Fork suspension adjustment

[tptp]

Riding a KDX220R -98 and searched the forum for fork adjustment and really found a couple of nice treads! But still confused on the secrets of the fork adjustment.
Used Racetech.com to find and changed to a .42 (stiffer) spring but it I think it now is to stiff...!
Shall I make the collar above the spring shorter? The new spring is longer than stock spring.
Compression, do I need to make it softer, now 9 clicks out from bottom?
What about rebound? My Owner´s manual says "more oil will make the fork rebound more quickly, less oil more slowly". Does less oil make the fork softer and compression softer.

Great place this, thanks to all helpful people!

 

[tptp]

Ok, not a lot of answers...found some by searching:

"Shall I make the collar above the spring shorter? The new spring is longer than stock spring."

Yas I shall adjust the collar to get the proper sag. In different threds I found 5-30mm longer total length to get right preload. My collar is far to long! I´ll test 10mm and se what it feels like. Im trying to get 20mm static sag and 70 mm race sag.

"Compression, do I need to make it softer, now 9 clicks out from bottom?"

I found some info about how to get the right adjustment - will est i harder if it bottoms down or harder if it turns to easy in corners.

But still confused about rebound - the manual says less oil will make rebound slower, seams to be the way to adjust rebound sence no clicker exist for it.

Please anyone who knows better? Can´t find any info about it in this forum (yet?!)

 

[CaptainObvious]

Adjust the spacer in the forks so you get 25-30mm of free sag. Don't forget to check the rear sag as you make changes to te front.

What weight oil did you use in the forks and at what height?

No one can tell you how to set the clickers. Trial and error (or success) is te best tool for that.

 

[bikepilot]

Here's how oil level affects suspension action. The forks have a certain volume of space ocupied by nothing but air. As the forks compress, so does this air, the more travel used up the more the air is compressed. Thus, the air acts like a spring, but is most effective in the latter portions of the travel. Changing the oil level changes the air volume, less volume means more pressure when the forks are compressed which translates in to stiffer forks in the latter portion of the fork travel. Obviously, the more pressure, the more rebound you'll get, but the effect of oil level on rebound is generally not noticeable as its only noticeable affect is in the last 1/3rd of travel or so.

Too much oil will prevent full travel and can make the forks feel harsh in the mid stroke. Too little and you'll find yourself bottoming out more than you like. Given that you find your forks on the stiff side you'd be best off running the oil level near the lower end of the spectrum given in the manual. Stick with stock weight oil (5wt, cartrid rated oil). You'll probably find that your forks perform best with the compression clickers nearly all the way out.

good luck

 

[QLD_KDX]

To get the most out of your forks, try revalving them. You can go with the GoldValves, or if you are mechanically minded you can pull your valves out and modify them yourself by removing two of the 10 shims you will find there. It makes an enormous difference, and it's free.

Cheers,
Andrew

 

[tptp]

CaptainObviuos:
Is free sag when I am sitting on the bike? Like race sag (and static sag?)
I fell like there are no sag when I am on the bike - to hard..!
Im using 5W and 110mm.

Bikepilot:
Thanks! That explaines the secrets of rebound at the last 1/3 of travel - nice!
I´ll try with clickers more out/softer compression.

OLD_KDX:
In what way does the shims work?
Think I have to search the forum on this to :-) and make this my next project when the forks works fine after my spring change.

Thanks a lot!

 

[QLD_KDX]

Shims

Tptp, Doing a search on fork shims in the suspension forums is a great idea - I spent a number of hours there to get a good idea of how everything works.
To answer your question very basically, the shims restrict the oil flow on the initial part of the fork stroke (also refered to as the high speed damping). The shims are very thin, and flex under the flow of oil past them as the fork starts to compress. The number and size of the shims in the shim stack determine how hard or soft/supple the initial stroke will be. On rocks and roots, we want it to be a bit more supple than what Kawasaki give us as standard (they gave us soft springs instead, to make it seem supple, but they still suck on rocks, and they're too soft on jumps :bang: ).
The stock shim stack is a straight stack (not tapered) and has 10 shims of the same diameter. Removing two of them will give a 20% reduction in resistence to oil flow, resulting in a softer high speed damping.
An aftermarket shim stack such as that supplied by RaceTech is a tapered stack where the larger diameter shims are at the top and they progressively get smaller down to the bottom, like a pyramid upside down. The larger ones flex more easily than the smaller ones below, so it is a lot more 'tunable' with more possible combinations than you could care to think about. Which is great if you have the money for them - if not, removing those shims from the stock valve is the next best thing.

