Re: Full Showa USD fork/RM125 shock conversion
Posted: 05:59 pm Sep 05 2022
Lol well I appreciate the info you supplied!
Discussion group for KDX enthusiasts
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Hey Chuck, where'd you get those purple fork guards? Great looking bike by the way!Chuck78 wrote: ↑10:38 am Aug 28 2022SS109, assuming the KDX has an average linkage leverage ratio of 3:1 (I've read this is fairly standard for a lot of bikes???), & the fact that he used a shorter spring perch, Donnie must've lowered that shock some internally or used a shorter shaft if the DRZ400 shaft is shorter, as otherwise I'd think the shock would give the KDX CONSIDERABLE ride height increase to the tune of nearly 2"-3"...Being 1" longer shock length and using the same length clevis as the stock RM shock. That's why I think he used the shorter DRZ400 spring cup/perch/collar to compensate and use the stock length RM spring still despite the shock being likely internally shortened a bit.SS109 wrote: ↑06:47 pm Aug 27 2022 The shock he built for me considerably raised the height of my KDX which, of course, works well with the 47mm twin chamber Showa forks. I did not ask him to make it the exact same length as the stock KDX shock but he might have done some parts swapping internally to get them closer to the same length. That said, I have no clue what he actually did inside.
But also, your shock is definitely a fair bit longer than the stock KDX from reading your past accounts, as I do remember you saying that you had to compress the shock 1/4" just to get it to install on the KDX.
I just threw my '99 220 with stock shock & stock 112.5 links up on a stand to get it at full droop to study the linkage.
Based on the fact that your '01-'06 RM125 shock after custom rebuild was still 1/4" too long, and looking at my linkage vs frame, tells me that your shock must still be fairly close to stock RM length, as a noticeably longer shock would in fact appear to push the rocker linkage into the frame crossmember that it mounts to, the KDX's frame would be the limiting factor on shock fully extended length.
I measured approximately 5-1/4" of exposed shaft on the RM125 2003 shock, versus just a hair over 5" on the KDX shock. I'm guessing that neither of them use the full shaft travel range at least I hope! Wouldn't hurt to do a mockup with a spring removed or just use 2 ratchet straps to fully crank down the KDX rear suspension to test this out before making any internal shock changes. If 3:1 leverage ratio is in the approximate range of the KDX, lowering the RM 125 Showa internally 5/8" or 7/8" should be no issue. But as they say, "to measure is to know."
I've actually been meaning to mark the shock shaft and use a ratchet strap to compress the rear suspension, with a tape measure in hand, and measure shock travel vs rear wheel travel, to give myself a rough approximation of the actual rear wheel/swingarm vs shock travel leverage ratio, for making rough guesstimated calculations on suspension alterations.
Honestly I'd really consider just leaving the shock a decent bit longer but running a lot more than the standard 100mm-110mm of rider sag when seated, just to get the geometry in the realm of where it needs to be to match a fork that's set up at 5/8" or 7/8" taller than stock and maintain somewhat proper steering caster angle. I'm thinking to lower the shock 5/8" internally perhaps, run a shorter (or custom) spring seat/perch/collar, and just back the preload off to achieve desired rear ride height.
I'm quite pleased with the revalved KLX300R fork / stock rear shock with 100mm sag set + low psi Tubliss, but I just can't leave any of my toys alone when there's other cool and significant improvements that can be made...especially when they will be of substantial benefit when riding the nasty gnarly terrain that I gravitate towards...
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VTMTcowboy wrote: ↑11:45 am Sep 09 2022Hey Chuck, where'd you get those purple fork guards? Great looking bike by the way!
Here ya go:VTMTcowboy wrote: ↑11:45 am Sep 09 2022
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Hey Chuck, where'd you get those purple fork guards? Great looking bike by the way!
My forks are from an '06 Kawasaki KX250F and the shock was "built" from parts to bolt in to any '01-'06 Suzuki RM125. I can't see any real changes in the early 47mm Showa forks vs the later ones but I haven't worked on that many of them or really measured everything out. That said, there shouldn't be anything in the newer version Showa 47's that you couldn't install in the older models if there is a difference. On the shock, not sure if shaft size changed on the shock or whatever differences there are. I just know mine works great.