KX125/220 hybrid vs upgraded suspension on 95-06 KDX

[Slick_Nick]

The KDX is a heavy bike, but it's still nimble. It's achilies heel is that it carries so much of the weight up high, as fuel. I notice a huge difference in the feel of the bike when it's down to a half tank or less, vs a full tank.

[Chuck78]

The KDX is a heavy bike, but it's still nimble. It's achilies heel is that it carries so much of the weight up high, as fuel. I notice a huge difference in the feel of the bike when it's down to a half tank or less, vs a full tank.

Working out of town living in hotels, I took my street bike in the work truck with me often... When tinkering on the 1977 Suzuki GS750 at the hotel, I once took it for a spin around the parking lot to load it in the work truck, without the gas tank (they'll run 45 seconds or so light throttle just off the fuel in the bowls).
WOW... The difference in feel just doing a wide 25mph circle and up the ramp into the truck was mind blowingly different! Such a light feel losing that weight up high...

This is how an H-Series KDX "feels heavier" than a Beta XTrainer which actually tips the scales a bit more hefty...

[Chuck78]

I know it's a bit more work but don't forget about the '04-'05 Kawazuki KX250F/RM250F chassis'. They handle great, are steel framed, etc. These bikes were great other than the Suzuki designed engine they came with.

I really don't care for the stylings of those, & those are beyond the Revolution 2 vintage/post-vintage race classes, so no go for vintage events.
I don't even care for the '03-'05 stylings honestly, and each year 03-05 uses different swingarm and linkage parts, but 04-05 may be interchangeable - same design but slightly altered.




There seems to be a ton of parts support for the '99-'02 era, based on looking at the IMS website, Devol Racing, and Clarke Mfg.
https://imsproducts.com/pages/product-r ... 25~yr_2000


But really I'm now seeing the mass centralization design fully when browsing photos of the 95-98 vs 99-02 & 03-05. The KX's handle and feel better than the KDX because they not only have a 2.17-2.2 gallon fuel tank vs 2.9+ on a KDX, BUT you're basically SITTING ON TOP of a larger majority of the fuel tank on the '99-'08 KX125/250, moreso than this same positioning on the '95-'98 even. This also makes the bikes taller, and also on the 99-08, makes the seats very thin on padding... The 95-98 era have the thickest seat, which would be more comfortable for trail riding. BUT that also probably screws up the clearance to fit a SmartCarb SC2 36 in there.
95-98 has the least options and least desirable looking options for oversized fuel tanks. The custom order 3.1 gallon requires cutting the upper fuel filler cap area of the shrouds off, and IMS doesn't even have a photo of it.
The '99-'02 3.1 gallon IMS tank is he best looking, but another big concern is that the oversized tanks will have interference issues on a hybrid with the engine, petcock, spark plug, etc, and the 3.1 gallon hangs extra low at least on the pipe side. They offer a 3.2 gallon as well,which doesn't sit so tight to the pipe and carb/head which may be the better choice for a 200/220 hybrid as the 125 engine's cylinder jug is absolutely tipped forward more vs the 200/220. I'll have to read into this a bit more to figure out exactly where the clearance issues lie, but I only recall the build thread reference stating "desert tank" clearance issues requiring heating up the tank and forming some clearance into the plastic.
IMS 3.1 gallon '99-'02:

IMS 3.2 gallon '99-'02:


I think if I ran a 95-98 125, I'd absolutely have to keep stock 220 port height (which is always the preferred route if you wish to preserve the best traits of the 220) and run a Lectron Billetron Pro Series carb, both done in order to get better fuel efficiency. On long hauls, I could always attach a small auxillary fuel tank behind the left rear side plate, which would also keep with the theme of lower center of gravity and mass centralization... Keeping the factory 2.2 gallon tank on the '96-era.

The 99-02 still have excellent geometry for tight woods riding and hard enduro, so some aesthetic alterations may be in order here.

I browsed for a cheap basket case 95-05 KX125 last night, but nothing much available. A guy parting out a roller with no engine in Kentucky, 2001, that was it... I'll be watching this winter for one!

