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Suspension Encyclopedia - OEM Valving Specs
This page is a part of my promise to bring free to consumer, objective information about suspensions to the masses. As often as i can remember to do so, i have been writting down the valving specs from shocks i take apart. I offer this up as a baseline and as a tool to understand valving.
Tacoma
2G tacoma front 2.5 king coilover, no adj
600 lb springs, 3 rebound holes open, significant leaking at time of rebuild
12
12
12
15
15
15
15
Piston
12
12
10 - flutter
20
20
20
20
2g tacoma rear 2.5 king smoothie, no adj
2 bleed holes open, 1 set screw.
8
8
8
10
10
10
piston
12
8 - flutter
12
12
12
12
12
2g tacoma front 2.5 king coilover, w/ adj
These are custom tuned by a local shop for the end user. They were pressurized to 180 psi on arrival, the customer had ride quality complaints although they were in desperate need of a rebuild.
20
20
20
15
15
15
Piston - 2 bleed holes
10 (shim is added, backed by same diameter 12 after flutter)
8 flutter
12s all the way down
2g tacoma rear 2.5 king smoothie, w/ adj
These are tuned by a local shop for the end user.
All 8s
piston - 2 bleed holes
10
8 flutter, smallest disc possible
Missing normal shim 2 size here
8s all the way down
3g tacoma front 2.5 fox coilover, no adj
Looks like a low flow linear style piston. In testing this shock it was one of the worst rides i've experienced. We brought it back to test against 2.0s for this season of shock value and it came in 2nd place to 5100s. We were hoping to get 2.0s to test but fox declined sending us any further shocks to perform blind tests on.
4 washers
(4) 20 x.8"
12x.95"
12x1.1"
12x1.35"
12x1.42"
12x1.6"
low flow piston, one .171 bleed hole
8x1.8"
20x0.8" flutter
8s from here
and a 20x.8 at the end
2g tacoma front +2" total chaos long travel spec 2.5 fox coilover w/ dsc
2 large bleed holes on linear style piston
15
15
15
10
10
10
piston- photos below
8
6 - same 1.6" dia
.8 x .010 flutter
8 - same 1.6" dia
.8 x .010 flutter
10 - same 1.6" dia
10
12
10
10
20
2g tacoma rear 2.5 2 tube bypass, custom valved for spring under kit
1 small bleed hole
All 12s
piston
Dual .015 x 1.8 shims
all 15s
1g tacoma front 2.5 king coilover, ifp (no reservoir)
12
12
12
15
15
15
15
3 open bleed holes
12
12
10 - flutter x 1.15
20
20
20
20
1g tacoma front 14" fox coilover, w/ dsc. Tuned for 3 link w/ dana 60
This was from a popular tuner, it had 30/90 with a flutter and 2 large bleed holes. On a 14x2.5 with DSC. I did not ride in the vehicle to verify performance. My guess is you can lighten the main stack and rely more heavily on the DSC to get some initial shaft speed on nuissance stuff, but i didn't test it.
2g tacoma front 2.5 fox coilover, w/ dsc
These are custom tuned by a local shop for the end user.
15s
2 bleed holes, gold piston
1.8x8
1.425x10
0.95x10
1.8x10
1.6x12
1.425x12
1.35x12
1.1x12
0.95x12
.8x20
1g tacoma rear 2.5" king smooth bodies, w/ adj
These were really cool I've never seen a 1st gen tacoma rear built like this.
It had almost a race series seal head assembly, the main U cup seal was held in with a snap ring. It also had a gold series piston with a spacer on the rebound side, i believe this preloads the shims a bit? Still waiting for confirmation. This shock was also outfitted with a welded lower uniball for increased travel.
It had all 8s on rebound and 10s on compression with the standard 2,1 flutter
Photos below:
4runner/Lexus/FJ cruiser
5g 4runner front 2.5 king coilover, w/ adj
3 bleed holes open. Came in pressurized to 135 psi. Leaked in the normal spot for kings, very small hose fittings. Not sure if these have been revalved or not as they did not match with the valving from the next set i did.
All 20s
piston
10
10
10 - flutter
20s
Customer complained they weren't getting enough shaft speed at low speeds which is crazy with 3 bleed holes. I ended up swapping the rebound stack to 15s for the first 3 and the comp to 8s for the first 2. I also closed 1 of the bleed holes, in my opinion on a mechanical advantage like an IFS front end 3 bleed holes is alot.
