KDXRIDER.NET

KDX Experts,

I used the search function and found much contradictory information.

Bike: 2001 KDX200
Forks: 1999 KX250
Having RB do the stem swap and axle.
Having Factory Connection do the fork rebuild.

Questions:
1. Should I have the KX 250 forks lowered while they're being rebuilt?
2. If so, by how much?
3. Will this risk them hitting the fender on a full bottom out?
4. Is it better to just have them rebuilt at full length and slid up in the clamps?

Thank you! I'll post a pic when the bike is done!

Just leave them stock length. You’ll want the travel. Slide them up in the clamps if you want. That upper clamp should have solid bar mounts, so you’ll be limited to how much you can move them up, but they’ll be fine.

1999 KX125 had solid bar mounts, not KX250 / KX500.

Ok. Thank you for the input. beautiful work on that 220 btw.

i realized that I have basically zero space to slide them up due to handguard mounts.

So I'm thinking I'll have them lowered 3/4" - 1". I like the stock geometry and don't want to mess with it much.

Someone please chime in if they think that's a mistake.

Thanks

You'll be fine shortening them. Just make sure whoever you have do the work does it the right way. Only aluminum spacers should be used IMO. No PVC spacer crap.

I know I didn't shorten mine and I take the risk of bottoming out against the fender/lower triple. I have heard the tire touch more than a few times and have the marks on the fender to prove it. I actually run one size up on my fork springs (normally .38 but running .40 on the KDX) to help counter this. However, I have considered going ahead and shortening them just so I can go back to my normal spring without having to worry.

Having them internally lowered is definitely the best way to go about this. You may likely have to buy a shorter pair of fork springs though, that's an added expense unless you already needed a different spring rate to suit your weight and riding style. I believe the stock fork springs in those are a progressive rate, which is frowned upon by many, so you may be best off upgrading to a straight rate spring regardless, and a shorter one if having it lowered.

I'd strongly recommend having them internally lowered 1/2", 5/8", or 3/4" depending on how much you can slide the triples down on the fork tubes to correct the geometry.

What you need to do is look up the advertised travel for a '99 KX250, and then figure that around 1/2 of that is the false advertising of the top-out spring being fully compressed (which basically never happens), and then do a lot of measuring to make sure that your tire still will have clearance at full bottoming without striking the underside of the triple clamp / fender mounting bolts. This could potentially be really bad if this happened at high speeds, sending you over the bars with the bike crashing down on top of you immediately...
I did a web search and was having trouble finding the advertised specs of suspension travel for a 1999 model, so you might be better off just measuring travel yourself.
The KDX fork travel is 11.6" advertised, KLX fork swaps give 11.4" advertised travel, which is still plenty enough for most woods riding, so reducing the *approximately* 12.2" of travel on the motocross forks down 3/4" or 7/8" is no big deal.

The biggest thing is tire clearance. Also take into account that you might want a "Fatty" front tire, a 90/100-21, at some point if you run lower pressure in gnarly nasty rocky terrain - as they allow more cushion before pinch flatting etc but they do slow the steering a bit (most who need the taller tire will consider this a worthwhile tradeoff).
So mock up the fork in the triples with the triples slid down at least 10mm on the fork tubes or more (you want to keep as much travel as you can when making up for the forks being approximately 1" taller), with the KX wheel and tire installed, and measure the distance, suspension topped out, between the tire and the bottom of the fender, and compare to the advertised travel of the 1999 KX250 forks. If you still have about 11.7" (full advertised travel is a misleading spec as it usually includes the top-out springs being fully compressed which never is a factor here, only happens when airborne after hitting a jump), then you can afford to possibly slide the triples down even further on the fork tubes, and then only have lowered the amount that will then prevent your tire from contacting the fender when bottoming out the suspension...
you can also play it risky and run a higher fork oil level in order to increase bottoming resistance deeper in the stroke. This reduces the amount of air space inside the forks, which effectively increases the progressive air spring effect when compressing the air in the sealed forks. This isn't the best way to do it as it will make fork travel deeper in the stroke a bit more harsh, but this will allow you to slide the tubes up in the triples or slide the triples down on the tubes a bit further. Not really recommended though, I'd look at lowering them 5/8" approximately, and running minimal preload on the fork springs to allow for a bit more suspension sag when seated on the bike, and using that to equalize the front vs rear ride heights.

Thank you for the detailed response. I will do just that and will post a picture in this thread when they're done!

Thanks again. Love this community.

Win