MTRHEAD

Member
Oct 26, 1999
41
0
So what direction should you go to get your forks to work better in rocky, rooty, clapped out trail conditions?

Do you just lighten the hi speed stack?

Would removing the cylinder valve seals help this?

Other than a little "spiking" they work good on less "abused" trails.

They are '99 YZ forks with the mid-valves disabled, cylinder valve seals and RT pistons.
 

MACE

LIFETIME SPONSOR
Nov 13, 1999
441
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Jinkies Scoob, I'm chasing the same Grail...

I'd run the lowest tire pressure you think will work in the rocks. Push the envelope a bit when trail riding and figure out how low you can go. This helps on roots - hurts on steering precision and of course increases likelyhood of flats.

If you don't have ProTapers, ovalize the bolt holes in your crossbar so they can flex. I also use ProGrip Dualsport grips which are real cushy.

That Mobil One is really slick stuff. It's for real.

I think the RT CV seals are hurting you for stiction, but it is such a bitch to remove them I'd let them be.

I'm a grease under the wiper believer. Opinions vary on that one. Seems to reduce stiction. I have the original seals in my 98 - no leaks - believe it or not!

I'd try two steps softer on the RT CHx charts.

If your soft springs are too soft and stiff springs too stiff - run one of each. That's what I ended up with when I had GVs.

Have fun and please let us know how it turns out.


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MACE

"Prime Directive - Serve the public trust, protect the innocent, uphold the law."
 

MTRHEAD

Member
Oct 26, 1999
41
0
Thanks for answering Mace. I had about given up on getting any input.

I run Pro-Tapers, Emig T-clamp with rubber mounted bar clamps and 12psi. in the tires. 12psi. seems to me to be the best all-around setting for my S12's.

I have been both ways on the grease under the dust seals. Right now I'm not running any. Maybe I need to.

Removing the CV seals isn't that big a deal and I think that might help with the "spiking" and "slap downs". I'm also having problems with harshness on "slap downs". In general, my forks seem to be resistant to any sudden changes and I'm thinking that might have something to do with loosing the additional blow-off with the CV seals.

Now, RT recomends going two steps stiffer WITHOUT the seals installed. So removing them is going to effectively do what you suggested to the "CH" stack. But, it will also effect the "CL" the same.

With that in mind, I have tried the M-1 ATF and felt that it did add some addittional damping. So would you suggest just leaving the stacks the same and trying the M-1 ATF or increasing the "CL" also?

I may also give the spring thing a try. The stock spring feels a little soft but, the .44's seem like they add to much.

BTW- if you still have the same seals in you aren't getting the daily recomended allowance of mud riding.
smile.gif
 

MACE

LIFETIME SPONSOR
Nov 13, 1999
441
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MTRHEAD, first off, I think you know at least as much about suspension as I do - so take my inputs FWIW...

I'd really like to see you just remove the RT seals and do no other changes so you can isolate the effect of that one change. Changing fluid and base valving is something you can do later without total disassembly. One of my problems with sorting my forks has been my propensity of making numerous changes all at once. This makes it so I never learn what any single change does. I also have a problem of riding in so many different terrains that it's hard to compare week to week (this is a wonderful problem to have don't you think).

As for my magic everyouthful seals. I'm replacing them right now along with new bushings. I expect the new seals will leak like everyone elses do....

I live in Washington State and ride year round. I KNOW mud. My favourite part is when you put your goggles on after a break and all the mud gets swiped off the back of your helmet - AND DOWN YOUR COLLAR... Yeeeee-Haahhh!!!



------------------
MACE

"Prime Directive - Serve the public trust, protect the innocent, uphold the law."
 

MTRHEAD

Member
Oct 26, 1999
41
0
I understand what you are saying, but I want to get them right fast. There are so many races this time of year I don't have time to test a lot.

Another thing is they work pretty good on a faster, less beat up course.

I could get lucky and have them work perfect after the seal removal. Nah, impossible.
 

James Dean

Member
May 17, 2000
137
0
I may be out of my league here but,

The dozen or so tries I have had looking for plushness on rocks and roots without causing a mushy ride have led me to this:

Back up and reduce the high speed stack - pull a few HS shims and add a thin crossover. Keep the low speed stack firm and clickers at a low setting to prevent the mushy or loose feeling ride. Raise the oil level for g-outs and use the softer springs.

Even though I weight 195 in gear, my riding style is smooth and rarely bottom out.

