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Rocky, rooty trail settings.

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Posted by: MTRHEAD---------------------

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.



Posted by: MACE---------------------

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.


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

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


Posted by: MTRHEAD---------------------

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. http://dirtrider.net/ubb2/smile.gif


Posted by: MACE---------------------

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."


Posted by: MTRHEAD---------------------

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.


Posted by: James Dean---------------------

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


Posted by: MTRHEAD---------------------

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.




Posted by: James Dean---------------------

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


Posted by: James Dean---------------------

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. http://dirtrider.net/ubb2/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).]


Posted by: MTRHEAD---------------------

Now you are in the same boat as me. What does what for sure and how much?

That is why I use the RT kits. The CHART.


Posted by: MACE---------------------

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).]


Posted by: James Dean---------------------

That 1368 needle is easy compared to the subtle complexities here. http://dirtrider.net/ubb2/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. http://dirtrider.net/ubb2/biggrin.gif

James Dean

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


Posted by: MACE---------------------

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.


Posted by: MTRHEAD---------------------

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.


Posted by: Jeff Howe---------------------

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.


Posted by: MN KDXer---------------------

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. http://dirtrider.net/ubb2/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. http://dirtrider.net/ubb2/smile.gif

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


Posted by: MACE---------------------

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...


Posted by: James Dean---------------------

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. http://dirtrider.net/ubb2/confused.gif

James


Posted by: MN KDXer---------------------

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! http://dirtrider.net/ubb2/smile.gif

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


Posted by: James Dean---------------------

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).]


Posted by: MN KDXer---------------------

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? http://dirtrider.net/ubb2/wink.gif

btw, $.15 coffee? You mean $.50! http://dirtrider.net/ubb2/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).]


Posted by: MACE---------------------

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."


Posted by: MN KDXer---------------------

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. http://dirtrider.net/ubb2/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).]


Posted by: James Dean---------------------

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. http://dirtrider.net/ubb2/confused.gif

James

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


Posted by: Jeff Howe---------------------

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.


Posted by: marcusgunby---------------------

You guys are very naughty children and im going to tell Jer when he comes back.The teacher will be very cross with you.I can here him flexing his cane right now.


Posted by: James Dean---------------------

Some time ago Jeremy said the shim stack actually opens very little, this is very important, to know how far the shim stiffness is really effective.

How do we know?? http://dirtrider.net/ubb2/eek.gif


Posted by: MN KDXer---------------------

James D,

EXCELLENT stuff, Man! I've been kicking around the diameter/crossover/bottom shim for a while, but couldn't quite get it to add up. Every time, I'd end up stumbling all over the possible varibles, and give up. So, I'd try to keep the profile the same, but change shim number and thknesses. So, basically, I was fuzzy-mathin' the tapering effect, but correctly computing the thkness factors. It did work quite well.

In a real example, my computation resulted in about a 15% reduction in HS dampening, and the change was quite noticeable. The bike went from "OUCH, this sucks!!!" on the rootsy stuff, to "Ahhhh... What root??" However, I did start to bust a few spokes with my higher speed.

Now, to apply all this to my new RM250. http://dirtrider.net/ubb2/smile.gif

Shocknut,
Actually, we engineers are kinda boring to listen to, UNLESS you like every last detail picked to the bone! btw, bring your own pocket liner! http://dirtrider.net/ubb2/wink.gif

Marcus,
Naughty boys, eh? Maybe "we" are the teachers today!

------------------
-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).]


Posted by: Jeff Howe---------------------

MnKDXer,

I have no pocket liners. Your getting warmer. What about your PPS? You like it?


Posted by: MN KDXer---------------------

Shockster,

Do you mean "warmer" as in reference to the 15%? Am I hearing to go a little more than that? "Pocket liner" is an engineer stereotype joke, btw. I don't have/wear one either. http://dirtrider.net/ubb2/wink.gif

The PPS shock on the Polaris sled... I haven't ridden it yet. I bought the sled last April, so I've gone up and down the lawn once, and up + down the trailer. Ask me again in a couple of weeks. My last sled has the Xtra-10, but only the Indy Select shock. Do you have any experience w/ the PPS?

