Really struggling

[Nighthawk016]

Hoping you guys can help me. I came off of a rm250 that I added a few things for woods riding, flywheel weight, regear, the normal stuff. Suspension wise, all I did on the rm is go through the forks, clean everything up, reassemble and set the rear sag.

I got myself a kdx, I've got 12-15hrs of ride time on it now. On the kdx ive jetted the carb, new top end, and had the suspension resprung for my weight. I have the sag set properly at right around 90mm. I was expecting the kdx to a night and day difference better than the rm, but I am struggling. My biggest positive is, I can do 25-30 miles of tight single track in the woods and im not beat to snot like the rm. However, I am not sure if its my riding style or what, but I am significantly slower on the kdx. Even with the rebuilt and resprung suspension, the whooped out sections, which are a big portion of my riding, are a huge struggle.

What I need to know is, do I need to change suspension settings, gearing, tires? Or maybe it's a skill issue and i need to completely change my riding style?

Any advice is appreciated.

[Chuck78]

I believe I'm at around 103mm suspension sag on the rear, as 95 was not enough, although I'm 160lbs and running a 5.0kg spring on one shock and a 4.9kg on the other, when I should be at a 4.7kg.

I was always under the impression that with around 300mm rear suspension travel, you needed 100mm sag, as 1/3 of your travel generally should be rider mounted rear sag on a long travel suspension setup. 90mm sag is a firmer ride, which I'd think would be mire suited to whoops, but perhaps not...??? Maybe KDXGarage or other can chime in on this. Valving setup us also a huge part to play in this issue, but the sag stood out to me as not enough. Proper spring rates are critical, perhaps your rear spring rate is not quite ideal?


For whoops, perhaps a CRF250X front end swap would suit you far better... Whoops vs tight singletracks are night and day difference, requiring different suspension settings, but a well built closed chamber KYB or Showa fork can be set up to give initial plushness while still having bottoming resistance.

Closed / Twin Chamber forks are best for aggressive race use and whoops etc, the RM had Showa Twin Chamber forks (or 01-04? were KYB?), but setup for, whoops will in fact tire you out on a 30 mile technical ride most definitely, while some open chamber KYB forks valved plush for technical singletracks will in fact allow uou to fo 35-75 mile days with a fair bit of technical terrain without wearing you out drastically.

It's a compromise, but I really feel the Showa Twin Chamber CRF250X forks set up for initial plushness but with bottoming resistance will be the best of both worlds for your exact terrain.

What areas do you ride?

Alternately, a 2005+ YZ250 2-stroke triple clamp with similar year 2005+ YZ125 fork legs could be valved very nicely as well for this purpose, but you'll need a generic chinese 28x47x15 upper steering stem bearing, as no name brand bearings are available for this non standard size.

EDIT - if you're heavier, the CRF450X or YZ250 2-stroke forks are better than my 250X / 125 2-stroke recommendations

[Nighthawk016]

I believe I'm at around 103mm suspension sag on the rear, as 95 was not enough, although I'm 160lbs and running a 5.0kg spring on one shock and a 4.9kg on the other, when I should be at a 4.7kg.

I was always under the impression that with around 300mm rear suspension travel, you needed 100mm sag, as 1/3 of your travel generally should be rider mounted rear sag on a long travel suspension setup. 90mm sag is a firmer ride, which I'd think would be mire suited to whoops, but perhaps not...??? Maybe KDXGarage or other can chime in on this. Valving setup us also a huge part to play in this issue, but the sag stood out to me as not enough. Proper spring rates are critical, perhaps your rear spring rate is not quite ideal?


For whoops, perhaps a CRF250X front end swap would suit you far better... Whoops vs tight singletracks are night and day difference, requiring different suspension settings, but a well built closed chamber KYB or Showa fork can be set up to give initial plushness while still having bottoming resistance.

Closed / Twin Chamber forks are best for aggressive race use and whoops etc, the RM had Showa Twin Chamber forks (or 01-04? were KYB?), but setup for, whoops will in fact tire you out on a 30 mile technical ride most definitely, while some open chamber KYB forks valved plush for technical singletracks will in fact allow uou to fo 35-75 mile days with a fair bit of technical terrain without wearing you out drastically.

It's a compromise, but I really feel the Showa Twin Chamber CRF250X forks set up for initial plushness but with bottoming resistance will be the best of both worlds for your exact terrain.

What areas do you ride?

