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Shimming a stock valve.

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Hey guys, thanks in advance for helping me out. I've read a number of TT forums on the Race Tech Gold Valves. In the process I've discovered that for my particular bike, 02' yz426f, it's not neccessarily the valves themselves that make a big difference, but the valve shims. I realize that this can be argued, but let's just say that they're at least comparable and that no "hydrolic lock" is taking place. If that's the case, how does a "novice" mechanic figure out how to shim his own stock valves without the kind of help that race tech gives its customers? If I had Race Tech Gold Valves I could call them up and say, "This is what I ride, how big I am, and what style I ride, what would you suggest?" Is there any way I could do that with my KYB forks with another manufacturer, race tech, or even another company- or is it just trial and error? Thanks!

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Trial, error & TESTING. That is why suspension companies charge for what they do ...... 100's of hours testing with each bike.

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Traction12,

The short answer is that often this information gets shared, or you can trial and error the process. There is no one other than Race Tech that offers a matrix of shim stacks but there are others that sell pistons that may be willing to also sell a given configuration.

Now, there is also the infamous Shim Program web site that many TT'ers reference. It appears to use a basic load equation based on spring deflection, but in my opinion, the Shim Program is to damping design as sugar is to a good diet. Long story.

In the long run, and this is a big concern with Race Tech as well, is that there is a small window in which measurable and consistent tuning can be achieved within just the base assembly, given that compression damping is harmoniously controlled between this and the mid-valve stack. In other words, when you decrease or increase at the base you are often just re-deflecting the flows elsewhere.

They go hand-in-hand, so look at the fork as a complete assembly.

So yes, it's going to be a bit of an educational process or you can simply send the forks out to someone who really knows their stuff.

I can detail a few more issues as well if you want to continue.

DaveJ

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Dave,

I'm one of those guys who takes pride in my machine because I work on it. It's the difference between a rich kid who buys the fully loaded classic car (because he can afford it) and the guy who built his from the ground up. I want to know that the bike I'm racing is the bike I rebuilt. I love learning, so if you are willing to write, I'm willing to read. :applause:

ps. I've been working through the shim program site, so it's interesting that you brought it up.

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Dave,

Like Traction12, I too am looking to further my knowledge on suspension set-ups and the different theories on suspension tuning. Is there a particular book or video or even a website to look at so one could soak up some good info to hopefully gain the confidence in tuning their own suspension. I think I am beyond the clicker adjustments as far as knowledge go's, so I am looking for the info that you usually can't find easily. I watched the shop revalve my suspension. Took 2 hours for them to complete. Lots O' money! Seems the complexity is in the shim stack. Any such info would be great! Thanks, Matt

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I'm not quite sure where to start, but let's begin with matters involving the Shim Program.

First, you can't collectively calculate a damping curve based on the sum of independent values. In other words, the Shim Program simply takes the known force that it takes to deflect a single shim (that shim in particular) and adds that value into the sum as you add each new shim.

It does not take into consideration the torque (lever) that is applied to each shim from the precluding shim, nor does it consider the distance, size and number of forces being applied to the stack via the piston design.

Lastly, it can't determine the effects of a gap between a shim or shim stacks, say with a two-stage configuration.

Additionally, when you decrease or increase flows in the base assembly, you simply re-route all circuits associated with compression damping, (oil pressure will always bleed to the route with least resistance). Even adjusting the clicker on this valve means more or less flows about the mid-valve.

So, you'll never get the actual performance that you're expecting, that is, until someone gets a little more comprehensive with the math.

With that, you simply have to study the shim stack for yourself and decide on what sort of changes you want and how to go about getting that. If you're not sure, post the stack(s) and there will always be some great input from others on the board.

With a little bit of effort, you'll be as well understood on this topic as most of the suspension shops are, since most of them don't know much beyond the trial-and-error aspects of things.

With that, let me know what else we need to cover. Others will chime in with some good stuff as well.

DaveJ

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Dave,

I just want to say, "Thank you!" for the advice. I understand what you're saying about the shim stack program. It seems as though without a "more comprehensive" mathematical formula for shim stacks we will all be forced to go through the trial and error phase. I've read some of your other posts concerning the race tech gold valves and was wondering... do they actually allow less restricted oil flow as they claim? Because if not, and the stock valves are comparable to the gold valves, wouldn't the race tech configuration concerning shims work equally as well with the stock valve? I do realize that the two valves are different in many ways (diameter, shape etc.), but I would think that the proper shim setup would be directly related to oil flow. Forgive me if I'm over simplifying. :applause: Thanks!

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I would suggest that you gain the knowledge and confidence to work on your own base valve, midvalve, etc., followed by learning some general information about what effects larger/smaller diameter or thicker/thinner shims would have, then make a big change and go ride. You may then say, "WOW. That is way too soft/stiff. I need to go back some toward the starting point." The more fine tuned you want it, the more trial and error/seat time it will take to get it how you like it.

I hope this helps.

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These aren't Racetech valves they are Suspension tech stealth valves.

Apparently they are similar so it might give you some idea.

Bike is an 04 WR450. Stock on the left.

sidebyside3.jpg

Picture is a bit dark but notice how every second port directs oil out the side of the piston. On the new piston it's straight through and a lot bigger.

sidebyside2.jpg

I would say the flow would be nearly doubled as well as be directed to totally different areas of the stack.