Gives you another perspective,

James Dean
 

MTRHEAD

Member
Oct 26, 1999
41
0
Nah Jimmy, you be right in the mix.

Actually I think you gave a pretty text book approach to problem and other than running a heavier spring I think I'm there.

I weigh the same as you and with the additional hardware and fuel I think the heavier springs work better. With the stock springs the front end seems to settle in pretty deep.
 

James Dean

Member
May 17, 2000
137
0
Here is a theory, and thats all it is:

Soft springs shift steering geometry more (steeper) when you move forward on the bike. Since I like tight woods riding, shifting forward gives better turning. Shifting back (within reason) helps extend the front for whoops. Whoops are a small percentage of what I ride. Higher fork oil level stiffens the last 1/3 of the travel which has a similar effect to the stiffer springs. The majority of the time it will be using the less stiff rate.

In the shop the forks feel like firm damping and medium spring rate, but riding feels balanced without sharp hits.

Sometimes I feel reluctant to voice that stiffer springs aren't the answer for every rider. Seems that stiffer springs are the automatic fix for the general population. Just not for me.

James
 

James Dean

Member
May 17, 2000
137
0
MTRHEAD & Mace, Others...

Here's my stock '00WR400 fork valving. I was changing the front tire and was inspired by this thread and take a look. First time apart for this bike. What would you think about changing the valving for a softer ride through rocky and rooted sections?

-------------------------------
Starting from compression valve face- (8mm ID on all shims)

(6 shims) - 24 X .1mm (low speed stack)

14 X .1 (cross over)

24 X .1 (start of high speed)
22 X .1
20 X .1
18 X .1
16 X .15
14 X .15
12 X .15
11 X .25

18 X .50 (at base)
----------------------

Was considering taking the 12 X .15 and moving it below the 14 X .1 crossover. Shifting the high speed stack back by .15 and making a smaller crossover diameter should soften accross the range. Too much? Ideas??

I could just send the works to Jeremy and let a Pro do it, but it's sitting out there ready to play.
biggrin.gif
Hope this isn't breaking etiquette.

BTW whats the torque for the valving stack nut?

James


[This message has been edited by James Dean (edited 11-12-2000).]
 

MACE

LIFETIME SPONSOR
Nov 13, 1999
441
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All I KNOW is that you torque the nut to 48 INCH-lbs. Use some blue loctite too.

The rest of this is probably all wrong and is based on trying to read trends on the Gold Valve charts and a little bit of logic. I'm pretty short on the practical experience part.

I don't think you'll get what you want with a minor change to the HSC stack spring rate and an increased "crossover" distance.

I'd go more radical in the valve spring rate change.

Remove two of the LSC shims.

Leave the LSC clamping shim "crossover" as is.

Remove the 16 x .15 from HSC

Rember that the HSC is affected by LSC. The HSC never deflects until LSC has deflected by the thickness of the clamping shim. Only then does the LSC <oops, edit, that should say HSC> do anything. Remember too that the OD of the clamping shims has a great affect on the stack spring rate. Removing one 16 x .15 will affect the rate a lot more than removing one 14 x .15.

And yes, Jeremy's cheese valves are great. Gold valve documentation is great. I think Jer's valves are fundamentally superior and I'm getting close to being pretty happy with mine.

Now that 1368 needle - I'm not quite sure....

------------------
MACE

"Prime Directive - Serve the public trust, protect the innocent, uphold the law."

[This message has been edited by MACE (edited 11-13-2000).]
 

James Dean

Member
May 17, 2000
137
0
That 1368 needle is easy compared to the subtle complexities here.
smile.gif


-----------------

Moving that 1 shim has 3 consequences that I can see. It looks like a significant change.

1)Changing the crossover from .1mm to .25mm is the big one. For the shims to open .25mm at the outer edge will only take the 6 LS shims to flex. Keeping the .1mm crossover would have taken both stacks to move past .1mm, LS and HS stacks.

2)The reduction in diameter of the crossover shim to 12mm allows the low speed stack to flex more like a stack of 4 shims. This matches your suggestion, Mace.

3)Pulling the 12 off the HS stack softens this stack slightly. Not nearly as much as a 16 X .15, though like you said. Maybe I will pull the 16 X .15 too.
biggrin.gif


James Dean

[This message has been edited by James Dean (edited 11-13-2000).]
 

MACE

LIFETIME SPONSOR
Nov 13, 1999
441
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My comments on increasing crossovers are based only on what I've observed in the GV charts and reading between the lines on this forum. Logically, you are correct. Be sure to let us know what you end up doing and your results.
 