Alternately, a 2005+ YZ250 2-stroke triple clamp with similar year 2005+ YZ125 fork legs could be valved very nicely as well for this purpose, but you'll need a generic chinese 28x47x15 upper steering stem bearing, as no name brand bearings are available for this non standard size.

The rm has 49mm showa twin chamber conventional forks, they are definitely something else. I'd like to stick to conventional forks if possible. I was considering xr400 forks. The rear of the bike felt really good, I didn't feel like I was getting bucked, but the forks felt like pogo sticks.
I ride mostly mid-michigan trails, evart, horseshoe, holton, and cedar creek. The first three are a mix of black dirt and sand, with some of the trails being heavily whooped out. Cedar creek is all sand, and basically all whoops.

This is definitely a start. Do you think I should seriously conside the kyb sss forks?

[Chuck78]

Sand requires fast riding... And whoops are often found in the Michigan sandy trail areas...

I actually have several sets of those 1998 RM 125 forks and one set of 250 forks.... Those are known as the best woods forks of all time to a faction of veteran trail riders.

I actually have a multi-page thread here on this forum dedicated to those forks and a hybrid shock that I built out of RM 125 parts from various years as well as a second one out of DRZ400 shock parts mixed with some RM parts...

Those forks are excellent.

Look up my Showa 49mm thread on here if you're curious, the triple clamps do not bolt right on, but with the steering stem swap and milling off that raised lower bearing seat as I have a picture of in the thread, you can swap them onto a KDX frame.

Finding a set of those that still has good chrome in the seal travel area can be difficult though, which is why I have so many sets of them... Every seller guaranteed that the chrome was good, but then most ended up having rust pits and chips...

The XR400R forks are nice but other than having adjustable rebound and less under hanging tube below the axle, and being a lot lighter, they're going to function the same as the KDX fork. In my opinion though, they are much better as a base due to the benefits mentioned. I wouldn't hesitate putting all the upgrades into those in the form of upgraded springs if needed, Race Tech Gold Valves, OEM bushings and SKF seals etc

A CRF250 2004 steering stem should press right into those after milling the raised step on the lower bearing seat

[SS109]

IMO, your sag is way off. 100mm is what Pro Circuit recommends as a baseline for the '95+ KDX chassis and I think I'm at 104-105mm with my modified setup. Static should be between 30-40mm.

Also, you say you ride a lot of whoops. The stock KDX forks suck for whoops and anything requiring speed over rough ground. They just flex too much and don't have the adjustment needed to make them work well. I'm a mid-pack B Racer and the stock forks would get me in trouble on a regular basis, due to flex, sending me off trail and sometimes crashing hard. Went to USD forks and have never looked back.

You know, I have never understood why people wouldn't want USD forks. There is a reason all race bikes use uSD forks and it's not just marketing. They are superior for numerous reasons. Conventionals just have too much flex unless you get into those Showa 49mm conventionals and then you still have to deal with the underhang which can get you hurt in ruts/rocks. Also, since they are so beefy the underhang risk is even greater on those than other thinner conventionals.

[Chuck78]

Conventionals just have too much flex unless you get into those Showa 49mm conventionals and then you still have to deal with the underhang which can get you hurt in ruts/rocks. Also, since they are so beefy the underhang risk is even greater on those than other thinner conventionals.

FYI the '96 Showa conventionals do have a fair amount of underhanging fork tube below the axle, but the '97-'98 Showa RM conventionals and the DR-Z400 49mm (but open chamber, no mid-valve) Showa conventionals both have a very minimal amount of underhanging tube pretty similar to 96-98 and 03-05 KX forks. Running a DRZ400 billet front rotor guard can smooth out that hang up point, and if you're at risk of bashing rocks, you need that anyways.

But all that said, the inverted CRF250X (or for heavy riders, CRF450X) forks 2004-2017 should swap right in with an All Balls 30x47x12 upper conversion bearing kit which includes a 3mm spacer since the frames are 15mm tall in the bearing pocket but the bearing is only 12mm tall. Or else YZ250 2-stroke triples (250 2-stroke has taller stem than 250F and 125 2-stroke) and YZ250 2-stroke or TZ125 2-stroke fork legs and a generic Chinese non-standard conversion bearing size off of AliExpress, Amazon, or eBay in 28x47x15. Valve them for initial plushness but with bottoming resistance in mind. Volume spacers will help with the bottoming resistance, if you can find a suspension company who makes those for the Showa 47mm USD forks.