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


Posted by: Jeff Howe---------------------

I discussed the PPS concept with the GM & Tech Director at Penske when I was there. I had my opinion of it. Upfront I thought it rather strange to throw a hole in your damping curve and all. If you can picture the damping curve of this type of shock compared to the amount of shock travel you can probably see why aggressive riders were lessening the effect or even converting it back to standard design. However, some seem to like it and it would be hard to argue that it is wrong for them. For the aggresive guy, no way! Those wearing drop seat bibs,maybe,yes. Spring selection would be even more critical in my opinion with this shock. Drop me a note from time to time with your impressions. If you ride hard I would guess you will be looking for something better after a good round of objective testing. I can tell you this, the better you can dial your setup to reflect maximum front arm travel the better your ride will be. You know how to do this I assume. Transfer is the key. After that you valve for personal preference. We have to rap on this privately though as some have been getting speared for talking sleds on this site. Proper etiquette and all.

Warmer means in general. 15% would equate to a noticeable change. Figure at least 10% to notice it and maybe as much as 20% for those asleep at the bars. If it's right it's right!
I figured as much about the pocket liner. I was envisioning smocks as well. BTW, does your last name start with a Z?


Posted by: MACE---------------------

Are sleds kind of like quads?

I rode a quad for the first time Saturday.

Yuck!

I think I'll leave this "alternative lifestyle" stuff to the Dems.


Posted by: slowpokedennis---------------------

Would somebody please explain all this to me in plain english. http://dirtrider.net/ubb2/smile.gif This is way over my head. But very interesting.

------------------
Dennis********************************************Col Oh
99husqvarna wr250



Posted by: Jeff Howe---------------------

You don't get plain english out of these engineer types. This is about as close as you can come with them right here. Borrow a pocket liner if you don't have one.


Posted by: James Dean---------------------

In the discussions from the first half of this thread I tried to emphasize the importance of assessing shim force versus deflection rather than looking at shim stack stiffness.

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

Here is an example of why: Take half the shims out of the LS stack and put them in the HS stack. The HS stack becomes much stiffer, but does this increase HS damping??

The answer is no - it reduces LS and HS damping force.

Something to ponder. http://dirtrider.net/ubb2/wink.gif

The stiffness of the combined LS and HS shim stacks is the same and it opens wider for a given force. Sort of like backing off the the shims spring preload. Stiff shims don't always make for high damping force when they are put further back from the compression valve.

James

[This message has been edited by James Dean (edited 11-20-2000).]


Posted by: MACE---------------------

So if you have gargantuan ports like our buddies at RT brag about do you ever develop enough shim deflection to "crossover" into the HSC - or do you expose enough peripheral port area to bleed off the pressure differential at low shim deflection? (THAT was one "H" of a fine runonsentence.....)

Could this explain the "don't increase the crossover thickness" disciples?


Posted by: James Dean---------------------

Mace,

The Race Tech Gold Valves have 3 large openings that expose the shims far more. They will open with less pressure and flow more with comparable shims. Yes, the crossover is exceeded, and generally with a higher speed. I think the valving problems and loss of precise control stem from this higher speed.

The extra flow is usually good for rocks and roots, giving a softer ride. It's not that good when you want more high speed and bottoming resistance. The crossover issue should be handled by changing in smaller increments, say switching from .1mm to .15mm instead of jumping to .2mm.

Either RT or stock compression valves will work well with the right combination of shims. An exception would be a 14mm cartridge rod without extra relief. It flows so much more and is reacted with a larger area that sharp impacts need the extra flow. The advantage of RT is the package of shims and charts for those who want to work on it.

Looking at the charts, I'm surprised that RT isn't showing thinner or thicker crossovers or using thicker .2mm or .25mm shims on the HS stack at the higher settings. This is where the experienced suspension tuner will still have an advantage. Those that I know with RT Gold Valves never hit the right combination in less than 2 or 3 tries. Maybe they're just a picky bunch http://dirtrider.net/ubb2/eek.gif .

James

[This message has been edited by James Dean (edited 11-21-2000).]


Posted by: Shrimp on the barbie Jer---------------------

WOW! Guys I have to say that was fun reading. I liked it and think this is a area where your specific expertises can be very much used. I've done lots of math and related in school but frnkly this stuff goes beyound my capablites.(If you want real numbers) (Calc 3) (Or at least ablity to apply it)

The truth is and I have alluded to this before, in many situations I could not produce a number or direct answer for much of anything it just gets to complex. The werid thingis MNKDXER is dead nuts. I have made a point of studing ratio's of all things volumes, realtive displacements etc and created my own (Albiet seceret) propprtions and relations. These numbers are what i use to determine changes but in realality they have evrery thing to do with %'s..

