somewhat softened mid with a float in the .25-.30 range, and correct rate fork main springs with minimal preload (there's a lot of preload from the factory).

*****Check those forks (you'll need to disassemble them) to see if the bottoming cup at the base is installed correctly. If it wasn't (and it's easy to not install it correctly) then the damping rod cartridge hammers it every time the forks compress. I had a set that happened to. It's very dangerous if you don't catch it. -gotanubike on KDXRider

Some have used this thread on DR-Z 400 49mm open chamber conventional fork valving as a basis for modeling woods valving on the Showa 49mm twin chamber valving on the RM fork swaps, although the compression piston diameters are different, the valving and shim sizes are not going to be directly compatible without some adjustments for the added flow of a larger piston etc:
https://www.thumpertalk.com/forums/topi ... ns/page/8/

also look at the Thumper Talk thread with a subject/title regarding How to make Showa Closed Chamber forks plush for woods riding. I'll post that link later if it's not in this jumbled aggregation of my notes elsewhere already.

------------

Drop the oil level down quite a bit lower then what RT recommends for the RM twin chambers, and work your way up. Measure your fork springs as my set had negative preload and if you do too then make some spacers to bring it up to 0-3mm.

I'm running this right now for woods but I'm always playing with the base/mid.

20X.1

18X.1
16X.1

14X.1

13X.1
12X.20

11X.20

11x.25
11.35X.40

Rebound - Stock
Midvalve
20X.1 (3)
08X1.35 (collar)
11X.20 (2)
Float - .0mm (??? really ???)

And here's another shim stack that a rider simulated through the ReStakor software:

I've been doing lots of reading and also playing with the demo version of Restackor to get ideas on how certain changes effect the damping profile. For the base valve I'd just like to soften the whole thing up to re-center the clickers on my near full soft setting. I'll add a crossover to soften the LS and remove some from the taper to soften HS.


('96 shim sizes same size as KDX base valve compression pistons, 20mm pistons are 3mm smaller than 23mm '97-'98, use 17mm face shims vs 20mm)
BV Stock BV Mod

17x.1 17x.1

17x.1 11x.1
14x.1 17x.1
12x.1 12x.1
10x.1 9x.2
9x.2 11.4x.4 (4)
11.4x.4 (4) 12.54x2.54
12.54x2.54


Same thing for the rebound, I just want to make the whole thing softer and recenter the clickers. Accomplished by moving the crossover closer to the face to soften the LS and removing a few from the taper to soften the HS.

Reb Stock Reb Mod
17x.1 (3) 17x.1
9x.2 9.2
17x.1 17x.1 (3)
15x.1 15x.1
13x.1 13.1
11x.1 9x.2
9x.2 11.4x.4 (2)
11.4x.4 (2) 12.54x2.54
12.54x2.54


On the mid valve is where I'll try to help with the deflection off roots and rocks. I'll pull one of the face shims, which will also add some float.

Mid Stock Mid Mod

13.3x.1 13.3x.1
17x.15 17x.15
17x.1 (4) 17x.1 (3)
8x1.7 (collar) 8x1.7 (collar)
10x.15 10x.15
12x.15 12x.15

0mm float 0.1mm float (??? again, no mid valve float, initially??? seems odd.)

EDIT - I'm digging up a lot of good woods valving from searching ThumperTalk for Honda CR250R woods valving, as the '97-'02 CR250R, '97-'04 RM125, '97-'00 RM250, and '02 CRF450R all use the same Showa fork base valve pistons... This expands my search quite a lot for searching what shim stacks have worked for others in these "early Showa 20mm piston forks." (the pistons are actually 23mm o.d., but the face shims (largest shims to match piston ports) are 20mm.
Also some good news for woods valving is that so many bikes 1998+ use the same Showa 50mm shock pistons, so I'm finding a lot of good woods valving stacks from CRF250X's (woods models), 06+ KX250F's, 97-08 RM125 and 97-00/05-08 RM250, 08-??? RM-Z 250, and even the DRZ400E. Most of these bikes except the mid-period/later RM-Z's have a similar spring rate on the rear shock as what I'll need, so they should be fairly close. The 2001+ shocks (2002+ on the DR-Z 400) have the high/low speed compression adjusters, and a lot of the valving is handled through the small shim stack in those adjusters. I plan to run the Lanier compression adjuster assembly (with their optional Enduro shim stack) in order to get a more wide range of external adjustments, especially since I'm going into a relatively untested custom shock swap territory. SS109's suspension guy did a great job on setting up the RM125 shock for his KDX, but I'm really trying to learn this in-depth myself, although it will of course involve a fair bit of trial and error...




