Showa Twin Chamber 49mm conventional forks 96 97 98 RM125/250 + inverted Showa TC & RM shocks, & DRZ400 49mm forks

[Chuck78]

Here's some of the best info on DRZ400 shock valving I've found:

https://www.thumpertalk.com/forums/topi ... tor-valve/

Terry Hay's valving stack is my #1 pick so far, tuned specifically for the DRZ shock with a rebound separator added. I've got a handful of open tabs on my phone of other Showa 50mm shock woods valving to sift through as well. Apparently the rebound and bleed orifice on the DRZ is sized differently than most other 50mm Showas, so the DRZ based valving may have slightly different requirements than an RM, RMZ, or KXF 50mm Showa, but one needs to approach DIY revalving, even when copying someone's pretty successful settings for their machine, with the understanding that even pro shops don't get it right the first time typically, unless they are HIGHLY FAMILIAR and HIGHLY EXPERIENCED with your particular model. Drew Smith and company at Works Enduro Rider / WER Products have been in business longer than most, and have extensive experience and an extensive database of valving combos, including both the '96-'98 RM forks and the DRZ400 conventionals, and I'm sure could do wonders with the 50mm Showa shock setup as well.

Here's another good one with some detailed info (in a DRZ400 revalve thread primarily about the forks) about the shock compression adjuster stack, very detailed hand drawn sketch of the adjuster, and a ReStakor modeling chart of the valving... page 12 on my browser midway down, by McGyver:

https://www.thumpertalk.com/forums/topi ... t=12543148

[Chuck78]

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Also, I found that JFG makes cheap billet aluminum anodized front rotor guards for the DRZ400 (& '97-'98 RM) Showa 49mm conventional forks!
$35 on eBay or AliExpress, as low as $23+$4 shipping on AliExpress if you prefer blue instead of gold anodized.

https://jfgmotor.com/products/front-bra ... XUgAYCq9rp

[billie_morini]

Wow! Britannica encyclopedia and Wikipedia do NOT hold a candle to Chuckpedia!

thx, Chuck. Copied and filed on external hard drive for future reference.

[Chuck78]

The DRZ400 clevis made contact with the top of the KDX's suspension linkage rocker at top-out, but I was still able to tilt the shock forward to get the frame's upper shock mounting bolt through the shock, although it does need filed slightly.

The '01-'04 RM clevis, with it's rocker mounting bolt holes drilled 5.5mm higher, won't even cone close to tilting forward to bolt unto the upper frame mount without some significant filing and dremel work to bevel the front facing horizontal surface crotch edge of the clevis.

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The '98 RM shock looks great installed, but is a close fit in a few areas of the frame, one which I'd massage by grinding off unnecessary metal.

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There is some unnecessary metal protruding from the upper shock mount needs trimmed off, as it's rubbing the RM compression adjuster portion of the shock body. Additionally, the bottom of the reservoir is pretty close to the frame, but clears.

Reservoir clearance on the '98 RM250 shock is close to the frame, but works. I'd have no issue heating the frame with my oxy-acetylene torch and dimpling it with a ball peen hammer here to gain more clearance, but probably never necessary, as with the full weight of the bike on the ground, the shock will swing backwards. The modern Showa 50mm shock is such a significant upgrade that I'll go to great lengths to make it fit perfectly.

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****Here's where no one prior had made any comments about required spring clocking due to engine case interference... You need to rotate the spring so that with suspension topped out, the gap in the coils is aligned with where the spring would otherwise rub the engine case swingarm / engine mount bolt area. As soon as travel starts, the shock moves further away from the engine case, but at initial travel, this needs to be clear and aligned strategically. I have no issue filing a bit of clearance into the engine case halves here, as this is a substantially improved rear suspension over stock... I just wouldn't want to file all the way through into the bore of the swingarm/engine mounting bolt.