It started along time ago.. Currently Shocknut is working with to see if he can tweak it but it is a program that give a real albiet bogus unit. It was writen by Kevin Stiwell.(Who remmbers him) It gives some good relationships but is no much more than a neat compaison..

It might be neat to let you guy disect it..

As for the piston issuses the seceret is in the low deflections and that is fundementaly why in our shaft speed ranges a low flow piston will perform better than anything else. Are there other issues.. You beet.. So low flow is not the only thing to consider.


What I like about this conversation is its about ideas.. I'm all for that..Thanks for contributing.. I sertianly don't know everything to every degree.. But I make it point to try..This Forum sparks the flame for me and lots of others I know that.

Regards,
JER


Posted by: James Dean---------------------

Ideas, yes,

How about a REAL brainstorm. http://dirtrider.net/ubb2/rolleyes.gif

I have a bunch of ideas floating around on these shim stacks. Math is a strong point too, calculus through differential equations and linear algebra helps. My question is what is the relationship of FORCE (F) to VELOCITY (V) with a shim stack producing stiffness Ks ??? I don't want absolute force in lbs, just a mathematical relationship.

Tell me where I'm wrong because these relationships are a real puzzle for me. See if you can follow.

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

Starting with a damper having a fixed orifice and a relationship of F= C * V**2 gives a nonlinear increasing resistance to motion. F is force, C is a damping coefficient, and V is compressive velocity.
V**2 is velocity squared or V*V.

With a flexing shim stack C is no longer a constant. It is a function of the pressure exerted on the shims, flexing to reduce the force. So change the name to C(p).

F = C(p) * V**2

Now the tricky part. If the shim deflection doubles, what does C(p) do? The fluid velocity past the shims is cut in half when the damper speed is unchanged. The force was proportional to V**2, so the pressure and therefore force (F) is cut down by 1/4. Does this mean that C(p) is proportional to 1/(deflection)**2? I think its in the ballpark.

Next, consider the shim deflection is close to proportional to force divided by stiffness Ks. This is getting ugly, I know.

The resulting relationship appears to be,

F = (c*Ks/F)**2 * V**2

where c is a constant.

Solving for force as a function of V gives,
------------------------

F = (c * Ks * V)**.66 http://dirtrider.net/ubb2/eek.gif

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

Now substitute your shim stiffness (Ks) as a % change in the stackup to see the change in force from the fork damping. Whew!!

Maybe you engineer types can come up with something better. Try graphing it and things look very interesting. (Also graph F=c*V**2 to get the feel) Next comes crossovers.

James (on the far side)


[This message has been edited by James Dean (edited 11-24-2000).]


Posted by: marcusgunby---------------------

Yes thats what i was going to write-NOT


Posted by: MN KDXer---------------------

James D,

OOooh, Man, were you stuck at the in-laws this weekend? http://dirtrider.net/ubb2/wink.gif

Deep, deep, thoughts you have! Here's a few tidbits of fluid flow you'll also need to factor into your shim deflection vs flow analysis-

a) Fluid flow is not proportional to only the cross section area of the orfice. Factors such as surface edge drag, length of orfice, sharpness of inlet & oulet edges, and viscosity of fluid, are just a few of the considerations which can be a science in itself.

b) The exit side of the piston has some constrictions that are not similar around the entire port circumference. The fluid's escape path is not uniform around the entire orfice.

c) The shim stack does not open parallel to the surface of the piston orfice.

These factors will toss plenty of wrenches into the system and, most likely, confuse most of us waaaay beyond recovery.

Maybe, it's time to put down the calculator and start getting oil on our fingers. http://dirtrider.net/ubb2/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 11-25-2000).]


Posted by: James Dean---------------------

I aggree with you,

The concept was that whatever percentage change is made to the shim stack stiffness, the resulting change in force will be something less. http://dirtrider.net/ubb2/smile.gif

(yes, we went to the in-laws too)

James

[This message has been edited by James Dean (edited 11-26-2000).]