I'm also scrapping the RM steering stem in favor of a perfect KDX length aluminum Suzuki V-Strom DL1000 steering stem and milling off the raised protruding portion of the lower bearing seat on the RM triples down to the flat portion with only minimal seat area being raised - bringing it to the height of the press fit VStrom stem area.


Also the other option may be the KX Guru Racing steering stems for the KX500's (same stem bearing diameter/spacing dimensions as the KDX), which are aluminum stems that are made in the slightly larger press fit area diameter (.003" larger than the KDX stems) so that they can be pressed into many more modern fork swaps' triple clamps.
Emig Racing may be the manufacturer of those, as Emig will make a custom stem in any size / spec you want, so a custom billet aluminum steering stem for virtually any fork swap could always be an option.

[Chuck78]

Well my 99 that's a waiting rebuild is sitting right in the middle of my basement shop... I'm really looking forward to tearing into this thing full bore, at which point I might as well build up two sets of the same suspension since I have several of these '98 RM125 forks. I might even pick up a 97-98 or 99-02 KX125 chassis to build a KDX220 hybrid out of and use these forks. With some steering stop trimming, putting them on a chassis that was designed for a 46 mm inverted fork (upoer tubes are significantly fatter), I could probably manage to have the tightest lock to lock turning radius of any bike out there, when running conventional forks were inverted forks previously were. That's some very highly beneficial goat trail singletracking goodness there!



So I've got 2 RM125 01-'04 shocks which are a well known good swap onto our bikes but are 23mm longer than stock and require at least 8mm internal lowering just to fit in the frame without topping out the rocker into frame contact, not to mention back that this would put the rear ride height couple inches taller than stock. As I mentioned before I'll be using internal lowering AND the longer KLX 300 suspension links / pull rods / dog bones which will act as a 7/8" or 15/16" inch lowering links.

The 05-08 RM125/250 shocks ('01-'04 RM250's ran KYB) are very similar Showas, but have longer clevises and a different shaft needle rebound aduuster assembly + 18mm shaft vs 16mm.
'07-'16-ish RM-Z 250/450 are basically the same, but with much firmer spring rates and valving tailored to their linkage design.
06-16 KX250F/450F are the longer clevis variety but use the 16mm shaft like the 01-04 RM125.
Honda CR 125/250 & CRF 250/450 also use very similar shocks but I believe the body configuration is quite different.
All of those 2000's & later shocks are generally all longer, except I'm uncertain on the Honda CR 2-strokes.

The modern Showa 50mm shocks are pretty standard across all top tier bikes running Japanese suspension, but weighing these RM125 shocks, they weigh a slightly bit more than the KDX shock, so really I might have been better off if trying to save weight by looking at some 1996-1997 46mm Showas or KX125 KYB shocks early 2000's (KDX shocks are 44mm KYB's and shorter height - I would like more ground clearance like a 94-02 KX125!).
Running a 2mm shorter DRZ400 shock shaft will drop a small bit of weight, as well as aluminum spring preload collars (makes up for the weight of adding my PivotWorks shock spring thrust bearing kit), and running the RCS titanium spring or some lightweight silicon-chrome spring steel coils from Diverse Spring. Then I'm not at as much of a weight gain on these, as I'm also trying hard to build a much lighter KDX overall...

