Shock valving for dummies

I'm creating this thread for the sole purpose of helping people like me, who don't really know much about how shocks work or how different "valving" affects ride characteristics. When I first bought my Tacoma a few months ago I instantly became interested in some of the high performance coilovers offered by companies like King, ADS, Fox, and Icon. I realized there was no way I could choose the right shock for me without knowing the first damn thing about shocks. So I've spent countless hours googling and asking questions until I finally stumbled across http://www.crawlpedia.com/index.htm
This website has some great information about how a shock works. All of the information I post here can be found on their website if you look for it, but to make it easier for people on TW I'll copy and paste the info here and post the examples of different forms of valving provided on their page.

From CrawlPedia:
"How Shocks and Shock Valving Works
Shock absorbers dampen the suspension movement of a vehicle to improve handling and performance by forcing specially formulated shock oil through tightly controlled holes (ports) in the shock piston to convert kinetic energy (movement) into thermal energy (heat).

Most high performance shocks are similar in design and feature a piston attached to a shock shaft that moves up and down inside the shock cylinder which is filled with shock oil. Shims placed on either side of the piston, then control the movement of oil through the ports depending on their arrangement.
As the shock shaft moves within the shock body, oil is forced through openings in the piston to push against the shim stack on the opposite side. The faster and harder the shock moves, the higher the force of the oil pressing against the shims becomes. Controlling how much force is needed to allow the oil to move past the shims at any given speed is how shock valving is determined.

Standard Shim Stacks
Shock valving shims are precision machined in various thicknesses and are heat treated to hold up to temperatures exceeding 500 degrees without losing strength. The most common configuration is a pyramid style stack made up of progressively smaller diameter shims which offers excellent damping at all speeds. The harder and/or faster the shock moves, the higher the force of oil being pressed through the shock piston ports gets and the more shims in the shim stack come into play. As more and more force is applied to the shock, the harder the shims press against the oil to dampen the movement.

An important thing to keep in mind is that all forces absorbed by the shock absorber are converted to heat which is dissipated through the shock oil and out through the shock body. Every shock absorber has a limit to the amount of force it can absorb over a given period of time before the heat generated causes the shock oil to break down or expand to the point of cavitation where the piston hydro-locks. This is why it is not only critical to get the shock valving correct, but to also make sure that your shock is the appropriate size and properly equipped to match the performance of the vehicle.

Off-Road Shock Tuning Guide
Without getting too advanced, shock tuning is about selecting the right combination of compression and rebound shims and stacking them in the proper order to get the shock damping characteristics you are after.

While shock tuning is as much of an art as it is a science which takes a lifetime to master, basic shock tuning is quite simple and something any off-road enthusiast can do.

Shock Shim Stack Basics
As is covered in our Shock Valving Guide, every shock features two shim stacks: one for the compression tuning and one for rebound tuning. (Remember that the shims are placed on the opposite side of the piston from the direction of travel.)

The most common shock valving configuration (standard valving), is a progressive shim stack, or pyramid shim stack made up of 5 to 10 shims of the same thickness and varying diameters stacked in order from largest to smallest.

Shims come in various thicknesses and are measured in thousandths of an inch. The thicker the shims are, the less they want to bend, thus making the shock stiffer.

When referring to the valving specifications of a shock, you simply list the shim stack thickness as "compression over rebound". For example, a shock with .015" compression shims and .012" rebound shims would have "15/12" valving.

Standard Shim Stack Configuration
The standard pyramid style shim stack is the most common configuration for a reason - it works very well. It gives the shock progressive damping which allows it to be relatively soft during slow speed movement like rock crawling or driving around town and stiffer at higher speeds like blasting through the desert or hitting a pothole on the highway. This is why a standard progressive shim stack is the way to go most of the time.
Another advantage of standard shock valving in this structure is that it is very easy to adjust. If the shock feels too soft, use thicker shims and if it's too stiff, use thinner shims. King offers shims in .08", .010", .012", .015", and .020" thicknesses and they are all readily available on-line at Filthy Motorsports.

Advanced Tuning: Flutter Shim Stack
A flutter stack is a configuration were a smaller diameter shim (gap shim) is placed between two larger diameter shims, usually on the compression side and within one or two shims from the piston face.

