I just finished a frame-up build on an ‘03 Kx250 including a suspension respring/revalve. I surprisingly love the way this bike turns more than many ‘23/‘24 2 and 4 stroke bikes I’ve ridden. However, I just can’t seem to get the KYB open bath cartridges where I want even after messing with clickers and the change in valving/spring rate. The dampening is just not compliant in the big stuff.
I ride mx and the bike is great when the track is smooth, but once the big tracks get rough, it’s almost unrideable. I loved the SSS stuff I’ve ridden, and after scouring forums have decided the ‘09-‘12 Kx450f forks are my best bet. They have the same technology but will be a close to direct swap with triple clamps. I know MxTech used to make a cartridge for my forks but don’t anymore, so I’m thinking a swap is my last option.
After talking to a local shop, I was told not to do the swap because the rigidity of the fork tubes were meant for bigger aluminum frame bikes and will absolutely ruin the handling of my bike. My question for anyone who’s done this: Did you notice a dramatically improved/worse change in performance? If worse, are there any other options?
Thanks for the help.
You might find some help in this thread.
Thoughts on 2007 KX250 smoker - Moto-Related - Motocross Forums / Message Boards - Vital MX
If you don't mind me asking what is your skill level?
Thanks! Judging by the responses it seems like the swap is the correct move.
Just started riding again the past 6 months after around a year of not really riding at all. Ride all my local tracks and have done a few B races placing mid-pack. From looking it doesn’t seem like I would notice the rigidity differences at my skill level if I’m not mistaken
The Shop
Luxon 4-Post Bar Mounts
$189.95 - $239.95
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
I am not so sure. For the riding you do the rework stockers should be serviceable.
You said the end of the stroke is too much. Have you checked to see how much travel you are using?
I have the same bike/forks. Had them revalved but imo they aren’t great for Mx. B level is pretty quick and CC are going to handle MX better. I’d look for a CC setup. If your worried about the rigidity you can swap a SSS set from a yz250.
My bud has an ‘02 he put YZ SSS on it, had to make custom spacers to make it work.
If the ‘09-‘12 KX450 forks are a direct bolt on that’s a no-brainer.
Before you think the forks are the problem, you might want to check out the shock. I had an 03 with fresh suspension from ezno, no revalve, and the shock was horrible. The forks were ok with more oil and stiffer springs. Just something to think about.
Put 2011 kx250f forks on a 2004 kx125. Had the use the triple clamps and modify the steering stop from the newer bike to make them work. They were a little longer also if I remember correctly so I had to run them higher in the clamps.
Yes, it’s sprung correctly and I’m using all of the travel. Under hard braking/cornering, I’m pretty much settled at mid-stroke. It’s better than stock for sure and I love the way the chassis feels, I just can’t find confidence in the suspension.
How did you like it? I found a really good deal on 2011 kx450f forks and triple clamps. I decided to pull the trigger being that the whole set-up was less than another re-spring/re-valve for my current forks including the rebuild (which I’ll do myself). I’m going to go ahead and purchase the trick engineering steering stop adapter as well.
Understood, I didn’t think to look at the shock because I heard it’s extremely expensive to replace because ohlins and mx-tech are the only two companies that make shocks for the bike (over $1600 for the cheapest all the way to $3000+). How did you remedy the shock, and is there any way to get a modern 250f/450 shock on the bike without cutting and re-welding a new mount on the frame?
Have you checked the clamp offset between the bikes?
I just dealt with it until I sold the bike. It was a second bike so not the biggest deal to me.
A revalve should get you were you need to be. Personally I would just send it out to Enzo and be done with it. Not too expensive and you know what you are getting.
I'm pretty confident the 03 KX250 is 23mm offset and so is the 2012 KX450. They should mount right up; he'll only need the steering stop mod that Trick Eng. makes.
I wouldn’t be so confident if I was you. My unofficial findings indicate otherwise.
UNoffically the KX250 25mm and as far as I know The older KX450's are 22mm. He said he LOVED the way it handled. Do you think he will feel the same way you did?
Actually, after doing some looking PC says the 2011 KX450 is 24.5mm, the 2012 was 23mm. So, if he liked the way it turned and as you say the 03 KX250 was 25 then he will be fine. If he wanted it to turn better he could find some 2012 triple clamps, he might give up some straight line stability though.
I went from 25mm on my 2005 KX250 to 22.5MM and it turned much better.
Triple Clamp Kit KX450F '06-12
Pit Row
I’ve found 25 mm was stock as well. The ‘03 chassis didn’t have the turning issues the ‘05-‘07 did, so I’m fine with stock offset. I plan to get aftermarket triples later on and may go down to 23 mm depending on if I think they’ll help.
Makes sense, thanks for the advice. The rear shock is already re-valved and re-sprung and hasn’t been too bad for me. This is going to be an ongoing, secondary project bike so I don’t plan to sell it. Since everything is new and replaced on the bike, I plan to just keep wrenching and messing with it until it’s where I want it. Want to do races with it like 2 stroke nationals at Glen Helen.
Post a reply to: ‘03 Kx250 Forks Swap