I'm realizing now that perceived weight of right side up forks may feel heavier with the twin chamber compression valves up top AND the steel tubes being up top vs modern inverted forks having less weight up top. The aluminum VStrom steering stem will help shed some weight up top vs most typical KDX fork swap approaches making mods to retain the KDX steel stem. Additionally, all the titanium hardware I can manage all over the bike will also reduce the weight and feel. Heck I might even shave the end of my seat pan down in height so it ends lower on the tank slightly, just to drop some unneeded material weight up top while retaining that comfy sofa of a KDX seat! Another reason I'm looking at 96-98 KX125's as well, the 94-98 thick cushy seat foam! [/I]

These aftermarket Lainer shock compression adusters not only add high vs low speed damping adjustability, and doing so more than the stock '01/'02+ Showa dual adjusters do, but they also add a considerably wider range of damping adjustment on the clickers, as well as being more of an actual high speed damping adjustment vs low speed, whereas when the KYB and Showa shocks started coming with a dual "high speed / low speed" compression adjuster on the shocks, they really only functioned more like a low speed / low-mid speed damping adjustment. Lainer also sells the same rebound separators as Race Tech, and sell their own shock pistons as well, including a "Works" version that's shorter height and aluminum, to save weight and supposedly add a slight advantage in performance for racers.

KYB_kit-AV-2.jpg (304.01 KiB) Viewed 11687 times

I'm also looking at a replacement for my purple 1998 RM250 4.8kg shock springs that I was adamant about obtaining. Race Tech says I can get away with a 4.57kg spring, and I have a line on a NOS '96 RM125 "optional 4.5kg/mm" purple shock spring... lighter rate is less steel = lighter weight!
A 4.8kg purple '98 RM250 shock spring weighs 3lbs 0.1oz.
Diverse Spring's Superlight Chrome Silicon 4.8kg red springs weigh 2.6lbs with torsion bushing included. I'd have to get a bulk length of purple heat shrink tubing and wrap that spring to get the aesthetic I'm after , as red is the only color they offer them in, Showa & KYB large body applications...
RCS / Renton Coil Spring titanium 4.8kg springs weigh 2lbs...
Raw Ti finish matches a green/purple Kaw just fine, & drops 1lb of centralized weight! I just worked a ton of overtime last week, so I'm likely to make another big purchase of titanium hardware, and I might see a total weight reduction of 12 or 13 lbs if I go through with all of it on the KDX. That offsets swapping on larger better forks and shock, skid plate, bark busters, handlebar bag, regulator rectifier, etc...
Titanium springs are a lot more lively, they react a lot faster, which some pro riders really like, but some suspension tuners hate because they aren't familiar with valving for them. I would think that I'd perhaps need a bit more rebound damping?

[Chuck78]

.

[Chuck78]

For those wanting a slightly more straightforward stem swap while still retaining an aluminum stem, still requiring some machine shop work but not as much (for those such as myself who have yet to learn how to cut threads on a lathe! Let alone metric threads on an old US-made SAE lathe), KX Guru Racing makes an aluminum steering stem that is the press fit diameter of most modern triples, at least newer Kawasaki Showa triple clamps such as a 2014 KX450F Twin Chamber SFF 48mm inverted fork, basically the best of the best modern coil spring fork technology if you don't mind an inverted persuasion. This may work for the 96-98 RM & DRZ400 triples after machining down the lower step, but will still likely require an upper triple clamp bushing (very easy to make one on a metal lathe).

http://www.kxriders.com/forums/index.ph ... 396.0.html




I've emailed Oscar @ KX Guru Racing for some dimensions on the press fit portion as well as press fit height. He sells these for $150, but I would pay that to not have to cut down a VStrom stem and rethread to smaller upper bearing i.d. and more importantly to not have to use a heavy steel steering stem!
Also, to remind you, this will use KX500 OEM bearing sizes which are also KDX/KLX bearing sizes!
These could be useful in fitting modern KX250F Showa Twin Chamber forks and Showa Twin Chamber SFF forks as well... The 2011-2016 or 2018 Showa Twin Chamber SFF 47mm and 48mm inverted forks in my opinion are truly the best forks ever built to date. They of course need revalved for woods however... and a lighter ICS spring. BUT... with only one side doing damping, you only have the need for one ICS spring (the equivalent of the nitrogen bladder in our shocks, also ICS springs don't exist on open chamber forks, only closed chamber / twin chamber). Only one ICS spring and only one base valve and mid valve means you have half as much resistance, and therefor you will have a much more plush ride with less stiction, once revalved for woods. Truly the ultimate. I will still hold my stance for the 96-98 RM125/250 right side up dual spring etc versions though, due to my hatred for leaking inverted fork seals packed full of mud/clay dust!!!!

