KDX to KX Geometry Solutions

[AZRickD]

Since the KX forks are an inch longer than the KX forks, setting up the geometry is critical to getting the bike to behave .

Some have noticed that improperly set up modded bikes will handle poorly in different conditions.

It has been suggested that the KX fork tubes be stuffed up the TTs as much as 3/4 to 1 inch. But the forks in my KDX were up about 1/2 inch or so, as result, that doesn't buy me much.

My KX shocks perform nicely over whoops and such, but when I'm rushing up an incline, the front tire likes to rise up. Giving it sufficient gas to do a long, steep climb will get the front tire liftng, approaching loop-status if I don't let off.

So, folks have said set the sag, but are we sure that this 90-100 mm race sag applies to a KDX/KX? Does the engineering back that up? Is it universal? Static sag at 25mm? Are we sure?

How does setting dampening affect this? If my tire tends to rise up, if I slow up the rebound will that be effective? What about putting a tall tire in rear, and/or a low profile tire up front?

My forks are stuffed up about 11/16th of an inch up. The little nut on the top keeps me from going any higher. Any flush-mounted clickers that can be put on them? Higher-rise bar clamps?

Thanks,

Rick

[Indawoods]

There are lots of solutions out there.... just have to find one for your particular situation.

I have to figure out a frontend sag solution which I will be working on this winter. Testing will be involved so nothing is cut and dried.

Is your bike lowered Rick?

Just get some 1 1/8" bar adaptors and that will give you plenty of room.

[AZRickD]

It's not lowered as far as I know. Ask QuailChaser.

I am sorta considering getting taller clamps. The bike came with fat-bars. Just burns me that I just bought some standard height ones.

My front forks are so stictiony now that I can't say that there is much sag there at all. Maybe an inch along the tube?

When I was hang gliding, pilots would often talk about the mods they made to their wing. We used to say, "sure, be a test pilot."

I'm a test pilot. :(

BTW, what is your "front-end sag situation?"

Rick

[Indawoods]

No sag... stiff springs and lots of preload. I like the .43 springs but may go down to .38 or .40 and cut them to reduce the preload if there is not a spacer in there like I remember. The fiche shows a preload spacer. We will see....

The frontend is so light that it just floats.... but I am used to it. It doesn't bother me even though I know it's not right.

[strider80]

Did you tighten up the front end with the right proceedure?
http://www.transworldmotocross.com/mx/h ... 66,00.html

I had sticktion too when I first put it together, then I bought a beam-type torque wrench and did it the Trans-world way and it is way better.

[Indawoods]

This sounds like the important part:

"This is important… Always tighten the bottom clamps first!"

[AZRickD]

That's pretty much how I did it. But the stiction is there whether the top or bottom clamps are tight or loose. The forks were just rebuilt, so I kinda expect it for the time being.

I don't know that the stiction is an issue at this point (I'll check and recheck), but I don't want to get this thread lost on that goat trail just yet.

Rick

[Indawoods]

Geometry... very important and one that needs to be hammered to death!

[IdahoCharley]

This sounds like the important part:

"This is important… Always tighten the bottom clamps first!"

In the sequence of what was happening in the steps of the article tightening the upper clamps last makes complete sense. i.e. The stem nut has not been fully tightened/ final check.

If the upper triple tree was tightened to the fork tubes the stem would not be able to 'float' through the upper triple tree when the stem nut was tightened.

[strider80]

Yea, it took me twice to get it right. I thought I did it right the first time, but I either overtorqued or did the steps out of order. It had a lot of sticktion, I followed the steps carefully the second time and now it feels great.

[AZRickD]

Okay, then. The question remains. Will stiction, or stiffy springs or too tall front tires or too squart rear tires affect the geometry of rake & trail and are these reasonable methods to tune this out?

I understand that not everyone wants a low profile tire in the front (those who take big root/rock hits or like to run low pressures).

And if I find during my ride this weekend that during hill climbs my front is lofting again, I'll have to look into reducing static sag to about 20mm and see how much under 3" I want race sag to be reduced.

What is the issue behind too little static and race sag?

Rick

[IdahoCharley]

Q 1 - "So, folks have said set the sag, but are we sure that this 90-100 mm race sag applies to a KDX/KX? Does the engineering back that up? Is it universal? Static sag at 25mm? Are we sure?"