If 03-08, I'd go 03 for the shorter swingarm. The 27° rake is a bit more high speed friendly than I'd care for, but forks could be dropped lower to get 26.5° or 26.25° and also lower the ride height slightly. The wheelbase will still be a noticeable bit longer than a KDX200/220 and 94-02 KX125. I'm aiming for a lighter weight lower center of gravity nimble agile & highly flickable hard enduro weapon here... And the 220 engine with a modded head and supporting pipe, carb, & ignition mods I've already determined is an absolutely awesome engine for this type of riding... Noticeably more suited to this type of terrain and riding than a KDX200 or KTM 200. The 220 chassis with suspension mods does pretty darn well, but it's just that high center of gravity top heavy feel that bothers me a bit (and also makes it a bit harder to pick up in very compromising steep gnarly hillside flops, which is why I was even considering a 144cc, 151cc, or 167cc big bore or big bore/stroker engine).
I still have a lot of titanium to swap out onto my 97 or 99 220 to drop the weight down, but the weight is significantly more noticeable up high than it is down low, so the fuel tank positioning/shape issue is a hard issue to work around, and really the only reason that I would consider building a hybrid over a modified H series chassis. The slimmer seat on the '99+ and an aluminum subframe will also drop a little bit of top heavy weight on a hybrid, I should add.

[Chuck78]

Really I'll probably end up swapping out the forks on whatever I'd build for a set of '98 RM125 forks and possibly an '01-'04 RM125 shock or '05+ RM125/'06+ KX250F/'07+ RM-Z250 if more length was needed on the KX chassis of choice.
I've got several sets of the '98 RM 49mm Showa Twin Chamber forks stockpiled now enough to build 3 or 4 good pairs.
One big advantage however is that the '03+ have a taller steering stem, so I'd be able to directly swap in a pair of 2013-ish KX250F SFF single function Showa Twin Chambers in. Those are really the ultimate as far as smoothness goes with a closed chamber fork design... Only available in inverted format, no right side up versions of these were ever made, the 96-98 RM right side ups are as good as it gets with right side up fork technology...

[Chuck78]

In summary, for what I'm wanting to do - hard enduro and tight woods riding, very little in the way of high-speed 55+mph riding where long wheelbase and more relaxed steering angle would be preferable, the shorter wheelbase and steeper steering rake angle on the 95-98/99-02 is definitely preferred, and although I really want a 96 for the purple plastics and the thicker more comfortable seat, the '99-'02 really seems to be the best candidate for me in terms of aftermarket parts availability. The amount of oversized tanks available is fantastic, lots of options, skid plates, radiator guards, rotor guards front and rear, etc....

1996:

maxresdefault.jpg (307.57 KiB) Viewed 50730 times

1999-2002:

I think I could get the 1996 KDX style shroud graphics printed on a full sheet with no cutout, so that I could get all black plastics for the 99-02, and lay my own cut out of the 96 KDX graphics on top of it, like what I have now custom, with the KX checkered flag.
This 99-02 picture here helps me visualize it better with graphics on it to break up plain or less desirable looking shrouds and side plastics on this era.

On the larger side plates looking goofy to me, if I did all black side plates with a white background in just the number area, that will take away from the goofy 99-02 appearance, although I would much prefer the 95-98 style... Also, 95-98 would put me in Revolution 1 racing classes at vintage events...



I think either of these would do well for me although I might have to custom make some radiator guards for the 96 era and just deal with a smaller gas tank, as well as struggle to fit a SmartCarb SC2 36 or else go with the proven fitment Lectron Billetron Pro Series. Carrying less gasoline is critical for handling, and the only way to go the same distance and carry less gasoline is have a perfect week tuned bike with a metering rod carb. Even the best tuned PWK setup will use more fuel than a metering rod carb...


Also, Guts offers a stepped seat foam insert to glue on top of the rear of the seat, which gives you thicker padding in the thin rearmost areas as well as giving a slight step or bump to act as a stop to keep the rider forward more when seated during aggressive maneuvering. I think this would help out a fair bit. I could even shave it a little bit so that the bump up to the stepped portion isn't noticeable if I want to be able to slide back and forth on the seat to my preferred position depending on cruising versus attack mode / preparing to attack... Most of the time when hitting aggressive sections we should be standing up, but there are times where you need to keep low in a corner and be seated or near seated and tucked, while staying forward.