[Chuck78]

I'm getting a better idea now of the Showa RM125 > H-Series KDX rear suspension setup mods and ride height after alterations. I've been going back and editing and correcting info in my info-heavy posts.

As installed on the KDX frames, the '97-'98 RM125 forks distance from the center of the front wheel axle up to the bottom of the lower steering stem bearing is over an inch longer. The available travel range on the chrome inner fork tubes between the dust seal and the lower triple clamp will be right around 11.6" with the forks into the upper triple down as low as acceptable with the 49mm diameter portion of the base valve top cap outer hex area just flush with the tops of the triples (chrome tubes about 2mm down in the triples). I was assuming these MX forks had a typical 12.2" of travel as most modern MX bikes do, and so I was worried I'd have to reduce the travel and lower these internally. Then I made a nice discovery, 11.4" advertised travel! I was hoping for more, but the benefits of running a Twin Chamber RIGHT SIDE UP "conventional" fork may outweigh an extra 0.60" of travel?

28689918922_2bef51eb15_k.jpg (849.88 KiB) Viewed 10057 times

52616502484_54cef4e9b7_k.jpg (538.75 KiB) Viewed 10057 times

Well... After coming up at a loss trying to find '98 fork travel specifications listed, I found the 1997 and 1998 brochures on flicker amongst a massive collection of bike brochure info from Tony Blazier. Guess what? It lists the 97 & 98 RM125/RM250 forks at 11.4 inches fork travel!

Most fork travel is advertised with including the unrealistic specification of having the top out springs fully compressed, which basically never happens unless your rebound is set extremely soft/fast and you unload the front end rapidly off a jump. Perhaps the 11.4 inches IS NOT including the compression of the top out springs? But that would be the first I've actually seen real world travel advertised, meaning the amount of suspension travel with the complete bike having the front wheel and tire and fork hanging in the air as if on a stand.
I'll have to actually physically measure these myself to confirm for real world travel, as this would be a huge help as the forks may not need any internal lowering at all if I can slide the triples down as much as 0.80" / 20.3mm down on the fork tubes with no worries of risking the fork dust wiper seals bottoming out on the triple clamp, or the tire bottoming out on the fender bolts.



Here's a link to the source of those OEM Suzuki brochure photos, Tony Blazier's Flickr photo album collection with a TON of KX, KDX, RM, etc literature scans of sales brochures, ads, magazine articles and reviews, and other motocross and other unrelated categories:

https://www.flickr.com/photos/tblazier/ ... 9395909367

[Chuck78]

To match the Showa Twin Chamber fork upgrade or DRZ400/400E / '02+ DRZ400S fork upgrade, or any '01+ Showa 47mm/48mm coil spring Twin Chamber fork upgrade, I've been developing a recipe for a building a 50mm Showa rear shock fitment onto the H-Series KDX chassis for a while now, out of the best parts dimensionally from multiple various models of Showa 50mm shocks, & making some good progress recently...

The '01-'04 RM125 Showa has been successfully fit by a few others, although the length of the shock is around 23mm or 24mm longer than the stock KDX shock at around 448-449mm overall length center to center, so the preload must be backed out all the way on the spring (& shorter lower spring seat from a DRZ400 or '98-'00 RM is preferred) as the shock has to compress 11mm to even fit within the frame/rocker linkage limitations of the KDX200H/220R.



I've got an '02 DRZ400E Showa shock in my testbed '99 KDX220R in my shop (temporarily retired - awaiting rebuild) currently. This shock is about 449mm overall length, and has a 6mm shorter body and roughly a 2mm shorter shaft than the '01-'04 RM125 Showa (but a 5.5mm longer clevis due to the mounting bolt hole being drilled lower, could be welded up and machined to clone the '01-'04 RM125 bolt hole location) but requiring significant filing/beveling of the inside horizontal front facing edge in the crotch of the clevis to not interfere with the rocker, otherwise it won't lay down forward enough to mount the top shock bolt.
The stock DRZ400/400E/400S shock still has to be compressed roughly 9mm-10mm to fit into the KDX. I've measured with the rocker linkage nearly topped out (able to slide a piece of paper between the frame and the rocker), and around 440mm or 17.27" is the absolute maximum length for a swap shock to prevent hard top-outs of the rocker link arm against the H-Series KDX frame. 439mm would give a better margin, and move the rocker top-out starting position to move the shock spring further away from it's potential interference with the engine case swingarm/engine mounting bolt area. Internal spacers and/or sealhead lowering spacers should be used to achieve this, and it's best for maximum travel range to mix and match the components which best fit - primarily shortest lengths of the modern components - shock body & clevis.