5G 4RUNNER FRONT 2.5 KING COILOVER, W/ ADJ
Not sure if these have been revalved or if the previous set has. 2 bleed holes, 1 set screw.
All 15s
piston
12
12
10 - flutter
15
15
15
15
15
5g 4runner rear 2.5 king bypass
1 tiny bleed hole, this seems standard for bypasses industry wide.
All 12s
piston
All 12s
5g 4runner rear 2.5 smoothies, w/ adj
All 12s
2 bleed holes open on piston
12
12
10 - flutter
15
15
15
15
15
2.0 resi. Comp side seems high considering it has adjusters. Some shops will add a 10 thou face shim with an 8 thou flutter directly behind it, sort of how ADS does their valving.
5g 4runner front 2.5 king coilover, w/ adj
Not sure why these were valved differently from the ones above
all 20s
3 bleed holes
8
8
10- flutter
15s
3g 4runner front 2.5 king coilover for total chaos long travel
Came with 500s, customer swapped to 650s. I think 600s would be more appropriate or 550s with less bleed. Had 3 bleed holes open with no set screws in place on kings standard high flow piston.
Rebound
All .010s
Piston
.012
.012
.08 Flutter, 1" diameter
.015
.016
.016
.016 (i know there arent 16s but they all measured .016)
lexus gx470 front 2.5 icon coilover
15
15
15
15
18
30
15
(2) 18s
15 preload
3 bleed holes open (out of 4) in piston
15 preload
15 face shim
15 x .925 flutter
all 15s
lexus lx470 rear 2.5 smoothies, w/ adj
These have a 2.0 res on them which is a very small nitrogen volume for the shaft displacement. This is likely to mount the reservoir in the fenderwell for branding purposes without having tire fitment issues. Other brands will have long hoses and mount the reservoir closer to the rear bumper.
2 bleed holes open 1 set screw
All 12s
piston
12
12
10 - flutter
15
15
15
15
15
Customer was complaining about how soft it was all around, has a dirtbike hitch carrier and it pogo's bad with the bike on the back even with the comp adjuster all the way firm.
Upon opening the shock i found lots of air and nitrogen was leaking past the IFP. I ended up just closing 1 of the bleed holes and rebuilding it with no air in the shock although i did consider swapping the comp side to all 15s.
fj cruiser front 2.5 fox coilover, no adj
These had 600 lb springs on them and 8 hole linear piston. Rebound holes were .25 and comp holes were .344". 1/16" bleed hole.
Rebound
.8 x .020
.8 x .020
.95 x .015
1.1 x .015
1.25 x .012
1.35 x .012
1.425 x .010
1.6 x .010
Piston
1.8 x .012
.8 x .008 - Flutter
1.6 x .010
1.425 x .010
1.35 x .012
1.1 x .012
0.95 x .012
0.8 x .020
5g 4runner rear 2.5 king smoothies, w/ adj
15s
2 bleed holes in piston
12
12
10 - flutter
15
15
15
15
15
5g 4runner front 2.5 king coilover, w/ adj
20s
2 bleed holes in piston
10
10
10 flutter
20s
lexus gx460 front 2.5 fox coilover, w/ dsc
This coilover had an insane amount of valving and the low flow piston. Many of the shims are double or triple stacked as noted below.
20
40
40
40
30
30
15x3
15x2
piston
5 thou bleed shim
15x3
15x2s from here down
5G 4Runner Front 2.5 King Coilover, w/ adj. Custom tuned for RCLT
These shocks were sent out with +3 rod ends however they had to be swapped to +2s. It's an 8" travel coilover limited to 7.75" of travel. The RCLT kit nets roughly 10" of travel after 20-30 hours extra work to make it cycle correctly, according to the installer.
An interesting note about these is they have less initial rebound valving than the stock version and less high speed compressoin but significantly more low speed compression. Likely this is so the mid range adjuster can take over some of the high speed/high shaft displacement damping.
20
20
20
20
15
15
1 bleed hole in main piston
12
8- flutter (1.3 diameter)
12
12
15
15
15
Tundra
2g tundra front king 2.5 long travel coilover, w/ adj
12s
3 bleed holes
12
12
20s
No flutter, which is typical for long travel coilovers due to the increased motion ratio. These are not valved to work with the bypasses they are paired with.