Inside the shock, a flutter stack increases the distance that the largest shim(s) has to move before it contacts the stiffer shims above it. This gap extends the "soft" zone of the shock and the more thick the gap shim is, the larger that zone becomes.

In a real world application, this would allow your suspension to better soak up high movement, low force terrain like a washboard while still absorbing big hits when they happen. (A secondary bypass shock, however, would normally be better choice for this application though.)


Advanced Tuning: Rate Plate
In contrast to a flutter stack that extends a flow zone, a rate plate does the complete opposite by setting a dead stop, similar to a door stop. This sudden stop makes for a dramatic change is shock valving which works well in some applications but is often reserved for racing as it can be very difficult to get right.

Rate plates are almost exclusively used on the compression stroke of the shock and are nothing more than an extra thick, non-flexible shim. The fewer shims there are between the rate plate and the shock piston, the faster it comes into play which is why they are most often placed near the top third of the stack

Because rate plates don't flex, they create a (practically) linear damping force that is predictable and makes pairing them with secondary shocks and tuning bypass shocks easier in advanced setups.


Advanced Tuning: Doubled Shims (+1)
For extreme and heavy vehicle applications like mud trucks and monster trucks where .020" shims might not be enough, doubling up on the shims or every other shim ("+1") is one option that will add damping force.

While this is usually only done with .20" shims, it will also work in situations where thicker shims aren't available but two thinner shims are at hand. Keep in mind that two .010" do not act the same as one .020" shim, and will be a bit softer.

A major drawback to doubled up .020" shims, however, is a significantly increased temperature since the shock is working harder. For mud trucks and monster trucks that run 20 minutes at a time, this isn't much of an issue but desert race trucks would be far better off upgrading to a larger shock body or adding a secondary bypass shock.

Advanced Tuning: Additional Tips and Tricks

• Using more thinner shims instead of a few thicker shims will give you smoother damping.
• Increasing the pressure in the reservoir is a simple way to temporarily increase compression damping.
• Drilling holes in or sanding edges off your shims is one way to soften them up in a crunch.
• In most cases, rebound damping does not need to be changed unless the spring rate is changed.
• For faster rebound in soft shocks, you can drill free-bleed holes in the shock piston to bypass the shims.
• If your shocks are too soft and they overheat too fast, you need a bigger or secondary shock.

Off-Road Racing Shocks Shim Stack Examples
The following table contains several sample compression and rebound shock valving shim stacks ranging from extra soft to extra firm.











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Hopefully this information is as helpful to someone new to the world of off-road racing shocks as it was to me. If you have any further questions beyond what's been posted here, I'm not the guy to ask cause chances are I won't know the answer to them But don't worry, I'm sure the experts will be along shortly to chime in on this thread.

 

Awesome! I'm sure this info will come in handy.

 

I figured someone would find it as useful as I did

 

thanks for posting this. i found it very informative

 

Sweet thanks for the info. I put on some Fox 2.5 last year and had them revalved in MI by B & L Motorsports.
Unfortunately it seams like they are selling the business so I may have to do the final revalve myself..
They changed the coil overs to std valving but I don't know what stack they put in.
I hope they keep records and I can get a hold of them.
Worse case I'll have to pull the shocks apart and ck and myself.

So using there terminology, I need to go up 1 or 2 more steps of compression and 1 step rebound damping.
So I'm guessing 1 step is 1 step of the valving chart????

 

I re-valved my shock finally.
The hardest part was the caps were corroded onto the tube after 1 winter in the salt. Soaking in WD-40 for a day loosened them up.

With the fox shocks they had a #70 stack with a flutter valve on compression and a version of the 75 for rebound.
I decided to jump to the #80 and run the flutter stack and a 85 rebound that has an extra 1.250 .012 shim from fox so I left it in for now.

Compression

.012 ----------------------------- 1.800
.012 ----- .800
.012 ----------------------- 1.600
.015 ----------------- 1.425
.015 ------------- 1.350
.015 --------- 1.100
.015 ------ .950
.015 ---- .800

Rebound

.012 ----------------------- 1.600
.015 ----------------- 1.425
.015 ------------- 1.350
.012 ----------- 1.250 ???? just left it in for now.....
.015 --------- 1.100
.015 ------ .950
.015 ---- .800

 

@desertjunkie760 @Prayn4surf

 

Also went up to a 650 pound spring...
much less preload, still rides good, 2 1/4 up travel to start...
Figure the springs may settle a little at the dunes, going for 2 1/2" up travel.