If a single shock were to be chosen as the best, right now I'd say that would be the 2002-2024 DRZ400/400E/400S shocks. The standard offroad/dual sport DRZ400/400E/400S shafts are roughly 2mm shorter than the '01-'04 RM125 shafts, and bodies 6mm shorter.
This will give around 11.4" of suspension travel, and around 1.5" of increased ride height. Stock KDX is 11.8" travel.
The DRZ400SM Supermoto model shocks have a taller shock piston (16mm thick vs 12mm irrc) which has it's shaft step machined down further to accommodate the piston on otherwise the same length shaft as the DRZ400/400E/400S models, effectively lowering the shock internally by 4mm further than the offroad and dual sport models. This brings the DRZ400SM down to around 444mm overall length - still requiring compressing slight to install or else running 4mm to 6mm of internal lowering spacer stack to avoid constant smacking of the rocker arm link against the KDX frame on top-out situations. This will yield around 10.65" of total rear wheel travel if installed with the stock DRZ400 lower clevis (I believe the 400SM clevis is identical, but have not been able to verify). The shorter '01-'04 RM125 clevis or welded up & machined / shortened DRZ clevis really is key to gaining back the proper shock travel to achieve 11.8" of travel.

Welding up and redrilling the DRZ400 lower clevis higher like the '01-'04 RM 125 or else swapping a clevis from an '01-'04 RM125 donor shock (and beveling the top front edge of the crotch of the clevis in order to properly lay down forward to mount the upper shock mounting bolt without being restricted by the rocker/clevis interference) will take the approximate length of the DRZ400SM shock down to 438.5mm roughly, which will yield around 11.4" or 11.5" of travel, and alao will no longer be banging the rocker linkage against the frame when topping out the suspension.
, but will leave you with around 124mm shock shaft travel vs a preferred 127mm to 130mm.

The stock KDX shock allows 300mm rear wheel travel or 11.8" wheel travel as advertised edit - corrction on travels, KDX200H/220R achieves this 11.8" wheel travel through 118mm shock shaft travel*** - the spring seat bottoms out on the seal head bottom out bump cap with a portion of the shaft never even seeing the bump cap stop).
The KDX's fork travel is listed at 11.4", so even 11.4" rear travel will still be a fair match to this. Running a longer chain and having the axle further back in the adjustment range will slightly improve hill climb stability, add slightly to plushness of the rear suspension, AND will bring the travel measurement back to near what the original advertised KDX's travel is, although 11.5"-ish vs 11.8" is a very negligible amount.

I will likely alter the frame's upper shock mount this winter when the frame is torn down for painting and Yamaha bolt-on footpeg mounts (and Trail Tech kickstand 2010 YZ footpeg/kickstand combo mount!), bump it rearward 5mm, and raise it upward 5.5mm to utilize the full available 130mm of shaft travel of the '01-'04 RM shafts.

These shocks with stock 112.5mm pull rod dogbone links will yield around 1.8" taller rear ride height than stock. Adding KLX300 117mm pull rod suspension link "dog bones" and their matching linkage bolts (slightly wider for the steel versions, significantly wider bolts for the aluminum versions) will drop the ride height increase back down to around 7/8" taller than a stock KDX, which is a great match to most fork swap upgrades after sliding the triples down over the fork tubes to correct the steering geometry and front ride height to match the rear.
I wouldn't recommend any aftermarket lowering links any longer than this due to getting into more significant altering of the suspension leverage ratio curve. 115mm KLX650R and 117mm KLX300 links will "correct" the linkage geometry slightly from the longer shock rocking the rocker linkage further back into deeper leverage ratio than the stock KDX shock's length would ever give it.