[Ridea200]

Hybrid...hybrid...hybrid
You know you wanna...

[Chuck78]

H-series KDX chassis:
26.5° rake / 4.3" trail
56.5" wheelbase
36.2" seat height
2.9 gallon tank
223lbs claimed dry weight



1994-1998 KX125:
26° rake / 4.3" trail
1,455mm (57.3") wheelbase (KX250 = 1,460mm)

1999 KX125:
26° rake / 4.3" trail
56.5" wheelbase

2000 KX125:
26° rake / 4.3" trail
56.3" wheelbase

2003 KX125:
27.5° rake / 3.9" trail
57.3" wheelbase

2004 KX125:
27° rake / 4.4" trail
57.9" wheelbase

'03-'04 KX125 Rake/Trail: 27.5° / 3.9 in.
2005 KX125 Rake/Trail: 27.5°/ 4.3 in

After my last 2 rides, doing some really steep hill climbs, granted without enough speed at the bottom l, I definitely was wheelie'ing up the upper steepest parts almost to the point of looping as I had to give more throttle to make it up on my H-Series chassis.
I was thinking that perhaps a longer wheelbase wouldn't be so bad, especially after talking to a guy who swore his 2019 Beta 250RR was the best handling bike he's ever ridden, better than his KX/KDX hybrid. That has over a 58" wheelbase... '04-'05 KX125 is 57.9".
Perhaps this is workable for me with hill climbs considered. The '05 triples/forks have more trail, so they'd do a lot better with sliding the triples down over the fork tubes to drop the lazy high speed 27.5° rake down to 26.5°-ish like the stock KDX (a 1" drop approximately), so this could really work out decently.

94-98 KX125 have a very slightly longer wheelbase vs the KDX H-series (57.3" vs 56.5")
99-02 have virtually identical wheelbase and rake/trail vs KDX H-series
2003 KX125 have 1.4" longer wheelbase (56.5 vs 57.3) vs KDX H-series
04-05 KX125 have 0.8" longer wheelbase (56.5 vs 57.9) vs KDX H-series

I think all of these would be workable as a tight woods bike, but I'd now probably choose at least the '05 125 triples (and forks? upgraded?) if running an '03-'04.

Ideally, I'd still gravitate towards an '03 in that generation in order to get the shorter swingarm with still a leverage advantage on steep climbs vs stock KDX, but I'd likely be selling the forks off and running a pair of my '98 RM125 49mm Showa Twin Chamber conventionals anyways. Then I could lower the front 1.1" from stock, and get nearly the exact rake and trail I'm after 26.4° rake / 4.3" trail, while having the slimmer chassis, and also having a VERY REASONABLE seat height on the '03+ (It's already close to the KDX, then lowering the front 1" to get the rake & trail specs I'm after would put it in the upper 35" range.

I'd personally try and upgrade the side cover plastics to KDX or 94-98/99-03 if in any way possible. I like the more retro looks, but now a 2003 still looks like quite a good candidate.
With my '98 RM125 forks, the 26° rake on the 94-02 would give 4.19" of trail, a bit faster steering again. 4.3" of trail would require running less shock spring preload to drop the rear down 1/2" lower, while keeping the fork tubes flush with the tops of the triples, and would give a taller seat height regardless. With rear sag set back up proper, a set of DRZ400E triples for the '98 RM125 forks may get the trail back to around 4.35".

[Slick_Nick]

That has way more to do with improper body position on the bike than it does the length of the chassis. Get your weight up off the seat, chin over the front fender.

[Chuck78]

That has way more to do with improper body position on the bike than it does the length of the chassis. Get your weight up off the seat, chin over the front fender.

Easier said than done in my examples referenced! When the climb seems close to vertical at the top (in reality over a 60° or perhaps 65° slope, STEEP!), it becomes increasingly more drastic of required body positioning that one needs to shift into. There is definitely a reason that hill climbers have extended swingarms on their bikes.
So really, I think it comes down to the combination of 3 factors,
1.) Giving it more throttle at the flat bottom and where the slope is 35° or 40°, so that less or minimal throttle is required when the slope picks up above 50°
2.) Intentional body positioning more forward over the bars/fender
3.) longer wheelbase

I suppose one could do a lot of moderate hill climbs with any variation of those 3, but when the hills get real steep and long, I bet all 3 in full effect will be a bonus...