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[Chuck78]

Here is a link to a pdf scan of some very detailed Showa shock rebuild instructions. No photos, but extremely descriptive. The bleeding procedure and making sure the rebound adjuster needle assembly is installed and set up correctly are critical.

https://www.southbayriders.com/forums/a ... ts/452117/

[Chuck78]

****NEWS!!!******

Browsing the Teknik Motorsport website, a big aftermarket suspension company based in Australia, they give specs on all these shocks... I don't believe they're all 100% accurate, but...as far as shock lengths, I've learned that according to them:
the 2002 DRZ400 shock is 450mm length (I measured 449mm-ish),
they claim the '01-'02 RM125 to be 453mm, close to my 451mm rough measurement,
AND....

'03-'04 RM125 are allegedly 448mm overall length, with the same travel as '01-'02!!!
I'm not 100% certain if this is a fact, as I've found several other errors in their numbers, but this measurement would work out to equal the '01 RM125 clevis & shaft lengths, + the 98-00 RM / DRZ400 body length, which is exactly what we're hoping for.... There are no 50mm Showas that are any shorter body or clevis than this so far in all my searching.

They advertise 140mm shock travel on all '01-'04 RM125, but both of these here have 130mm travel, and Teknik's total shock length is roughly the same as mine (mine are not lowered internally). I believe their '98 RM travel is also 10mm greater than actual measured travel @ 143mm (measured 133mm by me).

If this spec is correct, the '03-'04 RM125 have the shorter clevis, the shorter 98-00 style body, and likely the same shaft as '01-'02, making this the #1 KDX Showa swap with the DRZ400 2002+ being #2.

Without frame shock mounting relocation mods, the '03-'04 RM125 seems to be the #1 swap, & combinations of parts from '98-'00 RM125/250, DRZ400/400E/400S (2002+ preferably), DRZ400SM, & '01-'02 RM125 seem to be the best without modifying the frame.



Stock KDX200H shock shaft travel = 125mm with no bottom-out bumper in place (the Showa foam bumpers compression to less than 2mm @ bottoming, surprisingly)
Stock KDX rear suspension specs @ 11.8" / 300mm advertised travel
With my '01 RM125 shock mounted, granted sloppy linkage bearings slightly skewing topped out & bottomed out measurements, I measured 119mm installed available shaft travel. Add the 6mm shorter 98-00 RM (& '03-'04 RM125???) body swap, and that gives the shock 6mm further extension than the stock '01 RM125 shock clearanced to install on the KDX rocker linkage knuckle, so this shorter body gives around 125mm total shaft travel, same as stock KDX shock...

300mm advertised KDX200H travel ÷ 125mm stock KDX shock shaft travel = an average suspension leverage ratio of 2.40. I'd previously physically measured & calculated a leverage ratio of 2.38 (my axle adjustment is almost all the way forward - shorter chain length = shorter effective swingarm = higher suspension leverage ratio overall) so we'll use this 2.40 # for the new shock upgrades.

This shock has 130mm available travel total, so you'd really want to add roughly 5mm thickness worth of 16mm shaft diameter lowering spacers to keep the rocker from topping out on the frame harshly. So this setup gives nearly the same travel as stock, but higher ground clearance to match taller MX fork upgrades, and gives a larger shock piston, more fluid capacity (runs cooler), & added high speed - low speed compression adjustability externally.

Great news here after all these evenings geeking out, deliberating over online info, buying shocks, measuring, testing testing testing... Now to have someone confirm these numbers on an '03-'04 RM125 shock.


I'd recommend anyone to mock theirs up after clearancing the clevis, with rear wheel hanging in the air, and measure the actual available shaft travel (amount of shaft exposed with suspension linkage topped out and swingarm hanging to pull the shock down to full available extension), & then remove the shock to check the actual maximum shock shaft extension, and then give yourself a stack of 16mm shaft size internal lowering spacers that total the difference of available Showa travel installed vs fully extended available travel off the bike. Add maybe 1mm more in internal lowering spacers to protect the rocker linkage from topping out on the frame, & then build your shock up based on that length

[Chuck78]

Stock KDX200H shock shaft travel = 125mm
'02 DRZ400E (all 400/400E/400S?) = 128mm
'01-'02 ('01-'04?) RM125 shaft travel = 130mm
'98-'00 RM125/RM250 shaft travel = 133mm


For potentially running an even longer travel setup with no further gains in ride height,
I may eventually modify the KDX upper shock mount, to utilize all the travel available from my FrankenShowa combo possibilities...