2g tundra front fox 2.5 coilover
15s
12
2 large bleed holes
8
8
8
8 - flutter
12s
1g tundra front ads 2.5 coilover
I've only taken a few ADS shocks apart as they are not a common brand. Similar to the King carli kit which is trying to have directional bleed with step off shims, these had a 8 thou face shim and flutter underneath the normal shims which also sort of gives it directional bleed before engaging the stack. This is a way to get the good sides of bleed without the loss of control, however this vehicle performed poorly offroad.
Rear 2.5 smooth bodies with adjusters:
10s
8
8 flutter
8
Piston with 1 tiny bleed hole
8
8 flutter
8
10
10
12s
Front:
15s
Piston with 1 tiny bleed hole
8
10 flutter
8
10
10
12
15
15
Again the comp side face shim and the shim after the flutter are the same size. This setup was much too soft for all the weight and was a bit floaty and uncontrolled. The front had a jounce/rebound zone spring section which is cool, but there were a lot of aluminum shavings inside the shock from the spring rubbing its guides.
2g tundra rear bilstein 2.5 bypass
16x50
20x25
24x25
30x25
36x30
42x30
Linear piston, 1 small bleed hole
42x2
36x25
32x25
28x25
24x30
18x50
Ford trucks (and broncos)
f150 front 2.5 fox coilover, w/ dsc, valved for dirt king kit
all 12s
2 3/32 bleed holes in piston
8
8
10
12
12
12
f250 tremor front 2.5 king smoothies
This truck was really nice but came in complaining of ride quality issues. After pulling it apart i confirmed it was using carli's spec piston which has stepoff shims before the face shims. First thing i did was rebuild the shocks to have a good baseline, which helped alot. The stepoff shims make low velocity stuff really weird and jittery/unmetered feeling. I ordered standard pistons to swap it to. My best guess is that the stepoff shim area that is cutout of hte piston is 8 thousandths thick, so in theory a 12 thousandths shim will give you 4 thou stepoff for the face shim.
Front smooth bodies:
12
12
12
10
10
12 preload shim
piston
8 preload shim
12
12
10
10
8
8
Rear smooth bodies:
12
10s
10 preload
piston
9 preload
8s
1989 bronco front 2.5 king coilover, for solo motorsports ttb setup
12x2.5 coilovers. Rode insanely stiff before revalve
12s
3 bleed holes in piston
20
15
15
15
ended up adding a flutter after the 1st 15 on the comp side, the 20 takes so much force to initially lift off, this is likely to compensate for it being dual rate springs (think 300/500?) on an IFS setup which vastly reduces your spring rate. It sort of felt like it didn't have shocks but since they needed rebuilt so bad i didnt want to make big changes.
f250 tremor rear 2.5 king smoothies
12
10
10
10
10
10 thou step-off shim
piston
9 thou step-off shim?
All 8s
This is carlis spec piston with the stepoff shims. I personally dont like the ride compared with kings application specific valving they do.
Chevy trucks
newer gen 1500 rear 2.5 fox smoothie, w/ dsc
All 12s
piston - digressive style
bleed shim (sorry didnt measure total area)
1.8 x .008
0.8 x .015 flutter, probably to accomodate the DSC
all 8s
Bilstein Valving Specs
Bilsteins valving is notoriously complicated but also deceptively simple, here are the available stacks for various products.
All Bilstein valve stacks are listed by newtons of force at 0.52 m/s (around 20 in/s). Therefore 170/60 means it takes 1,700 newtons of force to move the shock on the rebound stroke at 0.52 m/s, and 600 on comp. Bilstein lists valving as rebound/compression, most brands will list compression over rebound.
7100 series valving
170/60
255/70
360/80
180/75
345/135
275/78
220/115
8125 valving
Unfortunately Bilsteins 60mm 8125s come valved at 370/110 which is possibly the worst universal valve spec of any brand. For solid axle swaps i suggest starting at 275/78 and slightly increasing the preload shim size (for less preload) and running much larger bleed disc, something around 18 mm squared total bleed area, for example 10 on rebound and 8 on comp.
9200 series coilovers come valved at 255/100 with a linear piston which is a really good starting point for solid axle swap front ends... although they only have 1 tiny bleed hole which could push it closer to digressive. Typically i will drill out the initial bleed hole and drill a second to around 1/16" or a bit more.