MTRHEAD

Member
Oct 26, 1999
41
0
I agree with Mr. Dean, the needle is simple.

Figuring out how to make a shim stack harder or softer by moving a stupid washer is much harder.
 

Jeff Howe

Member
Apr 19, 2000
456
1
I'm just going to say the change your proposing will be quite noticeable. Maybe more than you think. Consider that your total crossover gap will be the thickness of both the 12-.15 and the 14-.1 unless you plan to remove the 14.

If what your after is a softer fork your gonna get it! I would like to hear how it works out.
 

MN KDXer

Registered
Jun 7, 1999
194
0
Remember in your decisions, that the relative strength of each shim is a function of its thickness cubed. ie- thk x thk x thk. Which basically means that a shim that is twice as thick is eight times as strong.

Example- the .15 shims are as strong as 3.38 shims of .10 thickness.

The stepping of shim diameters (tapering) between shims gets a little complicated and is a bit of an engineering brain tangler. I've kicked that around, and decided at that point, it's time to expirement.
smile.gif


With this info, you can quantify your stack in an approximate "strength" value, and compare your results to other stacks that you try. And, it gives you somewhat of an idea of what % you have reduced the stack. Try about a 15% change to start it off. From there, you will know what to do next, whether softer or stiffer.

Have fun and report back.
smile.gif


------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
 

MACE

LIFETIME SPONSOR
Nov 13, 1999
441
0
Making a spreadsheet to calculate stack spring rates is one to the tasks on my long "to do" list. ECD early 2008.

Does anyone already have a stack "coeffient" calculator they are willing to share? (This is probably trade secret territory.)

(MN KDXer, have you looked into this problem enough to find that a correct answer degenerates into a whole slew of simultaneous equations to solve? That is what I envision if you start trying to get the deflections of adjacent shims to be compatible. There's never an engineering intern around when I need one.* Hey Dualsporter, need an extra credit problem?)

*make up your own Klinton joke...
 

James Dean

Member
May 17, 2000
137
0
MN KDXer,
The thickness cubed is proportional as you have pointed out and also the LENGTH cubed on a rigidly supported beam. Referring to overhang on the crossover and clamping shims.

So while (.15/.10)**3= 3.38 for thickness,

Also (24-12)/2=6mm is the shim overhang where previously it was (24-14)/2=5mm. The ratio of change in the crossover going to the 12mm is nearly (5/6)**3=.58 .

This is why the crossover and clamping shim diameters are so important.

All these numbers are useful to get a feel for relative changes, but riding the setup is the only way to observe the impact.
confused.gif


James
 

MN KDXer

Registered
Jun 7, 1999
194
0
JD,

OK, I knew that the lengths were simply proportional, but is it that straightforward to simply go on a tapered overhang based on the OD of the transition to the smallest (base) shim, and treat each shim as an individual component?

Like for example, how does the curling of the extended unsupported shim area factor into the equation? Certainly, there is a difference if the stack has a large change in shim diameters, compared to a smoother reduction in diameters.

If we get enough engineers on this problem, we will either solve it or finish of a LOT of coffee while getting nothing done!
smile.gif


------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
 

James Dean

Member
May 17, 2000
137
0
MN KDXer,
I agree with you that the tapered stack stiffness is much more complicated than a simple factor for the varied shim diameters and thicknesses. The stackup in this case is a series of multi-order terms combined. Usually I just compare it to the LS shims, try to pick an average of the stack, and work with past experience.

All this talk about valving stiffness is just a step towards quantifying the important part. This is the actual opening at a given velocity, which helps quantify the force.

----------------------

To get a visual representation of valving changes try graphing the stiffness as a slope. For example use the LS stack (6 shims @5mm overhang) as a nominal "unit" slope. Then graph the force vs. displacement of the shim stack to open. This slope extends to the point of crossover displacement. The gap is .1mm in the stock valving shown above.

Then combine the HS and LS stiffness to make a new slope and continue the graph upwards. Make a guess that the HS stack here is twice as stiff. This makes the combined stiffness 3 times as much. The new slope is 3 times steeper past .1mm to .4mm (??). Now this graph and $.15 gets you a cup of coffee.

This is a start on comparing the effects of differing shim configurations. More shims, thicker shims, and bigger clamping shims all stiffen and change the slope. Crossover gap shifts the transition. In the graph various shim stacks can be compared for number, thickness, clamping, and crossover shims.