One note on the DRZ shocks - the reservoirs clear everything fairly well, and you can run the KX250F Showa ('06+) aftermarket extended reservoir caps, but not any of the longer ones for other models due to exhaust clearance), but... the compression adjuster housing portion of the shock body contacts the KDX airbox slightly. I'd recommend using a heat gun to dimple the side of the airbox at this location, but this really is no big deal at all. The adjuster is still slightly shrouded by the side plate plastics just like the OEM KDX's KYB shock is.

Also, all of these shocks will require the donor bike's lower (or upper) shock mounting bolt as they use a nut and bolt attachment, longer bolt being needed, vs the KDX using a threaded clevis. Two upper KDX shock mounting bolts will also work perfectly, but the lower KDX mounting bolt is too narrow.
Additionally, the upper shock mount pocket for the KDX shock is significantly wider than the Showa shocks, and you will need somewhere around roughly 2mm of washers/spacers on each side of the upper shock bearing in order to sandwich it into the KDX frame properly.

I've also found that the Lainer Suspension aftermarket compression adjuster upgrade advertised for '09+ (-'16?) KX250F Showa shocks does in fact fit the older Showas despite their tech support guy saying that some of the older Showas are not compatible. It actually fit perfectly into the '98 RM250 shock body (& I believe'96-'97 also, the 46mm piston/body diameter version of the '98 & otherwise exact length dimensions), so I assume it will have good chances of fitting all of the older 50mm Showas.
It's well known that the KYB and especially Showa dual compression adjusters marked high vs low speed damping are really just a low speed / low mid speed damping adjustment. Also, they have a shim stack inside of them that have a significant amount of influence on the shock's compression damping. These aftermarket adjusters give them more of a true high speed damping adjustment range, and the two different circuits don't affect each other as much as the OEM style. Additionally, Lainer also sell an "enduro" shim stack for these for $10, as they are set up for MX use out of the box,
One other tip, the '02+ DRZ shocks have the dual compression adjuster, but '00-'01 have the older single compression adjustment. The DRZ400SM model came out later, so all SM shocks have the OEM dual adjuster.

Also pictured is a Race Tech rebound separator valve (Lainer sells these as well), which is a mandatory upgrade for any custom shock setup/rebuild, as this allows different flow rates for rebound vs compression through the shaft, which corrects the design flaws of nearly all shocks so that adjusting the rebound no longer has any effect on altering the compression damping flow rate. Lainer Suspension also sells nearly the exact same rebound separator product.





I've asked an eBay seller to measure an '07-'09 RM-Z 250 Showa shock overall body length for me to compare it to the DRZ400 / '98-'00 RM bodies (same length, different reservoir and compression adjuster positioning), but I think it'll be similar length body to the '01-'04 RM125 Showa body edit - its several millimeters longer), but with even better reservoir positioning (compression adjuster bore and reservoir mounting position is angled upwards to get the reservoir away from the near-frame-interference that the 98-00 RM125/250 & '01-'04 RM125 reservoir has, although all of the RM/RMZ compression adjusters are located in a better position than the original KDX's or the DRZ400 Showas or the '06+ KX250F Showas. The '05+ RM125/250 / '06+ KX250F / '07+ RM-Z 250 Showas have an extended clevis which absolutely won't work on the KDX swap, BUT they also are so long that they leave a blank slate for us to potentially shorten and redrill the mounting holes in the shortest possible configuration basically like the '01-'04 RM125's position. The body lengths on this newer generation seems to be longer like the '01-'04 RM, but I cannot verify although photo approximations tell me yes same or slightly longer, not short like the DRZ4 or 98-00 RM bodies.
One other perk to the '05-'08 RM125/250 and '07+ RM-Z 250 shocks is that they use a larger shock shaft. This is not done for strength reasons, but rather to allow more internal area in the hollow shaft for rebound needle orifice shock oil flow. The downfall is no OEM parts breakdown listing from Suzuki for any of the shocks, whereas if you need piston bands or o-rings, OEM sealhead parts, etc, you can look up an '06+ KX250F and use those parts for the '98-'00 RM125/250, '01-'04 RM125, and all DRZ400 shocks as they all use the slightly smaller shaft. Race Tech sells all the sealhead rebuild and bladder parts individually, but since they sell their own aftermarket Gold Valve pistons, they list no parts such as piston bands or o-rings for the OEM pistons, and I believe I'll find that all of these Showa shock pistons will already be of high quality and flow rate and not necessarily needing to be upgraded, although MX Tech does sell a nice low friction piston band upgrade. MX Tech and Lainer both I believe sell a shorter than stock piston as well, with matching piston band, the Works/A-Kit type piston that goes into the factory race team builds, as these are lighter in weight and give a very minuscule advantage due to this.