Yes, 30-33% of the total travel is the universal setting for setting race sag on a dirt bike shock. Shocks are normally designed and set-up with this in mine and of course it factors in the linkage ratio if applicable.

Static sag anywhere 20-35 mm IMHO

I would not really sweat going an additional 5 mm on either side of the stated value (race sag 90-100mm) but beyond that would be considered abnormal on a linkage dirt bike and would generally point or indicate a problem with the spring; provided everything else is OEM.

Q 2 - "How does setting dampening affect this? If my tire tends to rise up, if I slow up the rebound will that be effective? What about putting a tall tire in rear, and/or a low profile tire up front? "

Slowing up the shock rebound will not significantly affect the attitude of the bike on a uphill section. It IS NOT the thing to change in an attempt to fix your light front end. Slowing up your fork rebound may help if your front fronks are kicking up on obstructions on uphill runs and reducing your compression setting on the front forks may also help on uphill obstructions since your forks should become more compliant.

Taller tire in the rear will change some of weight bias towards the front and may help your existing problem. Low profile front tire would do the same.

S 1 - "My front forks are so stictiony now that I can't say that there is much sag there at all. Maybe an inch along the tube?"

Your FORKS should have 2 -2 1/2 inches of race sag typically for trail riding. 50-70mm is the most usual measurements that I have seen spec'd over the years for the modern dirt bikes. I believe this is likely the ROOT OF YOUR PROBLEM - Too much spring preload and/or too stiff of front springs for your weight. (Maybe too high of oil level)

S 2 - But the stiction is there whether the top or bottom clamps are tight or loose. The forks were just rebuilt, so I kinda expect it for the time being.

A little stiction due to new seals can be expected but should disappear within a couple of hours of riding provided seals/dust covers/bushings were installed correctly and there is not some sort of burr contributing to your friction problem.

S 3 - ... "if I find during my ride this weekend that during hill climbs my front is lofting again, I'll have to look into reducing static sag to about 20mm and see how much under 3" I want race sag to be reduced. "

You have mentioned reducing the race sag to under 3 inches a couple of times. It leads me to believe that you may not be using the correct terminology or under stand the meaning of race sag. How are you measuring "race sag?"

[AZRickD]

Well, I weigh about 210 in full gear (still losing weight, another ten + to go).

.43 springs in rebuilt 98KX forks. 5.2 spring on the shock. I orginally didn't have the shock spring cranked down (maybe a 1/4" or so).

On the calculation of static and race sag, please correct me if I'm wrong:

I measure the current 25mm static sag by lifting the back end and measuring a marked point on the fender. I let it drop and measure again. The amount of drop is the static sag.

Then I sit on the bike with gear (gear only drops it down 1/4"). The drop from static to me on the bike is the race sag.

[canyncarvr]

Re: 'What is the issue behind too little static and race sag? '

I'll take 'static sag' to be 'free sag'..the amount the bike drops of its own weight, and 'race sag' to be the amount the bike drops from topped out! to you sitting on it, with gear, in position, bike straight up, suspension not frozen cold.

A big thing free sag tells you is whether or not you have the correct spring. Example: Your spring is too stiff. To get an acceptable race sag, you end up squeezing the spring too much (more than a correct rate spring). Get off the bike to find your free sag is now a couple inches!

An excessive free sag indicates a too 'big' a spring.

Your question was 'too little'.

That's the opposite situation.

Example: Your spring is too small. To get the correct race sag, you end up lengthening the spring too much (more than you would the correct rate spring). Get off the bike to find no free sag at all!

No free sag, or less than 'accepted' means your spring is too puny.


How the free sag at the top works with the absorbing device is not something I can answer directly. I know the rule of thumb is it's gotta be there. Common sense would tell you you don't want to 'bang' the extended limits of your suspension with spring force everytime your rear wheel leaves the ground.

Again, how free sag works to the betterment of suspension action is not something you'll hear from me.

I don't see (or missed) that IC mentioned it...??

How 'bout it IC?


Certainly MISadjusting sag to impact front end loft isn't the way to go.

Example: Your riding technique is correct..your way up on the tank at least, probably kissing the front fender if it's steep. Your gear selection is correct (and your bike runs well enough to pull that gear without simply spinning) and you can use the clutch.