 

The 650 pound springs work great. If you are desert running 650 is a good spring.
The valving worked great, I think the compression is perfect.
Just needs a little more rebound.

 

@Maggot61

 

Sorry thought you ended up with another valving end result?

 

Yeah this is old, now I have the #80 with a flutter valve for compression and a custom #95 rebound, 650 spring and 180 psi front and rear, from the fox shock thread.

I found too little rebound makes it harsh over bumps and stiffer springs also need more rebound.
More rebound will hold turns flatter so it will handle better without adding stiffness but it will transfer less weight. I have almost as much rebound in the rear, a custom #85.5/90. the leafs need a lot of rebound to keep them from hopping over bumps.

Lowering the psi reduces the low speed harshness on and off road and has no effect on high speed, so you can run a stiffer stack and springs for big bumps and still drive around town and trails.

The stiffer springs have less preload for the same lift so the spring can work properly and on small bumps they can be softer than an over preloaded 600 spring..

My valves have 2 .095" rebound bleed holes, I don't know if this is standard on our shocks or if they drilled them, so without bleed holes you may need a little less rebound...

 

Front, works great overall hard to beat. I may be done, needs 1 more run at the dunes. Passed the up north run. A++

Compression

.012 ----------------------------- 1.800
.012 ----- .800
.012 ----------------------- 1.600
.015 ----------------- 1.425
.015 ------------- 1.350
.015 --------- 1.100
.015 ------ .950
.015 ---- .800 could be a .020

Rebound
2 .095" bleed holes
.012 ----------------------------1.800
.015 ----------------------- 1.600
.020 ----------------- 1.425
.020 ------------- 1.350
.015 --------- 1.100
.015 ------ .950
.015 ---- .800 could be a .020



Now that the front is working so good I'm doing the final tune to the rear but it's real close the way they set it up. High speed is good low speed can be a touch too harsh....

Compression I may change this stack to make it more progressive but it's so close, I would soften the low speed and stiffen the high speed to keep the overall stiffness the same....

.010 ----------------------------- 1.800 May go to a .008
.010 ----- .800
.010 ----------------------- 1.600
.010 ----------------- 1.425 and go to .015 in here
.010 ------------- 1.350
.010 --------- 1.100
.010 ------ .950
.015 ---- .800 could be a .020

Rebound
2 .095" bleed holes
.012 -----------------------------1.800
.015 ----------------------- 1.600
.015 ----------------- 1.425 May go to an .018
.018 ------------- 1.350 (.008 + .010)
.015 --------- 1.100
.015 ------ .950
.015 ---- .800 could be a .020

180 psi front and rear.........

 

Wow. this thread has some very useful info. Getting ready to rebuild my coilovers and rear shocks. I'm really happy to have come across this. Super thankful for you guys to making this info as straight forward and useful as it is..

 

I wish someone would do an article on splitting the comp stack when you run a comp adjuster on Kings/ads/fox

 

Where did you purchase your valves from? The op has a link but it appears to be for king coilovers. Could you point me in the right direction for parts? My next step will be to contact fox directly.

 

This is some good info.

 

This is an old post so I may be overly optimistic for a response..
I'm curious how successful I would be to copy paste your valving configurations on my taco.

I'm running steel skids and a stealth winch bumper. Can you add some details as to what kind of weight/ armor your vehicle was running at the time you did this valving??
-L

 

Hey all, servicing my Kings for the first time. Seems they have never been opened due to the single mark on the bottom of the seal cap. Anyways, they came with .020 stack and a .012 flutter and what looks to me is a rate plate. I’m changing it to a .015 stack with a .008 flutter but am wondering if this rate plate is necessary? (If it is one) I’m not racing, this is my daily driver/weekend warrior truck. Also with the flutter, I put it under the largest shim, is that a typical spot? Or underneath the second shim from the top? Here’s a pic for reference

 

Back from the dead! Wondering what shim stacks others have used when they re-built!