If one were to modify the KDX frame's upper shock mount to raise it 5mm and bring it back towards the airbox rubber boot 5-7mm or so for better spring clearance to the engine case rear swingarm mounting bolt, The KDX200H/220R can achieve 12.5"+ rear suspension travel with the RM shock bodies, preferably the '98-'00 RM body. This setup with an added inch or so of ground clearance using the KLX 115 or 117mm links and a '98 RM fork or '05+ RM/KX250F inverted fork will make the H-Series KDX really the ultimate in woods weaponry. More travel, 438-440mm shock giving the rocker ratio more initial leverage/plushness over stock, keeping with the KDX's 26.5 degree steering angle and shorter wheelbase (although I'm beginning to like the idea of a longer wheelbase from a more rearward chain/axle adjustment length on the steep steep technical slow hill climbs to help prevent looping out), really will make the KDX find it's ultimate form.

****One thing to note is that the larger shocks' springs, when the suspension is topped out, will interfere with the KDX engine case swingarm mounting bolt area if the spring is not rotated in a way to span around this. Once a rider is seated on the bike, the rider sag / race sag puts the shock further rearward due to the rocker arm rotating under compression, and this is out of the picture. This is a good reason to make sure that you have the proper washer at the top of the spring between the preload collar and the spring, or an aftermarket Pivot Works shock thrust bearing kit, or a Diverse Spring teflon thrust washer, to ensure that the shock spring rotation under compression (they all rotate slightly when compressed) occurs mainly on the upper portion of the coil spring.
If and when I modify the KDX frame's upper shock mount location higher up, I'll also bring it back a few millimeters towards the airbox rubber carb inlet boot, to better clear the cases.
I'd also have no problem slightly clearancing the engine case through bolt mounting area in this area ip to 5mm material removal (it's 7mm thick in the center of the swingarm pivot bolt engine mount area), but being careful to not daylight the bore of the engine/swingarm mount thru-bolt, as I don't want to be taking on water into that area as the steel bolts already can rust seize in there if not removed for regular suspension bearing servicing and greased. My KX500 titanium swingarm pivot bolt is exempt from rusting like steel, but I still would not take off enough to break into the bore of the swingarm/engine case mounting bolt. I'm also hoping to run this RCS / Renton Coil Spring titanium 4.9kg shock spring. Titanium shock springs use thicker wire, which will increase the o.d. of the spring, but luckily I believe they typically use less coils as part of the same logic, so I'll have a wider spacing between the coils if not choosing to do any upper shock mount relocation or engine case clearancing.

Granted the rear suspension swap test fitting has made me realize that the rear shock length and travel is one of the greatest benefits to building a KX125/KDX220 hybrid...as well as the 5lbs or so weight reduction the KX components give vs the KDX chassis components, although I'd still probably fork swap any '96-'02 KX125 woods bike / hybrid build personally...
I still may seek out a KX125 for a woods bike build, preferably a '97-'98, or a purple '96 with '97-'98 swingarm, or possibly a '99-'02 with retro '96-style purple graphics, but I think first I'd be throwing some money at the engine to build an ultralight and potent woods ported high compression woods weapon "KDX134R" or '96-'97 "KDX139R" (using a Honda CR125R piston and a '94 KX125 head to match up to the specs of the '94-'97 long rod KX125 engines with the CR piston and '94 head). This would be my purple '96-styled Kawasaki version of the modern YZ125X woods bike...but staying true to my Kawasaki fanaticism!