---------------
The stiffness is proportional to:
-Number of identical shims on a given overhang
-Thickness cubed
-Overhang to the clamp or crossover cubed

The crossover shifts the start of the HS stiffness and always to a steeper slope
-----------

This is a crude approximation, but a start for your spread sheet MACE.

-----------

For now I'm getting a few more shims and taking Shocknut's suggestion to try a slightly smaller .2mm crossover rather than .25mm.

James

(This is much like jetting, the needle taper doesn't mean as much as the position relative to the nozzle... the opening for fluid flow)

****** REVISED FOR CLARITY ******


[This message has been edited by James Dean (edited 11-14-2000).]
 

MN KDXer

Registered
Jun 7, 1999
194
0
JD,

OK, I'm all with the program now, except one more Q- Exactly, how do we treat those mm's of overhang, ie- as indivduals or as a group? I'm not sure what kind of units would I come up with, for example- would the L component overshadow the Thk component of the equation and make for some lop-sided result?

Right now, our units of measurement are-
(mm)cubed x (thk)cubed x constant which we can ignore + a whole bunch of flow factors we can't do much about, but they stay +/- constant so we ignore them, too.

The "flow factors" is where guys like Jer, WER, RT, etc, apply a different piston design system to change the outcome.

All this may sound vague, but when we base our next approach off past results, it works very well. And, actually, a plain old spreadsheet with these factors included will head us in the right general direction.

And, if we make some improvements to our bikes, and learn something, it was a good day!

Now, to tear apart my sled's shocks, and apply all this ramble to that machine, too. Know anything about Fox's Position Sensitive shocks?
wink.gif


btw, $.15 coffee? You mean $.50!
smile.gif


------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"

[This message has been edited by MN KDXer (edited 11-15-2000).]
 

MACE

LIFETIME SPONSOR
Nov 13, 1999
441
0
The overhangs will have to be considered separatly for each shim. We will have one equation for the supported portion of each shim and a second equation for the "free edge" with some initial slope constraint determined by slope continuity with the supporting stack.

A "correct" answer will not be easy to derive.

The SAE Shock Absorber Handbook shows a schematic of a valve Flow Bench.

I think MN KDXer is on the right track suggesting we concentrate on field testing. Brrrrrp-Brrrrrp!!!!

------------------
MACE

"Prime Directive - Serve the public trust, protect the innocent, uphold the law."
 

MN KDXer

Registered
Jun 7, 1999
194
0
Mace,

The situation goes beyond the shims overhangs, etc. We also need to consider that the contact patch of the force is in only four areas, but the shim stack is round, not a straight beam, etc. It gets ugly fast.

Maybe the best way to handle this potentially brain damaging problem is to simply relate everything as a percentage compared to a known stack, such as the factory spec.

Example- My proposed stack is --% of shim stiffness and --% of leverage stiffness. Multiplying the two percentages would result in a combination value with which we can make comparisons. Of course, we include the LS and HS into the mix for our analysis.

Meanwhile, you guys will have to do the field testing; I've got frozen ground until spring.
frown.gif


------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"

[This message has been edited by MN KDXer (edited 11-15-2000).]

[This message has been edited by MN KDXer (edited 11-15-2000).]
 

James Dean

Member
May 17, 2000
137
0
I aggree with the suggestion to use percentage changes in stiffness. I could run a structural finite element model in NASTRAN to determine deflection based on pressure, but it's not worth it.

For example, try graphing an estimated force vs. deflection with using the stiffness ratio of an existing to proposed thickness cubed and then also factored by existing to proposed lenghth of overhang cubed. To keep it simpler a tapered HS stack might need to be considered an average of the mix in thicknesses and diameters. Keeping in mind the outer edge is where the LS stack contacts the HS stack.

To compare the stock 6 shims, 24X.1mm thick, and a 14mm crossover to 3 shims, 24X.15, and a 12mm crossover, what to do??

3/6= .5 -fewer shims
(.15/.10)**3= 3.38 -thicker shims
[(24-14)/(24-12)]**3= .579 -smaller crossover diameter

.5 X 3.38 X .579 = .99 -result of combination

Is the resulting stack the same?? Maybe yes, maybe no -but should be close. At least the relationships go the right directions.
confused.gif


James

[This message has been edited by James Dean (edited 11-15-2000).]
 

Jeff Howe

Member
Apr 19, 2000
456
1
Wow! This has been so interesting. I would love to sit in on a chat with a bunch of engineers sometime. But, it might have to be a little more low profile than this. However, this is interesting.
 
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