Posted by: Jeff Howe---------------------

So then, would you figure a Dyno would be a useful shop tool? Worth the $20,000? I would sure love to have one.


Posted by: marcusgunby---------------------

A local suspension guy in the uk has recently got a dyno-im hoping to go over to see him in the next few weeks and have a play.


Posted by: Jeff Howe---------------------

Addictive Marcus, very addictive. Be careful.
I NEED one now. Just having a spring tester is nice, but a dyno would be a real treat. You can get some that will test springs as well.


Posted by: P_Taylor---------------------

Shocknut,
Check around the local shops that build stock cars. I found a machine shop/race shop less than 45 minutes away that has a shock dyno. It looks like I will be trading CNC and CAD/CAM know how for their shock dyno know how.



Posted by: Jeff Howe---------------------

I don't think we have big enough involvement up here for guys to buy a $20,000 shock Dyno. But, thanks for the tip, I'll look into it.


Posted by: James Dean---------------------

I owe you guys a report back on the altered fork valving on my WR. This is what I went with -

(5) 24 X .1mm (was 6 shims)
14 X .1
12 X .1 (new)

24 X .1
22 X .1
20 X .1
18 X .1
16 X .1 (was 16 X .15)
14 X .15
12 X .15
11 X .25

18 X .5
------------

My riding impressions were in tight to medium woods riding with lots of rocks and roots. The forks still had a good firm controlled feel but lost alot of harshness in the rocks and roots. I found myself looking further ahead and riding faster as it was building confidence. It used to make me tense up for sharp hits and the change allowed me to just keep the throttle open more. The few whoops we had were still handled well. I had 2 KTM 520exc's to chase and be chased by during the ride. They had been giving me trouble in these conditions before, but not now. Except when I stalled, those e-start bikes aren't fair. http://dirtrider.net/ubb2/mad.gif

It's tempting to try softening more, but I didn't feel the bike was holding me back.

My thoughts are that the increased crossover gap (.2mm) was the biggest change, followed by 1 less shim on the LS (6 to 5). The reduced size (12 X .1 - new) on the crossover may not be as effective from a number of factors such as curvature and having a 4 port layout. The 16 X .1 softened the HS slightly also gave a little extra thread coverage putting it back together.

Insights anyone?

James


Posted by: MN KDXer---------------------

James,

Thanks for the feedback. The 16 x .10 might be a little more significant than you're giving it credit for. Despite that it's lower in the stack, it is closer to the mid point, so its strength is reflected upwards at a fairly good ratio. By dropping to .10, you've essentially went from 3.38 shims of .10 thickness to only one.

The extra crossover shim... Yes indeed, that shim was significant in extending the distance the LS stack flexes before contacting the HS.

Keep careful notes and keep having fun.

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


Posted by: Jeremy Wilkey---------------------

Well I'm about usless on this topic, As for the dyno well we are actually in process of building one. The cheaper models have limintations in terms of speed and acelration, so we are designing one that has some of the real exspensive features while saving money one certain fluff type operations. I can only say it is a fun process and that it will be a useful tool in terms of figuruing a lot of the variables, and getting real world numbers.

Jer


Posted by: yzguy15---------------------

Thinks to self "Wow, if I only knew what these guys were talking about." Yall are really into some deep stuff! How'd you guys learn this?


Posted by: MACE---------------------

Quote:
Originally posted by Jeremy Wilkey:
Well I'm about usless on this topic


(Cough, cough.... mmmmmmmm....)


Quote:
Originally posted by Jeremy Wilkey:

As for the dyno well we are actually in process of building one
Jer



Are you building one of the single stroke pneumatic jobs or a "scotch yoke" or something else? What about the valve "flow bench"? That might actually help in isolating and quantifying the effects or valve changes better than a dyno. Any idea what kind of operating pressures a flow bench that would require?


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

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


Posted by: James Dean---------------------

Jeremy,

A dyno to figure out the variables sounds like fun stuff. I would also like to here about what special features you will have.

James


Posted by: Jeff Howe---------------------

He has no hair currently. That what you mean by special features?