Cheers,
Andrew

 

[tptp]

So, am I in the ballpark?
The spring due to Racetech (they maybe are a little stiff??).
Cut the collar to get 10mm preload?
Adjust low speed compression (high jumps) and rebound by alter the oil level, more oil=harder compression and faster rebound?
Adjust high speed compression and rebound? (small bumps) with the screw at the bottom of the legs (number of clicks)?
Adjust low-speed compression and rebound by lowering the amount of shims from 10 to 8?
Use 5W forkoil?

Check rear sag, and so on.
Adjust forklegs up or down to change the steering geometri?
Move rearwheel front or back to adjust wheelbase?

Ball parked?

 

[QLD_KDX]

about high speed damping: we can only adjust compression, not rebound. Adjusting your shimstack will reduce that - I had my clickers all the way out (soft) and it wasn't enough. Adjust the shim stack and now you're in the ballpark and can fine tune it with the clickers, oil weight and height etc.
Once you've done that your fork springs won't seem so stiff - you'll actually like them better because they are what soaks up the big hits. Set your spring preload to about 10-15 mm.

Yes mate, you're in the ballpark.

Cheers,
Andrew

 

[Rhodester]

Your clickers on the forks only adjust low speed compression. You must revalve by some means (like Gold Valves, etc.) to change high speed compression. My forks and shock were both ridiculously harsh (ie. too much) on high speed compression.

 

[QLD_KDX]

Your clickers on the forks only adjust low speed compression. You must revalve by some means (like Gold Valves, etc.) to change high speed compression.

Someone please correct me if I'm wrong, but I'm pretty sure your clickers adjust high speed compression damping, along with the shims in the valve. Low speed compression is controlled with the fork spring rate and oil height/weight.

That is why the stock KDX fork setup is so hopeless - it is too harsh on rocks/roots from too much high speed damping, yet it bottoms easily because it has a very soft spring.

Andrew

 

[Rhodester]

The shims in the valve stack effect high speed and low speed compression. I run a 2 stage stack with my Gold Valves which supposedly separates the high speed from the low speed stacks. I run cL6 (middle of the road low speed compression stack) and a cH1 (as light as I can get high speed compression stack). I have my clickers set on 11 to 13 clicks out (depending on conditions) to adjust my low speed compression. Although spring rate does influence all of the end results it doesn't have anything to do with compression damping per se.

You are right; High speed compression in both the forks and shock are ridiculously high (for my riding style anyway).

BTW, I run .43kg Eibach springs for XR400 with 3mm of preload (I'm 230lbs). I would suggest getting your spring rate right first (set up for the proper sag) and then start modifying the damping.

 

[QLD_KDX]

OK, happy to be corrected! Whatever controls what, it is still all f***d up on the KDX.

I have .41 eibach springs (for xr400), 10mm of preload, and two shims removed from the shim stack, clickers about 10-12 out.

prior to removing the shims I was trying zero preload, clickers all the way out, extra light oil, nothing worked. Revalve and, Voila!

Andrew

 

[tptp]

Spring rate and collar lenghts to set the preload and sag.
Oil level and viskosity sets the low speed compression and rebound (high jump).
Number of shims and clicker position sets the high speed compression and rebound (small bumps).

I start with the spring and preload to get proper balance on the bike, together with rear sag settings.
Next step is to set oil level and viskosity to nearly buttom out in big jumps. Depending of type of riding conditions - slow speed adjustments.
After that I will maybe need to taka away one or two shims from the stock ten, to get softer high speed compression and rebound. Then fine tune with klickers.

Another way to try to be in the ballpark?