Also, I have been stuck running my KDX chain/axle in the front half of the swingarm axle dropout slots perpetually for years. Next time I'll go back to a clip style master link perhaps, so that I can run it longer and shorten up the chain if I run out of adjustment.
Hopefully my next chain & gearing change to 13/48 will yield more favorable axle positioning on chain length.

[Chuck78]

Hmmm..... 2000 KX125 bare rolling chassis, $60 + fuel/time! I need to try and sneak this one in somewhere somehow, so the wife doesn't kill me!!!!
2 hours from home, or 1 hour off the 1.5 hour route to get to the furthest riding area that we hit once or twice a year in southern ohio...

Having an airbox & seat would be nice, but it's tough to beat for basically $100 & a half day!
I revisited this last night after thinking about the potential weight differences between an aluminum seat subframe and steel. I was looking KX frame subframe mounting points by the top shock mount, and thought that drafting a 99-02 KX aluminum seat subframe and probably airbox and rear fender onto a KDX frame, the beneficial to have a strap KX frame to cut points off of, and this would also give us smart carb, as shock mount frame crossmember area is an arched front half back half press formed piece, instead of a straight round tube with a slight dimple pressed into the bottom for carburetor clearance, that the 95-06 KDX has.


If this frame or not able to be titled, I could at least use it as a donor for that.

Screenshot_20231116-082011~2.png (1.61 MiB) Viewed 44844 times

The KX front upper perimeter frame sections do appear to mount about a half inch lower than the KDX, very slightly reducing the center of gravity for the fuel tank weight, but the bigger difference is the KX's standard 2.2 gallon capacity versus 3 gallon capacity of the KDX. Both are perimeter frames, and I feel that using all the race spec steel bolts from a KX with dished out heads, and the lower fuel capacity, say using 2.2 gallons in the KDX instead of 3 gallons filled to the brim, would get rid of most of the difference in the top heavy feel KX hybrid vs KDX. KDX seat is really not as thick as it appears, and didn't seem alarmingly heavy to me, and also that is one area I would like a little more comfort in all day rides the point of exhaustion. You can't stand up for 7 hours out of a 9 hour riding day (w/ 2 hrs of breaks total).


My 98 RM125 4.6kg purple shock spring weighs in at 2lb 15 oz, & my 98 RM250 4.8kg purple spring @ 3lbs 1 oz, Diverse Spring's Chrome-Silicon lightweight steel 4.8kg spring is 2.5lbs iirc, 1174 grams they said, and the RCS / Renton Coil Spring 4.8kg Titanium spring is 2.1lbs iirc, so this is another area of substantial potential weight savings to compensate for the KDX seat and extra fuel capacity.

I'll be looking into long case cover bolts as well if Partzilla lists the dimensions of all. Mettec & Titan Classics have some really good prices on Ti bolts, although unless on clearance for $175, the Mettec axles cost an astronomical amount at $300-$500! No thanks...

[Chuck78]

I've also got a guy who has the remnants of his '98 KX125 parts bike, frame, swingarm, some plastics, stock tank, airbox etc 3 hours north. 98 has no desirable looking oversized tanks due to the shrouds wrapping over the whole tank and requiring aftermarket o.s. tank shrouds, or else cutting the factory shrouds top portions, and no radiator guards available, but they do fit the OEM purple plastics and have better looking side plates and shrouds

I'm speculating from KDX carb clearance photos on a "A Path Less Traveled - 97 KX hybrid" posts, I'd possibly have to modify the frame to fit a SmartCarb SC2 36 on the 220 transplant, but if I'm already modifying the frame substantially to fit the 220 engine, what's the diff?!
Compact geometry is nice.

I'd run some of my '98 RM125 forks and hope that a 98-04 RM125 shock would fit.