Posted by: Jeremy Wilkey---------------------

The dnyo! Well we are looking at having a "yook" type with basically an electric motor driving a mast that is indexed in 2 locations. The moter will give us the ablity to drive it at virtually infinat (To a obvoius limit, so I had better say an infinant range with in a range.) And acelerate at any point so as to model linkage movement and multtiple sincarios. Obvously we will be runing this off a three phase electrical system and we are tring to figure what motor we will need right now. IT's a big deal beacuse we don't have three phase at the shop and will need to run a phase conveter so power lose is an issue.

As for the system we are seeting it up to have enought stroke to work with forks as well and hopefully we can work a motor speed combination that will get use in the ballpark. The sytem will measur postion and speed and interface with with a basic software package that we are writing the code for, or at least that is the plan. IT will be crude but the process is what I'm after. We want to have it done in a year.

As for the flow bench man I have thought about that forever!!! KXVET (PA SA)and I have been throwing that around and he thinks he can do something with it. Hes got some resources and I hope it will go somewhere. It's been my exspereince that many times things like this don't turn out as planed but seem to really educate along the way..

Regards,
Jer




Posted by: MTRHEAD---------------------

JD- looking at the stack you put together, I'd tend to think that both Hi and Lo are both much softer. Are you getting a lot more dive or hanging lower with that set up?

I would also think that the LS stack is forced to do a lot more of the work now.


Posted by: James Dean---------------------

Mtrhead,

The front does not dive or ride too low for my conditions. It does turn pretty good though in the tight stuff. The forks are slid up 5mm and the oil level was increased about 20mm. The LS stack is getting more work with the larger gap for sure. The most noticeable change is the reduced mid to high speed harshness.

It could probably be better, but I'm riding faster now than before in my favorite area. http://dirtrider.net/ubb2/smile.gif

James


Posted by: MTRHEAD---------------------

This place needs more threads like this!

Where has everyone gone?


Posted by: yamadawg---------------------

Mtrhead,

Here is my take.First what is the problem excatly.I the front end deflecting,harsh,I dont know so since I ride on alot of the same conditions here is what I would do.

1.Do your springs match your ride weight.if they are to light then the front end is going to already be into the stroke causing the forks to be harsh.you are already into the stiff part of the valving.

2.fork hight in the tripple tree will be the main factor in how the bike steers the higher the fork is in the tree the quicker the bike will steer.just the opp. when they are lower in the tree it will be slower.

3.if your in alot of muddy conditons then the more mud hince more weight and the bike ends up in the travel and creates harshness.

other than that suspension takes time,alot of time,to get right and you still have to plan for later race conditions..

Start out making small adjustments and do make to many at one time.keep a log on your changes so you know what is working and not working.Also try to keep your fork oil and shock oil as fresh as possible.

Also remember that usually you should adjust things just the oppisite from what you think.

It just takes time, I know that you dont have alot of it so good luck and hope that this helps...

------------------
it dont hurt till the bone shows.

2001 YZ 250


Posted by: JTT---------------------

Quote:
Originally posted by yamadawg:
you are already into the stiff part of the valving.


...please explain...


------------------
JTT
Logic Over Hype Coalition


Posted by: yamadawg---------------------

if you are through the stroke than oil has already been pushed through the valve and shim stacks less travel left less oil=harsh ride.

------------------
it dont hurt till the bone shows.

2001 YZ 250


Posted by: Jeremy Wilkey---------------------

Yamadawg,
What do you mean?
Jer


Posted by: MTRHEAD---------------------

This was a prompting type post used to generate discussion, much like "derhwurm" and his "shim shuffle" or "4bangers" thread asking for opinions on his stack.

I'd just like to see more threads of that nature. I find them very interesting and enjoy reading the input from guys like Mace, Shocknut, JamesDean, MN KDXers, Marcus and others.

There are a lot of very bright folks here providing far more contribution than they are given credit. Without them things are pretty dull.


Posted by: Jeremy Wilkey---------------------

Quote:
Originally posted by MTRHEAD:

-- --- -----


MTRHEAD, Could you spell that out more clearly? I thought it might have said "so (Water flowing over bridge)-----
' but I could not get the last part... Just curious...

Regards,
Jer



Posted by: svi---------------------

[QUOTE]Originally posted by MN KDXer:
[B]James D,


c) The shim stack does not open parallel to the surface of the piston orfice.