Short answer I doubt that Race tech settings will be even close with a standard piston.

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Thanks a lot for the pics! It certainly looks like the stealth valves would allow more oil flow. Doesn't it seem odd thought that KYB would create a valve that seems so restrictive? Correct me if I'm wrong, but if the shims are supposed to be the real regulating force behind oil flow, then does that mean the valves would be most effective with the maximum amount of oil flowing through them, thus allowing the shims to do their job? Other than speculating whether stock valves are more restrictive just by looking at them, is there some kind of measured research on the difference between stock and aftermarket valves?

:excuseme:Sorry, I'm full of questions!

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Guys,

I'm just going to throw this out there as food for thought, but I really think people need to put some thought into the whole concept of the pistons "restricting" flow, and some "flowing" more than others.

Perhaps even give some thought to the mechanics of fluid flow.

:applause:

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SC Spode

Good point, we need to look at exactly how much or actually how little fluid flows throught the base valve to determine what port size would cause a restriction.

A KTM fork with a 14mm piston rod will displace about 1.5 ounces of fluid through the base valve over roughly 12 inches of fork travel. A 12mm YZ piston rod will displace just over an ounce through the same amount of fork travel.

Once we realize the quantity of fluid that flows through a base valve, we can have a better understanding how small a piston port must be to restrict fluid flow, of course, shaft speed plays a big factor in this also.

As a side note, on an average, about 3 times as much fluid flows past the midvalve as compared to the base valve.

Take Care, John

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SC Spode

Good point, we need to look at exactly how much or actually how little fluid flows throught the base valve to determine what port size would cause a restriction.

A KTM fork with a 14mm piston rod will displace about 1.5 ounces of fluid through the base valve over roughly 12 inches of fork travel. A 12mm YZ piston rod will displace just over an ounce through the same amount of fork travel.

Once we realize the quantity of fluid that flows through a base valve, we can have a better understanding how small a piston port must be to restrict fluid flow, of course, shaft speed plays a big factor in this also.

As a side note, on an average, about 3 times as much fluid flows past the midvalve as compared to the base valve. Take Care, John

That red statement explains a buttload to me....

Thank you very very much. :D

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derek,

The same amount of fluid will flow through the compression side of the midvalve whether its a check plate design or has an actual shim stack. A check plate will let the fluid flow without any resistence. A shimstack design (depending on the stack configuration and the amount of float) will add to the overall damping equation.

I need to have a flash program developed showing the action of the cartridge displacing fluid, it would make the definition of this process so much easier to understand.

Take Care, John

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Thanks John. I think I know what you are talking about now.

As the piston moves through the fluid with a check plate only, there is no dampening occuring, but with a mid-valve, there is dampening.

So in reality, a check plate just lets the dampening rod move more freely through its stroke, so you have shim the compression valve stiffer to compensate.

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It sounds like you have the hydralic lock thing figured out. (there is none with stock piston designs) And, since the stock pistons work fairly well, if a rider wants to alter his suspensions performance, all he needs to adjust would be the shim stack.

Orignially Posted by DaveJ

1. First, you can't collectively calculate a damping curve based on the sum of independent values. In other words, the Shim Program simply takes the known force that it takes to deflect a single shim (that shim in particular) and adds that value into the sum as you add each new shim.

2. It does not take into consideration the torque (lever) that is applied to each shim from the precluding shim, nor does it consider the distance, size and number of forces being applied to the stack via the piston design.

3. Lastly, it can't determine the effects of a gap between a shim or shim stacks, say with a two-stage configuration.

Some of DaveJ's observations are correct, and some incorrect.

1. The Shim Program does not calculate the damping curve. It simply calculates the stiffness of the shim stack. (think of shims as flat springs)

The program does calculate the stiffness that each shim contributes to the stack. I can't think of any other way to calculate a stack, as each shim has to contribute it's individual resistance to the entire stack. It does not calculate any forces from friction etc produced as the shims rub against each other.

2. It does take into account the leverage/deflection of each shim in the stack. That is how the loads are calculated. In fact, we know exactly how much any given shim in the stack is deflecting.

It does not take into account the forces being applied by the piston. The program is designed to make comparisons between valving changes to the same shock (i.e. same piston).

3. It does take into account the gap between the low speed stack and the high speed stack. That is, in essence, what makes a two stage stack work.

So, in a nutshell, the program lets you see how shim changes affect the stiffness of the stack. If you started from dead scratch, and just started swapping shims around, you would be in for a long a tedious testing process just to get the basic feel for what the shims are actually doing. And half the time, you would thing the shims are doing something that they are not.

It's also helpful to know the piston velocities and exact shim stack deflections. Then you can pinpoint the area of the damping curve you want to alter.

Regards

Kevin Stillwell

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Hi John,

We have just started the process of comparing Shim Program "load" changes to the dyno's "damping curve" (roehrig 10vs). Obviously, the two do not match up exactly. But, for the most part, the changes predicted by the program can be reproduced on the dyno.

Future plans for the program include a "conversion/simulation" where the program's loads would mimmic or mirror the damping curve. This will definately take some time, but should yield interesting results.

Regards

Kevin

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