There will come a point when the answer is simple...and what you don't have. Maybe a +6 swingarm!

I have a solution that works fine for me. If it's so steep that I can't keep the front end down, it's too steep and I shouldn't be there!

Traction is usually gone long before then.

Technique is certainly a big part of it.

Anecdotal example: We call it 'Rock Face'. It's literally a face of rock that is dang steep. Just preceeding it is a good sized water bar. At first look, you might think speed is important, but when you're in the air over that water bar..you're losing ground! When you smack into the rock you're in altogether the wrong attitude to get to the top. The water bar needs to be gotten over slow enough to keep in-air time to a minimum so you can get GOing again at the bottom of the face..NOT run into it like it's a twin tower.

Oppositely, there's another hillclimb that you'd better be screaming..like topped out in 4th..at the bottom, else when you get to the top you'll be grabbing for 1st..and up comes the front-end.

No, I'm not a hillclimber. I avoid 'em if I can. Just not my cuppa tea.

Where'd I put my drink?....it had a pink umbrella in it.............

**edit**
Your post beat mine.

Note your 'race sag' definition is incorrect.

Good job IC!!!

[tim]

try this it may help

http://www.teamgreennews.ca/pdf/2005Jun ... ingSag.pdf

[canyncarvr]

That's good. The 'adjust to suit' part gets kind'a iffy.

37mm is a bit too much static, seems to me.

Well, in my case anyway.

I've tried 5mm variances up and down myself..100mm race sag is what I liked the best. That gave me less than 30-40 (the KX figure)..but the handling overall suits me.

My KX forks are up a good 20+. I got that with no interference from other stuff by spacing the top clamp as far as I could get it and still get a full nut-bite of threads from the top nut.

No headshake, the bike is level (same measurement as with the OEM forks), front-end stays planted well in high(er) speed corners. A couple clicks more rebound (screw on top in) helped that a whole lot.

Indeed it is 'whatever suits'.

A 220# rider on the OEM ('H') 5.0 spring isn't ever going to get it adjusted it 'right'.

What? Oh..yeah..imo and all.

[AZRickD]

That means my race sag is about 4 inches, not just 3 inches. I've got room to play -- maybe another 1/2 inch or so.

I'm still having problems with the concept where KX forks that are 1 inch longer are still subject to the same saggy rear end.

All I know is that my front end comes up much more when climbing than before. I'll have to correct that or riding around here won't be very much fun for me.

Rick

[Indawoods]

It's just a matter of working it out... we will work through this together since I am having similar issues.

[Colorado Mike]

Mine does that too, but I think it may have a lot to do with the front being lighter. I adapted pretty quickly, and kind of like it now. I seem to be able to float the front over things I want a little easier now. I just have to use better form than I used to, as in getting over the tank a bit more, and on hills I need to pay attention.

What I wonder about is the huge amounts you guys are getting your forks up out of the triple clamps. Mine can only go up about an eighth inch or so before the center nut on the cap is mighty close to the bars. Maybe that is because the '03's are different or something, or maybe because I used a custom machined spacer that lifts the upper triple clamp up a good 1/4". Maybe I need to rethink that. Fortunately on my last ride, I had one of the seals completely blow out so it's a great opportunity to look at swapping things around.

[canyncarvr]

Re: 'What I wonder about is the huge amounts you guys are getting your forks up out of the triple clamps. Mine can only go up about an eighth inch or so before the center nut on the cap is mighty close to the bars.'

My KX setup is off a '99..so they are smaller than you 'big' guys'.

Still...my intention was to level the bike as it had been. My level measurement before I started is what got me to the large 'sticking up' I have now. I wanted to ensure it was the same attitude it had been.

Yeah...I do harp on that a lot. I don't see anyone else doing it that way..but I do read the problems of NOT doing it.

I've seen pics of converted bikes that are obviously going uphill just sitting there. ..didn't want that.




A 4" race sag is pretty close...100mm.

Again, it all has to fit together. A 4" race sag that gets you a messed up free sag gets you, well, messed up.

Re: 'lighter'

Who weighed the entire KDX front-end..with wheel..and knows what the difference is compared to the KX setup?

I didn't.