Following on from this I have often wondered how shims bend. With a 3 port piston do the shims bend in 3 planes ? I am guessing the 2 large ports on some Ohlins pistons will simply fold the shim. With a 4 port would that fold the shim, bend it up in a cone or would it just lift at the port opening ?


Posted by: Jeremy Wilkey---------------------

Having whatched the patterns on shims and pistons for years i feel the stacks fold in planes along the edge of the port, and clamping shim. This cause them to crease in the oposite area. Many manufactures have placed lands that go out from the center of the radius to prevent them from folding inward..

Jer


Posted by: MACE---------------------

Has anyone else noticed that a heck of a lot of great threads have floated off to oblivion? I've started to copy the good ones to Word files so they aren't lost totally.

Man, first I can't access from work, then a bunch of classics turn up missing and now we need to become paying members....

Perhaps the lack of archive space and the need for memberships are related problems.

MACE (trying to not flame.....)


Posted by: MTRHEAD---------------------

Yes Mace, I agree. Very little good stuff here any more.


Posted by: Joe Turner---------------------

Quote:
Originally posted by MTRHEAD
BTW- -- --- ----- = in the click


If you are going to come in here and insult people at least have the courtesy to pick up a dictionary and spell the insult CORRECTLY . It's clique genius.

Rather than moan about the lack of content why not try PROVIDING SOME from your vast tuning background.


Posted by: MACE---------------------

I am just quite upset that the we only have about one month of archive here now. I probably should realize that the storage of the old posts cost money, but we've lost two years and thousands of posts of really good discussion.

I feel like the library burned down or something...

MACE (a sensitive, caring new-age Alan Alda sort of guy - with a Desert Eagle)


Posted by: MACE---------------------

Bump once more. Please disregard the last few cranky sounding threads. :thumb:
:slap:


Posted by: Papakeith---------------------

Honestly, I miss threads like this one. I was never able to really add any content, but they afforded me to think about my suspension in ways that I never would have otherwise.
Did you ever find the root and rock grail Mace?


Posted by: marcusgunby---------------------

I tried to set up a thread recently concerning using midvalve lift as a method of tuning a fork to rider speed but with jer away and few others around it soon died.I have felt a bit lonely here ,JTT has kept me company but few others have joined the party


Posted by: Papakeith---------------------

I've read the posts, but I don't have anything to bring to the table, so I generally just read it and move on. Maybe I could show interest by bumping it up, or just try to answer, and get b-slapped by the more learned suspension people here when I'm off-base. I'd love to see this forum come alive again.


Posted by: KTM-Lew---------------------

Hey Marcus....I just happen to be doing an up-date on my forks. I had done an MX-Tech self-install when I bought my bike in Sept of last year. I intend to try a little experimenting with the float after I get all the new parts installed.

If I reveal too much Jer will have me shot but I'll try to participate.


Posted by: marcusgunby---------------------

hurray someone to play with-if we only talk of midvalve float and not reveal shim stacks then it should be ok.What have you got?you show me yours and i will show you mine


Posted by: Jeremy Wilkey---------------------

Guys this forum is very healthy actually.. It gets old and slow from time to time but thats part of the process. I've resigned myslef to not answer every question, for one because I've got other more grave concearns, I don't want to be taged as "overwhelming"..

Now call me a dork, but what I don't understand is this and maybe some of you can help me. Honestly while I was out and away it was nice not dealing with certain induviduals who forget that you have real respsonablites and comiments. They forget that with out this or forums like these that they still think fluid was pushed by a fork piston.

I mean honestly, its exstemely easy for some local with nothing to lose to speak there opion, yet for someone like myself or other couleges we take our time to educate, sure we have or petpeves etc but I think by and large we are concearned and genuily intrested in the better ment of our beloved profression.

I'm not asking for sympathy here, I don't want or need it. And I also completly realize that with my postion there will be cuntless losers taken stabs when they don't have anything better to do with there worthless lives. My only advice is go somewhere eles, quite bitchin and just try to deal with joe-public on some level that potentially involves your arse being in a sling ever time you walk in the door. When succesfully run that gauntlet for a few years you can come here and complain about something, but sufice it to say I'd speculate your weak nature will have been so trampled apon you won't show up.

If I read something wrong into this I applogize..

As far as I can tell the new, partianlly green are allways welcomed here with kindness, so by all means contribute, I promise you won't get b-slapped... I don't think any of the postive induviduals on this forum would ever do that to a decent intent.