[Nighthawk016]

IMO, your sag is way off. 100mm is what Pro Circuit recommends as a baseline for the '95+ KDX chassis and I think I'm at 104-105mm with my modified setup. Static should be between 30-40mm.

Also, you say you ride a lot of whoops. The stock KDX forks suck for whoops and anything requiring speed over rough ground. They just flex too much and don't have the adjustment needed to make them work well. I'm a mid-pack B Racer and the stock forks would get me in trouble on a regular basis, due to flex, sending me off trail and sometimes crashing hard. Went to USD forks and have never looked back.

You know, I have never understood why people wouldn't want USD forks. There is a reason all race bikes use uSD forks and it's not just marketing. They are superior for numerous reasons. Conventionals just have too much flex unless you get into those Showa 49mm conventionals and then you still have to deal with the underhang which can get you hurt in ruts/rocks. Also, since they are so beefy the underhang risk is even greater on those than other thinner conventionals.

Thanks for the updated sag info, I could swear I saw 90mm somewhere, so im surprised, the rear felt pretty good.

Just confirming here, your opinion is, stock forks won't work for whoops just in general, the 49mm conventionals are the way to go if im sticking with conventional forks, and the best solution is swapping in usd forks from some other bike.

Conventionals just have too much flex unless you get into those Showa 49mm conventionals and then you still have to deal with the underhang which can get you hurt in ruts/rocks. Also, since they are so beefy the underhang risk is even greater on those than other thinner conventionals.

FYI the '96 Showa conventionals do have a fair amount of underhanging fork tube below the axle, but the '97-'98 Showa RM conventionals and the DR-Z400 49mm (but open chamber, no mid-valve) Showa conventionals both have a very minimal amount of underhanging tube pretty similar to 96-98 and 03-05 KX forks. Running a DRZ400 billet front rotor guard can smooth out that hang up point, and if you're at risk of bashing rocks, you need that anyways.

But all that said, the inverted CRF250X (or for heavy riders, CRF450X) forks 2004-2017 should swap right in with an All Balls 30x47x12 upper conversion bearing kit which includes a 3mm spacer since the frames are 15mm tall in the bearing pocket but the bearing is only 12mm tall. Or else YZ250 2-stroke triples (250 2-stroke has taller stem than 250F and 125 2-stroke) and YZ250 2-stroke or TZ125 2-stroke fork legs and a generic Chinese non-standard conversion bearing size off of AliExpress, Amazon, or eBay in 28x47x15. Valve them for initial plushness but with bottoming resistance in mind. Volume spacers will help with the bottoming resistance, if you can find a suspension company who makes those for the Showa 47mm USD forks.

And you are saying crf450x forks or yz 250 forks would be best.

Is all of that correct?

[SS109]

Thanks for the updated sag info, I could swear I saw 90mm somewhere, so im surprised, the rear felt pretty good.

Just confirming here, your opinion is, stock forks won't work for whoops just in general, the 49mm conventionals are the way to go if im sticking with conventional forks, and the best solution is swapping in usd forks from some other bike.

Basically, yes. Don't get me wrong, there are plenty of people who have ridden whoops on the stock forks including me. If you do everything right then they will work fine. The problem is when you don't do everything right. You drop the wheel a little too much, don't hit the whoop square on, or you start to get off line while in a set of whoops, etc. That's when the flex can get you. Some flex is actually a good thing but the KDX 43mm forks have just way too much. The more aggressive of a rider you are the more a fork upgrade will benefit you.

The 49mm conventionals are a massive upgrade over the stock forks due to their lack of flex and full adjustability. It's hard to go wrong with a set of those. IMO, they would be good for 99% of riders out there. I like the more modern USD forks because they tend to be lighter weight, have less overhang, and parts are easier to find for them.

On the USD forks, pretty much all of them are good as long as they have compression and rebound adjustments. It doesn't matter what bike they come off of as they all will work. My favorites are the Showa 47mm twin chambers from an '06 KX250F that I had revalved for my type of riding. I have ridden on about every fork out there and there are lots of good ones to choose from. I ran a set of KYB 46mm from a '98 KX125 that were great and the KYB 48's are good as well. Kawasaki fitted forks tend to be a little easier to swap over normally but you gotta do your research.