255/100 9200 series valving - linear valving
brake
16x50
24x25
28x25
32x25
36x25
42x30
linear piston
42x25
36x20
32x20
28x20
24x20
16x50
16x50
brake
Fox Valving specs by number
Fox 2.0 valving
Fox 2.5 valving
Fox 3.0 valving
General Valving advice
Ultimately, valving is subjective... or at least that's what people say to avoid being wrong about valving. One thing I've learned from testing over 20 different sets of shocks completely blind on the same truck, at the same trail, is that everyone agrees about which one rides the best... the only thing that we disagree on is our recollection of the ride quality.
It's important to keep in mind that whatever you think feels good, is good. Despite having a finely tuned butt-dyno i still run into some situations where i prefer a different valving profile than a customer, which is totally fine.
Generally speaking if you are taking a vehicle and putting a firmer spring rate on it, you will want to lower compression valving to allow the up travel to be closer to what it had with the softer springs, and because you are not controlling as much of the spring energy on the compression side, you need to add in more rebound valving. This is not always the case as often folks are putting heavier springs on to compensate for heavier loads on the vehicle, a 650 lb spring is typically for 80-140 extra pounds of load, if a customer puts those springs on with 50 lbs of load or 200 lbs of additional load, the valving will have to change to compensate. The 50 lb load valving spec may be much softer on compression than the 200, which is why there are no true "rules of thumb" about valving.
For lightly sprung rock crawlers its common to have 15s on compression and 8s on rebound. Our personal truck has around an 80 lb/in main rate which will be really lazy and not want to re-accelerate the unsprung mass of the giant front axle. To compensate for that we run a ton of bleed, which helps the quick change of direction and fights seal friction. This does make the truck feel rather wobbly and flighty, however any performance offroad suspension will benefit from a sway bar as body roll is not the job of the shock absorber. Weight transfer to the outside corner in a turn is actually a net benefit so there is some thought about having an extremely floppy suspension setup that is controlled by a sway bar so you dont have excessive body roll but still have the extra pressure on the outside tire.
Vice versa if you take that same truck and do leading arms in the front (mounting the shock at a motion ratio) you can increase the spring rate and therefore reduce some of the piston bleed. An interesting thing about linked suspension setup is that you need to know how much down travel you want to have before figuring out how much anti-dive you'd like. Droop directly correlates to spring rate, if you have 10" droop at ride height you need a spring rate that is compressed at least 10" by your corner weight. Because this will be a lighter spring rate (unless you do a tender or semi tender setup, which has some drawbacks for crawling) you will need more bleed. Because you need more bleed, the driver will feel more anti dive than you would typically, so you can have the same exact truck setup with 10" coilovers and 5" of droop, or 16" coilovers with 10" of droop, and have different valving requirements and also different suspension geometry requirements.
To get shaft speed up over rzr burn and nuissance rocks, there's 2 general thoughts. The first option is to valve the lower speed inputs as firm as possible and let the tire pressure and vehicle speed handlee the inputs. The other option is the opposite, lots of bleed, compression side flutters etc. Having blind tested both options i can say that both actually work pretty good. RZR burn is tricky to valve for because its a high velocity, high frequency input, however the total travel the input is forcing to happen is very small. Because of this some extremely digressive pistons wont even be able to lift off the shims in time to change the direction, but honestly sometimes that rides better than a setup with alot of bleed. That's the annoying part about suspension valving.
A flutter on the compression side will also help with things like nuissance rocks and washboard as it reduces the initial lift-off force of the face shims. I typically dont like to use flutters on rebound since piston bleed acts more on rebound than compression. One caveat is that lightly sprung rock crawlers that want to drive fast in the desert can benefit from a rebound flutter, which will allow you to give them less bleed, which will greatly improve handling. It's a tricky proposition to get the rebound flutter right but in my testing i have found significant improvements in driveability without giving too much high speed movement.
There are plenty of general guides online about what adjustments to make when... my best advice is to go out and just do it for yourself, you will never learn it by only reading and even 1 or 2 revalves will teach you alot. That being said an important thing to keep in mind is you cannot revalve a shock that needs rebuilt... you will not get a clear indication of the actual ride quality of the damper if it was in perfect operating conditions, so it will likely feel too soft because of air in the body or a lack of nitrogen charge causing cavitation. The first thing to go will be your rebound feel... this makes sense intuitively because rebound forces are typically around 3x what compression valving forces are. The damper must be in perfect working condition before you decide to change things around, often times folks request a revalve and find what they actually need is a shock that isnt full of air.