Jer

Serious mode off...


Posted by: KTM-Lew---------------------

The orginal set-up was at .033".....sorry I'm metric'ly challanged......and I'm gonna go with .045" on the update. I am going to do the passive first and try it, then do the mid-valve so I can see what effect I get from each. There are some shim changes to do also so maybe I SHOULD try it at .033" first. Hmmm.

I am trying to get them better on 4-5" embeded rocks. The conv forks on the ATK spoiled me. That is about the only thing I miss.

Oh, by the way...we are working on the opposite end of the same problem...I'm strictly woods and you do MX. Still may be able to learn something. :thumb:


Posted by: KTM-Lew---------------------

Jer....I hope you're OK with me???? I'm not in any way bitching about what I purchased....the stock stuff was unrideable....your stuff was by far the best inverted fork I had ridden.

Just like the Six-Million-Dollar-Man, it can be better,stronger,faster....


Posted by: Jeremy Wilkey---------------------

KTM Lew,

Do the updates, then exsperiment.. Scientific methods only or your results are not valid

BR,
Jer

As for MX and offroad, they are diferent but I'm convinced that we can both learn from each other. John Curea has become quite the offroad guy, yet we have some of the stiffest and productive conversations. Sometimes when you become too specialzed you lose gripe of the big picture. When I was younger and did most of my own testing I was amazed that over the course of a year ot two how you could go from one side of the fence to the other in belief that you where onto something, only to find after a long time you've taken the wrong path. Thats the buety of what we do really. The only thing you can do is to learn the absolutes along the way, and then try to better aply what you actually know.

As an example the still ongoing debate over midvalves. The exact configuration is is YTBD but the fact that a fork works better when configured propelry is a fact. The details are why... So with the deconstructed why we learn how. Over time we peice more and more details together.. This avoids being lost in the woods as much as posible.


Posted by: Jeremy Wilkey---------------------

KTM-LEW not directed at you in the slightest.. Nore was it at 99% of the good people here at DRN.. And that includes people who I don't agree with.. I'm directing this at the winers, hecklers, spammers, and other misolancous low-life.. Anyway I'm being no better than them am I. Its cool and I've spoke my mind, so no worries I just had to get that off my chest..


Posted by: MACE---------------------

Quote:
Originally posted by Jeremy Wilkey
...They forget that with out this or forums like these that they still think fluid was pushed by a fork piston.


I remember that thread. You sort of explained what really happens and told me it would keep me awake until I figured it out. You were right. Somehow my wife wasn't as thrilled as I when I woke her up and explained it to her my newfound enlightenment.

Geez, wimmen.....


Posted by: KTM-Lew---------------------

Yea...everyone knows its a forked piston :silly:


Posted by: Papakeith---------------------

Sorry if you took offense at my words Jeremy, I meant no malice towards you or any of the people here who are willing to divulge their knowlege to the masses. I meant b-slapped as in a cuff to the back of the head with a nudge in the right direction if I was pointing north when I should be heading south. Giving me hints, without just spelling out the answer. Making me think. Kind of a teacher student thing.


Posted by: Jeremy Wilkey---------------------

PK,
No worries brother.. Nothing was ment towards you and I'm glad your contributing to the forum.

BR,
Jer


Posted by: mbaird---------------------

Are there any books out there that could help me understand
how forks work and what these guys just said ?

I really don't have the time or money to start taking my forks apart. ( and losing half of the internals !! )

These guys sure sound like they understand them intimately.
I have no illusions of being on their level, but would like to
understand the basic dynamics.

Maybe I should buy a set of used, shot forks and start taking them apart


Posted by: MRW---------------------

Quote:
Originally Posted by mbaird
Are there any books out there that could help me understand
how forks work and what these guys just said ?

I really don't have the time or money to start taking my forks apart. ( and losing half of the internals !! )

These guys sure sound like they understand them intimately.
I have no illusions of being on their level, but would like to
understand the basic dynamics.

Maybe I should buy a set of used, shot forks and start taking them apart


Eric Gorr`s books are always a good choice. With his books and reading here, you`ll be a pro in no time. Amazon.com has them. Eric is to dirt bikes as Harry Klemm is to jet ski`s.
To me anyways Ah man it`s late.....



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