[Chuck78]

The '98 RM125/250 "conventionals" (only conventional in a right side up reference, very modern otherwise) & their '97 RM125/250 versions (very similar but larger damping cartridge shaft and lacking the '98-present quick change base valve feature) are fantastic forks that are largely on par with the 2004/2006+ Showa Twin Chamber 47mm upside-down versions, but the newer '04+ versions have larger damping pistons and a few other refinements. They went back to 49mm in 2017/2019 depend on make. The '99-'00 49mm Showa Twin Chamber inverted forks we're not terribly popular as they were said to be too rigid at the time, but I believe a lot of that had to do with the damping setup. They went down to 47mm inverted in model year 2000, but back up to 49mm between 2017-2019 depending on the bike manufacturer.

These are all virtually the same forks including the KYB AOS closed chamber 48mm versions which Yamaha refers to as KYB S.S.S., but with changes and refinements over the years. Yamaha has long been known to have the best tuning setup for the internal damping systems out of all the manufacturers as stock, however, but did not offer a Woods fork version until 2016, and as such, basically any of these forks that you're going to be swapping on could use revolving or absolutely require revolving. Even the woods version, the softer of the Enduro bike version CRF models, the 250X/450X, still are not plush enough for many users who are accustomed to a an open chamber woods valving fork.

The 49mm conventional Showa Twin Chamber forks '97-'98 ('96 also, but this year had a but more underhanging tube) are the most sufficiently rigid of nearly all right side up forks, and the damping cartridge pistons are not going to be a limiting factor for 99% of riders, same as the limited amount of flex. Jeremy McGrath absolutely hated them for his #1 top pro racer professional level Supercross racing due to their flex vs 46mm inverted configurations, but McGrath is one of the greatest supercross/motocross racers of all time, whereas older woods riders call these same right side up (but otherwise unconventional) Showa 49mm Twin Chamber forks the greatest woods fork of all time....


The modern Showa Twin Chamber 49mm inverted forks (2019+ KX450 / 2025+ KX250, as measured by my 2025 KX450X forks) weigh 2lbs less than the stock KDX forks, whereas the '98 RM Showa 49mm Twin Chamber versions are only 1lbs lighter than the stock KDX forks, FYI. I suspect perhaps the 47mm inverted Showa Twin Chamber versions could potentially be slightly more than 2lbs lighter, but to get a fork that's 3 or 4lbs+ lighter than stock requires going to an open chamber KYB 48mm design, as open chamber forks have fewer internal parts, greater simplicity.


The inverted design in itself is much more rigid than identical sized tubes in a conventional format, which really helps in whoops, but the 49mm conventionals will still do quite well and on par with 46mm inverted for the majority of riders, just not Jeremy McGrath!

The closed chamber design, which Showa calls Twin Chamber (in reference to the damping oil being separate from the lubrication oil) is also greatly beneficial in whoops and fast terrain, as it prevents damping fade due to preventing cavitation of the damping oil (mixing with air creating and emulsified mixture of hundreds or thousands of tiny air bubbles which alter the viscosity of the oil considerably) which inevitably happens in open chamber forks no matter what you do, but closed chamber also makes it a little bit more difficult too achieve plushness for technical lower speed and mid-speed terrain. The closed chamber forks basically have the equivalent of a nitrogen charge in the rear shock, in the form of an internal chamber compensator spring which keeps pressure on the damping oil to keep it from becoming emulsified. The big difference between the nitrogen charge in the shock versus the ICS spring in the fork, is, that the pressure placed on the damping oil by the ICS spring in the fork is not subjected to a progressive linkage like the rear has, when utilizing this technology in the forks, there is no way to give it a progressive linkage. The tuning process and design process must be very intricate to give this woods-desired initial plushness. Tuners have some partial workarounds for this with the bottoming resistance portion of the spring perch inside the fork in conjunction with volume spacers to give more of a progressive air spring in the lubrication oil chamber of the closed chamber forks, as well as putting a lighter ICS spring in place. Putting a lighter ICS spring in place will allow more cavitation to take place, however, so you don't want to go too light or else your forks will function a bit more like an open chamber in the rough stuff. Tuners will put the fork springs in with a very very minimal amount of preload, the bare minimum, in order to achieve better initial plushness as well.