No radiator guards available for 94-98, so perhaps I'd try to graft KDX radiators on, or custom fab my own 94-98 KX radiator braces.
No frame guard hoops are welded to the motocross frames to my knowledge, so if I added these protections, a KX skid plate wouldn't fit. Perhaps use my Hyde Racing H-Series KDX skid plates, especially if I go the route of the guy's hybrid build here titled "A Path Less Traveled - 97 KX hybrid" and chop the engine cradle section out of the KDX frame to graft it into the KX frame. A guy in New Zealand that I'm online KDX buddies with, Mark Webb, he has a 96 or 98 KX125/220 hybrid and did not cut the frame up and graft the KDX cradle in. I'll have to evaluate his build as well.

viewtopic.php?f=111&t=25913

[Ridea200]

As far as carb fitment, all I did was clearance front to back. Im not sure how big the smart carb is, but you may need to also raise the bottom a bit. I want to get a vforce, and will have to do this as well.
Engine cradle wise, the way I did it isn't mandatory, but for me it provided motor mounts, pipe clearance, and the loops. I didn't want to reinvent the wheel. If you have any questions, just let me know.

[Chuck78]

Well, I missed out on the killer deal on the $60 2000 KX125 rolling chassis due to the 4 hour round trip not being something I could just immediately schedule...

I did however start chatting with a guy in a KX group who lives 2.5 hours north of me, and has an extra 98 125 frame, swing arm, tank, and a bunch of miscellaneous parts... It would be more to piece together since everything is in pieces, but this is also an option to keep on the back burner.

Apparently 97 and 98 were improved frames over the 94-95, and the 96, and a much more stout swingarm 97-98, yet they all take the same plastics which I really love a lot more, and they also have the thicker seat foam than 99+... But same compact geometry as the 99-02.
The 98 frames I've looked at have more carb clearance on the crossmember by the upper shock mount vs the older frames, as instead of a round piece of tubing bridging from one side of the perimeter frame to the other, it's a stamped clamshell type piece made from two halves, and is arched in the middle over the carb.

Art Simmoneau (I forgot his name here on the forums but he has a couple hybrids) really disliked the 3.1 gallon Clarke tank that he just bought for his KX hybrid, said it was too wide and tall and pushed the shrouds out further, totally changing the feel and look of the bike.
Art came up with a brilliant method of taking the stock KX tank on his hybrid, pressurizing it with air, and using a heat gun externally to heat up the plastic and allow the air pressure to pop out all of the dimpled indents in the KX tank's underside that were not necessary for the KDX engine in the KX chassis. He thought he gained perhaps even close to a half gallon of extra capacity, which will really help with those small tanks.
This was very encouraging, as I think you could probably expand most of these tanks on the bottom side a slight bit to get a little extra capacity without making it more top heavy like the KDX tank sits, up high in and above the perimeter frame. And also preserving the stock appearance.
This really brings the 96 or better yet 97 or 98 with purple shroud graphics on black shrouds, and a purple seat, back into the running. Every time I would look at a 99-02, I liked them better than the 03 Plus or the four-stroke steel frame or aluminum frame bikes, but nothing looks as awesome as the purple 96 KX 125 and it's siblings of the same generation.

I've still got a lot of big plans to rebuild at least one of my two KDX220's with a ton of titanium parts and all the other go fast parts and suspension goodies that I have, but I really am hoping to get a 125 chassis for a good deal and build up a hybrid as well in order to see how much lighter of a feel I can get.
Finding an AC Racing aluminum subframe for the 94-98 is a bit difficult, stock was steel, that was another reason for going with a 99-02. But apparently a 99-02 aluminum subframe will bolt onto the 98 frame, but apparently you need to use all 98 plastics tank. I might try and do some sort of hybrid of a hybrid and use the 99-02 aluminum subframe and air box, and draft on mounts for the 98 side plates and 98 seat and possibly rear fender.

It's all a pipe dream now and just brainstorming ways that I can get even further weight reduction on my 220 builds, especially with a lower center of gravity. I'll already be swapping different suspension onto both the KDX's and the proposed KX 125 hybrid, so the 125 suspension is not really of concern to me (sell it to another KDX'er as an upgrade) because I'll go with something better suited for tight woods riding anyway. I have at least three rebuildable sets of 98 RM125 forks + several more for parts with a few rust pits and chips in the chrome etc. Those are my go-to woods/enduro forks. DRZ400E & 96-98 RMX250 forks are right behind. And 01-04 RM125 shocks & other related 05+ Showa 50mm shocks on KXF, RM-Z, & RM '05-'08 models.