Looking at relocating the upper shock mount 18mm higher & 6mm rearward for a longer travel setup, the slightly longer shaft on the '98-'00 RM125/250 shocks (vs '01-'04) with it's shorter body and the slightly longer of the shorter older clevises, + adding a Lainer Suspension 2009-2015-ish KX250F compression adjuster, while cutting and welding on the frame to raise the upper mount, would really effectively give us the best reasonable longer travel setup if willing and able to modify the KDX frame...

133mm shaft travel x 2.4 average leverage ratio = 12.5" rear wheel travel....




The '07 RM-Z 250 shock body looks most ideal for a KDX200H, with the RM style reservoir position but raised higher with an angled compression adjuster bridge portion, BUT measures 6mm longer than the '01-'02 RM125 bodies, & 12mm longer body than the '98-'00 RM125/250 & 2002 (likely all years) DRZ400.
Most years RM-Z 450 are very similar.

The RMZ250 & nearly all KX450F, & KX250F 2006-2018 ('19-'23 KX250F = longer & KYB, '24 250F back @ Showa) all are around 475mm length (even the KYB years KX450F) with the long clevis.
The long clevises 2005+ RM and all Showa KXF/RMZ could be shortened by about 9mm to match the '01-'04 RM clevis length or just a hair longer than the '01-'04 RM125 clevis for less clearancing needed, but that's still at around 466mm length on a modded clevis '07 RMZ250 shock.
Our unmodified KDX frame target is 444mm max if not 442mm or 443mm for no rocker impacts on the frame acting as the topout limiter. With a 6mm longer body roughly, but having longer travel. These will swap, but with internal lowering spacers, will be in the 10.6" travel range. They'll have roughly 7mm(?) longer travel to go with that 6mm longer body though (137mm travel???) for anyone really ambitious and wanting to get an extra long travel KDX rear suspension setup. That'd give roughly 12.9" of rear suspension travel after moving the KDX's upper shock mount approximately 24mm higher... Our chassis has room for it, although that's an excessive amount of travel for most woods riders. You'd want to keep the clevis around the DRZ400 / '98-'00 RM length though to make it easier clearancing the rocker knuckle & requiring a less aggressive bevel on the crotch of the clevis, and just adjusting the upper mounting height closer to 26mm-28mm higher instead.

[Chuck78]

I think this winter, I'll cut & fabricate an extension to the KDX200H/220R upper shock mount to relocate it 16.5mm higher and roughly 6.5mm-7mm rearward, so that I can use the full '98-'99 (& '00? - Teknik's website specs show a slight variation in size on 200) shocks with the aftermarket Lainer Suspension compression adjuster or '02+ DRZ400 compression adjuster, and have the option to swap to the shorter '01-'04 RM125 clevis and even shaft if I desired a lower rear ride height...

The rearward movement will help the engine case clearance and keep from cutting into the frame crossmember to get the adequate height (possible but would need additional bracing/gusseting), but I'll need to see how far the middle of the shock spring moves rearward during suspension travel to verify how far I can go without a bottomed out shock/spring rubbing the airbox boot.

The 133mm shaft travel of the '98 RM250 shock I have will yield I believe I calculated 12.5" travel... The '01 130mm travel yields 12" or 12.1", refer to above calcs.

I feel that adding 1" - 1-5/8" ground clearance is a huge plus for hard enduro type terrain, and then I can run modified Yamaha 2000's footpegs that are offset 1/2" lower, and also shave my seat foam about 1" up front tapering to 5/8" shaved in the mid/rear, to lower the standover tip toeing height back closer to stock. This will all improve the bike in the hard enduro terrain. I also am going to start running a longer chain, as the steepness of some of our technical climbs really challenge me to keep the KDX front wheel from lofting and nearly looping out when on the throttle in the steep gnar... The short wheelbase is really nice for whipping around in tight trails in between the trees though.