So yes, any of the Showa 47mm inverted forks are an excellent choice, and I recommend the CRF250X & CRF450X as they are already an off-road model that is set up lighter and more plush than the newer version enduro racer CRF250RX / 450RX models, and have more internal components which give more free-flowing damping versus the Motocross models of the same forks from Honda (CRF250R etc), but still not the most plush thing out there despite them being sold as a Woods model with more accommodations for Woods plushness, they are still not plush enough, but far better than Motocross valving. You will find lots of threads on Thumper Talk about revalving them for better traction and bump compliance in the woods. The CR125/250 CRF250/450 steering stems are also the correct height or thereabouts for the KDX, and KX through 2002.

Suzuki RM125 1996+, RM250 , RM-Z 250 2007+, RM-Z 450, 2006+ KX250F, 2004+ Honda CRF250/450, 2005+ YZ125/250/250F/450F, KX450, a few years of Yamaha WR, Beta RR Race Edition models, many Sherco models,etc in these years generally all have closed chamber forks.

The CRF250X & CRF450X make great swaps. KX250F 2006-2010-ish as well. 2011 or 2012 through 2018 KX250F went to the SFF variant which is also great but there is less tuning knowledge out there depending on which tuner you are using. They have a spring in only one side, and damping-only in the other side, with both sides containing open bath lubrication oil. They are closed chamber design. You can very clearly spot them out by the way the top caps look, one side has adjustable spring preload, the other side has damping adjustment. They are quite nice, I would definitely not pass up on a set of those, but there is just a little bit less knowledge out there about them if you're trying to DIY it in particular. The first two years were 47 mm, then the remaining years of the KX250F's Showa SFF single function forks were 48mm tubes.

I hope this answers a lot of your questions and concerns.

Like I said, the YZ250 2-stroke triple clamps also work well and have the correct steering stem height, and the YZ 125 two-stroke fork legs also fit into them as long as you keep within the same year range. Not all YZ250F triple clamps have the correct steering stem length, there are actually three different YZ steering stem length, short, medium, and long. The long is a great fit, the medium will work, the short that was on some of the 250 F and all 125 models does not work on the KDX.
Also a reminder that there is no industry standard bearing size in the required dimensions for these, therefore you must use a generic eBay / Amazon 28x47x15 bearing or else machine in inner race adapter to sit down on top and through the bearing to neck a 30mm bearing down to 28mm.

[KDXGarage]

What is your weight with riding gear, water backpack, extra tools, extra parts, etc.?

What spring rates does it have front and rear?

Thank you.

[Nighthawk016]

What is your weight with riding gear, water backpack, extra tools, extra parts, etc.?

What spring rates does it have front and rear?

Thank you.

I need to ask the suspension shop what was installed in the bike. IIRC its .42kg in the front 5.0 or 5.2kg in the rear, I'd venture to guess close to 230lbs all geared up

[KDXGarage]

I think that is a little soft. I would think 0.48 and 5.4. A YZ250X is about 12 pounds lighter than a KDX and comes with 0.44. 175 pound rider in gear would be 0.45 and 5.0 based on that. You and I are about 2 steps above "dream rider of 175 pounds". About 25 pounds is 0.02 on forks and 0.2 on shock. ROUGHLY! :-)

[SS109]

Like I said, the YZ250 2-stroke triple clamps also work well and have the correct steering stem height, and the YZ 125 two-stroke fork legs also fit into them as long as you keep within the same year range. Not all YZ250F triple clamps have the correct steering stem length, there are actually three different YZ steering stem length, short, medium, and long. The long is a great fit, the medium will work, the short that was on some of the 250 F and all 125 models does not work on the KDX.
Also a reminder that there is no industry standard bearing size in the required dimensions for these, therefore you must use a generic eBay / Amazon 28x47x15 bearing or else machine in inner race adapter to sit down on top and through the bearing to neck a 30mm bearing down to 28mm.

Don't forget the option of doing a stem swap which is putting the KDX stem into whatever triple clamps are being used. This is how I have done all my fork swaps.

[Nighthawk016]

I think that is a little soft. I would think 0.48 and 5.4. A YZ250X is about 12 pounds lighter than a KDX and comes with 0.44. 175 pound rider in gear would be 0.45 and 5.0 based on that. You and I are about 2 steps above "dream rider of 175 pounds". About 25 pounds is 0.02 on forks and 0.2 on shock. ROUGHLY! :-)

I called the suspension shop, .44 front and 5.8 rear. I had my suspension done at proaction and like I said the rear feels good, not over sprung, and the front feels springy but definitely not undersprung. But maybe thats what it fighting me?